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diff --git a/doc/constants.texi b/doc/constants.texi new file mode 100644 index 0000000..afbc6a0 --- /dev/null +++ b/doc/constants.texi @@ -0,0 +1,2 @@ +@set DEFAULT_MAX_N_UNCHANGED_STATS_BETWEEN_OPENS 5 +@set SHRED_DEFAULT_PASSES 3 diff --git a/doc/coreutils.info b/doc/coreutils.info new file mode 100644 index 0000000..8071e5b --- /dev/null +++ b/doc/coreutils.info @@ -0,0 +1,21870 @@ +This is coreutils.info, produced by makeinfo version 7.0.2 from +coreutils.texi. + +This manual documents version 9.4 of the GNU core utilities, including +the standard programs for text and file manipulation. + + Copyright © 1994–2023 Free Software Foundation, Inc. + + Permission is granted to copy, distribute and/or modify this + document under the terms of the GNU Free Documentation License, + Version 1.3 or any later version published by the Free Software + Foundation; with no Invariant Sections, with no Front-Cover Texts, + and with no Back-Cover Texts. A copy of the license is included in + the section entitled “GNU Free Documentation License”. +INFO-DIR-SECTION Basics +START-INFO-DIR-ENTRY +* Coreutils: (coreutils). Core GNU (file, text, shell) utilities. +* Common options: (coreutils)Common options. +* File permissions: (coreutils)File permissions. Access modes. +* Date input formats: (coreutils)Date input formats. +END-INFO-DIR-ENTRY + +INFO-DIR-SECTION Individual utilities +START-INFO-DIR-ENTRY +* arch: (coreutils)arch invocation. Print machine hardware name. +* b2sum: (coreutils)b2sum invocation. Print or check BLAKE2 digests. +* base32: (coreutils)base32 invocation. Base32 encode/decode data. +* base64: (coreutils)base64 invocation. Base64 encode/decode data. +* basename: (coreutils)basename invocation. Strip directory and suffix. +* basenc: (coreutils)basenc invocation. Encoding/decoding of data. +* cat: (coreutils)cat invocation. Concatenate and write files. +* chcon: (coreutils)chcon invocation. Change SELinux CTX of files. +* chgrp: (coreutils)chgrp invocation. Change file groups. +* chmod: (coreutils)chmod invocation. Change access permissions. +* chown: (coreutils)chown invocation. Change file owners and groups. +* chroot: (coreutils)chroot invocation. Specify the root directory. +* cksum: (coreutils)cksum invocation. Print POSIX CRC checksum. +* comm: (coreutils)comm invocation. Compare sorted files by line. +* cp: (coreutils)cp invocation. Copy files. +* csplit: (coreutils)csplit invocation. Split by context. +* cut: (coreutils)cut invocation. Print selected parts of lines. +* date: (coreutils)date invocation. Print/set system date and time. +* dd: (coreutils)dd invocation. Copy and convert a file. +* df: (coreutils)df invocation. Report file system usage. +* dir: (coreutils)dir invocation. List directories briefly. +* dircolors: (coreutils)dircolors invocation. Color setup for ls. +* dirname: (coreutils)dirname invocation. Strip last file name component. +* du: (coreutils)du invocation. Report file usage. +* echo: (coreutils)echo invocation. Print a line of text. +* env: (coreutils)env invocation. Modify the environment. +* expand: (coreutils)expand invocation. Convert tabs to spaces. +* expr: (coreutils)expr invocation. Evaluate expressions. +* factor: (coreutils)factor invocation. Print prime factors +* false: (coreutils)false invocation. Do nothing, unsuccessfully. +* fmt: (coreutils)fmt invocation. Reformat paragraph text. +* fold: (coreutils)fold invocation. Wrap long input lines. +* groups: (coreutils)groups invocation. Print group names a user is in. +* head: (coreutils)head invocation. Output the first part of files. +* hostid: (coreutils)hostid invocation. Print numeric host identifier. +* hostname: (coreutils)hostname invocation. Print or set system name. +* id: (coreutils)id invocation. Print user identity. +* install: (coreutils)install invocation. Copy files and set attributes. +* join: (coreutils)join invocation. Join lines on a common field. +* kill: (coreutils)kill invocation. Send a signal to processes. +* link: (coreutils)link invocation. Make hard links between files. +* ln: (coreutils)ln invocation. Make links between files. +* logname: (coreutils)logname invocation. Print current login name. +* ls: (coreutils)ls invocation. List directory contents. +* md5sum: (coreutils)md5sum invocation. Print or check MD5 digests. +* mkdir: (coreutils)mkdir invocation. Create directories. +* mkfifo: (coreutils)mkfifo invocation. Create FIFOs (named pipes). +* mknod: (coreutils)mknod invocation. Create special files. +* mktemp: (coreutils)mktemp invocation. Create temporary files. +* mv: (coreutils)mv invocation. Rename files. +* nice: (coreutils)nice invocation. Modify niceness. +* nl: (coreutils)nl invocation. Number lines and write files. +* nohup: (coreutils)nohup invocation. Immunize to hangups. +* nproc: (coreutils)nproc invocation. Print the number of processors. +* numfmt: (coreutils)numfmt invocation. Reformat numbers. +* od: (coreutils)od invocation. Dump files in octal, etc. +* paste: (coreutils)paste invocation. Merge lines of files. +* pathchk: (coreutils)pathchk invocation. Check file name portability. +* pr: (coreutils)pr invocation. Paginate or columnate files. +* printenv: (coreutils)printenv invocation. Print environment variables. +* printf: (coreutils)printf invocation. Format and print data. +* ptx: (coreutils)ptx invocation. Produce permuted indexes. +* pwd: (coreutils)pwd invocation. Print working directory. +* readlink: (coreutils)readlink invocation. Print referent of a symlink. +* realpath: (coreutils)realpath invocation. Print resolved file names. +* rm: (coreutils)rm invocation. Remove files. +* rmdir: (coreutils)rmdir invocation. Remove empty directories. +* runcon: (coreutils)runcon invocation. Run in specified SELinux CTX. +* seq: (coreutils)seq invocation. Print numeric sequences +* sha1sum: (coreutils)sha1sum invocation. Print or check SHA-1 digests. +* sha2: (coreutils)sha2 utilities. Print or check SHA-2 digests. +* shred: (coreutils)shred invocation. Remove files more securely. +* shuf: (coreutils)shuf invocation. Shuffling text files. +* sleep: (coreutils)sleep invocation. Delay for a specified time. +* sort: (coreutils)sort invocation. Sort text files. +* split: (coreutils)split invocation. Split into pieces. +* stat: (coreutils)stat invocation. Report file(system) status. +* stdbuf: (coreutils)stdbuf invocation. Modify stdio buffering. +* stty: (coreutils)stty invocation. Print/change terminal settings. +* sum: (coreutils)sum invocation. Print traditional checksum. +* sync: (coreutils)sync invocation. Sync files to stable storage. +* tac: (coreutils)tac invocation. Reverse files. +* tail: (coreutils)tail invocation. Output the last part of files. +* tee: (coreutils)tee invocation. Redirect to multiple files. +* test: (coreutils)test invocation. File/string tests. +* timeout: (coreutils)timeout invocation. Run with time limit. +* touch: (coreutils)touch invocation. Change file timestamps. +* tr: (coreutils)tr invocation. Translate characters. +* true: (coreutils)true invocation. Do nothing, successfully. +* truncate: (coreutils)truncate invocation. Shrink/extend size of a file. +* tsort: (coreutils)tsort invocation. Topological sort. +* tty: (coreutils)tty invocation. Print terminal name. +* uname: (coreutils)uname invocation. Print system information. +* unexpand: (coreutils)unexpand invocation. Convert spaces to tabs. +* uniq: (coreutils)uniq invocation. Uniquify files. +* unlink: (coreutils)unlink invocation. Removal via unlink(2). +* uptime: (coreutils)uptime invocation. Print uptime and load. +* users: (coreutils)users invocation. Print current user names. +* vdir: (coreutils)vdir invocation. List directories verbosely. +* wc: (coreutils)wc invocation. Line, word, and byte counts. +* who: (coreutils)who invocation. Print who is logged in. +* whoami: (coreutils)whoami invocation. Print effective user ID. +* yes: (coreutils)yes invocation. Print a string indefinitely. +END-INFO-DIR-ENTRY + + +File: coreutils.info, Node: Top, Next: Introduction, Up: (dir) + +GNU Coreutils +************* + +This manual documents version 9.4 of the GNU core utilities, including +the standard programs for text and file manipulation. + + Copyright © 1994–2023 Free Software Foundation, Inc. + + Permission is granted to copy, distribute and/or modify this + document under the terms of the GNU Free Documentation License, + Version 1.3 or any later version published by the Free Software + Foundation; with no Invariant Sections, with no Front-Cover Texts, + and with no Back-Cover Texts. A copy of the license is included in + the section entitled “GNU Free Documentation License”. + +* Menu: + +* Introduction:: Caveats, overview, and authors +* Common options:: Common options +* Output of entire files:: cat tac nl od base32 base64 basenc +* Formatting file contents:: fmt pr fold +* Output of parts of files:: head tail split csplit +* Summarizing files:: wc sum cksum b2sum md5sum sha1sum sha2 +* Operating on sorted files:: sort shuf uniq comm ptx tsort +* Operating on fields:: cut paste join +* Operating on characters:: tr expand unexpand +* Directory listing:: ls dir vdir dircolors +* Basic operations:: cp dd install mv rm shred +* Special file types:: mkdir rmdir unlink mkfifo mknod ln link readlink +* Changing file attributes:: chgrp chmod chown touch +* File space usage:: df du stat sync truncate +* Printing text:: echo printf yes +* Conditions:: false true test expr +* Redirection:: tee +* File name manipulation:: dirname basename pathchk mktemp realpath +* Working context:: pwd stty printenv tty +* User information:: id logname whoami groups users who +* System context:: date arch nproc uname hostname hostid uptime +* SELinux context:: chcon runcon +* Modified command invocation:: chroot env nice nohup stdbuf timeout +* Process control:: kill +* Delaying:: sleep +* Numeric operations:: factor numfmt seq +* File permissions:: Access modes +* File timestamps:: File timestamp issues +* Date input formats:: Specifying date strings +* Version sort ordering:: Details on version-sort algorithm +* Opening the software toolbox:: The software tools philosophy +* GNU Free Documentation License:: Copying and sharing this manual +* Concept index:: General index + + — The Detailed Node Listing — + +Common Options + +* Exit status:: Indicating program success or failure +* Backup options:: Backup options +* Block size:: Block size +* Floating point:: Floating point number representation +* Signal specifications:: Specifying signals +* Disambiguating names and IDs:: chgrp, chown, chroot, id: user and group syntax +* Random sources:: Sources of random data +* Target directory:: Target directory +* Trailing slashes:: Trailing slashes +* Traversing symlinks:: Traversing symlinks to directories +* Treating / specially:: Treating / specially +* Standards conformance:: Standards conformance +* Multi-call invocation:: Multi-call program invocation + +Output of entire files + +* cat invocation:: Concatenate and write files +* tac invocation:: Concatenate and write files in reverse +* nl invocation:: Number lines and write files +* od invocation:: Write files in octal or other formats +* base32 invocation:: Transform data into printable data +* base64 invocation:: Transform data into printable data +* basenc invocation:: Transform data into printable data + +Formatting file contents + +* fmt invocation:: Reformat paragraph text +* pr invocation:: Paginate or columnate files for printing +* fold invocation:: Wrap input lines to fit in specified width + +Output of parts of files + +* head invocation:: Output the first part of files +* tail invocation:: Output the last part of files +* split invocation:: Split a file into fixed-size pieces +* csplit invocation:: Split a file into context-determined pieces + +Summarizing files + +* wc invocation:: Print newline, word, and byte counts +* sum invocation:: Print checksum and block counts +* cksum invocation:: Print CRC checksum and byte counts +* md5sum invocation:: Print or check MD5 digests +* b2sum invocation:: Print or check BLAKE2 digests +* sha1sum invocation:: Print or check SHA-1 digests +* sha2 utilities:: Print or check SHA-2 digests + +Operating on sorted files + +* sort invocation:: Sort text files +* shuf invocation:: Shuffle text files +* uniq invocation:: Uniquify files +* comm invocation:: Compare two sorted files line by line +* ptx invocation:: Produce a permuted index of file contents +* tsort invocation:: Topological sort + +‘ptx’: Produce permuted indexes + +* General options in ptx:: Options which affect general program behavior +* Charset selection in ptx:: Underlying character set considerations +* Input processing in ptx:: Input fields, contexts, and keyword selection +* Output formatting in ptx:: Types of output format, and sizing the fields +* Compatibility in ptx:: The GNU extensions to ‘ptx’ + +Operating on fields + +* cut invocation:: Print selected parts of lines +* paste invocation:: Merge lines of files +* join invocation:: Join lines on a common field + +Operating on characters + +* tr invocation:: Translate, squeeze, and/or delete characters +* expand invocation:: Convert tabs to spaces +* unexpand invocation:: Convert spaces to tabs + +‘tr’: Translate, squeeze, and/or delete characters + +* Character arrays:: Specifying arrays of characters +* Translating:: Changing one set of characters to another +* Squeezing and deleting:: Removing characters + +Directory listing + +* ls invocation:: List directory contents +* dir invocation:: Briefly list directory contents +* vdir invocation:: Verbosely list directory contents +* dircolors invocation:: Color setup for ‘ls’ + +‘ls’: List directory contents + +* Which files are listed:: Which files are listed +* What information is listed:: What information is listed +* Sorting the output:: Sorting the output +* General output formatting:: General output formatting +* Formatting the file names:: Formatting the file names + +Basic operations + +* cp invocation:: Copy files and directories +* dd invocation:: Convert and copy a file +* install invocation:: Copy files and set attributes +* mv invocation:: Move (rename) files +* rm invocation:: Remove files or directories +* shred invocation:: Remove files more securely + +Special file types + +* link invocation:: Make a hard link via the link syscall +* ln invocation:: Make links between files +* mkdir invocation:: Make directories +* mkfifo invocation:: Make FIFOs (named pipes) +* mknod invocation:: Make block or character special files +* readlink invocation:: Print value of a symlink or canonical file name +* rmdir invocation:: Remove empty directories +* unlink invocation:: Remove files via unlink syscall + +Changing file attributes + +* chown invocation:: Change file owner and group +* chgrp invocation:: Change group ownership +* chmod invocation:: Change access permissions +* touch invocation:: Change file timestamps + +File space usage + +* df invocation:: Report file system space usage +* du invocation:: Estimate file space usage +* stat invocation:: Report file or file system status +* sync invocation:: Synchronize cached writes to persistent storage +* truncate invocation:: Shrink or extend the size of a file + +Printing text + +* echo invocation:: Print a line of text +* printf invocation:: Format and print data +* yes invocation:: Print a string until interrupted + +Conditions + +* false invocation:: Do nothing, unsuccessfully +* true invocation:: Do nothing, successfully +* test invocation:: Check file types and compare values +* expr invocation:: Evaluate expressions + +‘test’: Check file types and compare values + +* File type tests:: File type tests +* Access permission tests:: Access permission tests +* File characteristic tests:: File characteristic tests +* String tests:: String tests +* Numeric tests:: Numeric tests + +‘expr’: Evaluate expression + +* String expressions:: ‘+ : match substr index length’ +* Numeric expressions:: ‘+ - * / %’ +* Relations for expr:: ‘| & < <= = == != >= >’ +* Examples of expr:: Examples of using ‘expr’ + +Redirection + +* tee invocation:: Redirect output to multiple files or processes + +File name manipulation + +* basename invocation:: Strip directory and suffix from a file name +* dirname invocation:: Strip last file name component +* pathchk invocation:: Check file name validity and portability +* mktemp invocation:: Create temporary file or directory +* realpath invocation:: Print resolved file names + +Working context + +* pwd invocation:: Print working directory +* stty invocation:: Print or change terminal characteristics +* printenv invocation:: Print all or some environment variables +* tty invocation:: Print file name of terminal on standard input + +‘stty’: Print or change terminal characteristics + +* Control:: Control settings +* Input:: Input settings +* Output:: Output settings +* Local:: Local settings +* Combination:: Combination settings +* Characters:: Special characters +* Special:: Special settings + +User information + +* id invocation:: Print user identity +* logname invocation:: Print current login name +* whoami invocation:: Print effective user ID +* groups invocation:: Print group names a user is in +* users invocation:: Print login names of users currently logged in +* who invocation:: Print who is currently logged in + +System context + +* arch invocation:: Print machine hardware name +* date invocation:: Print or set system date and time +* nproc invocation:: Print the number of processors +* uname invocation:: Print system information +* hostname invocation:: Print or set system name +* hostid invocation:: Print numeric host identifier +* uptime invocation:: Print system uptime and load + +‘date’: Print or set system date and time + +* Time conversion specifiers:: %[HIklMNpPrRsSTXzZ] +* Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY] +* Literal conversion specifiers:: %[%nt] +* Padding and other flags:: Pad with zeros, spaces, etc. +* Setting the time:: Changing the system clock +* Options for date:: Instead of the current time +* Date input formats:: Specifying date strings +* Examples of date:: Examples + +SELinux context + +* chcon invocation:: Change SELinux context of file +* runcon invocation:: Run a command in specified SELinux context + +Modified command invocation + +* chroot invocation:: Run a command with a different root directory +* env invocation:: Run a command in a modified environment +* nice invocation:: Run a command with modified niceness +* nohup invocation:: Run a command immune to hangups +* stdbuf invocation:: Run a command with modified I/O buffering +* timeout invocation:: Run a command with a time limit + +Process control + +* kill invocation:: Sending a signal to processes. + +Delaying + +* sleep invocation:: Delay for a specified time + +Numeric operations + +* factor invocation:: Print prime factors +* numfmt invocation:: Reformat numbers +* seq invocation:: Print numeric sequences + + +File timestamps + +* File timestamps:: File timestamp issues + +File permissions + +* Mode Structure:: Structure of file mode bits +* Symbolic Modes:: Mnemonic representation of file mode bits +* Numeric Modes:: File mode bits as octal numbers +* Directory Setuid and Setgid:: Set-user-ID and set-group-ID on directories + +Date input formats + +* General date syntax:: Common rules +* Calendar date items:: ‘14 Nov 2022’ +* Time of day items:: ‘9:02pm’ +* Time zone items:: ‘UTC’, ‘-0700’, ‘+0900’, ... +* Combined date and time of day items:: ‘2022-11-14T21:02:42,000000-0500’ +* Day of week items:: ‘Monday’ and others +* Relative items in date strings:: ‘next tuesday, 2 years ago’ +* Pure numbers in date strings:: ‘20221114’, ‘2102’ +* Seconds since the Epoch:: ‘@1668477762’ +* Specifying time zone rules:: ‘TZ="America/New_York"’, ‘TZ="UTC0"’ +* Authors of parse_datetime:: Bellovin, Eggert, Salz, Berets, et al. + +Version sorting order + +* Version sort overview:: +* Version sort implementation:: +* Differences from Debian version sort:: +* Advanced version sort topics:: + +Opening the software toolbox + +* Toolbox introduction:: Toolbox introduction +* I/O redirection:: I/O redirection +* The who command:: The ‘who’ command +* The cut command:: The ‘cut’ command +* The sort command:: The ‘sort’ command +* The uniq command:: The ‘uniq’ command +* Putting the tools together:: Putting the tools together + +Copying This Manual + +* GNU Free Documentation License:: Copying and sharing this manual + + + +File: coreutils.info, Node: Introduction, Next: Common options, Prev: Top, Up: Top + +1 Introduction +************** + +This manual is a work in progress: many sections make no attempt to +explain basic concepts in a way suitable for novices. Thus, if you are +interested, please get involved in improving this manual. The entire +GNU community will benefit. + + The GNU utilities documented here are mostly compatible with the +POSIX standard. + + Please report bugs to <bug-coreutils@gnu.org>. Include the version +number, machine architecture, input files, and any other information +needed to reproduce the bug: your input, what you expected, what you +got, and why it is wrong. + + If you have a problem with ‘sort’ or ‘date’, try using the ‘--debug’ +option, as it can often help find and fix problems without having to +wait for an answer to a bug report. If the debug output does not +suffice to fix the problem on your own, please compress and attach it to +the rest of your bug report. + + Although diffs are welcome, please include a description of the +problem as well, since this is sometimes difficult to infer. *Note +(gcc)Bugs::. + + This manual was originally derived from the Unix man pages in the +distributions, which were written by David MacKenzie and updated by Jim +Meyering. What you are reading now is the authoritative documentation +for these utilities; the man pages are no longer being maintained. The +original ‘fmt’ man page was written by Ross Paterson. François Pinard +did the initial conversion to Texinfo format. Karl Berry did the +indexing, some reorganization, and editing of the results. Brian +Youmans of the Free Software Foundation office staff combined the +manuals for textutils, fileutils, and sh-utils to produce the present +omnibus manual. Richard Stallman contributed his usual invaluable +insights to the overall process. + + +File: coreutils.info, Node: Common options, Next: Output of entire files, Prev: Introduction, Up: Top + +2 Common options +**************** + +Certain options are available in all of these programs. Rather than +writing identical descriptions for each of the programs, they are +described here. (In fact, every GNU program accepts (or should accept) +these options.) + + Normally options and operands can appear in any order, and programs +act as if all the options appear before any operands. For example, +‘sort -r passwd -t :’ acts like ‘sort -r -t : passwd’, since ‘:’ is an +option-argument of ‘-t’. However, if the ‘POSIXLY_CORRECT’ environment +variable is set, options must appear before operands, unless otherwise +specified for a particular command. + + A few programs can usefully have trailing operands with leading ‘-’. +With such a program, options must precede operands even if +‘POSIXLY_CORRECT’ is not set, and this fact is noted in the program +description. For example, the ‘env’ command’s options must appear +before its operands, since in some cases the operands specify a command +that itself contains options. + + Most programs that accept long options recognize unambiguous +abbreviations of those options. For example, ‘rmdir +--ignore-fail-on-non-empty’ can be invoked as ‘rmdir --ignore-fail’ or +even ‘rmdir --i’. Ambiguous options, such as ‘ls --h’, are identified +as such. + + Some of these programs recognize the ‘--help’ and ‘--version’ options +only when one of them is the sole command line argument. For these +programs, abbreviations of the long options are not always recognized. + +‘--help’ + Print a usage message listing all available options, then exit + successfully. + +‘--version’ + Print the version number, then exit successfully. + +‘--’ + Delimit the option list. Later arguments, if any, are treated as + operands even if they begin with ‘-’. For example, ‘sort -- -r’ + reads from the file named ‘-r’. + + A single ‘-’ operand is not really an option, though it looks like +one. It stands for a file operand, and some tools treat it as standard +input, or as standard output if that is clear from the context. For +example, ‘sort -’ reads from standard input, and is equivalent to plain +‘sort’. Unless otherwise specified, a ‘-’ can appear as any operand +that requires a file name. + +* Menu: + +Items shared between some programs: + +* Backup options:: ‘-b’ ‘-S’. +* Block size:: BLOCK_SIZE and ‘--block-size’. +* Signal specifications:: Specifying signals with ‘--signal’. +* Disambiguating names and IDs:: chgrp, chown, chroot, id: user and group syntax +* Random sources:: ‘--random-source’. +* Target directory:: Specifying a target directory. +* Trailing slashes:: ‘--strip-trailing-slashes’. +* Traversing symlinks:: ‘-H’, ‘-L’, or ‘-P’. +* Treating / specially:: ‘--preserve-root’ and the converse. +* Special built-in utilities:: ‘break’, ‘:’, ... + +Items applicable to all programs: + +* Exit status:: Indicating program success or failure. +* Floating point:: Floating point number representation. +* Standards conformance:: Conformance to the POSIX standard. +* Multi-call invocation:: Multi-call program invocation. + + +File: coreutils.info, Node: Backup options, Next: Block size, Up: Common options + +2.1 Backup options +================== + +Some GNU programs (at least ‘cp’, ‘install’, ‘ln’, and ‘mv’) optionally +make backups of files before writing new versions. These options +control the details of these backups. The options are also briefly +mentioned in the descriptions of the particular programs. + +‘-b’ +‘--backup[=METHOD]’ + Make a backup of each file that would otherwise be overwritten or + removed. Without this option, the original versions are destroyed. + Use METHOD to determine the type of backups to make. When this + option is used but METHOD is not specified, then the value of the + ‘VERSION_CONTROL’ environment variable is used. And if + ‘VERSION_CONTROL’ is not set, the default backup type is + ‘existing’. + + Note that the short form of this option, ‘-b’ does not accept any + argument. Using ‘-b’ is equivalent to using ‘--backup=existing’. + + This option corresponds to the Emacs variable ‘version-control’; + the values for METHOD are the same as those used in Emacs. This + option also accepts more descriptive names. The valid METHODs are + (unique abbreviations are accepted): + + ‘none’ + ‘off’ + Never make backups. + + ‘numbered’ + ‘t’ + Always make numbered backups. + + ‘existing’ + ‘nil’ + Make numbered backups of files that already have them, simple + backups of the others. + + ‘simple’ + ‘never’ + Always make simple backups. Please note ‘never’ is not to be + confused with ‘none’. + +‘-S SUFFIX’ +‘--suffix=SUFFIX’ + Append SUFFIX to each backup file made with ‘-b’. If this option + is not specified, the value of the ‘SIMPLE_BACKUP_SUFFIX’ + environment variable is used. And if ‘SIMPLE_BACKUP_SUFFIX’ is not + set, the default is ‘~’, just as in Emacs. + + +File: coreutils.info, Node: Block size, Next: Signal specifications, Prev: Backup options, Up: Common options + +2.2 Block size +============== + +Some GNU programs (at least ‘df’, ‘du’, and ‘ls’) display sizes in +“blocks”. You can adjust the block size and method of display to make +sizes easier to read. The block size used for display is independent of +any file system block size. Fractional block counts are rounded up to +the nearest integer. + + The default block size is chosen by examining the following +environment variables in turn; the first one that is set determines the +block size. + +‘DF_BLOCK_SIZE’ + This specifies the default block size for the ‘df’ command. + Similarly, ‘DU_BLOCK_SIZE’ specifies the default for ‘du’ and + ‘LS_BLOCK_SIZE’ for ‘ls’. + +‘BLOCK_SIZE’ + This specifies the default block size for all three commands, if + the above command-specific environment variables are not set. + +‘BLOCKSIZE’ + This specifies the default block size for all values that are + normally printed as blocks, if neither ‘BLOCK_SIZE’ nor the above + command-specific environment variables are set. Unlike the other + environment variables, ‘BLOCKSIZE’ does not affect values that are + normally printed as byte counts, e.g., the file sizes contained in + ‘ls -l’ output. + +‘POSIXLY_CORRECT’ + If neither ‘COMMAND_BLOCK_SIZE’, nor ‘BLOCK_SIZE’, nor ‘BLOCKSIZE’ + is set, but this variable is set, the block size defaults to 512. + + If none of the above environment variables are set, the block size +currently defaults to 1024 bytes in most contexts, but this number may +change in the future. For ‘ls’ file sizes, the block size defaults to 1 +byte. + + A block size specification can be a positive integer specifying the +number of bytes per block, or it can be ‘human-readable’ or ‘si’ to +select a human-readable format. Integers may be followed by suffixes +that are upward compatible with the SI prefixes +(http://www.bipm.org/en/publications/si-brochure/chapter3.html) for +decimal multiples and with the ISO/IEC 80000-13 (formerly IEC 60027-2) +prefixes (https://physics.nist.gov/cuu/Units/binary.html) for binary +multiples. + + With human-readable formats, output sizes are followed by a size +letter such as ‘M’ for megabytes. ‘BLOCK_SIZE=human-readable’ uses +powers of 1024; ‘M’ stands for 1,048,576 bytes. ‘BLOCK_SIZE=si’ is +similar, but uses powers of 1000 and appends ‘B’; ‘MB’ stands for +1,000,000 bytes. + + A block size specification preceded by ‘'’ causes output sizes to be +displayed with thousands separators. The ‘LC_NUMERIC’ locale specifies +the thousands separator and grouping. For example, in an American +English locale, ‘--block-size="'1kB"’ would cause a size of 1234000 +bytes to be displayed as ‘1,234’. In the default C locale, there is no +thousands separator so a leading ‘'’ has no effect. + + An integer block size can be followed by a suffix to specify a +multiple of that size. A bare size letter, or one followed by ‘iB’, +specifies a multiple using powers of 1024. A size letter followed by +‘B’ specifies powers of 1000 instead. For example, ‘1M’ and ‘1MiB’ are +equivalent to ‘1048576’, whereas ‘1MB’ is equivalent to ‘1000000’. + + A plain suffix without a preceding integer acts as if ‘1’ were +prepended, except that it causes a size indication to be appended to the +output. For example, ‘--block-size="kB"’ displays 3000 as ‘3kB’. + + The following suffixes are defined. Large sizes like ‘1Q’ may be +rejected by your computer due to limitations of its arithmetic. + +‘kB’ + kilobyte: 10^3 = 1000. +‘k’ +‘K’ +‘KiB’ + kibibyte: 2^{10} = 1024. ‘K’ is special: the SI prefix is ‘k’ and + the ISO/IEC 80000-13 prefix is ‘Ki’, but tradition and POSIX use + ‘k’ to mean ‘KiB’. +‘MB’ + megabyte: 10^6 = 1,000,000. +‘M’ +‘MiB’ + mebibyte: 2^{20} = 1,048,576. +‘GB’ + gigabyte: 10^9 = 1,000,000,000. +‘G’ +‘GiB’ + gibibyte: 2^{30} = 1,073,741,824. +‘TB’ + terabyte: 10^{12} = 1,000,000,000,000. +‘T’ +‘TiB’ + tebibyte: 2^{40} = 1,099,511,627,776. +‘PB’ + petabyte: 10^{15} = 1,000,000,000,000,000. +‘P’ +‘PiB’ + pebibyte: 2^{50} = 1,125,899,906,842,624. +‘EB’ + exabyte: 10^{18} = 1,000,000,000,000,000,000. +‘E’ +‘EiB’ + exbibyte: 2^{60} = 1,152,921,504,606,846,976. +‘ZB’ + zettabyte: 10^{21} = 1,000,000,000,000,000,000,000 +‘Z’ +‘ZiB’ + zebibyte: 2^{70} = 1,180,591,620,717,411,303,424. +‘YB’ + yottabyte: 10^{24} = 1,000,000,000,000,000,000,000,000. +‘Y’ +‘YiB’ + yobibyte: 2^{80} = 1,208,925,819,614,629,174,706,176. +‘RB’ + ronnabyte: 10^{27} = 1,000,000,000,000,000,000,000,000,000. +‘R’ +‘RiB’ + robibyte: 2^{90} = 1,237,940,039,285,380,274,899,124,224. +‘QB’ + quettabyte: 10^{30} = 1,000,000,000,000,000,000,000,000,000,000. +‘Q’ +‘QiB’ + quebibyte: 2^{100} = 1,267,650,600,228,229,401,496,703,205,376. + + Block size defaults can be overridden by an explicit +‘--block-size=SIZE’ option. The ‘-k’ option is equivalent to +‘--block-size=1K’, which is the default unless the ‘POSIXLY_CORRECT’ +environment variable is set. The ‘-h’ or ‘--human-readable’ option is +equivalent to ‘--block-size=human-readable’. The ‘--si’ option is +equivalent to ‘--block-size=si’. Note for ‘ls’ the ‘-k’ option does not +control the display of the apparent file sizes, whereas the +‘--block-size’ option does. + + +File: coreutils.info, Node: Signal specifications, Next: Disambiguating names and IDs, Prev: Block size, Up: Common options + +2.3 Signal specifications +========================= + +A SIGNAL may be a signal name like ‘HUP’, or a signal number like ‘1’, +or an exit status of a process terminated by the signal. A signal name +can be given in canonical form or prefixed by ‘SIG’. The case of the +letters is ignored. The following signal names and numbers are +supported on all POSIX compliant systems: + +‘HUP’ + 1. Hangup. +‘INT’ + 2. Terminal interrupt. +‘QUIT’ + 3. Terminal quit. +‘ABRT’ + 6. Process abort. +‘KILL’ + 9. Kill (cannot be caught or ignored). +‘ALRM’ + 14. Alarm Clock. +‘TERM’ + 15. Termination. + +Other supported signal names have system-dependent corresponding +numbers. All systems conforming to POSIX 1003.1-2001 also support the +following signals: + +‘BUS’ + Access to an undefined portion of a memory object. +‘CHLD’ + Child process terminated, stopped, or continued. +‘CONT’ + Continue executing, if stopped. +‘FPE’ + Erroneous arithmetic operation. +‘ILL’ + Illegal Instruction. +‘PIPE’ + Write on a pipe with no one to read it. +‘SEGV’ + Invalid memory reference. +‘STOP’ + Stop executing (cannot be caught or ignored). +‘TSTP’ + Terminal stop. +‘TTIN’ + Background process attempting read. +‘TTOU’ + Background process attempting write. +‘URG’ + High bandwidth data is available at a socket. +‘USR1’ + User-defined signal 1. +‘USR2’ + User-defined signal 2. + +POSIX 1003.1-2001 systems that support the XSI extension also support +the following signals: + +‘POLL’ + Pollable event. +‘PROF’ + Profiling timer expired. +‘SYS’ + Bad system call. +‘TRAP’ + Trace/breakpoint trap. +‘VTALRM’ + Virtual timer expired. +‘XCPU’ + CPU time limit exceeded. +‘XFSZ’ + File size limit exceeded. + +POSIX 1003.1-2001 systems that support the XRT extension also support at +least eight real-time signals called ‘RTMIN’, ‘RTMIN+1’, ..., ‘RTMAX-1’, +‘RTMAX’. + + +File: coreutils.info, Node: Disambiguating names and IDs, Next: Random sources, Prev: Signal specifications, Up: Common options + +2.4 chown, chgrp, chroot, id: Disambiguating user names and IDs +=============================================================== + +Since the USER and GROUP arguments to these commands may be specified as +names or numeric IDs, there is an apparent ambiguity. What if a user or +group _name_ is a string of digits? Should the command interpret it as +a user name or as an ID? (Using a number as a user name is common in +some environments.) POSIX requires that these commands first attempt to +resolve the specified string as a name, and only once that fails, then +try to interpret it as an ID. This is troublesome when you want to +specify a numeric ID, say 42, and it must work even in a pathological +situation where ‘42’ is a user name that maps to some other user ID, say +1000. Simply invoking ‘chown 42 F’, will set ‘F’s owner ID to 1000 – +not what you intended. + + GNU ‘chown’, ‘chgrp’, ‘chroot’, and ‘id’ provide a way to work around +this, that at the same time may result in a significant performance +improvement by eliminating a database look-up. Simply precede each +numeric user ID and/or group ID with a ‘+’, in order to force its +interpretation as an integer: + + chown +42 F + chgrp +$numeric_group_id another-file + chown +0:+0 / + + The name look-up process is skipped for each ‘+’-prefixed string, +because a string containing ‘+’ is never a valid user or group name. +This syntax is accepted on most common Unix systems, but not on Solaris +10. + + +File: coreutils.info, Node: Random sources, Next: Target directory, Prev: Disambiguating names and IDs, Up: Common options + +2.5 Sources of random data +========================== + +The ‘shuf’, ‘shred’, and ‘sort’ commands sometimes need random data to +do their work. For example, ‘sort -R’ must choose a hash function at +random, and it needs random data to make this selection. + + By default these commands use an internal pseudo-random generator +initialized by a small amount of entropy, but can be directed to use an +external source with the ‘--random-source=FILE’ option. An error is +reported if FILE does not contain enough bytes. + + For example, the device file ‘/dev/urandom’ could be used as the +source of random data. Typically, this device gathers environmental +noise from device drivers and other sources into an entropy pool, and +uses the pool to generate random bits. If the pool is short of data, +the device reuses the internal pool to produce more bits, using a +cryptographically secure pseudo-random number generator. But be aware +that this device is not designed for bulk random data generation and is +relatively slow. + + ‘/dev/urandom’ suffices for most practical uses, but applications +requiring high-value or long-term protection of private data may require +an alternate data source like ‘/dev/random’ or ‘/dev/arandom’. The set +of available sources depends on your operating system. + + To reproduce the results of an earlier invocation of a command, you +can save some random data into a file and then use that file as the +random source in earlier and later invocations of the command. Rather +than depending on a file, one can generate a reproducible arbitrary +amount of pseudo-random data given a seed value, using for example: + + get_seeded_random() + { + seed="$1" + openssl enc -aes-256-ctr -pass pass:"$seed" -nosalt \ + </dev/zero 2>/dev/null + } + + shuf -i1-100 --random-source=<(get_seeded_random 42) + + +File: coreutils.info, Node: Target directory, Next: Trailing slashes, Prev: Random sources, Up: Common options + +2.6 Target directory +==================== + +The ‘cp’, ‘install’, ‘ln’, and ‘mv’ commands normally treat the last +operand specially when it is a directory or a symbolic link to a +directory. For example, ‘cp source dest’ is equivalent to ‘cp source +dest/source’ if ‘dest’ is a directory. Sometimes this behavior is not +exactly what is wanted, so these commands support the following options +to allow more fine-grained control: + +‘-T’ +‘--no-target-directory’ + Do not treat the last operand specially when it is a directory or a + symbolic link to a directory. This can help avoid race conditions + in programs that operate in a shared area. For example, when the + command ‘mv /tmp/source /tmp/dest’ succeeds, there is no guarantee + that ‘/tmp/source’ was renamed to ‘/tmp/dest’: it could have been + renamed to ‘/tmp/dest/source’ instead, if some other process + created ‘/tmp/dest’ as a directory. However, if ‘mv -T /tmp/source + /tmp/dest’ succeeds, there is no question that ‘/tmp/source’ was + renamed to ‘/tmp/dest’. + + In the opposite situation, where you want the last operand to be + treated as a directory and want a diagnostic otherwise, you can use + the ‘--target-directory’ (‘-t’) option. + +‘-t DIRECTORY’ +‘--target-directory=DIRECTORY’ + Use DIRECTORY as the directory component of each destination file + name. + + The interface for most programs is that after processing options + and a finite (possibly zero) number of fixed-position arguments, + the remaining argument list is either expected to be empty, or is a + list of items (usually files) that will all be handled identically. + The ‘xargs’ program is designed to work well with this convention. + + The commands in the ‘mv’-family are unusual in that they take a + variable number of arguments with a special case at the _end_ + (namely, the target directory). This makes it nontrivial to + perform some operations, e.g., “move all files from here to ../d/”, + because ‘mv * ../d/’ might exhaust the argument space, and ‘ls | + xargs ...’ doesn’t have a clean way to specify an extra final + argument for each invocation of the subject command. (It can be + done by going through a shell command, but that requires more human + labor and brain power than it should.) + + The ‘--target-directory’ (‘-t’) option allows the ‘cp’, ‘install’, + ‘ln’, and ‘mv’ programs to be used conveniently with ‘xargs’. For + example, you can move the files from the current directory to a + sibling directory, ‘d’ like this: + + ls | xargs mv -t ../d -- + + However, this doesn’t move files whose names begin with ‘.’. If + you use the GNU ‘find’ program, you can move those files too, with + this command: + + find . -mindepth 1 -maxdepth 1 \ + | xargs mv -t ../d + + But both of the above approaches fail if there are no files in the + current directory, or if any file has a name containing a blank or + some other special characters. The following example removes those + limitations and requires both GNU ‘find’ and GNU ‘xargs’: + + find . -mindepth 1 -maxdepth 1 -print0 \ + | xargs --null --no-run-if-empty \ + mv -t ../d + +The ‘--target-directory’ (‘-t’) and ‘--no-target-directory’ (‘-T’) +options cannot be combined. + + +File: coreutils.info, Node: Trailing slashes, Next: Traversing symlinks, Prev: Target directory, Up: Common options + +2.7 Trailing slashes +==================== + +Some GNU programs (at least ‘cp’ and ‘mv’) allow you to remove any +trailing slashes from each SOURCE argument before operating on it. The +‘--strip-trailing-slashes’ option enables this behavior. + + This is useful when a SOURCE argument may have a trailing slash and +specify a symbolic link to a directory. This scenario is in fact rather +common because some shells can automatically append a trailing slash +when performing file name completion on such symbolic links. Without +this option, ‘mv’, for example, (via the system’s rename function) must +interpret a trailing slash as a request to dereference the symbolic link +and so must rename the indirectly referenced _directory_ and not the +symbolic link. Although it may seem surprising that such behavior be +the default, it is required by POSIX and is consistent with other parts +of that standard. + + +File: coreutils.info, Node: Traversing symlinks, Next: Treating / specially, Prev: Trailing slashes, Up: Common options + +2.8 Traversing symlinks +======================= + +The following options modify how ‘chown’ and ‘chgrp’ traverse a +hierarchy when the ‘--recursive’ (‘-R’) option is also specified. If +more than one of the following options is specified, only the final one +takes effect. These options specify whether processing a symbolic link +to a directory entails operating on just the symbolic link or on all +files in the hierarchy rooted at that directory. + + These options are independent of ‘--dereference’ and +‘--no-dereference’ (‘-h’), which control whether to modify a symlink or +its referent. + +‘-H’ + If ‘--recursive’ (‘-R’) is specified and a command line argument is + a symbolic link to a directory, traverse it. + +‘-L’ + In a recursive traversal, traverse every symbolic link to a + directory that is encountered. + +‘-P’ + Do not traverse any symbolic links. This is the default if none of + ‘-H’, ‘-L’, or ‘-P’ is specified. + + +File: coreutils.info, Node: Treating / specially, Next: Special built-in utilities, Prev: Traversing symlinks, Up: Common options + +2.9 Treating ‘/’ specially +========================== + +Certain commands can operate destructively on entire hierarchies. For +example, if a user with appropriate privileges mistakenly runs ‘rm -rf / +tmp/junk’, that may remove all files on the entire system. Since there +are so few legitimate uses for such a command, GNU ‘rm’ normally +declines to operate on any directory that resolves to ‘/’. If you +really want to try to remove all the files on your system, you can use +the ‘--no-preserve-root’ option, but the default behavior, specified by +the ‘--preserve-root’ option, is safer for most purposes. + + The commands ‘chgrp’, ‘chmod’ and ‘chown’ can also operate +destructively on entire hierarchies, so they too support these options. +Although, unlike ‘rm’, they don’t actually unlink files, these commands +are arguably more dangerous when operating recursively on ‘/’, since +they often work much more quickly, and hence damage more files before an +alert user can interrupt them. Tradition and POSIX require these +commands to operate recursively on ‘/’, so they default to +‘--no-preserve-root’, but using the ‘--preserve-root’ option makes them +safer for most purposes. For convenience you can specify +‘--preserve-root’ in an alias or in a shell function. + + Note that the ‘--preserve-root’ option also ensures that ‘chgrp’ and +‘chown’ do not modify ‘/’ even when dereferencing a symlink pointing to +‘/’. + + +File: coreutils.info, Node: Special built-in utilities, Next: Exit status, Prev: Treating / specially, Up: Common options + +2.10 Special built-in utilities +=============================== + +Some programs like ‘nice’ can invoke other programs; for example, the +command ‘nice cat file’ invokes the program ‘cat’ by executing the +command ‘cat file’. However, “special built-in utilities” like ‘exit’ +cannot be invoked this way. For example, the command ‘nice exit’ does +not have a well-defined behavior: it may generate an error message +instead of exiting. + + Here is a list of the special built-in utilities that are +standardized by POSIX 1003.1-2004. + + . : break continue eval exec exit export readonly return set shift + times trap unset + + For example, because ‘.’, ‘:’, and ‘exec’ are special, the commands +‘nice . foo.sh’, ‘nice :’, and ‘nice exec pwd’ do not work as you might +expect. + + Many shells extend this list. For example, Bash has several extra +special built-in utilities like ‘history’, and ‘suspend’, and with Bash +the command ‘nice suspend’ generates an error message instead of +suspending. + + +File: coreutils.info, Node: Exit status, Next: Floating point, Prev: Special built-in utilities, Up: Common options + +2.11 Exit status +================ + +Nearly every command invocation yields an integral “exit status” that +can be used to change how other commands work. For the vast majority of +commands, an exit status of zero indicates success. Failure is +indicated by a nonzero value – typically ‘1’, though it may differ on +unusual platforms as POSIX requires only that it be nonzero. + + However, some of the programs documented here do produce other exit +status values and a few associate different meanings with the values ‘0’ +and ‘1’. Here are the exceptions: ‘chroot’, ‘env’, ‘expr’, ‘ls’, +‘nice’, ‘nohup’, ‘numfmt’, ‘printenv’, ‘runcon’, ‘sort’, ‘stdbuf’, +‘test’, ‘timeout’, ‘tty’. + + +File: coreutils.info, Node: Floating point, Next: Standards conformance, Prev: Exit status, Up: Common options + +2.12 Floating point numbers +=========================== + +Commands that accept or produce floating point numbers employ the +floating point representation of the underlying system, and suffer from +rounding error, overflow, and similar floating-point issues. Almost all +modern systems use IEEE-754 floating point, and it is typically portable +to assume IEEE-754 behavior these days. IEEE-754 has positive and +negative infinity, distinguishes positive from negative zero, and uses +special values called NaNs to represent invalid computations such as +dividing zero by itself. For more information, please see David +Goldberg’s paper What Every Computer Scientist Should Know About +Floating-Point Arithmetic +(https://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html). + + Commands that accept floating point numbers as options, operands or +input use the standard C functions ‘strtod’ and ‘strtold’ to convert +from text to floating point numbers. These floating point numbers +therefore can use scientific notation like ‘1.0e-34’ and ‘-10e100’. +Commands that parse floating point also understand case-insensitive +‘inf’, ‘infinity’, and ‘NaN’, although whether such values are useful +depends on the command in question. Modern C implementations also +accept hexadecimal floating point numbers such as ‘-0x.ep-3’, which +stands for −14/16 times 2^-3, which equals −0.109375. *Note +(libc)Parsing of Floats::. + + Normally the ‘LC_NUMERIC’ locale determines the decimal-point +character. However, some commands’ descriptions specify that they +accept numbers in either the current or the C locale; for example, they +treat ‘3.14’ like ‘3,14’ if the current locale uses comma as a decimal +point. + + +File: coreutils.info, Node: Standards conformance, Next: Multi-call invocation, Prev: Floating point, Up: Common options + +2.13 Standards conformance +========================== + +In a few cases, the GNU utilities’ default behavior is incompatible with +the POSIX standard. To suppress these incompatibilities, define the +‘POSIXLY_CORRECT’ environment variable. Unless you are checking for +POSIX conformance, you probably do not need to define ‘POSIXLY_CORRECT’. + + Newer versions of POSIX are occasionally incompatible with older +versions. For example, older versions of POSIX required the command +‘sort +1’ to sort based on the second and succeeding fields in each +input line, but in POSIX 1003.1-2001 the same command is required to +sort the file named ‘+1’, and you must instead use the command ‘sort -k +2’ to get the field-based sort. To complicate things further, POSIX +1003.1-2008 allows an implementation to have either the old or the new +behavior. + + The GNU utilities normally conform to the version of POSIX that is +standard for your system. To cause them to conform to a different +version of POSIX, define the ‘_POSIX2_VERSION’ environment variable to a +value of the form YYYYMM specifying the year and month the standard was +adopted. Three values are currently supported for ‘_POSIX2_VERSION’: +‘199209’ stands for POSIX 1003.2-1992, ‘200112’ stands for POSIX +1003.1-2001, and ‘200809’ stands for POSIX 1003.1-2008. For example, if +you have a POSIX 1003.1-2001 system but are running software containing +traditional usage like ‘sort +1’ or ‘tail +10’, you can work around the +compatibility problems by setting ‘_POSIX2_VERSION=200809’ in your +environment. + + +File: coreutils.info, Node: Multi-call invocation, Prev: Standards conformance, Up: Common options + +2.14 ‘coreutils’: Multi-call program +==================================== + +The ‘coreutils’ command invokes an individual utility, either implicitly +selected by the last component of the name used to invoke ‘coreutils’, +or explicitly with the ‘--coreutils-prog’ option. Synopsis: + + coreutils --coreutils-prog=PROGRAM ... + + The ‘coreutils’ command is not installed by default, so portable +scripts should not rely on its existence. + + +File: coreutils.info, Node: Output of entire files, Next: Formatting file contents, Prev: Common options, Up: Top + +3 Output of entire files +************************ + +These commands read and write entire files, possibly transforming them +in some way. + +* Menu: + +* cat invocation:: Concatenate and write files. +* tac invocation:: Concatenate and write files in reverse. +* nl invocation:: Number lines and write files. +* od invocation:: Write files in octal or other formats. +* base32 invocation:: Transform data into printable data. +* base64 invocation:: Transform data into printable data. +* basenc invocation:: Transform data into printable data. + + +File: coreutils.info, Node: cat invocation, Next: tac invocation, Up: Output of entire files + +3.1 ‘cat’: Concatenate and write files +====================================== + +‘cat’ copies each FILE (‘-’ means standard input), or standard input if +none are given, to standard output. Synopsis: + + cat [OPTION] [FILE]... + + The program accepts the following options. Also see *note Common +options::. + +‘-A’ +‘--show-all’ + Equivalent to ‘-vET’. + +‘-b’ +‘--number-nonblank’ + Number all nonempty output lines, starting with 1. + +‘-e’ + Equivalent to ‘-vE’. + +‘-E’ +‘--show-ends’ + Display a ‘$’ after the end of each line. The ‘\r\n’ combination + is shown as ‘^M$’. + +‘-n’ +‘--number’ + Number all output lines, starting with 1. This option is ignored + if ‘-b’ is in effect. + +‘-s’ +‘--squeeze-blank’ + Suppress repeated adjacent blank lines; output just one empty line + instead of several. + +‘-t’ + Equivalent to ‘-vT’. + +‘-T’ +‘--show-tabs’ + Display TAB characters as ‘^I’. + +‘-u’ + Ignored; for POSIX compatibility. + +‘-v’ +‘--show-nonprinting’ + Display control characters except for LFD and TAB using ‘^’ + notation and precede characters that have the high bit set with + ‘M-’. + + On systems like MS-DOS that distinguish between text and binary +files, ‘cat’ normally reads and writes in binary mode. However, ‘cat’ +reads in text mode if one of the options ‘-bensAE’ is used or if ‘cat’ +is reading from standard input and standard input is a terminal. +Similarly, ‘cat’ writes in text mode if one of the options ‘-bensAE’ is +used or if standard output is a terminal. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + Examples: + + # Output f's contents, then standard input, then g's contents. + cat f - g + + # Copy standard input to standard output. + cat + + +File: coreutils.info, Node: tac invocation, Next: nl invocation, Prev: cat invocation, Up: Output of entire files + +3.2 ‘tac’: Concatenate and write files in reverse +================================================= + +‘tac’ copies each FILE (‘-’ means standard input), or standard input if +none are given, to standard output, reversing the records (lines by +default) in each separately. Synopsis: + + tac [OPTION]... [FILE]... + + “Records” are separated by instances of a string (newline by +default). By default, this separator string is attached to the end of +the record that it follows in the file. + + The program accepts the following options. Also see *note Common +options::. + +‘-b’ +‘--before’ + The separator is attached to the beginning of the record that it + precedes in the file. + +‘-r’ +‘--regex’ + Treat the separator string as a regular expression. + +‘-s SEPARATOR’ +‘--separator=SEPARATOR’ + Use SEPARATOR as the record separator, instead of newline. Note an + empty SEPARATOR is treated as a zero byte. I.e., input and output + items are delimited with ASCII NUL. + + On systems like MS-DOS that distinguish between text and binary +files, ‘tac’ reads and writes in binary mode. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + Example: + + # Reverse a file character by character. + tac -r -s 'x\|[^x]' + + +File: coreutils.info, Node: nl invocation, Next: od invocation, Prev: tac invocation, Up: Output of entire files + +3.3 ‘nl’: Number lines and write files +====================================== + +‘nl’ writes each FILE (‘-’ means standard input), or standard input if +none are given, to standard output, with line numbers added to some or +all of the lines. Synopsis: + + nl [OPTION]... [FILE]... + + ‘nl’ decomposes its input into (logical) page sections; by default, +the line number is reset to 1 at each logical page section. ‘nl’ treats +all of the input files as a single document; it does not reset line +numbers or logical pages between files. + + A logical page consists of three sections: header, body, and footer. +Any of the sections can be empty. Each can be numbered in a different +style from the others. + + The beginnings of the sections of logical pages are indicated in the +input file by a line containing exactly one of these delimiter strings: + +‘\:\:\:’ + start of header; +‘\:\:’ + start of body; +‘\:’ + start of footer. + + The characters from which these strings are made can be changed from +‘\’ and ‘:’ via options (see below), but the pattern of each string +cannot be changed. + + A section delimiter is replaced by an empty line on output. Any text +that comes before the first section delimiter string in the input file +is considered to be part of a body section, so ‘nl’ treats a file that +contains no section delimiters as a single body section. + + The program accepts the following options. Also see *note Common +options::. + +‘-b STYLE’ +‘--body-numbering=STYLE’ + Select the numbering style for lines in the body section of each + logical page. When a line is not numbered, the current line number + is not incremented, but the line number separator character is + still prepended to the line. The styles are: + + ‘a’ + number all lines, + ‘t’ + number only nonempty lines (default for body), + ‘n’ + do not number lines (default for header and footer), + ‘pBRE’ + number only lines that contain a match for the basic regular + expression BRE. *Note Regular Expressions: (grep)Regular + Expressions. + +‘-d CD’ +‘--section-delimiter=CD’ + Set the section delimiter characters to CD; default is ‘\:’. If + only C is given, the second remains ‘:’. As a GNU extension more + than two characters can be specified, and also if CD is empty (‘-d + ''’), then section matching is disabled. (Remember to protect ‘\’ + or other metacharacters from shell expansion with quotes or extra + backslashes.) + +‘-f STYLE’ +‘--footer-numbering=STYLE’ + Analogous to ‘--body-numbering’. + +‘-h STYLE’ +‘--header-numbering=STYLE’ + Analogous to ‘--body-numbering’. + +‘-i NUMBER’ +‘--line-increment=NUMBER’ + Increment line numbers by NUMBER (default 1). NUMBER can be + negative to decrement. + +‘-l NUMBER’ +‘--join-blank-lines=NUMBER’ + Consider NUMBER (default 1) consecutive empty lines to be one + logical line for numbering, and only number the last one. Where + fewer than NUMBER consecutive empty lines occur, do not number + them. An empty line is one that contains no characters, not even + spaces or tabs. + +‘-n FORMAT’ +‘--number-format=FORMAT’ + Select the line numbering format (default is ‘rn’): + + ‘ln’ + left justified, no leading zeros; + ‘rn’ + right justified, no leading zeros; + ‘rz’ + right justified, leading zeros. + +‘-p’ +‘--no-renumber’ + Do not reset the line number at the start of a logical page. + +‘-s STRING’ +‘--number-separator=STRING’ + Separate the line number from the text line in the output with + STRING (default is the TAB character). + +‘-v NUMBER’ +‘--starting-line-number=NUMBER’ + Set the initial line number on each logical page to NUMBER (default + 1). The starting NUMBER can be negative. + +‘-w NUMBER’ +‘--number-width=NUMBER’ + Use NUMBER characters for line numbers (default 6). + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: od invocation, Next: base32 invocation, Prev: nl invocation, Up: Output of entire files + +3.4 ‘od’: Write files in octal or other formats +=============================================== + +‘od’ writes an unambiguous representation of each FILE (‘-’ means +standard input), or standard input if none are given. Synopses: + + od [OPTION]... [FILE]... + od [-abcdfilosx]... [FILE] [[+]OFFSET[.][b]] + od [OPTION]... --traditional [FILE] [[+]OFFSET[.][b] [[+]LABEL[.][b]]] + + Each line of output consists of the offset in the input, followed by +groups of data from the file. By default, ‘od’ prints the offset in +octal, and each group of file data is a C ‘short int’’s worth of input +printed as a single octal number. + + If OFFSET is given, it specifies how many input bytes to skip before +formatting and writing. By default, it is interpreted as an octal +number, but the optional trailing decimal point causes it to be +interpreted as decimal. If no decimal is specified and the offset +begins with ‘0x’ or ‘0X’ it is interpreted as a hexadecimal number. If +there is a trailing ‘b’, the number of bytes skipped will be OFFSET +multiplied by 512. + + If a command is of both the first and second forms, the second form +is assumed if the last operand begins with ‘+’ or (if there are two +operands) a digit. For example, in ‘od foo 10’ and ‘od +10’ the ‘10’ is +an offset, whereas in ‘od 10’ the ‘10’ is a file name. + + The program accepts the following options. Also see *note Common +options::. + +‘-A RADIX’ +‘--address-radix=RADIX’ + Select the base in which file offsets are printed. RADIX can be + one of the following: + + ‘d’ + decimal; + ‘o’ + octal; + ‘x’ + hexadecimal; + ‘n’ + none (do not print offsets). + + The default is octal. + +‘--endian=ORDER’ + Reorder input bytes, to handle inputs with differing byte orders, + or to provide consistent output independent of the endian + convention of the current system. Swapping is performed according + to the specified ‘--type’ size and endian ORDER, which can be + ‘little’ or ‘big’. + +‘-j BYTES’ +‘--skip-bytes=BYTES’ + Skip BYTES input bytes before formatting and writing. If BYTES + begins with ‘0x’ or ‘0X’, it is interpreted in hexadecimal; + otherwise, if it begins with ‘0’, in octal; otherwise, in decimal. + BYTES may be, or may be an integer optionally followed by, one of + the following multiplicative suffixes: + ‘b’ => 512 ("blocks") + ‘KB’ => 1000 (KiloBytes) + ‘K’ => 1024 (KibiBytes) + ‘MB’ => 1000*1000 (MegaBytes) + ‘M’ => 1024*1024 (MebiBytes) + ‘GB’ => 1000*1000*1000 (GigaBytes) + ‘G’ => 1024*1024*1024 (GibiBytes) + and so on for ‘T’, ‘P’, ‘E’, ‘Z’, ‘Y’, ‘R’, and ‘Q’. Binary + prefixes can be used, too: ‘KiB’=‘K’, ‘MiB’=‘M’, and so on. + +‘-N BYTES’ +‘--read-bytes=BYTES’ + Output at most BYTES bytes of the input. Prefixes and suffixes on + ‘bytes’ are interpreted as for the ‘-j’ option. + +‘-S BYTES’ +‘--strings[=BYTES]’ + Instead of the normal output, output only “string constants”: at + least BYTES consecutive printable characters, followed by a zero + byte (ASCII NUL). Prefixes and suffixes on BYTES are interpreted as + for the ‘-j’ option. + + If BYTES is omitted with ‘--strings’, the default is 3. + +‘-t TYPE’ +‘--format=TYPE’ + Select the format in which to output the file data. TYPE is a + string of one or more of the below type indicator characters. If + you include more than one type indicator character in a single TYPE + string, or use this option more than once, ‘od’ writes one copy of + each output line using each of the data types that you specified, + in the order that you specified. + + Adding a trailing “z” to any type specification appends a display + of the single byte character representation of the printable + characters to the output line generated by the type specification. + + ‘a’ + named character, ignoring high-order bit + ‘c’ + printable single byte character, C backslash escape or a 3 + digit octal sequence + ‘d’ + signed decimal + ‘f’ + floating point (*note Floating point::) + ‘o’ + octal + ‘u’ + unsigned decimal + ‘x’ + hexadecimal + + The type ‘a’ outputs things like ‘sp’ for space, ‘nl’ for newline, + and ‘nul’ for a zero byte. Only the least significant seven bits + of each byte is used; the high-order bit is ignored. Type ‘c’ + outputs ‘ ’, ‘\n’, and ‘\0’, respectively. + + Except for types ‘a’ and ‘c’, you can specify the number of bytes + to use in interpreting each number in the given data type by + following the type indicator character with a decimal integer. + Alternately, you can specify the size of one of the C compiler’s + built-in data types by following the type indicator character with + one of the following characters. For integers (‘d’, ‘o’, ‘u’, + ‘x’): + + ‘C’ + char + ‘S’ + short + ‘I’ + int + ‘L’ + long + + For floating point (‘f’): + + F + float + D + double + L + long double + +‘-v’ +‘--output-duplicates’ + Output consecutive lines that are identical. By default, when two + or more consecutive output lines would be identical, ‘od’ outputs + only the first line, and puts just an asterisk on the following + line to indicate the elision. + +‘-w[N]’ +‘--width[=N]’ + Dump ‘n’ input bytes per output line. This must be a multiple of + the least common multiple of the sizes associated with the + specified output types. + + If this option is not given at all, the default is 16. If N is + omitted, the default is 32. + + The next several options are shorthands for format specifications. +GNU ‘od’ accepts any combination of shorthands and format specification +options. These options accumulate. + +‘-a’ + Output as named characters. Equivalent to ‘-t a’. + +‘-b’ + Output as octal bytes. Equivalent to ‘-t o1’. + +‘-c’ + Output as printable single byte characters, C backslash escapes or + 3 digit octal sequences. Equivalent to ‘-t c’. + +‘-d’ + Output as unsigned decimal two-byte units. Equivalent to ‘-t u2’. + +‘-f’ + Output as floats. Equivalent to ‘-t fF’. + +‘-i’ + Output as decimal ints. Equivalent to ‘-t dI’. + +‘-l’ + Output as decimal long ints. Equivalent to ‘-t dL’. + +‘-o’ + Output as octal two-byte units. Equivalent to ‘-t o2’. + +‘-s’ + Output as decimal two-byte units. Equivalent to ‘-t d2’. + +‘-x’ + Output as hexadecimal two-byte units. Equivalent to ‘-t x2’. + +‘--traditional’ + Recognize the non-option label argument that traditional ‘od’ + accepted. The following syntax: + + od --traditional [FILE] [[+]OFFSET[.][b] [[+]LABEL[.][b]]] + + can be used to specify at most one file and optional arguments + specifying an offset and a pseudo-start address, LABEL. The LABEL + argument is interpreted just like OFFSET, but it specifies an + initial pseudo-address. The pseudo-addresses are displayed in + parentheses following any normal address. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: base32 invocation, Next: base64 invocation, Prev: od invocation, Up: Output of entire files + +3.5 ‘base32’: Transform data into printable data +================================================ + +‘base32’ transforms data read from a file, or standard input, into (or +from) base32 encoded form. The base32 encoded form uses printable ASCII +characters to represent binary data. The usage and options of this +command are precisely the same as for ‘base64’. *Note base64 +invocation::. For more general encoding functionality see *note basenc +invocation::. + + +File: coreutils.info, Node: base64 invocation, Next: basenc invocation, Prev: base32 invocation, Up: Output of entire files + +3.6 ‘base64’: Transform data into printable data +================================================ + +‘base64’ transforms data read from a file, or standard input, into (or +from) base64 encoded form. The base64 encoded form uses printable ASCII +characters to represent binary data. Synopses: + + base64 [OPTION]... [FILE] + base64 --decode [OPTION]... [FILE] + + The base64 encoding expands data to roughly 133% of the original. +The base32 encoding expands data to roughly 160% of the original. The +format conforms to RFC 4648 (https://tools.ietf.org/search/rfc4648). + + For more general encoding functionality see *note basenc +invocation::. + + The program accepts the following options. Also see *note Common +options::. + +‘-w COLS’ +‘--wrap=COLS’ + During encoding, wrap lines after COLS characters. This must be a + positive number. + + The default is to wrap after 76 characters. Use the value 0 to + disable line wrapping altogether. + +‘-d’ +‘--decode’ + Change the mode of operation, from the default of encoding data, to + decoding data. Input is expected to be base64 encoded data, and + the output will be the original data. + +‘-i’ +‘--ignore-garbage’ + When decoding, newlines are always accepted. During decoding, + ignore unrecognized bytes, to permit distorted data to be decoded. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: basenc invocation, Prev: base64 invocation, Up: Output of entire files + +3.7 ‘basenc’: Transform data into printable data +================================================ + +‘basenc’ transforms data read from a file, or standard input, into (or +from) various common encoding forms. The encoded form uses printable +ASCII characters to represent binary data. + + Synopses: + + basenc ENCODING [OPTION]... [FILE] + basenc ENCODING --decode [OPTION]... [FILE] + + The ENCODING argument is required. If FILE is omitted, ‘basenc’ +reads from standard input. The ‘-w/--wrap’,‘-i/--ignore-garbage’, +‘-d/--decode’ options of this command are precisely the same as for +‘base64’. *Note base64 invocation::. + + Supported ENCODINGs are: + +‘--base64’ + Encode into (or decode from with ‘-d/--decode’) base64 form. The + format conforms to RFC 4648#4 + (https://tools.ietf.org/search/rfc4648#section-4). Equivalent to + the ‘base64’ command. + +‘--base64url’ + Encode into (or decode from with ‘-d/--decode’) file-and-url-safe + base64 form (using ‘_’ and ‘-’ instead of ‘+’ and ‘/’). The format + conforms to RFC 4648#5 + (https://tools.ietf.org/search/rfc4648#section-5). + +‘--base32’ + Encode into (or decode from with ‘-d/--decode’) base32 form. The + encoded data uses the ‘ABCDEFGHIJKLMNOPQRSTUVWXYZ234567=’ + characters. The format conforms to RFC 4648#6 + (https://tools.ietf.org/search/rfc4648#section-6). Equivalent to + the ‘base32’ command. + +‘--base32hex’ + Encode into (or decode from with ‘-d/--decode’) Extended Hex + Alphabet base32 form. The encoded data uses the + ‘0123456789ABCDEFGHIJKLMNOPQRSTUV=’ characters. The format + conforms to RFC 4648#7 + (https://tools.ietf.org/search/rfc4648#section-7). + +‘--base16’ + Encode into (or decode from with ‘-d/--decode’) base16 + (hexadecimal) form. The encoded data uses the ‘0123456789ABCDEF’ + characters. The format conforms to RFC 4648#8 + (https://tools.ietf.org/search/rfc4648#section-8). + +‘--base2lsbf’ + Encode into (or decode from with ‘-d/--decode’) binary string form + (‘0’ and ‘1’) with the _least_ significant bit of every byte first. + +‘--base2msbf’ + Encode into (or decode from with ‘-d/--decode’) binary string form + (‘0’ and ‘1’) with the _most_ significant bit of every byte first. + +‘--z85’ + Encode into (or decode from with ‘-d/--decode’) Z85 form (a + modified Ascii85 form). The encoded data uses the + ‘0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTU VWXYZ.-:+=^!/*?&<>()[]{}@%$#’. + characters. The format conforms to ZeroMQ spec:32/Z85 + (https://rfc.zeromq.org/spec:32/Z85/). + + When encoding with ‘--z85’, input length must be a multiple of 4; + when decoding with ‘--z85’, input length must be a multiple of 5. + + Encoding/decoding examples: + + $ printf '\376\117\202' | basenc --base64 + /k+C + + $ printf '\376\117\202' | basenc --base64url + _k-C + + $ printf '\376\117\202' | basenc --base32 + 7ZHYE=== + + $ printf '\376\117\202' | basenc --base32hex + VP7O4=== + + $ printf '\376\117\202' | basenc --base16 + FE4F82 + + $ printf '\376\117\202' | basenc --base2lsbf + 011111111111001001000001 + + $ printf '\376\117\202' | basenc --base2msbf + 111111100100111110000010 + + $ printf '\376\117\202\000' | basenc --z85 + @.FaC + + $ printf 01010100 | basenc --base2msbf --decode + T + + $ printf 01010100 | basenc --base2lsbf --decode + * + + +File: coreutils.info, Node: Formatting file contents, Next: Output of parts of files, Prev: Output of entire files, Up: Top + +4 Formatting file contents +************************** + +These commands reformat the contents of files. + +* Menu: + +* fmt invocation:: Reformat paragraph text. +* pr invocation:: Paginate or columnate files for printing. +* fold invocation:: Wrap input lines to fit in specified width. + + +File: coreutils.info, Node: fmt invocation, Next: pr invocation, Up: Formatting file contents + +4.1 ‘fmt’: Reformat paragraph text +================================== + +‘fmt’ fills and joins lines to produce output lines of (at most) a given +number of characters (75 by default). Synopsis: + + fmt [OPTION]... [FILE]... + + ‘fmt’ reads from the specified FILE arguments (or standard input if +none are given), and writes to standard output. + + By default, blank lines, spaces between words, and indentation are +preserved in the output; successive input lines with different +indentation are not joined; tabs are expanded on input and introduced on +output. + + ‘fmt’ prefers breaking lines at the end of a sentence, and tries to +avoid line breaks after the first word of a sentence or before the last +word of a sentence. A “sentence break” is defined as either the end of +a paragraph or a word ending in any of ‘.?!’, followed by two spaces or +end of line, ignoring any intervening parentheses or quotes. Like TeX, +‘fmt’ reads entire “paragraphs” before choosing line breaks; the +algorithm is a variant of that given by Donald E. Knuth and Michael F. +Plass in “Breaking Paragraphs Into Lines”, ‘Software: Practice & +Experience’ 11, 11 (November 1981), 1119–1184. + + The program accepts the following options. Also see *note Common +options::. + +‘-c’ +‘--crown-margin’ + “Crown margin” mode: preserve the indentation of the first two + lines within a paragraph, and align the left margin of each + subsequent line with that of the second line. + +‘-t’ +‘--tagged-paragraph’ + “Tagged paragraph” mode: like crown margin mode, except that if + indentation of the first line of a paragraph is the same as the + indentation of the second, the first line is treated as a one-line + paragraph. + +‘-s’ +‘--split-only’ + Split lines only. Do not join short lines to form longer ones. + This prevents sample lines of code, and other such “formatted” text + from being unduly combined. + +‘-u’ +‘--uniform-spacing’ + Uniform spacing. Reduce spacing between words to one space, and + spacing between sentences to two spaces. + +‘-WIDTH’ +‘-w WIDTH’ +‘--width=WIDTH’ + Fill output lines up to WIDTH characters (default 75 or GOAL plus + 10, if GOAL is provided). + +‘-g GOAL’ +‘--goal=GOAL’ + ‘fmt’ initially tries to make lines GOAL characters wide. By + default, this is 7% shorter than WIDTH. + +‘-p PREFIX’ +‘--prefix=PREFIX’ + Only lines beginning with PREFIX (possibly preceded by whitespace) + are subject to formatting. The prefix and any preceding whitespace + are stripped for the formatting and then re-attached to each + formatted output line. One use is to format certain kinds of + program comments, while leaving the code unchanged. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: pr invocation, Next: fold invocation, Prev: fmt invocation, Up: Formatting file contents + +4.2 ‘pr’: Paginate or columnate files for printing +================================================== + +‘pr’ writes each FILE (‘-’ means standard input), or standard input if +none are given, to standard output, paginating and optionally outputting +in multicolumn format; optionally merges all FILEs, printing all in +parallel, one per column. Synopsis: + + pr [OPTION]... [FILE]... + + By default, a 5-line header is printed at each page: two blank lines; +a line with the date, the file name, and the page count; and two more +blank lines. A footer of five blank lines is also printed. The default +PAGE_LENGTH is 66 lines. The default number of text lines is therefore +56. The text line of the header takes the form ‘DATE STRING PAGE’, with +spaces inserted around STRING so that the line takes up the full +PAGE_WIDTH. Here, DATE is the date (see the ‘-D’ or ‘--date-format’ +option for details), STRING is the centered header string, and PAGE +identifies the page number. The ‘LC_MESSAGES’ locale category affects +the spelling of PAGE; in the default C locale, it is ‘Page NUMBER’ where +NUMBER is the decimal page number. + + Form feeds in the input cause page breaks in the output. Multiple +form feeds produce empty pages. + + Columns are of equal width, separated by an optional string (default +is ‘space’). For multicolumn output, lines will always be truncated to +PAGE_WIDTH (default 72), unless you use the ‘-J’ option. For single +column output no line truncation occurs by default. Use ‘-W’ option to +truncate lines in that case. + + The program accepts the following options. Also see *note Common +options::. + +‘+FIRST_PAGE[:LAST_PAGE]’ +‘--pages=FIRST_PAGE[:LAST_PAGE]’ + Begin printing with page FIRST_PAGE and stop with LAST_PAGE. + Missing ‘:LAST_PAGE’ implies end of file. While estimating the + number of skipped pages each form feed in the input file results in + a new page. Page counting with and without ‘+FIRST_PAGE’ is + identical. By default, counting starts with the first page of + input file (not first page printed). Line numbering may be altered + by ‘-N’ option. + +‘-COLUMN’ +‘--columns=COLUMN’ + With each single FILE, produce COLUMN columns of output (default is + 1) and print columns down, unless ‘-a’ is used. The column width + is automatically decreased as COLUMN increases; unless you use the + ‘-W/-w’ option to increase PAGE_WIDTH as well. This option might + well cause some lines to be truncated. The number of lines in the + columns on each page are balanced. The options ‘-e’ and ‘-i’ are + on for multiple text-column output. Together with ‘-J’ option + column alignment and line truncation is turned off. Lines of full + length are joined in a free field format and ‘-S’ option may set + field separators. ‘-COLUMN’ may not be used with ‘-m’ option. + +‘-a’ +‘--across’ + With each single FILE, print columns across rather than down. The + ‘-COLUMN’ option must be given with COLUMN greater than one. If a + line is too long to fit in a column, it is truncated. + +‘-c’ +‘--show-control-chars’ + Print control characters using hat notation (e.g., ‘^G’); print + other nonprinting characters in octal backslash notation. By + default, nonprinting characters are not changed. + +‘-d’ +‘--double-space’ + Double space the output. + +‘-D FORMAT’ +‘--date-format=FORMAT’ + Format header dates using FORMAT, using the same conventions as for + the command ‘date +FORMAT’. *Note date invocation::. Except for + directives, which start with ‘%’, characters in FORMAT are printed + unchanged. You can use this option to specify an arbitrary string + in place of the header date, e.g., ‘--date-format="Monday + morning"’. + + The default date format is ‘%Y-%m-%d %H:%M’ (for example, + ‘2020-07-09 23:59’); but if the ‘POSIXLY_CORRECT’ environment + variable is set and the ‘LC_TIME’ locale category specifies the + POSIX locale, the default is ‘%b %e %H:%M %Y’ (for example, ‘Jul 9 + 23:59 2020’. + + Timestamps are listed according to the time zone rules specified by + the ‘TZ’ environment variable, or by the system default rules if + ‘TZ’ is not set. *Note Specifying the Time Zone with ‘TZ’: + (libc)TZ Variable. + +‘-e[IN-TABCHAR[IN-TABWIDTH]]’ +‘--expand-tabs[=IN-TABCHAR[IN-TABWIDTH]]’ + Expand TABs to spaces on input. Optional argument IN-TABCHAR is + the input tab character (default is the TAB character). Second + optional argument IN-TABWIDTH is the input tab character’s width + (default is 8). + +‘-f’ +‘-F’ +‘--form-feed’ + Use a form feed instead of newlines to separate output pages. This + does not alter the default page length of 66 lines. + +‘-h HEADER’ +‘--header=HEADER’ + Replace the file name in the header with the centered string + HEADER. When using the shell, HEADER should be quoted and should + be separated from ‘-h’ by a space. + +‘-i[OUT-TABCHAR[OUT-TABWIDTH]]’ +‘--output-tabs[=OUT-TABCHAR[OUT-TABWIDTH]]’ + Replace spaces with TABs on output. Optional argument OUT-TABCHAR + is the output tab character (default is the TAB character). Second + optional argument OUT-TABWIDTH is the output tab character’s width + (default is 8). + +‘-J’ +‘--join-lines’ + Merge lines of full length. Used together with the column options + ‘-COLUMN’, ‘-a -COLUMN’ or ‘-m’. Turns off ‘-W/-w’ line + truncation; no column alignment used; may be used with + ‘--sep-string[=STRING]’. ‘-J’ has been introduced (together with + ‘-W’ and ‘--sep-string’) to disentangle the old (POSIX-compliant) + options ‘-w’ and ‘-s’ along with the three column options. + +‘-l PAGE_LENGTH’ +‘--length=PAGE_LENGTH’ + Set the page length to PAGE_LENGTH (default 66) lines, including + the lines of the header [and the footer]. If PAGE_LENGTH is less + than or equal to 10, the header and footer are omitted, as if the + ‘-t’ option had been given. + +‘-m’ +‘--merge’ + Merge and print all FILEs in parallel, one in each column. If a + line is too long to fit in a column, it is truncated, unless the + ‘-J’ option is used. ‘--sep-string[=STRING]’ may be used. Empty + pages in some FILEs (form feeds set) produce empty columns, still + marked by STRING. The result is a continuous line numbering and + column marking throughout the whole merged file. Completely empty + merged pages show no separators or line numbers. The default + header becomes ‘DATE PAGE’ with spaces inserted in the middle; this + may be used with the ‘-h’ or ‘--header’ option to fill up the + middle blank part. + +‘-n[NUMBER-SEPARATOR[DIGITS]]’ +‘--number-lines[=NUMBER-SEPARATOR[DIGITS]]’ + Provide DIGITS digit line numbering (default for DIGITS is 5). + With multicolumn output the number occupies the first DIGITS column + positions of each text column or only each line of ‘-m’ output. + With single column output the number precedes each line just as + ‘-m’ does. Default counting of the line numbers starts with the + first line of the input file (not the first line printed, compare + the ‘--page’ option and ‘-N’ option). Optional argument + NUMBER-SEPARATOR is the character appended to the line number to + separate it from the text followed. The default separator is the + TAB character. In a strict sense a TAB is always printed with + single column output only. The TAB width varies with the TAB + position, e.g., with the left MARGIN specified by ‘-o’ option. + With multicolumn output priority is given to ‘equal width of output + columns’ (a POSIX specification). The TAB width is fixed to the + value of the first column and does not change with different values + of left MARGIN. That means a fixed number of spaces is always + printed in the place of the NUMBER-SEPARATOR TAB. The tabification + depends upon the output position. + +‘-N LINE_NUMBER’ +‘--first-line-number=LINE_NUMBER’ + Start line counting with the number LINE_NUMBER at first line of + first page printed (in most cases not the first line of the input + file). + +‘-o MARGIN’ +‘--indent=MARGIN’ + Indent each line with a margin MARGIN spaces wide (default is + zero). The total page width is the size of the margin plus the + PAGE_WIDTH set with the ‘-W/-w’ option. A limited overflow may + occur with numbered single column output (compare ‘-n’ option). + +‘-r’ +‘--no-file-warnings’ + Do not print a warning message when an argument FILE cannot be + opened. (The exit status will still be nonzero, however.) + +‘-s[CHAR]’ +‘--separator[=CHAR]’ + Separate columns by a single character CHAR. The default for CHAR + is the TAB character without ‘-w’ and ‘no character’ with ‘-w’. + Without ‘-s’ the default separator ‘space’ is set. ‘-s[char]’ + turns off line truncation of all three column options + (‘-COLUMN’|‘-a -COLUMN’|‘-m’) unless ‘-w’ is set. This is a + POSIX-compliant formulation. + +‘-S[STRING]’ +‘--sep-string[=STRING]’ + Use STRING to separate output columns. The ‘-S’ option doesn’t + affect the ‘-W/-w’ option, unlike the ‘-s’ option which does. It + does not affect line truncation or column alignment. Without ‘-S’, + and with ‘-J’, ‘pr’ uses the default output separator, TAB. + Without ‘-S’ or ‘-J’, ‘pr’ uses a ‘space’ (same as ‘-S" "’). If no + ‘STRING’ argument is specified, ‘""’ is assumed. + +‘-t’ +‘--omit-header’ + Do not print the usual header [and footer] on each page, and do not + fill out the bottom of pages (with blank lines or a form feed). No + page structure is produced, but form feeds set in the input files + are retained. The predefined pagination is not changed. ‘-t’ or + ‘-T’ may be useful together with other options; e.g.: ‘-t -e4’, + expand TAB characters in the input file to 4 spaces but don’t make + any other changes. Use of ‘-t’ overrides ‘-h’. + +‘-T’ +‘--omit-pagination’ + Do not print header [and footer]. In addition eliminate all form + feeds set in the input files. + +‘-v’ +‘--show-nonprinting’ + Print nonprinting characters in octal backslash notation. + +‘-w PAGE_WIDTH’ +‘--width=PAGE_WIDTH’ + Set page width to PAGE_WIDTH characters for multiple text-column + output only (default for PAGE_WIDTH is 72). The specified + PAGE_WIDTH is rounded down so that columns have equal width. + ‘-s[CHAR]’ turns off the default page width and any line truncation + and column alignment. Lines of full length are merged, regardless + of the column options set. No PAGE_WIDTH setting is possible with + single column output. A POSIX-compliant formulation. + +‘-W PAGE_WIDTH’ +‘--page_width=PAGE_WIDTH’ + Set the page width to PAGE_WIDTH characters, honored with and + without a column option. With a column option, the specified + PAGE_WIDTH is rounded down so that columns have equal width. Text + lines are truncated, unless ‘-J’ is used. Together with one of the + three column options (‘-COLUMN’, ‘-a -COLUMN’ or ‘-m’) column + alignment is always used. The separator options ‘-S’ or ‘-s’ don’t + disable the ‘-W’ option. Default is 72 characters. Without ‘-W + PAGE_WIDTH’ and without any of the column options NO line + truncation is used (defined to keep downward compatibility and to + meet most frequent tasks). That’s equivalent to ‘-W 72 -J’. The + header line is never truncated. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: fold invocation, Prev: pr invocation, Up: Formatting file contents + +4.3 ‘fold’: Wrap input lines to fit in specified width +====================================================== + +‘fold’ writes each FILE (‘-’ means standard input), or standard input if +none are given, to standard output, breaking long lines. Synopsis: + + fold [OPTION]... [FILE]... + + By default, ‘fold’ breaks lines wider than 80 columns. The output is +split into as many lines as necessary. + + ‘fold’ counts screen columns by default; thus, a tab may count more +than one column, backspace decreases the column count, and carriage +return sets the column to zero. + + The program accepts the following options. Also see *note Common +options::. + +‘-b’ +‘--bytes’ + Count bytes rather than columns, so that tabs, backspaces, and + carriage returns are each counted as taking up one column, just + like other characters. + +‘-s’ +‘--spaces’ + Break at word boundaries: the line is broken after the last blank + before the maximum line length. If the line contains no such + blanks, the line is broken at the maximum line length as usual. + +‘-w WIDTH’ +‘--width=WIDTH’ + Use a maximum line length of WIDTH columns instead of 80. + + For compatibility ‘fold’ supports an obsolete option syntax + ‘-WIDTH’. New scripts should use ‘-w WIDTH’ instead. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: Output of parts of files, Next: Summarizing files, Prev: Formatting file contents, Up: Top + +5 Output of parts of files +************************** + +These commands output pieces of the input. + +* Menu: + +* head invocation:: Output the first part of files. +* tail invocation:: Output the last part of files. +* split invocation:: Split a file into pieces. +* csplit invocation:: Split a file into context-determined pieces. + + +File: coreutils.info, Node: head invocation, Next: tail invocation, Up: Output of parts of files + +5.1 ‘head’: Output the first part of files +========================================== + +‘head’ prints the first part (10 lines by default) of each FILE; it +reads from standard input if no files are given or when given a FILE of +‘-’. Synopsis: + + head [OPTION]... [FILE]... + + If more than one FILE is specified, ‘head’ prints a one-line header +consisting of: + + ==> FILE NAME <== + +before the output for each FILE. + + The program accepts the following options. Also see *note Common +options::. + +‘-c [-]NUM’ +‘--bytes=[-]NUM’ + Print the first NUM bytes, instead of initial lines. However, if + NUM is prefixed with a ‘-’, print all but the last NUM bytes of + each file. NUM may be, or may be an integer optionally followed + by, one of the following multiplicative suffixes: + ‘b’ => 512 ("blocks") + ‘KB’ => 1000 (KiloBytes) + ‘K’ => 1024 (KibiBytes) + ‘MB’ => 1000*1000 (MegaBytes) + ‘M’ => 1024*1024 (MebiBytes) + ‘GB’ => 1000*1000*1000 (GigaBytes) + ‘G’ => 1024*1024*1024 (GibiBytes) + and so on for ‘T’, ‘P’, ‘E’, ‘Z’, ‘Y’, ‘R’, and ‘Q’. Binary + prefixes can be used, too: ‘KiB’=‘K’, ‘MiB’=‘M’, and so on. + +‘-n [-]NUM’ +‘--lines=[-]NUM’ + Output the first NUM lines. However, if NUM is prefixed with a + ‘-’, print all but the last NUM lines of each file. Size + multiplier suffixes are the same as with the ‘-c’ option. + +‘-q’ +‘--quiet’ +‘--silent’ + Never print file name headers. + +‘-v’ +‘--verbose’ + Always print file name headers. + +‘-z’ +‘--zero-terminated’ + Delimit items with a zero byte rather than a newline (ASCII LF). + I.e., treat input as items separated by ASCII NUL and terminate + output items with ASCII NUL. This option can be useful in + conjunction with ‘perl -0’ or ‘find -print0’ and ‘xargs -0’ which + do the same in order to reliably handle arbitrary file names (even + those containing blanks or other special characters). + + For compatibility ‘head’ also supports an obsolete option syntax +‘-[NUM][bkm][cqv]’, which is recognized only if it is specified first. +NUM is a decimal number optionally followed by a size letter (‘b’, ‘k’, +‘m’) as in ‘-c’, or ‘l’ to mean count by lines, or other option letters +(‘cqv’). Scripts intended for standard hosts should use ‘-c NUM’ or ‘-n +NUM’ instead. If your script must also run on hosts that support only +the obsolete syntax, it is usually simpler to avoid ‘head’, e.g., by +using ‘sed 5q’ instead of ‘head -5’. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: tail invocation, Next: split invocation, Prev: head invocation, Up: Output of parts of files + +5.2 ‘tail’: Output the last part of files +========================================= + +‘tail’ prints the last part (10 lines by default) of each FILE; it reads +from standard input if no files are given or when given a FILE of ‘-’. +Synopsis: + + tail [OPTION]... [FILE]... + + If more than one FILE is specified, ‘tail’ prints a one-line header +before the output for each FILE, consisting of: + + ==> FILE NAME <== + + For further processing of tail output, it can be useful to convert +the file headers to line prefixes, which can be done like: + + tail ... | + awk ' + /^==> .* <==$/ {prefix=substr($0,5,length-8)":"; next} + {print prefix$0} + ' | ... + + GNU ‘tail’ can output any amount of data (some other versions of +‘tail’ cannot). It also has no ‘-r’ option (print in reverse), since +reversing a file is really a different job from printing the end of a +file; BSD ‘tail’ (which is the one with ‘-r’) can only reverse files +that are at most as large as its buffer, which is typically 32 KiB. A +more reliable and versatile way to reverse files is the GNU ‘tac’ +command. + + The program accepts the following options. Also see *note Common +options::. + +‘-c [+]NUM’ +‘--bytes=[+]NUM’ + Output the last NUM bytes, instead of final lines. If NUM is + prefixed with a ‘+’, start printing with byte NUM from the start of + each file. For example to skip the first byte use ‘tail -c +2’, + while to skip all but the last byte use ‘tail -c 1’. NUM may be, + or may be an integer optionally followed by, one of the following + multiplicative suffixes: + ‘b’ => 512 ("blocks") + ‘KB’ => 1000 (KiloBytes) + ‘K’ => 1024 (KibiBytes) + ‘MB’ => 1000*1000 (MegaBytes) + ‘M’ => 1024*1024 (MebiBytes) + ‘GB’ => 1000*1000*1000 (GigaBytes) + ‘G’ => 1024*1024*1024 (GibiBytes) + and so on for ‘T’, ‘P’, ‘E’, ‘Z’, ‘Y’, ‘R’, and ‘Q’. Binary + prefixes can be used, too: ‘KiB’=‘K’, ‘MiB’=‘M’, and so on. + +‘-f’ +‘--follow[=HOW]’ + Loop forever trying to read more characters at the end of the file, + presumably because the file is growing. If more than one file is + given, ‘tail’ prints a header whenever it gets output from a + different file, to indicate which file that output is from. + + There are two ways to specify how you’d like to track files with + this option, but that difference is noticeable only when a followed + file is removed or renamed. If you’d like to continue to track the + end of a growing file even after it has been unlinked, use + ‘--follow=descriptor’. This is the default behavior, but it is not + useful if you’re tracking a log file that may be rotated (removed + or renamed, then reopened). In that case, use ‘--follow=name’ to + track the named file, perhaps by reopening it periodically to see + if it has been removed and recreated by some other program. Note + that the inotify-based implementation handles this case without the + need for any periodic reopening. + + No matter which method you use, if the tracked file is determined + to have shrunk, ‘tail’ prints a message saying the file has been + truncated and resumes tracking from the start of the file, assuming + it has been truncated to 0, which is the usual truncation operation + for log files. + + When a file is removed, ‘tail’’s behavior depends on whether it is + following the name or the descriptor. When following by name, tail + can detect that a file has been removed and gives a message to that + effect, and if ‘--retry’ has been specified it will continue + checking periodically to see if the file reappears. When following + a descriptor, tail does not detect that the file has been unlinked + or renamed and issues no message; even though the file may no + longer be accessible via its original name, it may still be + growing. + + The option values ‘descriptor’ and ‘name’ may be specified only + with the long form of the option, not with ‘-f’. + + The ‘-f’ option is ignored if no FILE operand is specified and + standard input is a FIFO or a pipe. Likewise, the ‘-f’ option has + no effect for any operand specified as ‘-’, when standard input is + a FIFO or a pipe. + + With kernel inotify support, output is triggered by file changes + and is generally very prompt. Otherwise, ‘tail’ sleeps for one + second between checks – use ‘--sleep-interval=N’ to change that + default – which can make the output appear slightly less responsive + or bursty. When using tail without inotify support, you can make + it more responsive by using a sub-second sleep interval, e.g., via + an alias like this: + + alias tail='tail -s.1' + +‘-F’ + This option is the same as ‘--follow=name --retry’. That is, tail + will attempt to reopen a file when it is removed. Should this + fail, tail will keep trying until it becomes accessible again. + +‘--max-unchanged-stats=N’ + When tailing a file by name, if there have been N (default n=5) + consecutive iterations for which the file has not changed, then + ‘open’/‘fstat’ the file to determine if that file name is still + associated with the same device/inode-number pair as before. When + following a log file that is rotated, this is approximately the + number of seconds between when tail prints the last pre-rotation + lines and when it prints the lines that have accumulated in the new + log file. This option is meaningful only when polling (i.e., + without inotify) and when following by name. + +‘-n [+]NUM’ +‘--lines=[+]’ + Output the last NUM lines. If NUM is prefixed with a ‘+’, start + printing with line NUM from the start of each file. For example to + skip the first line use ‘tail -n +2’, while to skip all but the + last line use ‘tail -n 1’. Size multiplier suffixes are the same + as with the ‘-c’ option. + +‘--pid=PID’ + When following by name or by descriptor, you may specify the + process ID, PID, of the sole writer of all FILE arguments. Then, + shortly after that process terminates, tail will also terminate. + This will work properly only if the writer and the tailing process + are running on the same machine. For example, to save the output + of a build in a file and to watch the file grow, if you invoke + ‘make’ and ‘tail’ like this then the tail process will stop when + your build completes. Without this option, you would have had to + kill the ‘tail -f’ process yourself. + + $ make >& makerr & tail --pid=$! -f makerr + + If you specify a PID that is not in use or that does not correspond + to the process that is writing to the tailed files, then ‘tail’ may + terminate long before any FILEs stop growing or it may not + terminate until long after the real writer has terminated. Note + that ‘--pid’ cannot be supported on some systems; ‘tail’ will print + a warning if this is the case. + +‘-q’ +‘--quiet’ +‘--silent’ + Never print file name headers. + +‘--retry’ + Indefinitely try to open the specified file. This option is useful + mainly when following (and otherwise issues a warning). + + When following by file descriptor (i.e., with + ‘--follow=descriptor’), this option only affects the initial open + of the file, as after a successful open, ‘tail’ will start + following the file descriptor. + + When following by name (i.e., with ‘--follow=name’), ‘tail’ + infinitely retries to re-open the given files until killed. + + Without this option, when ‘tail’ encounters a file that doesn’t + exist or is otherwise inaccessible, it reports that fact and never + checks it again. + +‘-s NUMBER’ +‘--sleep-interval=NUMBER’ + Change the number of seconds to wait between iterations (the + default is 1.0). During one iteration, every specified file is + checked to see if it has changed size. When ‘tail’ uses inotify, + this polling-related option is usually ignored. However, if you + also specify ‘--pid=P’, ‘tail’ checks whether process P is alive at + least every NUMBER seconds. The NUMBER must be non-negative and + can be a floating-point number in either the current or the C + locale. *Note Floating point::. + +‘-v’ +‘--verbose’ + Always print file name headers. + +‘-z’ +‘--zero-terminated’ + Delimit items with a zero byte rather than a newline (ASCII LF). + I.e., treat input as items separated by ASCII NUL and terminate + output items with ASCII NUL. This option can be useful in + conjunction with ‘perl -0’ or ‘find -print0’ and ‘xargs -0’ which + do the same in order to reliably handle arbitrary file names (even + those containing blanks or other special characters). + + For compatibility ‘tail’ also supports an obsolete usage ‘tail +-[NUM][bcl][f] [FILE]’, which is recognized only if it does not conflict +with the usage described above. This obsolete form uses exactly one +option and at most one file. In the option, NUM is an optional decimal +number optionally followed by a size letter (‘b’, ‘c’, ‘l’) to mean +count by 512-byte blocks, bytes, or lines, optionally followed by ‘f’ +which has the same meaning as ‘-f’. + + On systems not conforming to POSIX 1003.1-2001, the leading ‘-’ can +be replaced by ‘+’ in the traditional option syntax with the same +meaning as in counts, and on obsolete systems predating POSIX +1003.1-2001 traditional usage overrides normal usage when the two +conflict. This behavior can be controlled with the ‘_POSIX2_VERSION’ +environment variable (*note Standards conformance::). + + Scripts intended for use on standard hosts should avoid traditional +syntax and should use ‘-c NUM[b]’, ‘-n NUM’, and/or ‘-f’ instead. If +your script must also run on hosts that support only the traditional +syntax, you can often rewrite it to avoid problematic usages, e.g., by +using ‘sed -n '$p'’ rather than ‘tail -1’. If that’s not possible, the +script can use a test like ‘if tail -c +1 </dev/null >/dev/null 2>&1; +then ...’ to decide which syntax to use. + + Even if your script assumes the standard behavior, you should still +beware usages whose behaviors differ depending on the POSIX version. +For example, avoid ‘tail - main.c’, since it might be interpreted as +either ‘tail main.c’ or as ‘tail -- - main.c’; avoid ‘tail -c 4’, since +it might mean either ‘tail -c4’ or ‘tail -c 10 4’; and avoid ‘tail +4’, +since it might mean either ‘tail ./+4’ or ‘tail -n +4’. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: split invocation, Next: csplit invocation, Prev: tail invocation, Up: Output of parts of files + +5.3 ‘split’: Split a file into pieces. +====================================== + +‘split’ creates output files containing consecutive or interleaved +sections of INPUT (standard input if none is given or INPUT is ‘-’). +Synopsis: + + split [OPTION] [INPUT [PREFIX]] + + By default, ‘split’ puts 1000 lines of INPUT (or whatever is left +over for the last section), into each output file. + + The output files’ names consist of PREFIX (‘x’ by default) followed +by a group of characters (‘aa’, ‘ab’, ... by default), such that +concatenating the output files in traditional sorted order by file name +produces the original input file (except ‘-nr/N’). By default split +will initially create files with two generated suffix characters, and +will increase this width by two when the next most significant position +reaches the last character. (‘yz’, ‘zaaa’, ‘zaab’, ...). In this way +an arbitrary number of output files are supported, which sort as +described above, even in the presence of an ‘--additional-suffix’ +option. If the ‘-a’ option is specified and the output file names are +exhausted, ‘split’ reports an error without deleting the output files +that it did create. + + The program accepts the following options. Also see *note Common +options::. + +‘-l LINES’ +‘--lines=LINES’ + Put LINES lines of INPUT into each output file. If ‘--separator’ + is specified, then LINES determines the number of records. + + For compatibility ‘split’ also supports an obsolete option syntax + ‘-LINES’. New scripts should use ‘-l LINES’ instead. + +‘-b SIZE’ +‘--bytes=SIZE’ + Put SIZE bytes of INPUT into each output file. SIZE may be, or may + be an integer optionally followed by, one of the following + multiplicative suffixes: + ‘b’ => 512 ("blocks") + ‘KB’ => 1000 (KiloBytes) + ‘K’ => 1024 (KibiBytes) + ‘MB’ => 1000*1000 (MegaBytes) + ‘M’ => 1024*1024 (MebiBytes) + ‘GB’ => 1000*1000*1000 (GigaBytes) + ‘G’ => 1024*1024*1024 (GibiBytes) + and so on for ‘T’, ‘P’, ‘E’, ‘Z’, ‘Y’, ‘R’, and ‘Q’. Binary + prefixes can be used, too: ‘KiB’=‘K’, ‘MiB’=‘M’, and so on. + +‘-C SIZE’ +‘--line-bytes=SIZE’ + Put into each output file as many complete lines of INPUT as + possible without exceeding SIZE bytes. Individual lines or records + longer than SIZE bytes are broken into multiple files. SIZE has + the same format as for the ‘--bytes’ option. If ‘--separator’ is + specified, then LINES determines the number of records. + +‘--filter=COMMAND’ + With this option, rather than simply writing to each output file, + write through a pipe to the specified shell COMMAND for each output + file. COMMAND should use the $FILE environment variable, which is + set to a different output file name for each invocation of the + command. For example, imagine that you have a 1TiB compressed file + that, if uncompressed, would be too large to reside on secondary + storage, yet you must split it into individually-compressed pieces + of a more manageable size. To do that, you might run this command: + + xz -dc BIG.xz | split -b200G --filter='xz > $FILE.xz' - big- + + Assuming a 10:1 compression ratio, that would create about fifty + 20GiB files with names ‘big-aa.xz’, ‘big-ab.xz’, ‘big-ac.xz’, etc. + +‘-n CHUNKS’ +‘--number=CHUNKS’ + + Split INPUT to CHUNKS output files where CHUNKS may be: + + N generate N files based on current size of INPUT + K/N output only Kth of N to standard output + l/N generate N files without splitting lines or records + l/K/N likewise but output only Kth of N to stdout + r/N like ‘l’ but use round robin distribution + r/K/N likewise but output only Kth of N to stdout + + If the input size is not a multiple of N, early output files are + one byte longer than later output files, to make up the difference. + Any excess bytes appearing after the initial calculation are + discarded (except when using ‘r’ mode). + + All N files are created even if there are fewer than N lines, or + the INPUT is truncated. + + For ‘l’ mode, chunks are approximately INPUT size / N. Although + the INPUT is still partitioned as before into N regions of + approximately equal size, if a line _starts_ within a partition it + is written completely to the corresponding file. Since lines or + records are not split even if they overlap a partition, the files + written can be larger or smaller than the partition size, and even + empty if a line/record is so long as to completely overlap the + partition. + + When the input is a pipe or some other special file where the size + cannot easily be determined, there is no trouble for ‘r’ mode + because the size of the input is irrelevant. For other modes, such + an input is first copied to a temporary to determine its size. + +‘-a LENGTH’ +‘--suffix-length=LENGTH’ + Use suffixes of length LENGTH. If a LENGTH of 0 is specified, this + is the same as if (any previous) ‘-a’ was not specified, and thus + enables the default behavior, which starts the suffix length at 2, + and unless ‘-n’ or ‘--numeric-suffixes=FROM’ is specified, will + auto increase the length by 2 as required. + +‘-d’ +‘--numeric-suffixes[=FROM]’ + Use digits in suffixes rather than lower-case letters. The + numerical suffix counts from FROM if specified, 0 otherwise. + + FROM is supported with the long form option, and is used to either + set the initial suffix for a single run, or to set the suffix + offset for independently split inputs, and consequently the auto + suffix length expansion described above is disabled. Therefore you + may also want to use option ‘-a’ to allow suffixes beyond ‘99’. + Note if option ‘--number’ is specified and the number of files is + less than FROM, a single run is assumed and the minimum suffix + length required is automatically determined. + +‘-x’ +‘--hex-suffixes[=FROM]’ + Like ‘--numeric-suffixes’, but use hexadecimal numbers (in lower + case). + +‘--additional-suffix=SUFFIX’ + Append an additional SUFFIX to output file names. SUFFIX must not + contain slash. + +‘-e’ +‘--elide-empty-files’ + Suppress the generation of zero-length output files. This can + happen with the ‘--number’ option if a file is (truncated to be) + shorter than the number requested, or if a line is so long as to + completely span a chunk. The output file sequence numbers, always + run consecutively even when this option is specified. + +‘-t SEPARATOR’ +‘--separator=SEPARATOR’ + Use character SEPARATOR as the record separator instead of the + default newline character (ASCII LF). To specify ASCII NUL as the + separator, use the two-character string ‘\0’, e.g., ‘split -t + '\0'’. + +‘-u’ +‘--unbuffered’ + Immediately copy input to output in ‘--number r/...’ mode, which is + a much slower mode of operation. + +‘--verbose’ + Write a diagnostic just before each output file is opened. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + Here are a few examples to illustrate how the ‘--number’ (‘-n’) +option works: + + Notice how, by default, one line may be split onto two or more: + + $ seq -w 6 10 > k; split -n3 k; head xa? + ==> xaa <== + 06 + 07 + ==> xab <== + + 08 + 0 + ==> xac <== + 9 + 10 + + Use the "l/" modifier to suppress that: + + $ seq -w 6 10 > k; split -nl/3 k; head xa? + ==> xaa <== + 06 + 07 + + ==> xab <== + 08 + 09 + + ==> xac <== + 10 + + Use the "r/" modifier to distribute lines in a round-robin fashion: + + $ seq -w 6 10 > k; split -nr/3 k; head xa? + ==> xaa <== + 06 + 09 + + ==> xab <== + 07 + 10 + + ==> xac <== + 08 + + You can also extract just the Kth chunk. This extracts and prints +just the 7th "chunk" of 33: + + $ seq 100 > k; split -nl/7/33 k + 20 + 21 + 22 + + +File: coreutils.info, Node: csplit invocation, Prev: split invocation, Up: Output of parts of files + +5.4 ‘csplit’: Split a file into context-determined pieces +========================================================= + +‘csplit’ creates zero or more output files containing sections of INPUT +(standard input if INPUT is ‘-’). Synopsis: + + csplit [OPTION]... INPUT PATTERN... + + The contents of the output files are determined by the PATTERN +arguments, as detailed below. An error occurs if a PATTERN argument +refers to a nonexistent line of the input file (e.g., if no remaining +line matches a given regular expression). After every PATTERN has been +matched, any remaining input is copied into one last output file. + + By default, ‘csplit’ prints the number of bytes written to each +output file after it has been created. + + The types of pattern arguments are: + +‘N’ + Create an output file containing the input up to but not including + line N (a positive integer). If followed by a repeat count, also + create an output file containing the next N lines of the input file + once for each repeat. + +‘/REGEXP/[OFFSET]’ + Create an output file containing the current line up to (but not + including) the next line of the input file that contains a match + for REGEXP. The optional OFFSET is an integer, that can be + preceded by ‘+’ or ‘-’. If it is given, the input up to (but not + including) the matching line plus or minus OFFSET is put into the + output file, and the line after that begins the next section of + input. Note lines within a negative offset of a regexp pattern are + not matched in subsequent regexp patterns. + +‘%REGEXP%[OFFSET]’ + Like the previous type, except that it does not create an output + file, so that section of the input file is effectively ignored. + +‘{REPEAT-COUNT}’ + Repeat the previous pattern REPEAT-COUNT additional times. The + REPEAT-COUNT can either be a positive integer or an asterisk, + meaning repeat as many times as necessary until the input is + exhausted. + + The output files’ names consist of a prefix (‘xx’ by default) +followed by a suffix. By default, the suffix is an ascending sequence +of two-digit decimal numbers from ‘00’ to ‘99’. In any case, +concatenating the output files in sorted order by file name produces the +original input file, excluding portions skipped with a %REGEXP% pattern +or the ‘--suppress-matched’ option. + + By default, if ‘csplit’ encounters an error or receives a hangup, +interrupt, quit, or terminate signal, it removes any output files that +it has created so far before it exits. + + The program accepts the following options. Also see *note Common +options::. + +‘-f PREFIX’ +‘--prefix=PREFIX’ + Use PREFIX as the output file name prefix. + +‘-b FORMAT’ +‘--suffix-format=FORMAT’ + Use FORMAT as the output file name suffix. When this option is + specified, the suffix string must include exactly one + ‘printf(3)’-style conversion specification, possibly including + format specification flags, a field width, a precision + specification, or all of these kinds of modifiers. The format + letter must convert a binary unsigned integer argument to readable + form. The format letters ‘d’ and ‘i’ are aliases for ‘u’, and the + ‘u’, ‘o’, ‘x’, and ‘X’ conversions are allowed. The entire FORMAT + is given (with the current output file number) to ‘sprintf(3)’ to + form the file name suffixes for each of the individual output files + in turn. If this option is used, the ‘--digits’ option is ignored. + +‘-n DIGITS’ +‘--digits=DIGITS’ + Use output file names containing numbers that are DIGITS digits + long instead of the default 2. + +‘-k’ +‘--keep-files’ + Do not remove output files when errors are encountered. + +‘--suppress-matched’ + Do not output lines matching the specified PATTERN. I.e., suppress + the boundary line from the start of the second and subsequent + splits. + +‘-z’ +‘--elide-empty-files’ + Suppress the generation of zero-length output files. (In cases + where the section delimiters of the input file are supposed to mark + the first lines of each of the sections, the first output file will + generally be a zero-length file unless you use this option.) The + output file sequence numbers always run consecutively starting from + 0, even when this option is specified. + +‘-s’ +‘-q’ +‘--silent’ +‘--quiet’ + Do not print counts of output file sizes. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + Here is an example of its usage. First, create an empty directory +for the exercise, and cd into it: + + $ mkdir d && cd d + + Now, split the sequence of 1..14 on lines that end with 0 or 5: + + $ seq 14 | csplit - '/[05]$/' '{*}' + 8 + 10 + 15 + + Each number printed above is the size of an output file that csplit +has just created. List the names of those output files: + + $ ls + xx00 xx01 xx02 + + Use ‘head’ to show their contents: + + $ head xx* + ==> xx00 <== + 1 + 2 + 3 + 4 + + ==> xx01 <== + 5 + 6 + 7 + 8 + 9 + + ==> xx02 <== + 10 + 11 + 12 + 13 + 14 + + Example of splitting input by empty lines: + + $ csplit --suppress-matched INPUT.TXT '/^$/' '{*}' + + +File: coreutils.info, Node: Summarizing files, Next: Operating on sorted files, Prev: Output of parts of files, Up: Top + +6 Summarizing files +******************* + +These commands generate just a few numbers representing entire contents +of files. + +* Menu: + +* wc invocation:: Print newline, word, and byte counts. +* sum invocation:: Print checksum and block counts. +* cksum invocation:: Print CRC checksum and byte counts. +* md5sum invocation:: Print or check MD5 digests. +* b2sum invocation:: Print or check BLAKE2 digests. +* sha1sum invocation:: Print or check SHA-1 digests. +* sha2 utilities:: Print or check SHA-2 digests. + + +File: coreutils.info, Node: wc invocation, Next: sum invocation, Up: Summarizing files + +6.1 ‘wc’: Print newline, word, and byte counts +============================================== + +‘wc’ counts the number of bytes, characters, words, and newlines in each +given FILE, or standard input if none are given or for a FILE of ‘-’. A +word is a nonzero length sequence of printable characters delimited by +white space. Synopsis: + + wc [OPTION]... [FILE]... + + ‘wc’ prints one line of counts for each file, and if the file was +given as an argument, it prints the file name following the counts. By +default if more than one FILE is given, ‘wc’ prints a final line +containing the cumulative counts, with the file name ‘total’. This +‘total’ line can be controlled with the ‘--total’ option, which is a GNU +extension. The counts are printed in this order: newlines, words, +characters, bytes, maximum line length. Each count is printed +right-justified in a field with at least one space between fields so +that the numbers and file names normally line up nicely in columns. The +width of the count fields varies depending on the inputs, so you should +not depend on a particular field width. However, as a GNU extension, if +only one count is printed, it is guaranteed to be printed without +leading spaces. + + By default, ‘wc’ prints three counts: the newline, words, and byte +counts. Options can specify that only certain counts be printed. +Options do not undo others previously given, so + + wc --bytes --words + +prints both the byte counts and the word counts. + + With the ‘--max-line-length’ option, ‘wc’ prints the length of the +longest line per file, and if there is more than one file it prints the +maximum (not the sum) of those lengths. The line lengths here are +measured in screen columns, according to the current locale and assuming +tab positions in every 8th column. + + The program accepts the following options. Also see *note Common +options::. + +‘-c’ +‘--bytes’ + Print only the byte counts. + +‘-m’ +‘--chars’ + Print only the character counts, as per the current locale. + Invalid characters are not counted. + +‘-w’ +‘--words’ + Print only the word counts. A word is a nonzero length sequence of + printable characters separated by white space. + +‘-l’ +‘--lines’ + Print only the newline character counts. Note a file without a + trailing newline character, will not have that last portion + included in the line count. + +‘-L’ +‘--max-line-length’ + Print only the maximum display widths. Tabs are set at every 8th + column. Display widths of wide characters are considered. + Non-printable characters are given 0 width. + +‘--total=WHEN’ + Control when and how the final line with cumulative counts is + printed. WHEN is one of: + • auto - This is the default mode of ‘wc’ when no ‘--total’ + option is specified. Output a total line if more than one + FILE is specified. + • always - Always output a total line, irrespective of the + number of files processed. + • only - Only output total counts. I.e., don’t print individual + file counts, suppress any leading spaces, and don’t print the + ‘total’ word itself, to simplify subsequent processing. + • never - Never output a total line. + +‘--files0-from=FILE’ + Disallow processing files named on the command line, and instead + process those named in file FILE; each name being terminated by a + zero byte (ASCII NUL). This is useful when the list of file names + is so long that it may exceed a command line length limitation. In + such cases, running ‘wc’ via ‘xargs’ is undesirable because it + splits the list into pieces and makes ‘wc’ print a total for each + sublist rather than for the entire list. One way to produce a list + of ASCII NUL terminated file names is with GNU ‘find’, using its + ‘-print0’ predicate. If FILE is ‘-’ then the ASCII NUL terminated + file names are read from standard input. + + For example, to find the length of the longest line in any ‘.c’ or + ‘.h’ file in the current hierarchy, do this: + + find . -name '*.[ch]' -print0 | + wc -L --files0-from=- | tail -n1 + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: sum invocation, Next: cksum invocation, Prev: wc invocation, Up: Summarizing files + +6.2 ‘sum’: Print checksum and block counts +========================================== + +‘sum’ computes a 16-bit checksum for each given FILE, or standard input +if none are given or for a FILE of ‘-’. Synopsis: + + sum [OPTION]... [FILE]... + + ‘sum’ prints the checksum for each FILE followed by the number of +blocks in the file (rounded up). If at least one FILE is given, file +names are also printed. + + By default, GNU ‘sum’ computes checksums using an algorithm +compatible with BSD ‘sum’ and prints file sizes in units of 1024-byte +blocks. + + The program accepts the following options. Also see *note Common +options::. + +‘-r’ + Use the default (BSD compatible) algorithm. This option is + included for compatibility with the System V ‘sum’. Unless ‘-s’ + was also given, it has no effect. + +‘-s’ +‘--sysv’ + Compute checksums using an algorithm compatible with System V + ‘sum’’s default, and print file sizes in units of 512-byte blocks. + + ‘sum’ is provided for compatibility; the ‘cksum’ program (see next +section) is preferable in new applications. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: cksum invocation, Next: md5sum invocation, Prev: sum invocation, Up: Summarizing files + +6.3 ‘cksum’: Print and verify file checksums +============================================ + +‘cksum’ by default computes a 32-bit cyclic redundancy check (CRC) +checksum for each given FILE, or standard input if none are given or for +a FILE of ‘-’. + + cksum also supports the ‘-a/--algorithm’ option to select the digest +algorithm to use. ‘cksum’ is the preferred interface to these digests, +subsuming the other standalone checksumming utilities, which can be +emulated using ‘cksum -a md5 --untagged "$@"’ etc. Synopsis: + + cksum [OPTION]... [FILE]... + + ‘cksum’ is typically used to ensure that files have not been +corrupted, by comparing the ‘cksum’ output for the received files with +the ‘cksum’ output for the original files (typically given in the +distribution). + +* Menu: + +* cksum output modes:: Legacy and non Legacy output formats +* cksum general options:: Options supported only by cksum +* cksum common options:: Options supported also by standalone utilities + + +File: coreutils.info, Node: cksum output modes, Next: cksum general options, Up: cksum invocation + +Legacy output format + ‘cksum’ by default prints the POSIX standard CRC checksum for each + file along with the number of bytes in the file, and the file name + unless no arguments were given. The 32-bit CRC used is based on + the polynomial used for CRC error checking in the ISO/IEC + 8802-3:1996 standard (Ethernet). Similar output formats are used + for the other legacy checksums selectable with ‘--algorithm=sysv’ + or ‘--algorithm=bsd’, detailed at *note sum invocation::. + +Tagged output format + With the ‘--algorithm’ option selecting non legacy checksums, the + ‘cksum’ command defaults to output of the form: + DIGEST_NAME (FILE NAME) = DIGEST + Note the standalone checksum utilities can select this output mode + by using the ‘--tag’ option. + +Untagged output format + With the ‘--untagged’ option and the ‘--algorithm’ option selecting + non legacy checksums, the following output format is used. Note + this is the default output format of the standalone checksum + utilities. For each FILE, we print the checksum, a space, a flag + indicating binary or text input mode, and the file name. Binary + mode is indicated with ‘*’, text mode with ‘ ’ (space). Binary + mode is the default on systems where it’s significant, otherwise + text mode is the default. + + Note without ‘--zero’, and with non legacy output formats, if FILE +contains a backslash, newline, or carriage return, the line is started +with a backslash, and each problematic character in the file name is +escaped with a backslash, making the output unambiguous even in the +presence of arbitrary file names. Since the backslash character itself +is escaped, any other backslash escape sequences are reserved for future +use. + + +File: coreutils.info, Node: cksum general options, Next: cksum common options, Prev: cksum output modes, Up: cksum invocation + +‘-a’ +‘--algorithm’ + Compute checksums using the specified digest algorithm. + + Supported legacy checksums (which are not supported by ‘--check’): + ‘sysv’ equivalent to sum -s + ‘bsd’ equivalent to sum -r + ‘crc’ equivalent to cksum (the default) + + Supported more modern digest algorithms are: + ‘md5’ equivalent to md5sum + ‘sha1’ equivalent to sha1sum + ‘sha224’ equivalent to sha224sum + ‘sha256’ equivalent to sha256sum + ‘sha384’ equivalent to sha384sum + ‘sha512’ equivalent to sha512sum + ‘blake2b’ equivalent to b2sum + ‘sm3’ only available through cksum + +‘--base64’ + Print base64-encoded digests not hexadecimal. This option is + ignored with ‘--check’. The format conforms to RFC 4648#4 + (https://tools.ietf.org/search/rfc4648#section-4). + + Note that each base64-encoded digest has zero, one or two trailing + padding (‘=’) bytes. The length of that padding is the + checksum-bit-length modulo 3, and the ‘--check’ parser requires + precisely the same input digest string as what is output. I.e., + removing or adding any ‘=’ padding renders a digest non-matching. + +‘--debug’ + Output extra information to stderr, like the checksum + implementation being used. + +‘-l’ +‘--length’ + Change (shorten) the default digest length. This is specified in + bits and thus must be a multiple of 8. This option is ignored when + ‘--check’ is specified, as the length is automatically determined + when checking. + +‘--raw’ + Print only the unencoded raw binary digest for a single input. Do + not output the file name or anything else. Use network byte order + (big endian) where applicable: for ‘bsd’, ‘crc’, and ‘sysv’. This + option works only with a single input. Unlike other output + formats, ‘cksum’ provides no way to ‘--check’ a ‘--raw’ checksum. + +‘--untagged’ + Output using the original Coreutils format used by the other + standalone checksum utilities like ‘md5sum’ for example. This + format has the checksum at the start of the line, and may be more + amenable to further processing by other utilities, especially in + combination with the ‘--zero’ option. Note this does not identify + the digest algorithm used for the checksum. *Note cksum output + modes:: for details of this format. + + +File: coreutils.info, Node: cksum common options, Prev: cksum general options, Up: cksum invocation + +‘-b’ +‘--binary’ + Note this option is not supported by the ‘cksum’ command, as it + operates in binary mode exclusively. Treat each input file as + binary, by reading it in binary mode and outputting a ‘*’ flag. + This is the inverse of ‘--text’. On systems like GNU that do not + distinguish between binary and text files, this option merely flags + each input mode as binary: the checksum is unaffected. This option + is the default on systems like MS-DOS that distinguish between + binary and text files, except for reading standard input when + standard input is a terminal. + +‘-c’ +‘--check’ + Read file names and checksum information (not data) from each FILE + (or from standard input if no FILE was specified) and report + whether the checksums match the contents of the named files. The + input to this mode is usually the output of a prior, + checksum-generating run of the command. + + Three input formats are supported. Either the default output + format described above, the ‘--tag’ output format, or the BSD + reversed mode format which is similar to the default mode, but + doesn’t use a character to distinguish binary and text modes. + + For the ‘cksum’ command, the ‘--check’ option supports + auto-detecting the digest algorithm to use, when presented with + checksum information in the ‘--tag’ output format. + + Also for the ‘cksum’ command, the ‘--check’ option auto-detects the + digest encoding, accepting both standard hexadecimal checksums and + those generated via ‘cksum’ with its ‘--base64’ option. + + Output with ‘--zero’ enabled is not supported by ‘--check’. + + For each such line, ‘cksum’ reads the named file and computes its + checksum. Then, if the computed message digest does not match the + one on the line with the file name, the file is noted as having + failed the test. Otherwise, the file passes the test. By default, + for each valid line, one line is written to standard output + indicating whether the named file passed the test. After all + checks have been performed, if there were any failures, a warning + is issued to standard error. Use the ‘--status’ option to inhibit + that output. If any listed file cannot be opened or read, if any + valid line has a checksum inconsistent with the associated file, or + if no valid line is found, ‘cksum’ exits with nonzero status. + Otherwise, it exits successfully. Note the ‘cksum’ command doesn’t + support ‘--check’ with the older ‘sysv’, ‘bsd’, or ‘crc’ + algorithms. + +‘--ignore-missing’ + This option is useful only when verifying checksums. When + verifying checksums, don’t fail or report any status for missing + files. This is useful when verifying a subset of downloaded files + given a larger list of checksums. + +‘--quiet’ + This option is useful only when verifying checksums. When + verifying checksums, don’t generate an ’OK’ message per + successfully checked file. Files that fail the verification are + reported in the default one-line-per-file format. If there is any + checksum mismatch, print a warning summarizing the failures to + standard error. + +‘--status’ + This option is useful only when verifying checksums. When + verifying checksums, don’t generate the default one-line-per-file + diagnostic and don’t output the warning summarizing any failures. + Failures to open or read a file still evoke individual diagnostics + to standard error. If all listed files are readable and are + consistent with the associated checksums, exit successfully. + Otherwise exit with a status code indicating there was a failure. + +‘--tag’ + Output BSD style checksums, which indicate the checksum algorithm + used. As a GNU extension, if ‘--zero’ is not used, file names with + problematic characters are escaped as described above, using the + same escaping indicator of ‘\’ at the start of the line, as used + with the other output format. The ‘--tag’ option implies binary + mode, and is disallowed with ‘--text’ mode as supporting that would + unnecessarily complicate the output format, while providing little + benefit. *Note cksum output modes:: for details of this format. + The ‘cksum’ command, uses ‘--tag’ as its default output format. + +‘-t’ +‘--text’ + Note this option is not supported by the ‘cksum’ command. Treat + each input file as text, by reading it in text mode and outputting + a ‘ ’ flag. This is the inverse of ‘--binary’. This option is the + default on systems like GNU that do not distinguish between binary + and text files. On other systems, it is the default for reading + standard input when standard input is a terminal. This mode is + never defaulted to if ‘--tag’ is used. + +‘-w’ +‘--warn’ + When verifying checksums, warn about improperly formatted checksum + lines. This option is useful only if all but a few lines in the + checked input are valid. + +‘--strict’ + When verifying checksums, if one or more input line is invalid, + exit nonzero after all warnings have been issued. + +‘-z’ +‘--zero’ + Output a zero byte (ASCII NUL) at the end of each line, rather than + a newline. This option enables other programs to parse the output + even when that output would contain data with embedded newlines. + Also file name escaping is not used. + + +File: coreutils.info, Node: md5sum invocation, Next: b2sum invocation, Prev: cksum invocation, Up: Summarizing files + +6.4 ‘md5sum’: Print or check MD5 digests +======================================== + +‘md5sum’ computes a 128-bit checksum (or “fingerprint” or +“message-digest”) for each specified FILE. + + Note: The MD5 digest is more reliable than a simple CRC (provided by +the ‘cksum’ command) for detecting accidental file corruption, as the +chances of accidentally having two files with identical MD5 are +vanishingly small. However, it should not be considered secure against +malicious tampering: although finding a file with a given MD5 +fingerprint is considered infeasible at the moment, it is known how to +modify certain files, including digital certificates, so that they +appear valid when signed with an MD5 digest. For more secure hashes, +consider using SHA-2, or the newer ‘b2sum’ command. *Note sha2 +utilities::. *Note b2sum invocation::. + + If a FILE is specified as ‘-’ or if no files are given ‘md5sum’ +computes the checksum for the standard input. ‘md5sum’ can also +determine whether a file and checksum are consistent. Synopsis: + + md5sum [OPTION]... [FILE]... + + ‘md5sum’ uses the ‘Untagged output format’ for each specified file, +as described at *note cksum output modes::. + + The program accepts *note cksum common options::. Also see *note +Common options::. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: b2sum invocation, Next: sha1sum invocation, Prev: md5sum invocation, Up: Summarizing files + +6.5 ‘b2sum’: Print or check BLAKE2 digests +========================================== + +‘b2sum’ computes a 512-bit checksum for each specified FILE. + + If a FILE is specified as ‘-’ or if no files are given ‘b2sum’ +computes the checksum for the standard input. ‘b2sum’ can also +determine whether a file and checksum are consistent. Synopsis: + + b2sum [OPTION]... [FILE]... + + ‘b2sum’ uses the ‘Untagged output format’ for each specified file, as +described at *note cksum output modes::. + + The program accepts *note cksum common options::. Also see *note +Common options::. + + In addition ‘b2sum’ supports the following options. + +‘-l’ +‘--length’ + Change (shorten) the default digest length. This is specified in + bits and thus must be a multiple of 8. This option is ignored when + ‘--check’ is specified, as the length is automatically determined + when checking. + + +File: coreutils.info, Node: sha1sum invocation, Next: sha2 utilities, Prev: b2sum invocation, Up: Summarizing files + +6.6 ‘sha1sum’: Print or check SHA-1 digests +=========================================== + +‘sha1sum’ computes a 160-bit checksum for each specified FILE. + + Note: The SHA-1 digest is more reliable than a simple CRC (provided +by the ‘cksum’ command) for detecting accidental file corruption, as the +chances of accidentally having two files with identical SHA-1 are +vanishingly small. However, it should not be considered secure against +malicious tampering: although finding a file with a given SHA-1 +fingerprint is considered infeasible at the moment, it is known how to +modify certain files, including digital certificates, so that they +appear valid when signed with an SHA-1 digest. For more secure hashes, +consider using SHA-2, or the newer ‘b2sum’ command. *Note sha2 +utilities::. *Note b2sum invocation::. + + If a FILE is specified as ‘-’ or if no files are given ‘sha1sum’ +computes the checksum for the standard input. ‘sha1sum’ can also +determine whether a file and checksum are consistent. Synopsis: + + sha1sum [OPTION]... [FILE]... + + ‘sha1sum’ uses the ‘Untagged output format’ for each specified file, +as described at *note cksum output modes::. + + The program accepts *note cksum common options::. Also see *note +Common options::. + + +File: coreutils.info, Node: sha2 utilities, Prev: sha1sum invocation, Up: Summarizing files + +6.7 sha2 utilities: Print or check SHA-2 digests +================================================ + +The commands ‘sha224sum’, ‘sha256sum’, ‘sha384sum’ and ‘sha512sum’ +compute checksums of various lengths (respectively 224, 256, 384 and 512 +bits), collectively known as the SHA-2 hashes. + + If a FILE is specified as ‘-’ or if no files are given ‘sha???sum’ +computes the checksum for the standard input. ‘sha???sum’ can also +determine whether a file and checksum are consistent. Synopsis: + + sha???sum [OPTION]... [FILE]... + + ‘sha???sum’ uses the ‘Untagged output format’ for each specified +file, as described at *note cksum output modes::. + + The program accepts *note cksum common options::. Also see *note +Common options::. + + +File: coreutils.info, Node: Operating on sorted files, Next: Operating on fields, Prev: Summarizing files, Up: Top + +7 Operating on sorted files +*************************** + +These commands work with (or produce) sorted files. + +* Menu: + +* sort invocation:: Sort text files. +* shuf invocation:: Shuffle text files. +* uniq invocation:: Uniquify files. +* comm invocation:: Compare two sorted files line by line. +* ptx invocation:: Produce a permuted index of file contents. +* tsort invocation:: Topological sort. + + +File: coreutils.info, Node: sort invocation, Next: shuf invocation, Up: Operating on sorted files + +7.1 ‘sort’: Sort text files +=========================== + +‘sort’ sorts, merges, or compares all the lines from the given files, or +standard input if none are given or for a FILE of ‘-’. By default, +‘sort’ writes the results to standard output. Synopsis: + + sort [OPTION]... [FILE]... + + Many options affect how ‘sort’ compares lines; if the results are +unexpected, try the ‘--debug’ option to see what happened. A pair of +lines is compared as follows: ‘sort’ compares each pair of fields (see +‘--key’), in the order specified on the command line, according to the +associated ordering options, until a difference is found or no fields +are left. If no key fields are specified, ‘sort’ uses a default key of +the entire line. Finally, as a last resort when all keys compare equal, +‘sort’ compares entire lines as if no ordering options other than +‘--reverse’ (‘-r’) were specified. The ‘--stable’ (‘-s’) option +disables this “last-resort comparison” so that lines in which all fields +compare equal are left in their original relative order. The ‘--unique’ +(‘-u’) option also disables the last-resort comparison. + + Unless otherwise specified, all comparisons use the character +collating sequence specified by the ‘LC_COLLATE’ locale.(1) A line’s +trailing newline is not part of the line for comparison purposes. If +the final byte of an input file is not a newline, GNU ‘sort’ silently +supplies one. GNU ‘sort’ (as specified for all GNU utilities) has no +limit on input line length or restrictions on bytes allowed within +lines. + + ‘sort’ has three modes of operation: sort (the default), merge, and +check for order. The following options change the operation mode: + +‘-c’ +‘--check’ +‘--check=diagnose-first’ + Check whether the given file is already sorted: if it is not all + sorted, print a diagnostic containing the first out-of-order line + and exit with a status of 1. Otherwise, exit successfully. At + most one input file can be given. + +‘-C’ +‘--check=quiet’ +‘--check=silent’ + Exit successfully if the given file is already sorted, and exit + with status 1 otherwise. At most one input file can be given. + This is like ‘-c’, except it does not print a diagnostic. + +‘-m’ +‘--merge’ + Merge the given files by sorting them as a group. Each input file + must always be individually sorted. It always works to sort + instead of merge; merging is provided because it is faster, in the + case where it works. + + Exit status: + + 0 if no error occurred + 1 if invoked with ‘-c’ or ‘-C’ and the input is not sorted + 2 if an error occurred + + If the environment variable ‘TMPDIR’ is set, ‘sort’ uses its value as +the directory for temporary files instead of ‘/tmp’. The +‘--temporary-directory’ (‘-T’) option in turn overrides the environment +variable. + + The following options affect the ordering of output lines. They may +be specified globally or as part of a specific key field. If no key +fields are specified, global options apply to comparison of entire +lines; otherwise the global options are inherited by key fields that do +not specify any special options of their own. In pre-POSIX versions of +‘sort’, global options affect only later key fields, so portable shell +scripts should specify global options first. + +‘-b’ +‘--ignore-leading-blanks’ + Ignore leading blanks when finding sort keys in each line. By + default a blank is a space or a tab, but the ‘LC_CTYPE’ locale can + change this. Note blanks may be ignored by your locale’s collating + rules, but without this option they will be significant for + character positions specified in keys with the ‘-k’ option. + +‘-d’ +‘--dictionary-order’ + Sort in “phone directory” order: ignore all characters except + letters, digits and blanks when sorting. By default letters and + digits are those of ASCII and a blank is a space or a tab, but the + ‘LC_CTYPE’ locale can change this. + +‘-f’ +‘--ignore-case’ + Fold lowercase characters into the equivalent uppercase characters + when comparing so that, for example, ‘b’ and ‘B’ sort as equal. + The ‘LC_CTYPE’ locale determines character types. When used with + ‘--unique’ those lower case equivalent lines are thrown away. + (There is currently no way to throw away the upper case equivalent + instead. (Any ‘--reverse’ given would only affect the final + result, after the throwing away.)) + +‘-g’ +‘--general-numeric-sort’ +‘--sort=general-numeric’ + Sort numerically, converting a prefix of each line to a long + double-precision floating point number. *Note Floating point::. + Do not report overflow, underflow, or conversion errors. Use the + following collating sequence: + + • Lines that do not start with numbers (all considered to be + equal). + • NaNs (“Not a Number” values, in IEEE floating point + arithmetic) in a consistent but machine-dependent order. + • Minus infinity. + • Finite numbers in ascending numeric order (with -0 and +0 + equal). + • Plus infinity. + + Use this option only if there is no alternative; it is much slower + than ‘--numeric-sort’ (‘-n’) and it can lose information when + converting to floating point. + + You can use this option to sort hexadecimal numbers prefixed with + ‘0x’ or ‘0X’, where those numbers are not fixed width, or of + varying case. However for hex numbers of consistent case, and left + padded with ‘0’ to a consistent width, a standard lexicographic + sort will be faster. + +‘-h’ +‘--human-numeric-sort’ +‘--sort=human-numeric’ + Sort numerically, first by numeric sign (negative, zero, or + positive); then by SI suffix (either empty, or ‘k’ or ‘K’, or one + of ‘MGTPEZYRQ’, in that order; *note Block size::); and finally by + numeric value. For example, ‘1023M’ sorts before ‘1G’ because ‘M’ + (mega) precedes ‘G’ (giga) as an SI suffix. This option sorts + values that are consistently scaled to the nearest suffix, + regardless of whether suffixes denote powers of 1000 or 1024, and + it therefore sorts the output of any single invocation of the ‘df’, + ‘du’, or ‘ls’ commands that are invoked with their + ‘--human-readable’ or ‘--si’ options. The syntax for numbers is + the same as for the ‘--numeric-sort’ option; the SI suffix must + immediately follow the number. Note also the ‘numfmt’ command, + which can be used to reformat numbers to human format _after_ the + sort, thus often allowing sort to operate on more accurate numbers. + +‘-i’ +‘--ignore-nonprinting’ + Ignore nonprinting characters. The ‘LC_CTYPE’ locale determines + character types. This option has no effect if the stronger + ‘--dictionary-order’ (‘-d’) option is also given. + +‘-M’ +‘--month-sort’ +‘--sort=month’ + An initial string, consisting of any amount of blanks, followed by + a month name abbreviation, is folded to UPPER case and compared in + the order ‘JAN’ < ‘FEB’ < ... < ‘DEC’. Invalid names compare low + to valid names. The ‘LC_TIME’ locale category determines the month + spellings. By default a blank is a space or a tab, but the + ‘LC_CTYPE’ locale can change this. + +‘-n’ +‘--numeric-sort’ +‘--sort=numeric’ + Sort numerically. The number begins each line and consists of + optional blanks, an optional ‘-’ sign, and zero or more digits + possibly separated by thousands separators, optionally followed by + a decimal-point character and zero or more digits. An empty number + is treated as ‘0’. The ‘LC_NUMERIC’ locale specifies the + decimal-point character and thousands separator. By default a + blank is a space or a tab, but the ‘LC_CTYPE’ locale can change + this. + + Comparison is exact; there is no rounding error. + + Neither a leading ‘+’ nor exponential notation is recognized. To + compare such strings numerically, use the ‘--general-numeric-sort’ + (‘-g’) option. + +‘-V’ +‘--version-sort’ + Sort by version name and number. It behaves like a standard sort, + except that each sequence of decimal digits is treated numerically + as an index/version number. (*Note Version sort ordering::.) + +‘-r’ +‘--reverse’ + Reverse the result of comparison, so that lines with greater key + values appear earlier in the output instead of later. + +‘-R’ +‘--random-sort’ +‘--sort=random’ + Sort by hashing the input keys and then sorting the hash values. + Choose the hash function at random, ensuring that it is free of + collisions so that differing keys have differing hash values. This + is like a random permutation of the inputs (*note shuf + invocation::), except that keys with the same value sort together. + + If multiple random sort fields are specified, the same random hash + function is used for all fields. To use different random hash + functions for different fields, you can invoke ‘sort’ more than + once. + + The choice of hash function is affected by the ‘--random-source’ + option. + + Other options are: + +‘--compress-program=PROG’ + Compress any temporary files with the program PROG. + + With no arguments, PROG must compress standard input to standard + output, and when given the ‘-d’ option it must decompress standard + input to standard output. + + Terminate with an error if PROG exits with nonzero status. + + White space and the backslash character should not appear in PROG; + they are reserved for future use. + +‘--files0-from=FILE’ + Disallow processing files named on the command line, and instead + process those named in file FILE; each name being terminated by a + zero byte (ASCII NUL). This is useful when the list of file names + is so long that it may exceed a command line length limitation. In + such cases, running ‘sort’ via ‘xargs’ is undesirable because it + splits the list into pieces and makes ‘sort’ print sorted output + for each sublist rather than for the entire list. One way to + produce a list of ASCII NUL terminated file names is with GNU + ‘find’, using its ‘-print0’ predicate. If FILE is ‘-’ then the + ASCII NUL terminated file names are read from standard input. + +‘-k POS1[,POS2]’ +‘--key=POS1[,POS2]’ + Specify a sort field that consists of the part of the line between + POS1 and POS2 (or the end of the line, if POS2 is omitted), + _inclusive_. + + In its simplest form POS specifies a field number (starting with + 1), with fields being separated by runs of blank characters, and by + default those blanks being included in the comparison at the start + of each field. To adjust the handling of blank characters see the + ‘-b’ and ‘-t’ options. + + More generally, each POS has the form ‘F[.C][OPTS]’, where F is the + number of the field to use, and C is the number of the first + character from the beginning of the field. Fields and character + positions are numbered starting with 1; a character position of + zero in POS2 indicates the field’s last character. If ‘.C’ is + omitted from POS1, it defaults to 1 (the beginning of the field); + if omitted from POS2, it defaults to 0 (the end of the field). + OPTS are ordering options, allowing individual keys to be sorted + according to different rules; see below for details. Keys can span + multiple fields. + + Example: To sort on the second field, use ‘--key=2,2’ (‘-k 2,2’). + See below for more notes on keys and more examples. See also the + ‘--debug’ option to help determine the part of the line being used + in the sort. + +‘--debug’ + Highlight the portion of each line used for sorting. Also issue + warnings about questionable usage to standard error. + +‘--batch-size=NMERGE’ + Merge at most NMERGE inputs at once. + + When ‘sort’ has to merge more than NMERGE inputs, it merges them in + groups of NMERGE, saving the result in a temporary file, which is + then used as an input in a subsequent merge. + + A large value of NMERGE may improve merge performance and decrease + temporary storage utilization at the expense of increased memory + usage and I/O. Conversely a small value of NMERGE may reduce + memory requirements and I/O at the expense of temporary storage + consumption and merge performance. + + The value of NMERGE must be at least 2. The default value is + currently 16, but this is implementation-dependent and may change + in the future. + + The value of NMERGE may be bounded by a resource limit for open + file descriptors. The commands ‘ulimit -n’ or ‘getconf OPEN_MAX’ + may display limits for your systems; these limits may be modified + further if your program already has some files open, or if the + operating system has other limits on the number of open files. If + the value of NMERGE exceeds the resource limit, ‘sort’ silently + uses a smaller value. + +‘-o OUTPUT-FILE’ +‘--output=OUTPUT-FILE’ + Write output to OUTPUT-FILE instead of standard output. Normally, + ‘sort’ reads all input before opening OUTPUT-FILE, so you can sort + a file in place by using commands like ‘sort -o F F’ and ‘cat F | + sort -o F’. However, it is often safer to output to an + otherwise-unused file, as data may be lost if the system crashes or + ‘sort’ encounters an I/O or other serious error while a file is + being sorted in place. Also, ‘sort’ with ‘--merge’ (‘-m’) can open + the output file before reading all input, so a command like ‘cat F + | sort -m -o F - G’ is not safe as ‘sort’ might start writing ‘F’ + before ‘cat’ is done reading it. + + On newer systems, ‘-o’ cannot appear after an input file if + ‘POSIXLY_CORRECT’ is set, e.g., ‘sort F -o F’. Portable scripts + should specify ‘-o OUTPUT-FILE’ before any input files. + +‘--random-source=FILE’ + Use FILE as a source of random data used to determine which random + hash function to use with the ‘-R’ option. *Note Random sources::. + +‘-s’ +‘--stable’ + + Make ‘sort’ stable by disabling its last-resort comparison. This + option has no effect if no fields or global ordering options other + than ‘--reverse’ (‘-r’) are specified. + +‘-S SIZE’ +‘--buffer-size=SIZE’ + Use a main-memory sort buffer of the given SIZE. By default, SIZE + is in units of 1024 bytes. Appending ‘%’ causes SIZE to be + interpreted as a percentage of physical memory. Appending ‘K’ + multiplies SIZE by 1024 (the default), ‘M’ by 1,048,576, ‘G’ by + 1,073,741,824, and so on for ‘T’, ‘P’, ‘E’, ‘Z’, ‘Y’, ‘R’, and ‘Q’. + Appending ‘b’ causes SIZE to be interpreted as a byte count, with + no multiplication. + + This option can improve the performance of ‘sort’ by causing it to + start with a larger or smaller sort buffer than the default. + However, this option affects only the initial buffer size. The + buffer grows beyond SIZE if ‘sort’ encounters input lines larger + than SIZE. + +‘-t SEPARATOR’ +‘--field-separator=SEPARATOR’ + Use character SEPARATOR as the field separator when finding the + sort keys in each line. By default, fields are separated by the + empty string between a non-blank character and a blank character. + By default a blank is a space or a tab, but the ‘LC_CTYPE’ locale + can change this. + + That is, given the input line ‘ foo bar’, ‘sort’ breaks it into + fields ‘ foo’ and ‘ bar’. The field separator is not considered to + be part of either the field preceding or the field following, so + with ‘sort -t " "’ the same input line has three fields: an empty + field, ‘foo’, and ‘bar’. However, fields that extend to the end of + the line, as ‘-k 2’, or fields consisting of a range, as ‘-k 2,3’, + retain the field separators present between the endpoints of the + range. + + To specify ASCII NUL as the field separator, use the two-character + string ‘\0’, e.g., ‘sort -t '\0'’. + +‘-T TEMPDIR’ +‘--temporary-directory=TEMPDIR’ + Use directory TEMPDIR to store temporary files, overriding the + ‘TMPDIR’ environment variable. If this option is given more than + once, temporary files are stored in all the directories given. If + you have a large sort or merge that is I/O-bound, you can often + improve performance by using this option to specify directories on + different file systems. + +‘--parallel=N’ + Set the number of sorts run in parallel to N. By default, N is set + to the number of available processors, but limited to 8, as there + are diminishing performance gains after that. Note also that using + N threads increases the memory usage by a factor of log N. Also + see *note nproc invocation::. + +‘-u’ +‘--unique’ + + Normally, output only the first of a sequence of lines that compare + equal. For the ‘--check’ (‘-c’ or ‘-C’) option, check that no pair + of consecutive lines compares equal. + + This option also disables the default last-resort comparison. + + The commands ‘sort -u’ and ‘sort | uniq’ are equivalent, but this + equivalence does not extend to arbitrary ‘sort’ options. For + example, ‘sort -n -u’ inspects only the value of the initial + numeric string when checking for uniqueness, whereas ‘sort -n | + uniq’ inspects the entire line. *Note uniq invocation::. + +‘-z’ +‘--zero-terminated’ + Delimit items with a zero byte rather than a newline (ASCII LF). + I.e., treat input as items separated by ASCII NUL and terminate + output items with ASCII NUL. This option can be useful in + conjunction with ‘perl -0’ or ‘find -print0’ and ‘xargs -0’ which + do the same in order to reliably handle arbitrary file names (even + those containing blanks or other special characters). + + Historical (BSD and System V) implementations of ‘sort’ have differed +in their interpretation of some options, particularly ‘-b’, ‘-f’, and +‘-n’. GNU sort follows the POSIX behavior, which is usually (but not +always!) like the System V behavior. According to POSIX, ‘-n’ no +longer implies ‘-b’. For consistency, ‘-M’ has been changed in the same +way. This may affect the meaning of character positions in field +specifications in obscure cases. The only fix is to add an explicit +‘-b’. + + A position in a sort field specified with ‘-k’ may have any of the +option letters ‘MbdfghinRrV’ appended to it, in which case no global +ordering options are inherited by that particular field. The ‘-b’ +option may be independently attached to either or both of the start and +end positions of a field specification, and if it is inherited from the +global options it will be attached to both. If input lines can contain +leading or adjacent blanks and ‘-t’ is not used, then ‘-k’ is typically +combined with ‘-b’ or an option that implicitly ignores leading blanks +(‘Mghn’) as otherwise the varying numbers of leading blanks in fields +can cause confusing results. + + If the start position in a sort field specifier falls after the end +of the line or after the end field, the field is empty. If the ‘-b’ +option was specified, the ‘.C’ part of a field specification is counted +from the first nonblank character of the field. + + On systems not conforming to POSIX 1003.1-2001, ‘sort’ supports a +traditional origin-zero syntax ‘+POS1 [-POS2]’ for specifying sort keys. +The traditional command ‘sort +A.X -B.Y’ is equivalent to ‘sort -k +A+1.X+1,B’ if Y is ‘0’ or absent, otherwise it is equivalent to ‘sort -k +A+1.X+1,B+1.Y’. + + This traditional behavior can be controlled with the +‘_POSIX2_VERSION’ environment variable (*note Standards conformance::); +it can also be enabled when ‘POSIXLY_CORRECT’ is not set by using the +traditional syntax with ‘-POS2’ present. + + Scripts intended for use on standard hosts should avoid traditional +syntax and should use ‘-k’ instead. For example, avoid ‘sort +2’, since +it might be interpreted as either ‘sort ./+2’ or ‘sort -k 3’. If your +script must also run on hosts that support only the traditional syntax, +it can use a test like ‘if sort -k 1 </dev/null >/dev/null 2>&1; then +...’ to decide which syntax to use. + + Here are some examples to illustrate various combinations of options. + + • Sort in descending (reverse) numeric order. + + sort -n -r + + • Run no more than 4 sorts concurrently, using a buffer size of 10M. + + sort --parallel=4 -S 10M + + • Sort alphabetically, omitting the first and second fields and the + blanks at the start of the third field. This uses a single key + composed of the characters beginning at the start of the first + nonblank character in field three and extending to the end of each + line. + + sort -k 3b + + • Sort numerically on the second field and resolve ties by sorting + alphabetically on the third and fourth characters of field five. + Use ‘:’ as the field delimiter. + + sort -t : -k 2,2n -k 5.3,5.4 + + Note that if you had written ‘-k 2n’ instead of ‘-k 2,2n’ ‘sort’ + would have used all characters beginning in the second field and + extending to the end of the line as the primary _numeric_ key. For + the large majority of applications, treating keys spanning more + than one field as numeric will not do what you expect. + + Also note that the ‘n’ modifier was applied to the field-end + specifier for the first key. It would have been equivalent to + specify ‘-k 2n,2’ or ‘-k 2n,2n’. All modifiers except ‘b’ apply to + the associated _field_, regardless of whether the modifier + character is attached to the field-start and/or the field-end part + of the key specifier. + + • Sort the password file on the fifth field and ignore any leading + blanks. Sort lines with equal values in field five on the numeric + user ID in field three. Fields are separated by ‘:’. + + sort -t : -k 5b,5 -k 3,3n /etc/passwd + sort -t : -n -k 5b,5 -k 3,3 /etc/passwd + sort -t : -b -k 5,5 -k 3,3n /etc/passwd + + These three commands have equivalent effect. The first specifies + that the first key’s start position ignores leading blanks and the + second key is sorted numerically. The other two commands rely on + global options being inherited by sort keys that lack modifiers. + The inheritance works in this case because ‘-k 5b,5b’ and ‘-k 5b,5’ + are equivalent, as the location of a field-end lacking a ‘.C’ + character position is not affected by whether initial blanks are + skipped. + + • Sort a set of log files, primarily by IPv4 address and secondarily + by timestamp. If two lines’ primary and secondary keys are + identical, output the lines in the same order that they were input. + The log files contain lines that look like this: + + 4.150.156.3 - - [01/Apr/2020:06:31:51 +0000] message 1 + 211.24.3.231 - - [24/Apr/2020:20:17:39 +0000] message 2 + + Fields are separated by exactly one space. Sort IPv4 addresses + lexicographically, e.g., 212.61.52.2 sorts before 212.129.233.201 + because 61 is less than 129. + + sort -s -t ' ' -k 4.9n -k 4.5M -k 4.2n -k 4.14,4.21 file*.log | + sort -s -t '.' -k 1,1n -k 2,2n -k 3,3n -k 4,4n + + This example cannot be done with a single POSIX ‘sort’ invocation, + since IPv4 address components are separated by ‘.’ while dates come + just after a space. So it is broken down into two invocations of + ‘sort’: the first sorts by timestamp and the second by IPv4 + address. The timestamp is sorted by year, then month, then day, + and finally by hour-minute-second field, using ‘-k’ to isolate each + field. Except for hour-minute-second there’s no need to specify + the end of each key field, since the ‘n’ and ‘M’ modifiers sort + based on leading prefixes that cannot cross field boundaries. The + IPv4 addresses are sorted lexicographically. The second sort uses + ‘-s’ so that ties in the primary key are broken by the secondary + key; the first sort uses ‘-s’ so that the combination of the two + sorts is stable. Note as a GNU extension, the above example could + be achieved in a single ‘sort’ invocation by sorting the IPv4 + address field using a ‘V’ version type, like ‘-k1,1V’. + + • Generate a tags file in case-insensitive sorted order. + + find src -type f -print0 | sort -z -f | xargs -0 etags --append + + The use of ‘-print0’, ‘-z’, and ‘-0’ in this case means that file + names that contain blanks or other special characters are not + broken up by the sort operation. + + • Use the common DSU, Decorate Sort Undecorate idiom to sort lines + according to their length. + + awk '{print length, $0}' /etc/passwd | sort -n | cut -f2- -d' ' + + In general this technique can be used to sort data that the ‘sort’ + command does not support, or is inefficient at, sorting directly. + + • Shuffle a list of directories, but preserve the order of files + within each directory. For instance, one could use this to + generate a music playlist in which albums are shuffled but the + songs of each album are played in order. + + ls */* | sort -t / -k 1,1R -k 2,2 + + ---------- Footnotes ---------- + + (1) If you use a non-POSIX locale (e.g., by setting ‘LC_ALL’ to +‘en_US’), then ‘sort’ may produce output that is sorted differently than +you’re accustomed to. In that case, set the ‘LC_ALL’ environment +variable to ‘C’. Note that setting only ‘LC_COLLATE’ has two problems. +First, it is ineffective if ‘LC_ALL’ is also set. Second, it has +undefined behavior if ‘LC_CTYPE’ (or ‘LANG’, if ‘LC_CTYPE’ is unset) is +set to an incompatible value. For example, you get undefined behavior +if ‘LC_CTYPE’ is ‘ja_JP.PCK’ but ‘LC_COLLATE’ is ‘en_US.UTF-8’. + + +File: coreutils.info, Node: shuf invocation, Next: uniq invocation, Prev: sort invocation, Up: Operating on sorted files + +7.2 ‘shuf’: Shuffling text +========================== + +‘shuf’ shuffles its input by outputting a random permutation of its +input lines. Each output permutation is equally likely. Synopses: + + shuf [OPTION]... [FILE] + shuf -e [OPTION]... [ARG]... + shuf -i LO-HI [OPTION]... + + ‘shuf’ has three modes of operation that affect where it obtains its +input lines. By default, it reads lines from standard input. The +following options change the operation mode: + +‘-e’ +‘--echo’ + Treat each command-line operand as an input line. + +‘-i LO-HI’ +‘--input-range=LO-HI’ + Act as if input came from a file containing the range of unsigned + decimal integers LO...HI, one per line. + + ‘shuf’’s other options can affect its behavior in all operation +modes: + +‘-n COUNT’ +‘--head-count=COUNT’ + Output at most COUNT lines. By default, all input lines are + output. + +‘-o OUTPUT-FILE’ +‘--output=OUTPUT-FILE’ + Write output to OUTPUT-FILE instead of standard output. ‘shuf’ + reads all input before opening OUTPUT-FILE, so you can safely + shuffle a file in place by using commands like ‘shuf -o F <F’ and + ‘cat F | shuf -o F’. + +‘--random-source=FILE’ + Use FILE as a source of random data used to determine which + permutation to generate. *Note Random sources::. + +‘-r’ +‘--repeat’ + Repeat output values, that is, select with replacement. With this + option the output is not a permutation of the input; instead, each + output line is randomly chosen from all the inputs. This option is + typically combined with ‘--head-count’; if ‘--head-count’ is not + given, ‘shuf’ repeats indefinitely. + +‘-z’ +‘--zero-terminated’ + Delimit items with a zero byte rather than a newline (ASCII LF). + I.e., treat input as items separated by ASCII NUL and terminate + output items with ASCII NUL. This option can be useful in + conjunction with ‘perl -0’ or ‘find -print0’ and ‘xargs -0’ which + do the same in order to reliably handle arbitrary file names (even + those containing blanks or other special characters). + + For example: + + shuf <<EOF + A man, + a plan, + a canal: + Panama! + EOF + +might produce the output + + Panama! + A man, + a canal: + a plan, + +Similarly, the command: + + shuf -e clubs hearts diamonds spades + +might output: + + clubs + diamonds + spades + hearts + +and the command ‘shuf -i 1-4’ might output: + + 4 + 2 + 1 + 3 + +The above examples all have four input lines, so ‘shuf’ might produce +any of the twenty-four possible permutations of the input. In general, +if there are N input lines, there are N! (i.e., N factorial, or N * (N +- 1) * ... * 1) possible output permutations. + +To output 50 random numbers each in the range 0 through 9, use: + + shuf -r -n 50 -i 0-9 + +To simulate 100 coin flips, use: + + shuf -r -n 100 -e Head Tail + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: uniq invocation, Next: comm invocation, Prev: shuf invocation, Up: Operating on sorted files + +7.3 ‘uniq’: Uniquify files +========================== + +‘uniq’ writes the unique lines in the given ‘input’, or standard input +if nothing is given or for an INPUT name of ‘-’. Synopsis: + + uniq [OPTION]... [INPUT [OUTPUT]] + + By default, ‘uniq’ prints its input lines, except that it discards +all but the first of adjacent repeated lines, so that no output lines +are repeated. Optionally, it can instead discard lines that are not +repeated, or all repeated lines. + + The input need not be sorted, but repeated input lines are detected +only if they are adjacent. If you want to discard non-adjacent +duplicate lines, perhaps you want to use ‘sort -u’. *Note sort +invocation::. + + Comparisons honor the rules specified by the ‘LC_COLLATE’ locale +category. + + If no OUTPUT file is specified, ‘uniq’ writes to standard output. + + The program accepts the following options. Also see *note Common +options::. + +‘-f N’ +‘--skip-fields=N’ + Skip N fields on each line before checking for uniqueness. Use a + null string for comparison if a line has fewer than N fields. + Fields are a sequence of blank characters followed by non-blank + characters. Field numbers are one based, i.e., ‘-f 1’ will skip + the first field (which may optionally have leading blanks). + + For compatibility ‘uniq’ supports a traditional option syntax ‘-N’. + New scripts should use ‘-f N’ instead. + +‘-s N’ +‘--skip-chars=N’ + Skip N characters before checking for uniqueness. Use a null + string for comparison if a line has fewer than N characters. If + you use both the field and character skipping options, fields are + skipped over first. + + On systems not conforming to POSIX 1003.1-2001, ‘uniq’ supports a + traditional option syntax ‘+N’. Although this traditional behavior + can be controlled with the ‘_POSIX2_VERSION’ environment variable + (*note Standards conformance::), portable scripts should avoid + commands whose behavior depends on this variable. For example, use + ‘uniq ./+10’ or ‘uniq -s 10’ rather than the ambiguous ‘uniq +10’. + +‘-c’ +‘--count’ + Print the number of times each line occurred along with the line. + +‘-i’ +‘--ignore-case’ + Ignore differences in case when comparing lines. + +‘-d’ +‘--repeated’ + Discard lines that are not repeated. When used by itself, this + option causes ‘uniq’ to print the first copy of each repeated line, + and nothing else. + +‘-D’ +‘--all-repeated[=DELIMIT-METHOD]’ + Do not discard the second and subsequent repeated input lines, but + discard lines that are not repeated. This option is useful mainly + in conjunction with other options e.g., to ignore case or to + compare only selected fields. The optional DELIMIT-METHOD, + supported with the long form option, specifies how to delimit + groups of repeated lines, and must be one of the following: + + ‘none’ + Do not delimit groups of repeated lines. This is equivalent + to ‘--all-repeated’ (‘-D’). + + ‘prepend’ + Output a newline before each group of repeated lines. With + ‘--zero-terminated’ (‘-z’), use a zero byte (ASCII NUL) + instead of a newline as the delimiter. + + ‘separate’ + Separate groups of repeated lines with a single newline. This + is the same as using ‘prepend’, except that no delimiter is + inserted before the first group, and hence may be better + suited for output direct to users. With ‘--zero-terminated’ + (‘-z’), use a zero byte (ASCII NUL) instead of a newline as + the delimiter. + + Note that when groups are delimited and the input stream contains + blank lines, then the output is ambiguous. To avoid that, filter + the input through ‘tr -s '\n'’ to remove blank lines. + + This is a GNU extension. + +‘--group[=DELIMIT-METHOD]’ + Output all lines, and delimit each unique group. With + ‘--zero-terminated’ (‘-z’), use a zero byte (ASCII NUL) instead of + a newline as the delimiter. The optional DELIMIT-METHOD specifies + how to delimit groups, and must be one of the following: + + ‘separate’ + Separate unique groups with a single delimiter. This is the + default delimiting method if none is specified, and better + suited for output direct to users. + + ‘prepend’ + Output a delimiter before each group of unique items. + + ‘append’ + Output a delimiter after each group of unique items. + + ‘both’ + Output a delimiter around each group of unique items. + + Note that when groups are delimited and the input stream contains + blank lines, then the output is ambiguous. To avoid that, filter + the input through ‘tr -s '\n'’ to remove blank lines. + + This is a GNU extension. + +‘-u’ +‘--unique’ + Discard the last line that would be output for a repeated input + group. When used by itself, this option causes ‘uniq’ to print + unique lines, and nothing else. + +‘-w N’ +‘--check-chars=N’ + Compare at most N characters on each line (after skipping any + specified fields and characters). By default the entire rest of + the lines are compared. + +‘-z’ +‘--zero-terminated’ + Delimit items with a zero byte rather than a newline (ASCII LF). + I.e., treat input as items separated by ASCII NUL and terminate + output items with ASCII NUL. This option can be useful in + conjunction with ‘perl -0’ or ‘find -print0’ and ‘xargs -0’ which + do the same in order to reliably handle arbitrary file names (even + those containing blanks or other special characters). Note with + ‘-z’ the newline character is treated as a field separator. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: comm invocation, Next: ptx invocation, Prev: uniq invocation, Up: Operating on sorted files + +7.4 ‘comm’: Compare two sorted files line by line +================================================= + +‘comm’ writes to standard output lines that are common, and lines that +are unique, to two input files; a file name of ‘-’ means standard input. +Synopsis: + + comm [OPTION]... FILE1 FILE2 + + Before ‘comm’ can be used, the input files must be sorted using the +collating sequence specified by the ‘LC_COLLATE’ locale. If an input +file ends in a non-newline character, a newline is silently appended. +The ‘sort’ command with no options always outputs a file that is +suitable input to ‘comm’. + + With no options, ‘comm’ produces three-column output. Column one +contains lines unique to FILE1, column two contains lines unique to +FILE2, and column three contains lines common to both files. Columns +are separated by a single TAB character. + + The options ‘-1’, ‘-2’, and ‘-3’ suppress printing of the +corresponding columns (and separators). Also see *note Common +options::. + + Unlike some other comparison utilities, ‘comm’ has an exit status +that does not depend on the result of the comparison. Upon normal +completion ‘comm’ produces an exit code of zero. If there is an error +it exits with nonzero status. + + If the ‘--check-order’ option is given, unsorted inputs will cause a +fatal error message. If the option ‘--nocheck-order’ is given, unsorted +inputs will never cause an error message. If neither of these options +is given, wrongly sorted inputs are diagnosed only if an input file is +found to contain unpairable lines. If an input file is diagnosed as +being unsorted, the ‘comm’ command will exit with a nonzero status (and +the output should not be used). + + Forcing ‘comm’ to process wrongly sorted input files containing +unpairable lines by specifying ‘--nocheck-order’ is not guaranteed to +produce any particular output. The output will probably not correspond +with whatever you hoped it would be. + +‘--check-order’ + Fail with an error message if either input file is wrongly ordered. + +‘--nocheck-order’ + Do not check that both input files are in sorted order. + + Other options are: + +‘--output-delimiter=STR’ + Print STR between adjacent output columns, rather than the default + of a single TAB character. + + The delimiter STR may be empty, in which case the ASCII NUL + character is used to delimit output columns. + +‘--total’ + Output a summary at the end. + + Similar to the regular output, column one contains the total number + of lines unique to FILE1, column two contains the total number of + lines unique to FILE2, and column three contains the total number + of lines common to both files, followed by the word ‘total’ in the + additional column four. + + In the following example, ‘comm’ omits the regular output (‘-123’), + thus just printing the summary: + + $ printf '%s\n' a b c d e > file1 + $ printf '%s\n' b c d e f g > file2 + $ comm --total -123 file1 file2 + 1 2 4 total + + This option is a GNU extension. Portable scripts should use ‘wc’ + to get the totals, e.g. for the above example files: + + $ comm -23 file1 file2 | wc -l # number of lines only in file1 + 1 + $ comm -13 file1 file2 | wc -l # number of lines only in file2 + 2 + $ comm -12 file1 file2 | wc -l # number of lines common to both files + 4 + +‘-z’ +‘--zero-terminated’ + Delimit items with a zero byte rather than a newline (ASCII LF). + I.e., treat input as items separated by ASCII NUL and terminate + output items with ASCII NUL. This option can be useful in + conjunction with ‘perl -0’ or ‘find -print0’ and ‘xargs -0’ which + do the same in order to reliably handle arbitrary file names (even + those containing blanks or other special characters). + + +File: coreutils.info, Node: ptx invocation, Next: tsort invocation, Prev: comm invocation, Up: Operating on sorted files + +7.5 ‘ptx’: Produce permuted indexes +=================================== + +‘ptx’ reads a text file and essentially produces a permuted index, with +each keyword in its context. The calling sketch is either one of: + + ptx [OPTION ...] [FILE ...] + ptx -G [OPTION ...] [INPUT [OUTPUT]] + + The ‘-G’ (or its equivalent: ‘--traditional’) option disables all GNU +extensions and reverts to traditional mode, thus introducing some +limitations and changing several of the program’s default option values. +When ‘-G’ is not specified, GNU extensions are always enabled. GNU +extensions to ‘ptx’ are documented wherever appropriate in this +document. *Note Compatibility in ptx::, for the full list. + + Individual options are explained in the following sections. + + When GNU extensions are enabled, there may be zero, one or several +FILEs after the options. If there is no FILE, the program reads the +standard input. If there is one or several FILEs, they give the name of +input files which are all read in turn, as if all the input files were +concatenated. However, there is a full contextual break between each +file and, when automatic referencing is requested, file names and line +numbers refer to individual text input files. In all cases, the program +outputs the permuted index to the standard output. + + When GNU extensions are _not_ enabled, that is, when the program +operates in traditional mode, there may be zero, one or two parameters +besides the options. If there are no parameters, the program reads the +standard input and outputs the permuted index to the standard output. +If there is only one parameter, it names the text INPUT to be read +instead of the standard input. If two parameters are given, they give +respectively the name of the INPUT file to read and the name of the +OUTPUT file to produce. _Be very careful_ to note that, in this case, +the contents of file given by the second parameter is destroyed. This +behavior is dictated by System V ‘ptx’ compatibility; GNU Standards +normally discourage output parameters not introduced by an option. + + Note that for _any_ file named as the value of an option or as an +input text file, a single dash ‘-’ may be used, in which case standard +input is assumed. However, it would not make sense to use this +convention more than once per program invocation. + +* Menu: + +* General options in ptx:: Options which affect general program behavior. +* Charset selection in ptx:: Underlying character set considerations. +* Input processing in ptx:: Input fields, contexts, and keyword selection. +* Output formatting in ptx:: Types of output format, and sizing the fields. +* Compatibility in ptx:: + + +File: coreutils.info, Node: General options in ptx, Next: Charset selection in ptx, Up: ptx invocation + +7.5.1 General options +--------------------- + +‘-G’ +‘--traditional’ + As already explained, this option disables all GNU extensions to + ‘ptx’ and switches to traditional mode. + +‘--help’ + Print a short help on standard output, then exit without further + processing. + +‘--version’ + Print the program version on standard output, then exit without + further processing. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: Charset selection in ptx, Next: Input processing in ptx, Prev: General options in ptx, Up: ptx invocation + +7.5.2 Charset selection +----------------------- + +As it is set up now, ‘ptx’ assumes that the input file is coded using +8-bit characters, and it may not work well in multibyte locales. In a +single-byte locale, the default regular expression for a keyword allows +foreign or diacriticized letters. Keyword sorting, however, is still +crude; it obeys the underlying character set ordering quite blindly. + + The output of ‘ptx’ assumes the locale’s character encoding. For +example, with ‘ptx’’s ‘-T’ option, if the locale uses the Latin-1 +encoding you may need a LaTeX directive like +‘\usepackage[latin1]{inputenc}’ to render non-ASCII characters +correctly. + +‘-f’ +‘--ignore-case’ + Fold lower case letters to upper case for sorting. + + +File: coreutils.info, Node: Input processing in ptx, Next: Output formatting in ptx, Prev: Charset selection in ptx, Up: ptx invocation + +7.5.3 Word selection and input processing +----------------------------------------- + +‘-b FILE’ +‘--break-file=FILE’ + + This option provides an alternative (to ‘-W’) method of describing + which characters make up words. It introduces the name of a file + which contains a list of characters which can_not_ be part of one + word; this file is called the “Break file”. Any character which is + not part of the Break file is a word constituent. If both options + ‘-b’ and ‘-W’ are specified, then ‘-W’ has precedence and ‘-b’ is + ignored. + + When GNU extensions are enabled, the only way to avoid newline as a + break character is to write all the break characters in the file + with no newline at all, not even at the end of the file. When GNU + extensions are disabled, spaces, tabs and newlines are always + considered as break characters even if not included in the Break + file. + +‘-i FILE’ +‘--ignore-file=FILE’ + + The file associated with this option contains a list of words which + will never be taken as keywords in concordance output. It is + called the “Ignore file”. The file contains exactly one word in + each line; the end of line separation of words is not subject to + the value of the ‘-S’ option. + +‘-o FILE’ +‘--only-file=FILE’ + + The file associated with this option contains a list of words which + will be retained in concordance output; any word not mentioned in + this file is ignored. The file is called the “Only file”. The + file contains exactly one word in each line; the end of line + separation of words is not subject to the value of the ‘-S’ option. + + There is no default for the Only file. When both an Only file and + an Ignore file are specified, a word is considered a keyword only + if it is listed in the Only file and not in the Ignore file. + +‘-r’ +‘--references’ + + On each input line, the leading sequence of non-white space + characters will be taken to be a reference that has the purpose of + identifying this input line in the resulting permuted index. *Note + Output formatting in ptx::, for more information about reference + production. Using this option changes the default value for option + ‘-S’. + + Using this option, the program does not try very hard to remove + references from contexts in output, but it succeeds in doing so + _when_ the context ends exactly at the newline. If option ‘-r’ is + used with ‘-S’ default value, or when GNU extensions are disabled, + this condition is always met and references are completely excluded + from the output contexts. + +‘-S REGEXP’ +‘--sentence-regexp=REGEXP’ + + This option selects which regular expression will describe the end + of a line or the end of a sentence. In fact, this regular + expression is not the only distinction between end of lines or end + of sentences, and input line boundaries have no special + significance outside this option. By default, when GNU extensions + are enabled and if ‘-r’ option is not used, end of sentences are + used. In this case, this REGEX is imported from GNU Emacs: + + [.?!][]\"')}]*\\($\\|\t\\| \\)[ \t\n]* + + Whenever GNU extensions are disabled or if ‘-r’ option is used, end + of lines are used; in this case, the default REGEXP is just: + + \n + + Using an empty REGEXP is equivalent to completely disabling end of + line or end of sentence recognition. In this case, the whole file + is considered to be a single big line or sentence. The user might + want to disallow all truncation flag generation as well, through + option ‘-F ""’. *Note Syntax of Regular Expressions: + (emacs)Regexps. + + When the keywords happen to be near the beginning of the input line + or sentence, this often creates an unused area at the beginning of + the output context line; when the keywords happen to be near the + end of the input line or sentence, this often creates an unused + area at the end of the output context line. The program tries to + fill those unused areas by wrapping around context in them; the + tail of the input line or sentence is used to fill the unused area + on the left of the output line; the head of the input line or + sentence is used to fill the unused area on the right of the output + line. + + As a matter of convenience to the user, many usual backslashed + escape sequences from the C language are recognized and converted + to the corresponding characters by ‘ptx’ itself. + +‘-W REGEXP’ +‘--word-regexp=REGEXP’ + + This option selects which regular expression will describe each + keyword. By default, if GNU extensions are enabled, a word is a + sequence of letters; the REGEXP used is ‘\w+’. When GNU extensions + are disabled, a word is by default anything which ends with a + space, a tab or a newline; the REGEXP used is ‘[^ \t\n]+’. + + An empty REGEXP is equivalent to not using this option. *Note + Syntax of Regular Expressions: (emacs)Regexps. + + As a matter of convenience to the user, many usual backslashed + escape sequences, as found in the C language, are recognized and + converted to the corresponding characters by ‘ptx’ itself. + + +File: coreutils.info, Node: Output formatting in ptx, Next: Compatibility in ptx, Prev: Input processing in ptx, Up: ptx invocation + +7.5.4 Output formatting +----------------------- + +Output format is mainly controlled by the ‘-O’ and ‘-T’ options +described in the table below. When neither ‘-O’ nor ‘-T’ are selected, +and if GNU extensions are enabled, the program chooses an output format +suitable for a dumb terminal. Each keyword occurrence is output to the +center of one line, surrounded by its left and right contexts. Each +field is properly justified, so the concordance output can be readily +observed. As a special feature, if automatic references are selected by +option ‘-A’ and are output before the left context, that is, if option +‘-R’ is _not_ selected, then a colon is added after the reference; this +nicely interfaces with GNU Emacs ‘next-error’ processing. In this +default output format, each white space character, like newline and tab, +is merely changed to exactly one space, with no special attempt to +compress consecutive spaces. This might change in the future. Except +for those white space characters, every other character of the +underlying set of 256 characters is transmitted verbatim. + + Output format is further controlled by the following options. + +‘-g NUMBER’ +‘--gap-size=NUMBER’ + + Select the size of the minimum white space gap between the fields + on the output line. + +‘-w NUMBER’ +‘--width=NUMBER’ + + Select the maximum output width of each final line. If references + are used, they are included or excluded from the maximum output + width depending on the value of option ‘-R’. If this option is not + selected, that is, when references are output before the left + context, the maximum output width takes into account the maximum + length of all references. If this option is selected, that is, + when references are output after the right context, the maximum + output width does not take into account the space taken by + references, nor the gap that precedes them. + +‘-A’ +‘--auto-reference’ + + Select automatic references. Each input line will have an + automatic reference made up of the file name and the line ordinal, + with a single colon between them. However, the file name will be + empty when standard input is being read. If both ‘-A’ and ‘-r’ are + selected, then the input reference is still read and skipped, but + the automatic reference is used at output time, overriding the + input reference. + +‘-R’ +‘--right-side-refs’ + + In the default output format, when option ‘-R’ is not used, any + references produced by the effect of options ‘-r’ or ‘-A’ are + placed to the far right of output lines, after the right context. + With default output format, when the ‘-R’ option is specified, + references are rather placed at the beginning of each output line, + before the left context. For any other output format, option ‘-R’ + is ignored, with one exception: with ‘-R’ the width of references + is _not_ taken into account in total output width given by ‘-w’. + + This option is automatically selected whenever GNU extensions are + disabled. + +‘-F STRING’ +‘--flag-truncation=STRING’ + + This option will request that any truncation in the output be + reported using the string STRING. Most output fields theoretically + extend towards the beginning or the end of the current line, or + current sentence, as selected with option ‘-S’. But there is a + maximum allowed output line width, changeable through option ‘-w’, + which is further divided into space for various output fields. + When a field has to be truncated because it cannot extend beyond + the beginning or the end of the current line to fit in, then a + truncation occurs. By default, the string used is a single slash, + as in ‘-F /’. + + STRING may have more than one character, as in ‘-F ...’. Also, in + the particular case when STRING is empty (‘-F ""’), truncation + flagging is disabled, and no truncation marks are appended in this + case. + + As a matter of convenience to the user, many usual backslashed + escape sequences, as found in the C language, are recognized and + converted to the corresponding characters by ‘ptx’ itself. + +‘-M STRING’ +‘--macro-name=STRING’ + + Select another STRING to be used instead of ‘xx’, while generating + output suitable for ‘nroff’, ‘troff’ or TeX. + +‘-O’ +‘--format=roff’ + + Choose an output format suitable for ‘nroff’ or ‘troff’ processing. + Each output line will look like: + + .xx "TAIL" "BEFORE" "KEYWORD_AND_AFTER" "HEAD" "REF" + + so it will be possible to write a ‘.xx’ roff macro to take care of + the output typesetting. This is the default output format when GNU + extensions are disabled. Option ‘-M’ can be used to change ‘xx’ to + another macro name. + + In this output format, each non-graphical character, like newline + and tab, is merely changed to exactly one space, with no special + attempt to compress consecutive spaces. Each quote character ‘"’ + is doubled so it will be correctly processed by ‘nroff’ or ‘troff’. + +‘-T’ +‘--format=tex’ + + Choose an output format suitable for TeX processing. Each output + line will look like: + + \xx {TAIL}{BEFORE}{KEYWORD}{AFTER}{HEAD}{REF} + + so it will be possible to write a ‘\xx’ definition to take care of + the output typesetting. Note that when references are not being + produced, that is, neither option ‘-A’ nor option ‘-r’ is selected, + the last parameter of each ‘\xx’ call is inhibited. Option ‘-M’ + can be used to change ‘xx’ to another macro name. + + In this output format, some special characters, like ‘$’, ‘%’, ‘&’, + ‘#’ and ‘_’ are automatically protected with a backslash. Curly + brackets ‘{’, ‘}’ are protected with a backslash and a pair of + dollar signs (to force mathematical mode). The backslash itself + produces the sequence ‘\backslash{}’. Circumflex and tilde + diacritical marks produce the sequence ‘^\{ }’ and ‘~\{ }’ + respectively. Other diacriticized characters of the underlying + character set produce an appropriate TeX sequence as far as + possible. The other non-graphical characters, like newline and + tab, and all other characters which are not part of ASCII, are + merely changed to exactly one space, with no special attempt to + compress consecutive spaces. Let me know how to improve this + special character processing for TeX. + + +File: coreutils.info, Node: Compatibility in ptx, Prev: Output formatting in ptx, Up: ptx invocation + +7.5.5 The GNU extensions to ‘ptx’ +--------------------------------- + +This version of ‘ptx’ contains a few features which do not exist in +System V ‘ptx’. These extra features are suppressed by using the ‘-G’ +command line option, unless overridden by other command line options. +Some GNU extensions cannot be recovered by overriding, so the simple +rule is to avoid ‘-G’ if you care about GNU extensions. Here are the +differences between this program and System V ‘ptx’. + + • This program can read many input files at once, it always writes + the resulting concordance on standard output. On the other hand, + System V ‘ptx’ reads only one file and sends the result to standard + output or, if a second FILE parameter is given on the command, to + that FILE. + + Having output parameters not introduced by options is a dangerous + practice which GNU avoids as far as possible. So, for using ‘ptx’ + portably between GNU and System V, you should always use it with a + single input file, and always expect the result on standard output. + You might also want to automatically configure in a ‘-G’ option to + ‘ptx’ calls in products using ‘ptx’, if the configurator finds that + the installed ‘ptx’ accepts ‘-G’. + + • The only options available in System V ‘ptx’ are options ‘-b’, + ‘-f’, ‘-g’, ‘-i’, ‘-o’, ‘-r’, ‘-t’ and ‘-w’. All other options are + GNU extensions and are not repeated in this enumeration. Moreover, + some options have a slightly different meaning when GNU extensions + are enabled, as explained below. + + • By default, concordance output is not formatted for ‘troff’ or + ‘nroff’. It is rather formatted for a dumb terminal. ‘troff’ or + ‘nroff’ output may still be selected through option ‘-O’. + + • Unless ‘-R’ option is used, the maximum reference width is + subtracted from the total output line width. With GNU extensions + disabled, width of references is not taken into account in the + output line width computations. + + • All 256 bytes, even ASCII NUL bytes, are always read and processed + from input file with no adverse effect, even if GNU extensions are + disabled. However, System V ‘ptx’ does not accept 8-bit + characters, a few control characters are rejected, and the tilde + ‘~’ is also rejected. + + • Input line length is only limited by available memory, even if GNU + extensions are disabled. However, System V ‘ptx’ processes only + the first 200 characters in each line. + + • The break (non-word) characters default to be every character + except all letters of the underlying character set, diacriticized + or not. When GNU extensions are disabled, the break characters + default to space, tab and newline only. + + • The program makes better use of output line width. If GNU + extensions are disabled, the program rather tries to imitate System + V ‘ptx’, but still, there are some slight disposition glitches this + program does not completely reproduce. + + • The user can specify both an Ignore file and an Only file. This is + not allowed with System V ‘ptx’. + + +File: coreutils.info, Node: tsort invocation, Prev: ptx invocation, Up: Operating on sorted files + +7.6 ‘tsort’: Topological sort +============================= + +‘tsort’ performs a topological sort on the given FILE, or standard input +if no input file is given or for a FILE of ‘-’. For more details and +some history, see *note tsort background::. Synopsis: + + tsort [OPTION] [FILE] + + ‘tsort’ reads its input as pairs of strings, separated by blanks, +indicating a partial ordering. The output is a total ordering that +corresponds to the given partial ordering. + + For example + + tsort <<EOF + a b c + d + e f + b c d e + EOF + +will produce the output + + a + b + c + d + e + f + + Consider a more realistic example. You have a large set of functions +all in one file, and they may all be declared static except one. +Currently that one (say ‘main’) is the first function defined in the +file, and the ones it calls directly follow it, followed by those they +call, etc. Let’s say that you are determined to take advantage of +prototypes, so you have to choose between declaring all of those +functions (which means duplicating a lot of information from the +definitions) and rearranging the functions so that as many as possible +are defined before they are used. One way to automate the latter +process is to get a list for each function of the functions it calls +directly. Many programs can generate such lists. They describe a call +graph. Consider the following list, in which a given line indicates +that the function on the left calls the one on the right directly. + + main parse_options + main tail_file + main tail_forever + tail_file pretty_name + tail_file write_header + tail_file tail + tail_forever recheck + tail_forever pretty_name + tail_forever write_header + tail_forever dump_remainder + tail tail_lines + tail tail_bytes + tail_lines start_lines + tail_lines dump_remainder + tail_lines file_lines + tail_lines pipe_lines + tail_bytes xlseek + tail_bytes start_bytes + tail_bytes dump_remainder + tail_bytes pipe_bytes + file_lines dump_remainder + recheck pretty_name + + then you can use ‘tsort’ to produce an ordering of those functions +that satisfies your requirement. + + example$ tsort call-graph | tac + dump_remainder + start_lines + file_lines + pipe_lines + xlseek + start_bytes + pipe_bytes + tail_lines + tail_bytes + pretty_name + write_header + tail + recheck + parse_options + tail_file + tail_forever + main + + ‘tsort’ detects any cycles in the input and writes the first cycle +encountered to standard error. + + Note that for a given partial ordering, generally there is no unique +total ordering. In the context of the call graph above, the function +‘parse_options’ may be placed anywhere in the list as long as it +precedes ‘main’. + + The only options are ‘--help’ and ‘--version’. *Note Common +options::. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + +* Menu: + +* tsort background:: Where tsort came from. + + +File: coreutils.info, Node: tsort background, Up: tsort invocation + +7.6.1 ‘tsort’: Background +------------------------- + +‘tsort’ exists because very early versions of the Unix linker processed +an archive file exactly once, and in order. As ‘ld’ read each object in +the archive, it decided whether it was needed in the program based on +whether it defined any symbols which were undefined at that point in the +link. + + This meant that dependencies within the archive had to be handled +specially. For example, ‘scanf’ probably calls ‘read’. That means that +in a single pass through an archive, it was important for ‘scanf.o’ to +appear before read.o, because otherwise a program which calls ‘scanf’ +but not ‘read’ might end up with an unexpected unresolved reference to +‘read’. + + The way to address this problem was to first generate a set of +dependencies of one object file on another. This was done by a shell +script called ‘lorder’. The GNU tools don’t provide a version of +lorder, as far as I know, but you can still find it in BSD +distributions. + + Then you ran ‘tsort’ over the ‘lorder’ output, and you used the +resulting sort to define the order in which you added objects to the +archive. + + This whole procedure has been obsolete since about 1980, because Unix +archives now contain a symbol table (traditionally built by ‘ranlib’, +now generally built by ‘ar’ itself), and the Unix linker uses the symbol +table to effectively make multiple passes over an archive file. + + Anyhow, that’s where tsort came from. To solve an old problem with +the way the linker handled archive files, which has since been solved in +different ways. + + +File: coreutils.info, Node: Operating on fields, Next: Operating on characters, Prev: Operating on sorted files, Up: Top + +8 Operating on fields +********************* + +* Menu: + +* cut invocation:: Print selected parts of lines. +* paste invocation:: Merge lines of files. +* join invocation:: Join lines on a common field. + + +File: coreutils.info, Node: cut invocation, Next: paste invocation, Up: Operating on fields + +8.1 ‘cut’: Print selected parts of lines +======================================== + +‘cut’ writes to standard output selected parts of each line of each +input file, or standard input if no files are given or for a file name +of ‘-’. Synopsis: + + cut OPTION... [FILE]... + + In the table which follows, the BYTE-LIST, CHARACTER-LIST, and +FIELD-LIST are one or more numbers or ranges (two numbers separated by a +dash) separated by commas. Bytes, characters, and fields are numbered +starting at 1. Incomplete ranges may be given: ‘-M’ means ‘1-M’; ‘N-’ +means ‘N’ through end of line or last field. The list elements can be +repeated, can overlap, and can be specified in any order; but the +selected input is written in the same order that it is read, and is +written exactly once. + + The program accepts the following options. Also see *note Common +options::. + +‘-b BYTE-LIST’ +‘--bytes=BYTE-LIST’ + Select for printing only the bytes in positions listed in + BYTE-LIST. Tabs and backspaces are treated like any other + character; they take up 1 byte. If an output delimiter is + specified, (see the description of ‘--output-delimiter’), then + output that string between ranges of selected bytes. + +‘-c CHARACTER-LIST’ +‘--characters=CHARACTER-LIST’ + Select for printing only the characters in positions listed in + CHARACTER-LIST. The same as ‘-b’ for now, but internationalization + will change that. Tabs and backspaces are treated like any other + character; they take up 1 character. If an output delimiter is + specified, (see the description of ‘--output-delimiter’), then + output that string between ranges of selected bytes. + +‘-f FIELD-LIST’ +‘--fields=FIELD-LIST’ + Select for printing only the fields listed in FIELD-LIST. Fields + are separated by a TAB character by default. Also print any line + that contains no delimiter character, unless the ‘--only-delimited’ + (‘-s’) option is specified. + + Note ‘awk’ supports more sophisticated field processing, like + reordering fields, and handling fields aligned with blank + characters. By default ‘awk’ uses (and discards) runs of blank + characters to separate fields, and ignores leading and trailing + blanks. + awk '{print $2}' # print the second field + awk '{print $(NF-1)}' # print the penultimate field + awk '{print $2,$1}' # reorder the first two fields + Note while ‘cut’ accepts field specifications in arbitrary order, + output is always in the order encountered in the file. + + In the unlikely event that ‘awk’ is unavailable, one can use the + ‘join’ command, to process blank characters as ‘awk’ does above. + join -a1 -o 1.2 - /dev/null # print the second field + join -a1 -o 1.2,1.1 - /dev/null # reorder the first two fields + +‘-d INPUT_DELIM_BYTE’ +‘--delimiter=INPUT_DELIM_BYTE’ + With ‘-f’, use the first byte of INPUT_DELIM_BYTE as the input + fields separator (default is TAB). + +‘-n’ + Do not split multi-byte characters (no-op for now). + +‘-s’ +‘--only-delimited’ + For ‘-f’, do not print lines that do not contain the field + separator character. Normally, any line without a field separator + is printed verbatim. + +‘--output-delimiter=OUTPUT_DELIM_STRING’ + With ‘-f’, output fields are separated by OUTPUT_DELIM_STRING. The + default with ‘-f’ is to use the input delimiter. When using ‘-b’ + or ‘-c’ to select ranges of byte or character offsets (as opposed + to ranges of fields), output OUTPUT_DELIM_STRING between + non-overlapping ranges of selected bytes. + +‘--complement’ + This option is a GNU extension. Select for printing the complement + of the bytes, characters or fields selected with the ‘-b’, ‘-c’ or + ‘-f’ options. In other words, do _not_ print the bytes, characters + or fields specified via those options. This option is useful when + you have many fields and want to print all but a few of them. + +‘-z’ +‘--zero-terminated’ + Delimit items with a zero byte rather than a newline (ASCII LF). + I.e., treat input as items separated by ASCII NUL and terminate + output items with ASCII NUL. This option can be useful in + conjunction with ‘perl -0’ or ‘find -print0’ and ‘xargs -0’ which + do the same in order to reliably handle arbitrary file names (even + those containing blanks or other special characters). + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: paste invocation, Next: join invocation, Prev: cut invocation, Up: Operating on fields + +8.2 ‘paste’: Merge lines of files +================================= + +‘paste’ writes to standard output lines consisting of sequentially +corresponding lines of each given file, separated by a TAB character. +Standard input is used for a file name of ‘-’ or if no input files are +given. + + Synopsis: + + paste [OPTION]... [FILE]... + + For example, with: + $ cat num2 + 1 + 2 + $ cat let3 + a + b + c + + Take lines sequentially from each file: + $ paste num2 let3 + 1 a + 2 b + c + + Duplicate lines from a file: + $ paste num2 let3 num2 + 1 a 1 + 2 b 2 + c + + Intermix lines from standard input: + $ paste - let3 - < num2 + 1 a 2 + b + c + + Join consecutive lines with a space: + $ seq 4 | paste -d ' ' - - + 1 2 + 3 4 + + The program accepts the following options. Also see *note Common +options::. + +‘-s’ +‘--serial’ + Paste the lines of one file at a time rather than one line from + each file. Using the above example data: + + $ paste -s num2 let3 + 1 2 + a b c + +‘-d DELIM-LIST’ +‘--delimiters=DELIM-LIST’ + Consecutively use the characters in DELIM-LIST instead of TAB to + separate merged lines. When DELIM-LIST is exhausted, start again + at its beginning. Using the above example data: + + $ paste -d '%_' num2 let3 num2 + 1%a_1 + 2%b_2 + %c_ + +‘-z’ +‘--zero-terminated’ + Delimit items with a zero byte rather than a newline (ASCII LF). + I.e., treat input as items separated by ASCII NUL and terminate + output items with ASCII NUL. This option can be useful in + conjunction with ‘perl -0’ or ‘find -print0’ and ‘xargs -0’ which + do the same in order to reliably handle arbitrary file names (even + those containing blanks or other special characters). + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: join invocation, Prev: paste invocation, Up: Operating on fields + +8.3 ‘join’: Join lines on a common field +======================================== + +‘join’ writes to standard output a line for each pair of input lines +that have identical join fields. Synopsis: + + join [OPTION]... FILE1 FILE2 + + Either FILE1 or FILE2 (but not both) can be ‘-’, meaning standard +input. FILE1 and FILE2 should be sorted on the join fields. + + $ cat file1 + a 1 + b 2 + e 5 + + $ cat file2 + a X + e Y + f Z + + $ join file1 file2 + a 1 X + e 5 Y + +‘join’’s default behavior (when no options are given): + • the join field is the first field in each line; + • fields in the input are separated by one or more blanks, with + leading blanks on the line ignored; + • fields in the output are separated by a space; + • each output line consists of the join field, the remaining fields + from FILE1, then the remaining fields from FILE2. + +* Menu: + +* General options in join:: Options which affect general program behavior. +* Sorting files for join:: Using ‘sort’ before ‘join’. +* Working with fields:: Joining on different fields. +* Paired and unpaired lines:: Controlling ‘join’’s field matching. +* Header lines:: Working with header lines in files. +* Set operations:: Union, Intersection and Difference of files. + + +File: coreutils.info, Node: General options in join, Next: Sorting files for join, Up: join invocation + +8.3.1 General options +--------------------- + +The program accepts the following options. Also see *note Common +options::. + +‘-a FILE-NUMBER’ + Print a line for each unpairable line in file FILE-NUMBER (either + ‘1’ or ‘2’), in addition to the normal output. + +‘--check-order’ + Fail with an error message if either input file is wrongly ordered. + +‘--nocheck-order’ + Do not check that both input files are in sorted order. This is + the default. + +‘-e STRING’ + Replace those output fields that are missing in the input with + STRING. I.e., missing fields specified with the ‘-12jo’ options. + +‘--header’ + Treat the first line of each input file as a header line. The + header lines will be joined and printed as the first output line. + If ‘-o’ is used to specify output format, the header line will be + printed according to the specified format. The header lines will + not be checked for ordering even if ‘--check-order’ is specified. + Also if the header lines from each file do not match, the heading + fields from the first file will be used. + +‘-i’ +‘--ignore-case’ + Ignore differences in case when comparing keys. With this option, + the lines of the input files must be ordered in the same way. Use + ‘sort -f’ to produce this ordering. + +‘-1 FIELD’ + Join on field FIELD (a positive integer) of file 1. + +‘-2 FIELD’ + Join on field FIELD (a positive integer) of file 2. + +‘-j FIELD’ + Equivalent to ‘-1 FIELD -2 FIELD’. + +‘-o FIELD-LIST’ +‘-o auto’ + If the keyword ‘auto’ is specified, infer the output format from + the first line in each file. This is the same as the default + output format but also ensures the same number of fields are output + for each line. Missing fields are replaced with the ‘-e’ option + and extra fields are discarded. + + Otherwise, construct each output line according to the format in + FIELD-LIST. Each element in FIELD-LIST is either the single + character ‘0’ or has the form M.N where the file number, M, is ‘1’ + or ‘2’ and N is a positive field number. + + A field specification of ‘0’ denotes the join field. In most + cases, the functionality of the ‘0’ field spec may be reproduced + using the explicit M.N that corresponds to the join field. + However, when printing unpairable lines (using either of the ‘-a’ + or ‘-v’ options), there is no way to specify the join field using + M.N in FIELD-LIST if there are unpairable lines in both files. To + give ‘join’ that functionality, POSIX invented the ‘0’ field + specification notation. + + The elements in FIELD-LIST are separated by commas or blanks. + Blank separators typically need to be quoted for the shell. For + example, the commands ‘join -o 1.2,2.2’ and ‘join -o '1.2 2.2'’ are + equivalent. + + All output lines – including those printed because of any ‘-a’ or + ‘-v’ option – are subject to the specified FIELD-LIST. + +‘-t CHAR’ + Use character CHAR as the input and output field separator. Treat + as significant each occurrence of CHAR in the input file. Use + ‘sort -t CHAR’, without the ‘-b’ option of ‘sort’, to produce this + ordering. If ‘join -t ''’ is specified, the whole line is + considered, matching the default operation of sort. If ‘-t '\0'’ + is specified then the ASCII NUL character is used to delimit the + fields. + +‘-v FILE-NUMBER’ + Print a line for each unpairable line in file FILE-NUMBER (either + ‘1’ or ‘2’), instead of the normal output. + +‘-z’ +‘--zero-terminated’ + Delimit items with a zero byte rather than a newline (ASCII LF). + I.e., treat input as items separated by ASCII NUL and terminate + output items with ASCII NUL. This option can be useful in + conjunction with ‘perl -0’ or ‘find -print0’ and ‘xargs -0’ which + do the same in order to reliably handle arbitrary file names (even + those containing blanks or other special characters). Note with + ‘-z’ the newline character is treated as a field separator. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + If the ‘--check-order’ option is given, unsorted inputs will cause a +fatal error message. If the option ‘--nocheck-order’ is given, unsorted +inputs will never cause an error message. If neither of these options +is given, wrongly sorted inputs are diagnosed only if an input file is +found to contain unpairable lines, and when both input files are non +empty. If an input file is diagnosed as being unsorted, the ‘join’ +command will exit with a nonzero status (and the output should not be +used). + + Forcing ‘join’ to process wrongly sorted input files containing +unpairable lines by specifying ‘--nocheck-order’ is not guaranteed to +produce any particular output. The output will probably not correspond +with whatever you hoped it would be. + + +File: coreutils.info, Node: Sorting files for join, Next: Working with fields, Prev: General options in join, Up: join invocation + +8.3.2 Pre-sorting +----------------- + +‘join’ requires sorted input files. Each input file should be sorted +according to the key (=field/column number) used in ‘join’. The +recommended sorting option is ‘sort -k 1b,1’ (assuming the desired key +is in the first column). + +Typical usage: + $ sort -k 1b,1 file1 > file1.sorted + $ sort -k 1b,1 file2 > file2.sorted + $ join file1.sorted file2.sorted > file3 + + Normally, the sort order is that of the collating sequence specified +by the ‘LC_COLLATE’ locale. Unless the ‘-t’ option is given, the sort +comparison ignores blanks at the start of the join field, as in ‘sort +-b’. If the ‘--ignore-case’ option is given, the sort comparison +ignores the case of characters in the join field, as in ‘sort -f’: + + $ sort -k 1bf,1 file1 > file1.sorted + $ sort -k 1bf,1 file2 > file2.sorted + $ join --ignore-case file1.sorted file2.sorted > file3 + + The ‘sort’ and ‘join’ commands should use consistent locales and +options if the output of ‘sort’ is fed to ‘join’. You can use a command +like ‘sort -k 1b,1’ to sort a file on its default join field, but if you +select a non-default locale, join field, separator, or comparison +options, then you should do so consistently between ‘join’ and ‘sort’. + +To avoid any locale-related issues, it is recommended to use the ‘C’ +locale for both commands: + + $ LC_ALL=C sort -k 1b,1 file1 > file1.sorted + $ LC_ALL=C sort -k 1b,1 file2 > file2.sorted + $ LC_ALL=C join file1.sorted file2.sorted > file3 + + +File: coreutils.info, Node: Working with fields, Next: Paired and unpaired lines, Prev: Sorting files for join, Up: join invocation + +8.3.3 Working with fields +------------------------- + +Use ‘-1’,‘-2’ to set the key fields for each of the input files. Ensure +the preceding ‘sort’ commands operated on the same fields. + +The following example joins two files, using the values from seventh +field of the first file and the third field of the second file: + + $ sort -k 7b,7 file1 > file1.sorted + $ sort -k 3b,3 file2 > file2.sorted + $ join -1 7 -2 3 file1.sorted file2.sorted > file3 + +If the field number is the same for both files, use ‘-j’: + + $ sort -k4b,4 file1 > file1.sorted + $ sort -k4b,4 file2 > file2.sorted + $ join -j4 file1.sorted file2.sorted > file3 + +Both ‘sort’ and ‘join’ operate of whitespace-delimited fields. To +specify a different delimiter, use ‘-t’ in _both_: + + $ sort -t, -k3b,3 file1 > file1.sorted + $ sort -t, -k3b,3 file2 > file2.sorted + $ join -t, -j3 file1.sorted file2.sorted > file3 + +To specify a tab (ASCII 0x09) character instead of whitespace, use:(1) + + $ sort -t$'\t' -k3b,3 file1 > file1.sorted + $ sort -t$'\t' -k3b,3 file2 > file2.sorted + $ join -t$'\t' -j3 file1.sorted file2.sorted > file3 + +If ‘join -t ''’ is specified then the whole line is considered which +matches the default operation of sort: + + $ sort file1 > file1.sorted + $ sort file2 > file2.sorted + $ join -t '' file1.sorted file2.sorted > file3 + + ---------- Footnotes ---------- + + (1) the ‘$'\t'’ is supported in most modern shells. For older +shells, use a literal tab. + + +File: coreutils.info, Node: Paired and unpaired lines, Next: Header lines, Prev: Working with fields, Up: join invocation + +8.3.4 Controlling ‘join’’s field matching +----------------------------------------- + +In this section the ‘sort’ commands are omitted for brevity. Sorting +the files before joining is still required. + + ‘join’’s default behavior is to print only lines common to both input +files. Use ‘-a’ and ‘-v’ to print unpairable lines from one or both +files. + +All examples below use the following two (pre-sorted) input files: + + $ cat file1 $ cat file2 + a 1 a A + b 2 c C + +Command Outcome + +-------------------------------------------------------------------------- + $ join file1 file2 common lines (_intersection_) + a 1 A + $ join -a 1 file1 file2 common lines _and_ unpaired lines + a 1 A from the first file + b 2 + $ join -a 2 file1 file2 common lines _and_ unpaired lines + a 1 A from the second file + c C + $ join -a 1 -a 2 file1 file2 all lines (paired and unpaired) + a 1 A from both files (_union_). + b 2 see note below regarding ‘-o + c C auto’. + + $ join -v 1 file1 file2 unpaired lines from the first file + b 2 (_difference_) + + $ join -v 2 file1 file2 unpaired lines from the second + c C file (_difference_) + + $ join -v 1 -v 2 file1 file2 unpaired lines from both files, + b 2 omitting common lines (_symmetric + c C difference_). + + +The ‘-o auto -e X’ options are useful when dealing with unpaired lines. +The following example prints all lines (common and unpaired) from both +files. Without ‘-o auto’ it is not easy to discern which fields +originate from which file: + + $ join -a 1 -a 2 file1 file2 + a 1 A + b 2 + c C + + $ join -o auto -e X -a 1 -a 2 file1 file2 + a 1 A + b 2 X + c X C + + If the input has no unpairable lines, a GNU extension is available; +the sort order can be any order that considers two fields to be equal if +and only if the sort comparison described above considers them to be +equal. For example: + + $ cat file1 + a a1 + c c1 + b b1 + + $ cat file2 + a a2 + c c2 + b b2 + + $ join file1 file2 + a a1 a2 + c c1 c2 + b b1 b2 + + +File: coreutils.info, Node: Header lines, Next: Set operations, Prev: Paired and unpaired lines, Up: join invocation + +8.3.5 Header lines +------------------ + +The ‘--header’ option can be used when the files to join have a header +line which is not sorted: + + $ cat file1 + Name Age + Alice 25 + Charlie 34 + + $ cat file2 + Name Country + Alice France + Bob Spain + + $ join --header -o auto -e NA -a1 -a2 file1 file2 + Name Age Country + Alice 25 France + Bob NA Spain + Charlie 34 NA + + To sort a file with a header line, use GNU ‘sed -u’. The following +example sort the files but keeps the first line of each file in place: + + $ ( sed -u 1q ; sort -k2b,2 ) < file1 > file1.sorted + $ ( sed -u 1q ; sort -k2b,2 ) < file2 > file2.sorted + $ join --header -o auto -e NA -a1 -a2 file1.sorted file2.sorted > file3 + + +File: coreutils.info, Node: Set operations, Prev: Header lines, Up: join invocation + +8.3.6 Union, Intersection and Difference of files +------------------------------------------------- + +Combine ‘sort’, ‘uniq’ and ‘join’ to perform the equivalent of set +operations on files: + +Command outcome +-------------------------------------------------------------------------- +‘sort -u file1 file2’ Union of unsorted files + +‘sort file1 file2 | uniq -d’ Intersection of unsorted files + +‘sort file1 file1 file2 | uniq -u’ Difference of unsorted files + +‘sort file1 file2 | uniq -u’ Symmetric Difference of unsorted + files + +‘join -t '' -a1 -a2 file1 file2’ Union of sorted files + +‘join -t '' file1 file2’ Intersection of sorted files + +‘join -t '' -v2 file1 file2’ Difference of sorted files + +‘join -t '' -v1 -v2 file1 file2’ Symmetric Difference of sorted + files + + + All examples above operate on entire lines and not on specific +fields: ‘sort’ without ‘-k’ and ‘join -t ''’ both consider entire lines +as the key. + + +File: coreutils.info, Node: Operating on characters, Next: Directory listing, Prev: Operating on fields, Up: Top + +9 Operating on characters +************************* + +These commands operate on individual characters. + +* Menu: + +* tr invocation:: Translate, squeeze, and/or delete characters. +* expand invocation:: Convert tabs to spaces. +* unexpand invocation:: Convert spaces to tabs. + + +File: coreutils.info, Node: tr invocation, Next: expand invocation, Up: Operating on characters + +9.1 ‘tr’: Translate, squeeze, and/or delete characters +====================================================== + +Synopsis: + + tr [OPTION]... STRING1 [STRING2] + + ‘tr’ copies standard input to standard output, performing one of the +following operations: + + • translate, and optionally squeeze repeated characters in the + result, + • squeeze repeated characters, + • delete characters, + • delete characters, then squeeze repeated characters from the + result. + + The STRING1 and STRING2 operands define arrays of characters ARRAY1 +and ARRAY2. By default ARRAY1 lists input characters that ‘tr’ operates +on, and ARRAY2 lists corresponding translations. In some cases the +second operand is omitted. + + The program accepts the following options. Also see *note Common +options::. Options must precede operands. + +‘-c’ +‘-C’ +‘--complement’ + Instead of ARRAY1, use its complement (all characters not specified + by STRING1), in ascending order. Use this option with caution in + multibyte locales where its meaning is not always clear or + portable; see *note Character arrays::. + +‘-d’ +‘--delete’ + Delete characters in ARRAY1; do not translate. + +‘-s’ +‘--squeeze-repeats’ + Replace each sequence of a repeated character that is listed in the + last specified ARRAY, with a single occurrence of that character. + +‘-t’ +‘--truncate-set1’ + Truncate ARRAY1 to the length of ARRAY2. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + +* Menu: + +* Character arrays:: Specifying arrays of characters. +* Translating:: Changing characters to other characters. +* Squeezing and deleting:: Removing characters. + + +File: coreutils.info, Node: Character arrays, Next: Translating, Up: tr invocation + +9.1.1 Specifying arrays of characters +------------------------------------- + +The STRING1 and STRING2 operands are not regular expressions, even +though they may look similar. Instead, they merely represent arrays of +characters. As a GNU extension to POSIX, an empty string operand +represents an empty array of characters. + + The interpretation of STRING1 and STRING2 depends on locale. GNU +‘tr’ fully supports only safe single-byte locales, where each possible +input byte represents a single character. Unfortunately, this means GNU +‘tr’ will not handle commands like ‘tr ö Ł’ the way you might expect, +since (assuming a UTF-8 encoding) this is equivalent to ‘tr '\303\266' +'\305\201'’ and GNU ‘tr’ will simply transliterate all ‘\303’ bytes to +‘\305’ bytes, etc. POSIX does not clearly specify the behavior of ‘tr’ +in locales where characters are represented by byte sequences instead of +by individual bytes, or where data might contain invalid bytes that are +encoding errors. To avoid problems in this area, you can run ‘tr’ in a +safe single-byte locale by using a shell command like ‘LC_ALL=C tr’ +instead of plain ‘tr’. + + Although most characters simply represent themselves in STRING1 and +STRING2, the strings can contain shorthands listed below, for +convenience. Some shorthands can be used only in STRING1 or STRING2, as +noted below. + +Backslash escapes + + The following backslash escape sequences are recognized: + + ‘\a’ + Bell (BEL, Control-G). + ‘\b’ + Backspace (BS, Control-H). + ‘\f’ + Form feed (FF, Control-L). + ‘\n’ + Newline (LF, Control-J). + ‘\r’ + Carriage return (CR, Control-M). + ‘\t’ + Tab (HT, Control-I). + ‘\v’ + Vertical tab (VT, Control-K). + ‘\OOO’ + The eight-bit byte with the value given by OOO, which is the + longest sequence of one to three octal digits following the + backslash. For portability, OOO should represent a value that + fits in eight bits. As a GNU extension to POSIX, if the value + would not fit, then only the first two digits of OOO are used, + e.g., ‘\400’ is equivalent to ‘\0400’ and represents a + two-byte sequence. + ‘\\’ + A backslash. + + It is an error if no character follows an unescaped backslash. As + a GNU extension, a backslash followed by a character not listed + above is interpreted as that character, removing any special + significance; this can be used to escape the characters ‘[’ and ‘-’ + when they would otherwise be special. + +Ranges + + The notation ‘M-N’ expands to the characters from M through N, in + ascending order. M should not collate after N; if it does, an + error results. As an example, ‘0-9’ is the same as ‘0123456789’. + + GNU ‘tr’ does not support the System V syntax that uses square + brackets to enclose ranges. Translations specified in that format + sometimes work as expected, since the brackets are often + transliterated to themselves. However, they should be avoided + because they sometimes behave unexpectedly. For example, ‘tr -d + '[0-9]'’ deletes brackets as well as digits. + + Many historically common and even accepted uses of ranges are not + fully portable. For example, on EBCDIC hosts using the ‘A-Z’ range + will not do what most would expect because ‘A’ through ‘Z’ are not + contiguous as they are in ASCII. One way to work around this is to + use character classes (see below). Otherwise, it is most portable + (and most ugly) to enumerate the members of the ranges. + +Repeated characters + + The notation ‘[C*N]’ in STRING2 expands to N copies of character C. + Thus, ‘[y*6]’ is the same as ‘yyyyyy’. The notation ‘[C*]’ in + STRING2 expands to as many copies of C as are needed to make ARRAY2 + as long as ARRAY1. If N begins with ‘0’, it is interpreted in + octal, otherwise in decimal. A zero-valued N is treated as if it + were absent. + +Character classes + + The notation ‘[:CLASS:]’ expands to all characters in the + (predefined) class CLASS. When the ‘--delete’ (‘-d’) and + ‘--squeeze-repeats’ (‘-s’) options are both given, any character + class can be used in STRING2. Otherwise, only the character + classes ‘lower’ and ‘upper’ are accepted in STRING2, and then only + if the corresponding character class (‘upper’ and ‘lower’, + respectively) is specified in the same relative position in + STRING1. Doing this specifies case conversion. Except for case + conversion, a class’s characters appear in no particular order. + The class names are given below; an error results when an invalid + class name is given. + + ‘alnum’ + Letters and digits. + ‘alpha’ + Letters. + ‘blank’ + Horizontal whitespace. + ‘cntrl’ + Control characters. + ‘digit’ + Digits. + ‘graph’ + Printable characters, not including space. + ‘lower’ + Lowercase letters. + ‘print’ + Printable characters, including space. + ‘punct’ + Punctuation characters. + ‘space’ + Horizontal or vertical whitespace. + ‘upper’ + Uppercase letters. + ‘xdigit’ + Hexadecimal digits. + +Equivalence classes + + The syntax ‘[=C=]’ expands to all characters equivalent to C, in no + particular order. These equivalence classes are allowed in STRING2 + only when ‘--delete’ (‘-d’) and ‘--squeeze-repeats’ ‘-s’ are both + given. + + Although equivalence classes are intended to support non-English + alphabets, there seems to be no standard way to define them or + determine their contents. Therefore, they are not fully + implemented in GNU ‘tr’; each character’s equivalence class + consists only of that character, which is of no particular use. + + +File: coreutils.info, Node: Translating, Next: Squeezing and deleting, Prev: Character arrays, Up: tr invocation + +9.1.2 Translating +----------------- + +‘tr’ performs translation when STRING1 and STRING2 are both given and +the ‘--delete’ (‘-d’) option is not given. ‘tr’ translates each +character of its input that is in ARRAY1 to the corresponding character +in ARRAY2. Characters not in ARRAY1 are passed through unchanged. + + As a GNU extension to POSIX, when a character appears more than once +in ARRAY1, only the final instance is used. For example, these two +commands are equivalent: + + tr aaa xyz + tr a z + + A common use of ‘tr’ is to convert lowercase characters to uppercase. +This can be done in many ways. Here are three of them: + + tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ + tr a-z A-Z + tr '[:lower:]' '[:upper:]' + +However, ranges like ‘a-z’ are not portable outside the C locale. + + When ‘tr’ is performing translation, ARRAY1 and ARRAY2 typically have +the same length. If ARRAY1 is shorter than ARRAY2, the extra characters +at the end of ARRAY2 are ignored. + + On the other hand, making ARRAY1 longer than ARRAY2 is not portable; +POSIX says that the result is undefined. In this situation, BSD ‘tr’ +pads ARRAY2 to the length of ARRAY1 by repeating the last character of +ARRAY2 as many times as necessary. System V ‘tr’ truncates ARRAY1 to +the length of ARRAY2. + + By default, GNU ‘tr’ handles this case like BSD ‘tr’. When the +‘--truncate-set1’ (‘-t’) option is given, GNU ‘tr’ handles this case +like the System V ‘tr’ instead. This option is ignored for operations +other than translation. + + Acting like System V ‘tr’ in this case breaks the relatively common +BSD idiom: + + tr -cs A-Za-z0-9 '\012' + +because it converts only zero bytes (the first element in the complement +of ARRAY1), rather than all non-alphanumerics, to newlines. + +By the way, the above idiom is not portable because it uses ranges, and +it assumes that the octal code for newline is 012. Here is a better way +to write it: + + tr -cs '[:alnum:]' '[\n*]' + + +File: coreutils.info, Node: Squeezing and deleting, Prev: Translating, Up: tr invocation + +9.1.3 Squeezing repeats and deleting +------------------------------------ + +When given just the ‘--delete’ (‘-d’) option, ‘tr’ removes any input +characters that are in ARRAY1. + + When given just the ‘--squeeze-repeats’ (‘-s’) option and not +translating, ‘tr’ replaces each input sequence of a repeated character +that is in ARRAY1 with a single occurrence of that character. + + When given both ‘--delete’ and ‘--squeeze-repeats’, ‘tr’ first +performs any deletions using ARRAY1, then squeezes repeats from any +remaining characters using ARRAY2. + + The ‘--squeeze-repeats’ option may also be used when translating, in +which case ‘tr’ first performs translation, then squeezes repeats from +any remaining characters using ARRAY2. + + Here are some examples to illustrate various combinations of options: + + • Remove all zero bytes: + + tr -d '\0' + + • Put all words on lines by themselves. This converts all + non-alphanumeric characters to newlines, then squeezes each string + of repeated newlines into a single newline: + + tr -cs '[:alnum:]' '[\n*]' + + • Convert each sequence of repeated newlines to a single newline. + I.e., delete empty lines: + + tr -s '\n' + + • Find doubled occurrences of words in a document. For example, + people often write “the the” with the repeated words separated by a + newline. The Bourne shell script below works first by converting + each sequence of punctuation and blank characters to a single + newline. That puts each “word” on a line by itself. Next it maps + all uppercase characters to lower case, and finally it runs ‘uniq’ + with the ‘-d’ option to print out only the words that were + repeated. + + #!/bin/sh + cat -- "$@" \ + | tr -s '[:punct:][:blank:]' '[\n*]' \ + | tr '[:upper:]' '[:lower:]' \ + | uniq -d + + • Deleting a small set of characters is usually straightforward. For + example, to remove all ‘a’s, ‘x’s, and ‘M’s you would do this: + + tr -d axM + + However, when ‘-’ is one of those characters, it can be tricky + because ‘-’ has special meanings. Performing the same task as + above but also removing all ‘-’ characters, we might try ‘tr -d + -axM’, but that would fail because ‘tr’ would try to interpret ‘-a’ + as a command-line option. Alternatively, we could try putting the + hyphen inside the string, ‘tr -d a-xM’, but that wouldn’t work + either because it would make ‘tr’ interpret ‘a-x’ as the range of + characters ‘a’...‘x’ rather than the three. One way to solve the + problem is to put the hyphen at the end of the list of characters: + + tr -d axM- + + Or you can use ‘--’ to terminate option processing: + + tr -d -- -axM + + +File: coreutils.info, Node: expand invocation, Next: unexpand invocation, Prev: tr invocation, Up: Operating on characters + +9.2 ‘expand’: Convert tabs to spaces +==================================== + +‘expand’ writes the contents of each given FILE, or standard input if +none are given or for a FILE of ‘-’, to standard output, with tab +characters converted to the appropriate number of spaces. Synopsis: + + expand [OPTION]... [FILE]... + + By default, ‘expand’ converts all tabs to spaces. It preserves +backspace characters in the output; they decrement the column count for +tab calculations. The default action is equivalent to ‘-t 8’ (set tabs +every 8 columns). + + The program accepts the following options. Also see *note Common +options::. + +‘-t TAB1[,TAB2]...’ +‘--tabs=TAB1[,TAB2]...’ + If only one tab stop is given, set the tabs TAB1 spaces apart + (default is 8). Otherwise, set the tabs at columns TAB1, TAB2, ... + (numbered from 0), and replace any tabs beyond the last tab stop + given with single spaces. Tab stops can be separated by blanks as + well as by commas. + + As a GNU extension the last TAB specified can be prefixed with a + ‘/’ to indicate a tab size to use for remaining positions. For + example, ‘--tabs=2,4,/8’ will set tab stops at position 2 and 4, + and every multiple of 8 after that. + + Also the last TAB specified can be prefixed with a ‘+’ to indicate + a tab size to use for remaining positions, offset from the final + explicitly specified tab stop. For example, to ignore the 1 + character gutter present in diff output, one can specify a 1 + character offset using ‘--tabs=1,+8’, which will set tab stops at + positions 1,9,17,... + + For compatibility, GNU ‘expand’ also accepts the obsolete option + syntax, ‘-T1[,T2]...’. New scripts should use ‘-t T1[,T2]...’ + instead. + +‘-i’ +‘--initial’ + Only convert initial tabs (those that precede all non-space or + non-tab characters) on each line to spaces. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: unexpand invocation, Prev: expand invocation, Up: Operating on characters + +9.3 ‘unexpand’: Convert spaces to tabs +====================================== + +‘unexpand’ writes the contents of each given FILE, or standard input if +none are given or for a FILE of ‘-’, to standard output, converting +blanks at the beginning of each line into as many tab characters as +needed. In the default POSIX locale, a “blank” is a space or a tab; +other locales may specify additional blank characters. Synopsis: + + unexpand [OPTION]... [FILE]... + + By default, ‘unexpand’ converts only initial blanks (those that +precede all non-blank characters) on each line. It preserves backspace +characters in the output; they decrement the column count for tab +calculations. By default, tabs are set at every 8th column. + + The program accepts the following options. Also see *note Common +options::. + +‘-t TAB1[,TAB2]...’ +‘--tabs=TAB1[,TAB2]...’ + If only one tab stop is given, set the tabs TAB1 columns apart + instead of the default 8. Otherwise, set the tabs at columns TAB1, + TAB2, ... (numbered from 0), and leave blanks beyond the tab stops + given unchanged. Tab stops can be separated by blanks as well as + by commas. + + As a GNU extension the last TAB specified can be prefixed with a + ‘/’ to indicate a tab size to use for remaining positions. For + example, ‘--tabs=2,4,/8’ will set tab stops at position 2 and 4, + and every multiple of 8 after that. + + Also the last TAB specified can be prefixed with a ‘+’ to indicate + a tab size to use for remaining positions, offset from the final + explicitly specified tab stop. For example, to ignore the 1 + character gutter present in diff output, one can specify a 1 + character offset using ‘--tabs=1,+8’, which will set tab stops at + positions 1,9,17,... + + This option implies the ‘-a’ option. + + For compatibility, GNU ‘unexpand’ supports the obsolete option + syntax, ‘-TAB1[,TAB2]...’, where tab stops must be separated by + commas. (Unlike ‘-t’, this obsolete option does not imply ‘-a’.) + New scripts should use ‘--first-only -t TAB1[,TAB2]...’ instead. + +‘-a’ +‘--all’ + Also convert all sequences of two or more blanks just before a tab + stop, even if they occur after non-blank characters in a line. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: Directory listing, Next: Basic operations, Prev: Operating on characters, Up: Top + +10 Directory listing +******************** + +This chapter describes the ‘ls’ command and its variants ‘dir’ and +‘vdir’, which list information about files. + +* Menu: + +* ls invocation:: List directory contents. +* dir invocation:: Briefly ls. +* vdir invocation:: Verbosely ls. +* dircolors invocation:: Color setup for ls, etc. + + +File: coreutils.info, Node: ls invocation, Next: dir invocation, Up: Directory listing + +10.1 ‘ls’: List directory contents +================================== + +The ‘ls’ program lists information about files (of any type, including +directories). Options and file arguments can be intermixed arbitrarily, +as usual. Later options override earlier options that are incompatible. + + For non-option command-line arguments that are directories, by +default ‘ls’ lists the contents of directories, not recursively, and +omitting files with names beginning with ‘.’. For other non-option +arguments, by default ‘ls’ lists just the file name. If no non-option +argument is specified, ‘ls’ operates on the current directory, acting as +if it had been invoked with a single argument of ‘.’. + + By default, the output is sorted alphabetically, according to the +locale settings in effect.(1) If standard output is a terminal, the +output is in columns (sorted vertically) and control characters are +output as question marks; otherwise, the output is listed one per line +and control characters are output as-is. + + Because ‘ls’ is such a fundamental program, it has accumulated many +options over the years. They are described in the subsections below; +within each section, options are listed alphabetically (ignoring case). +The division of options into the subsections is not absolute, since some +options affect more than one aspect of ‘ls’’s operation. + + Exit status: + + 0 success + 1 minor problems (e.g., failure to access a file or directory not + specified as a command line argument. This happens when listing a + directory in which entries are actively being removed or renamed.) + 2 serious trouble (e.g., memory exhausted, invalid option, failure + to access a file or directory specified as a command line argument + or a directory loop) + + Also see *note Common options::. + +* Menu: + +* Which files are listed:: +* What information is listed:: +* Sorting the output:: +* General output formatting:: +* Formatting file timestamps:: +* Formatting the file names:: + + ---------- Footnotes ---------- + + (1) If you use a non-POSIX locale (e.g., by setting ‘LC_ALL’ to +‘en_US’), then ‘ls’ may produce output that is sorted differently than +you’re accustomed to. In that case, set the ‘LC_ALL’ environment +variable to ‘C’. + + +File: coreutils.info, Node: Which files are listed, Next: What information is listed, Up: ls invocation + +10.1.1 Which files are listed +----------------------------- + +These options determine which files ‘ls’ lists information for. By +default, ‘ls’ lists files and the contents of any directories on the +command line, except that in directories it ignores files whose names +start with ‘.’. + +‘-a’ +‘--all’ + In directories, do not ignore file names that start with ‘.’. + +‘-A’ +‘--almost-all’ + In directories, do not ignore all file names that start with ‘.’; + ignore only ‘.’ and ‘..’. The ‘--all’ (‘-a’) option overrides this + option. + +‘-B’ +‘--ignore-backups’ + In directories, ignore files that end with ‘~’. This option is + equivalent to ‘--ignore='*~' --ignore='.*~'’. + +‘-d’ +‘--directory’ + List just the names of directories, as with other types of files, + rather than listing their contents. Do not follow symbolic links + listed on the command line unless the ‘--dereference-command-line’ + (‘-H’), ‘--dereference’ (‘-L’), or + ‘--dereference-command-line-symlink-to-dir’ options are specified. + +‘-H’ +‘--dereference-command-line’ + If a command line argument specifies a symbolic link, show + information for the file the link references rather than for the + link itself. + +‘--dereference-command-line-symlink-to-dir’ + Do not dereference symbolic links, with one exception: if a command + line argument specifies a symbolic link that refers to a directory, + show information for that directory rather than for the link + itself. This is the default behavior unless long format is being + used or any of the following options is in effect: ‘--classify’ + (‘-F’), ‘--directory’ (‘-d’), ‘--dereference’ (‘-L’), or + ‘--dereference-command-line’ (‘-H’)). + +‘--group-directories-first’ + Group all the directories before the files and then sort the + directories and the files separately using the selected sort key + (see ‘--sort’ option). That is, this option specifies a primary + sort key, and the ‘--sort’ option specifies a secondary key. + However, any use of ‘--sort=none’ (‘-U’) disables this option + altogether. + +‘--hide=PATTERN’ + In directories, ignore files whose names match the shell pattern + PATTERN, unless the ‘--all’ (‘-a’) or ‘--almost-all’ (‘-A’) is also + given. This option acts like ‘--ignore=PATTERN’ except that it has + no effect if ‘--all’ (‘-a’) or ‘--almost-all’ (‘-A’) is also given. + + This option can be useful in shell aliases. For example, if ‘lx’ + is an alias for ‘ls --hide='*~'’ and ‘ly’ is an alias for ‘ls + --ignore='*~'’, then the command ‘lx -A’ lists the file ‘README~’ + even though ‘ly -A’ would not. + +‘-I PATTERN’ +‘--ignore=PATTERN’ + In directories, ignore files whose names match the shell pattern + (not regular expression) PATTERN. As in the shell, an initial ‘.’ + in a file name does not match a wildcard at the start of PATTERN. + Sometimes it is useful to give this option several times. For + example, + + $ ls --ignore='.??*' --ignore='.[^.]' --ignore='#*' + + The first option ignores names of length 3 or more that start with + ‘.’, the second ignores all two-character names that start with ‘.’ + except ‘..’, and the third ignores names that start with ‘#’. + +‘-L’ +‘--dereference’ + When showing file information for a symbolic link, show information + for the file the link references rather than the link itself. + However, even with this option, ‘ls’ still prints the name of the + link itself, not the name of the file that the link points to. + +‘-R’ +‘--recursive’ + List the contents of all directories recursively. + + +File: coreutils.info, Node: What information is listed, Next: Sorting the output, Prev: Which files are listed, Up: ls invocation + +10.1.2 What information is listed +--------------------------------- + +These options affect the information that ‘ls’ displays. By default, +only file names are shown. + +‘--author’ + In long format, list each file’s author. In GNU/Hurd, file authors + can differ from their owners, but in other operating systems the + two are the same. + +‘-D’ +‘--dired’ + Print an additional line after the main output: + + //DIRED// BEG1 END1 BEG2 END2 ... + + The BEGN and ENDN are unsigned integers that record the byte + position of the beginning and end of each file name in the output. + This makes it easy for Emacs to find the names, even when they + contain unusual characters such as space or newline, without fancy + searching. + + If directories are being listed recursively via ‘--recursive’ + (‘-R’), output a similar line with offsets for each subdirectory + name: + + //SUBDIRED// BEG1 END1 ... + + Finally, output a line of the form: + + //DIRED-OPTIONS// --quoting-style=WORD + + where WORD is the quoting style (*note Formatting the file + names::). + + Here is an actual example: + + $ mkdir -p a/sub/deeper a/sub2 + $ touch a/f1 a/f2 + $ touch a/sub/deeper/file + $ ls -gloRF --dired a + a: + total 8 + -rw-r--r-- 1 0 Jun 10 12:27 f1 + -rw-r--r-- 1 0 Jun 10 12:27 f2 + drwxr-xr-x 3 4096 Jun 10 12:27 sub/ + drwxr-xr-x 2 4096 Jun 10 12:27 sub2/ + + a/sub: + total 4 + drwxr-xr-x 2 4096 Jun 10 12:27 deeper/ + + a/sub/deeper: + total 0 + -rw-r--r-- 1 0 Jun 10 12:27 file + + a/sub2: + total 0 + //DIRED// 48 50 84 86 120 123 158 162 217 223 282 286 + //SUBDIRED// 2 3 167 172 228 240 290 296 + //DIRED-OPTIONS// --quoting-style=literal + + The pairs of offsets on the ‘//DIRED//’ line above delimit these + names: ‘f1’, ‘f2’, ‘sub’, ‘sub2’, ‘deeper’, ‘file’. The offsets on + the ‘//SUBDIRED//’ line delimit the following directory names: ‘a’, + ‘a/sub’, ‘a/sub/deeper’, ‘a/sub2’. + + Here is an example of how to extract the fifth entry name, + ‘deeper’, corresponding to the pair of offsets, 222 and 228: + + $ ls -gloRF --dired a > out + $ dd bs=1 skip=222 count=6 < out 2>/dev/null; echo + deeper + + Although the listing above includes a trailing slash for the + ‘deeper’ entry, the offsets select the name without the trailing + slash. However, if you invoke ‘ls’ with ‘--dired’ (‘-D’) along + with an option like ‘--escape’ (‘-b’) and operate on a file whose + name contains special characters, the backslash _is_ included: + + $ touch 'a b' + $ ls -blog --dired 'a b' + -rw-r--r-- 1 0 Jun 10 12:28 a\ b + //DIRED// 30 34 + //DIRED-OPTIONS// --quoting-style=escape + + If you use a quoting style like ‘--quoting-style=c’ (‘-Q’) that + adds quote marks, then the offsets include the quote marks. So + beware that the user may select the quoting style via the + environment variable ‘QUOTING_STYLE’. Hence, applications using + ‘--dired’ should either specify an explicit + ‘--quoting-style=literal’ (‘-N’) option on the command line, or + else be prepared to parse the escaped names. + + The ‘--dired’ (‘-D’) option has well-defined behavior only when + long format is in effect and hyperlinks are disabled (e.g., + ‘--hyperlink=none’). + +‘--full-time’ + Produce long format, and list times in full. It is equivalent to + using ‘--format=long’ (‘-l’) with ‘--time-style=full-iso’ (*note + Formatting file timestamps::). + +‘-g’ + Produce long format, but omit owner information. + +‘-G’ +‘--no-group’ + Inhibit display of group information in long format. (This is the + default in some non-GNU versions of ‘ls’, so we provide this option + for compatibility.) + +‘-h’ +‘--human-readable’ + Append a size letter to each size, such as ‘M’ for mebibytes. + Powers of 1024 are used, not 1000; ‘M’ stands for 1,048,576 bytes. + This option is equivalent to ‘--block-size=human-readable’. Use + the ‘--si’ option if you prefer powers of 1000. + +‘-i’ +‘--inode’ + Print the inode number (also called the file serial number and + index number) of each file to the left of the file name. (This + number uniquely identifies each file within a particular file + system.) + +‘-l’ +‘--format=long’ +‘--format=verbose’ + Produce long format. In addition to the name of each file, print + the file type, file mode bits, number of hard links, owner name, + group name, size, and timestamp (*note Formatting file + timestamps::), normally the modification timestamp (the mtime, + *note File timestamps::). If the owner or group name cannot be + determined, print the owner or group ID instead, right-justified as + a cue that it is a number rather than a textual name. Print + question marks for other information that cannot be determined. + + Normally the size is printed as a byte count without punctuation, + but this can be overridden (*note Block size::). For example, + ‘--human-readable’ (‘-h’) prints an abbreviated, human-readable + count, and ‘--block-size="'1"’ prints a byte count with the + thousands separator of the current locale. + + For each directory that is listed, preface the files with a line + ‘total BLOCKS’, where BLOCKS is the file system allocation for all + files in that directory. The block size currently defaults to 1024 + bytes, but this can be overridden (*note Block size::). The BLOCKS + computed counts each hard link separately; this is arguably a + deficiency. + + The file type is one of the following characters: + + ‘-’ + regular file + ‘b’ + block special file + ‘c’ + character special file + ‘C’ + high performance (“contiguous data”) file + ‘d’ + directory + ‘D’ + door (Solaris) + ‘l’ + symbolic link + ‘M’ + off-line (“migrated”) file (Cray DMF) + ‘n’ + network special file (HP-UX) + ‘p’ + FIFO (named pipe) + ‘P’ + port (Solaris) + ‘s’ + socket + ‘?’ + some other file type + + The file mode bits listed are similar to symbolic mode + specifications (*note Symbolic Modes::). But ‘ls’ combines + multiple bits into the third character of each set of permissions + as follows: + + ‘s’ + If the set-user-ID or set-group-ID bit and the corresponding + executable bit are both set. + + ‘S’ + If the set-user-ID or set-group-ID bit is set but the + corresponding executable bit is not set. + + ‘t’ + If the restricted deletion flag or sticky bit, and the + other-executable bit, are both set. The restricted deletion + flag is another name for the sticky bit. *Note Mode + Structure::. + + ‘T’ + If the restricted deletion flag or sticky bit is set but the + other-executable bit is not set. + + ‘x’ + If the executable bit is set and none of the above apply. + + ‘-’ + Otherwise. + + Following the file mode bits is a single character that specifies + whether an alternate access method such as an access control list + applies to the file. When the character following the file mode + bits is a space, there is no alternate access method. When it is a + printing character, then there is such a method. + + GNU ‘ls’ uses a ‘.’ character to indicate a file with a security + context, but no other alternate access method. + + A file with any other combination of alternate access methods is + marked with a ‘+’ character. + +‘-n’ +‘--numeric-uid-gid’ + Produce long format, but display right-justified numeric user and + group IDs instead of left-justified owner and group names. + +‘-o’ + Produce long format, but omit group information. It is equivalent + to using ‘--format=long’ (‘-l’) with ‘--no-group’ (‘-G’). + +‘-s’ +‘--size’ + Print the file system allocation of each file to the left of the + file name. This is the amount of file system space used by the + file, which is usually a bit more than the file’s size, but it can + be less if the file has holes. + + Normally the allocation is printed in units of 1024 bytes, but this + can be overridden (*note Block size::). + + For files that are NFS-mounted from an HP-UX system to a BSD + system, this option reports sizes that are half the correct values. + On HP-UX systems, it reports sizes that are twice the correct + values for files that are NFS-mounted from BSD systems. This is + due to a flaw in HP-UX; it also affects the HP-UX ‘ls’ program. + +‘--si’ + Append an SI-style abbreviation to each size, such as ‘M’ for + megabytes. Powers of 1000 are used, not 1024; ‘M’ stands for + 1,000,000 bytes. This option is equivalent to ‘--block-size=si’. + Use the ‘-h’ or ‘--human-readable’ option if you prefer powers of + 1024. + +‘-Z’ +‘--context’ + Display the SELinux security context or ‘?’ if none is found. In + long format, print the security context to the left of the size + column. + + +File: coreutils.info, Node: Sorting the output, Next: General output formatting, Prev: What information is listed, Up: ls invocation + +10.1.3 Sorting the output +------------------------- + +These options change the order in which ‘ls’ sorts the information it +outputs. By default, sorting is done by character code (e.g., ASCII +order). + +‘-c’ +‘--time=ctime’ +‘--time=status’ + In long format, print the status change timestamp (the ctime) + instead of the mtime. When sorting by time or when not using long + format, sort according to the ctime. *Note File timestamps::. + +‘-f’ + Produce an unsorted directory listing. This is equivalent to the + combination of ‘--all’ (‘-a’), ‘--sort=none’ (‘-U’), ‘-1’, + ‘--color=none’, and ‘--hyperlink=none’, while also disabling any + previous use of ‘--size’ (‘-s’). + +‘-r’ +‘--reverse’ + Reverse whatever the sorting method is – e.g., list files in + reverse alphabetical order, youngest first, smallest first, or + whatever. This option has no effect when ‘--sort=none’ (‘-U’) is + in effect. + +‘-S’ +‘--sort=size’ + Sort by file size, largest first. + +‘-t’ +‘--sort=time’ + Sort by modification timestamp (mtime) by default, newest first. + The timestamp to order by can be changed with the ‘--time’ option. + *Note File timestamps::. + +‘-u’ +‘--time=atime’ +‘--time=access’ +‘--time=use’ + In long format, print the last access timestamp (the atime). When + sorting by time or when not using long format, sort according to + the atime. *Note File timestamps::. + +‘--time=mtime’ +‘--time=modification’ + This is the default timestamp display and sorting mode. In long + format, print the last data modification timestamp (the mtime). + When sorting by time or when not using long format, sort according + to the mtime. *Note File timestamps::. + +‘--time=birth’ +‘--time=creation’ + In long format, print the file creation timestamp if available, + falling back to the file modification timestamp (mtime) if not. + When sorting by time or when not using long format, sort according + to the birth time. *Note File timestamps::. + +‘-U’ +‘--sort=none’ + Do not sort; list the files in whatever order they are stored in + the directory. (Do not do any of the other unrelated things that + ‘-f’ does.) This can be useful when listing large directories, + where sorting can take some time. + +‘-v’ +‘--sort=version’ + Sort by version name and number, lowest first. It behaves like a + default sort, except that each sequence of decimal digits is + treated numerically as an index/version number. *Note Version sort + ordering::. + +‘--sort=width’ + Sort by printed width of file names. This can be useful with the + ‘--format=vertical’ (‘-C’) output format, to most densely display + the listed files. + +‘-X’ +‘--sort=extension’ + Sort directory contents alphabetically by file extension + (characters after the last ‘.’); files with no extension are sorted + first. + + +File: coreutils.info, Node: General output formatting, Next: Formatting file timestamps, Prev: Sorting the output, Up: ls invocation + +10.1.4 General output formatting +-------------------------------- + +These options affect the appearance of the overall output. + +‘--format=single-column’ + List one file name per line, with no other information. This is + the default for ‘ls’ when standard output is not a terminal. See + also the ‘--escape’ (‘-b’), ‘--hide-control-chars’ (‘-q’), and + ‘--zero’ options to disambiguate output of file names containing + newline characters. + +‘-1’ + List one file per line. This is like ‘--format=single-column’ + except that it has no effect if long format is also in effect. + +‘-C’ +‘--format=vertical’ + List files in columns, sorted vertically, with no other + information. This is the default for ‘ls’ if standard output is a + terminal. It is always the default for the ‘dir’ program. GNU + ‘ls’ uses variable width columns to display as many files as + possible in the fewest lines. + +‘--color [=WHEN]’ + Specify whether to use color for distinguishing file types; WHEN + may be omitted, or one of: + • none - Do not use color at all. This is the default. + • auto - Only use color if standard output is a terminal. + • always - Always use color. + Specifying ‘--color’ and no WHEN is equivalent to ‘--color=always’. + If piping a colored listing through a pager like ‘less’, use the + pager’s ‘-R’ option to pass the color codes to the terminal. + + Using the ‘--color’ option may incur a noticeable performance + penalty when run in a large directory, because the default settings + require that ‘ls’ ‘stat’ every single file it lists. However, if + you would like most of the file-type coloring but can live without + the other coloring options (e.g., executable, orphan, sticky, + other-writable, capability), use ‘dircolors’ to set the ‘LS_COLORS’ + environment variable like this, + eval $(dircolors -p | perl -pe \ + 's/^((CAP|S[ET]|O[TR]|M|E)\w+).*/$1 00/' | dircolors -) + and on a ‘dirent.d_type’-capable file system, ‘ls’ will perform + only one ‘stat’ call per command line argument. + +‘-F’ +‘--classify [=WHEN]’ +‘--indicator-style=classify’ + Append a character to each file name indicating the file type. + Also, for regular files that are executable, append ‘*’. The file + type indicators are ‘/’ for directories, ‘@’ for symbolic links, + ‘|’ for FIFOs, ‘=’ for sockets, ‘>’ for doors, and nothing for + regular files. WHEN may be omitted, or one of: + • none - Do not classify. This is the default. + • auto - Only classify if standard output is a terminal. + • always - Always classify. + Specifying ‘--classify’ and no WHEN is equivalent to + ‘--classify=always’. Do not follow symbolic links listed on the + command line unless the ‘--dereference-command-line’ (‘-H’), + ‘--dereference’ (‘-L’), or + ‘--dereference-command-line-symlink-to-dir’ options are specified. + +‘--file-type’ +‘--indicator-style=file-type’ + Append a character to each file name indicating the file type. + This is like ‘--classify’ (‘-F’, except that executables are not + marked. + +‘--hyperlink [=WHEN]’ + Output codes recognized by some terminals to link to files using + the ‘file://’ URI format. WHEN may be omitted, or one of: + • none - Do not use hyperlinks at all. This is the default. + • auto - Only use hyperlinks if standard output is a terminal. + • always - Always use hyperlinks. + Specifying ‘--hyperlink’ and no WHEN is equivalent to + ‘--hyperlink=always’. + +‘--indicator-style=WORD’ + Append a character indicator with style WORD to entry names, as + follows: + + ‘none’ + Do not append any character indicator; this is the default. + ‘slash’ + Append ‘/’ for directories. This is the same as the ‘-p’ + option. + ‘file-type’ + Append ‘/’ for directories, ‘@’ for symbolic links, ‘|’ for + FIFOs, ‘=’ for sockets, and nothing for regular files. This + is the same as the ‘--file-type’ option. + ‘classify’ + Append ‘*’ for executable regular files, otherwise behave as + for ‘file-type’. This is the same as the ‘--classify’ (‘-F’) + option. + +‘-k’ +‘--kibibytes’ + Set the default block size to its normal value of 1024 bytes, + overriding any contrary specification in environment variables + (*note Block size::). If ‘--block-size’, ‘--human-readable’ + (‘-h’), or ‘--si’ options are used, they take precedence even if + ‘--kibibytes’ (‘-k’) is placed after + + The ‘--kibibytes’ (‘-k’) option affects the per-directory block + count written in long format, and the file system allocation + written by the ‘--size’ (‘-s’) option. It does not affect the file + size in bytes that is written in long format. + +‘-m’ +‘--format=commas’ + List files horizontally, with as many as will fit on each line, + separated by ‘, ’ (a comma and a space), and with no other + information. + +‘-p’ +‘--indicator-style=slash’ + Append a ‘/’ to directory names. + +‘-x’ +‘--format=across’ +‘--format=horizontal’ + List the files in columns, sorted horizontally. + +‘-T COLS’ +‘--tabsize=COLS’ + Assume that each tab stop is COLS columns wide. The default is 8. + ‘ls’ uses tabs where possible in the output, for efficiency. If + COLS is zero, do not use tabs at all. + + Some terminal emulators might not properly align columns to the + right of a TAB following a non-ASCII byte. You can avoid that + issue by using the ‘-T0’ option or put ‘TABSIZE=0’ in your + environment, to tell ‘ls’ to align using spaces, not tabs. + + If you set a terminal’s hardware tabs to anything other than the + default, you should also use a ‘--tabsize’ option or ‘TABSIZE’ + environment variable either to match the hardware tabs, or to + disable the use of hardware tabs. Otherwise, the output of ‘ls’ + may not line up. For example, if you run the shell command ‘tabs + -4’ to set hardware tabs to every four columns, you should also run + ‘export TABSIZE=4’ or ‘export TABSIZE=0’, or use the corresponding + ‘--tabsize’ options. + +‘-w COLS’ +‘--width=COLS’ + Assume the screen is COLS columns wide. The default is taken from + the terminal settings if possible; otherwise the environment + variable ‘COLUMNS’ is used if it is set; otherwise the default is + 80. With a COLS value of ‘0’, there is no limit on the length of + the output line, and that single output line will be delimited with + spaces, not tabs. + +‘--zero’ + Output a zero byte (ASCII NUL) at the end of each line, rather than + a newline. This option enables other programs to parse the output + even when that output would contain data with embedded newlines. + This option is incompatible with the ‘--dired’ (‘-D’) option. This + option also implies the options ‘--show-control-chars’, ‘-1’, + ‘--color=none’, and ‘--quoting-style=literal’ (‘-N’). + + +File: coreutils.info, Node: Formatting file timestamps, Next: Formatting the file names, Prev: General output formatting, Up: ls invocation + +10.1.5 Formatting file timestamps +--------------------------------- + +By default, file timestamps are listed in abbreviated form, using a date +like ‘Mar 30 2020’ for non-recent timestamps, and a date-without-year +and time like ‘Mar 30 23:45’ for recent timestamps. This format can +change depending on the current locale as detailed below. + + A timestamp is considered to be “recent” if it is less than six +months old, and is not dated in the future. If a timestamp dated today +is not listed in recent form, the timestamp is in the future, which +means you probably have clock skew problems which may break programs +like ‘make’ that rely on file timestamps. *Note File timestamps::. + + Timestamps are listed according to the time zone rules specified by +the ‘TZ’ environment variable, or by the system default rules if ‘TZ’ is +not set. *Note Specifying the Time Zone with ‘TZ’: (libc)TZ Variable. + + The following option changes how file timestamps are printed. + +‘--time-style=STYLE’ + List timestamps in style STYLE. The STYLE should be one of the + following: + + ‘+FORMAT’ + List timestamps using FORMAT, where FORMAT is interpreted like + the format argument of ‘date’ (*note date invocation::). For + example, ‘--time-style="+%Y-%m-%d %H:%M:%S"’ causes ‘ls’ to + list timestamps like ‘2020-03-30 23:45:56’. As with ‘date’, + FORMAT’s interpretation is affected by the ‘LC_TIME’ locale + category. + + If FORMAT contains two format strings separated by a newline, + the former is used for non-recent files and the latter for + recent files; if you want output columns to line up, you may + need to insert spaces in one of the two formats. + + ‘full-iso’ + List timestamps in full using ISO 8601-like date, time, and + time zone components with nanosecond precision, e.g., + ‘2020-07-21 23:45:56.477817180 -0400’. This style is + equivalent to ‘+%Y-%m-%d %H:%M:%S.%N %z’. + + This is useful because the time output includes all the + information that is available from the operating system. For + example, this can help explain ‘make’’s behavior, since GNU + ‘make’ uses the full timestamp to determine whether a file is + out of date. + + ‘long-iso’ + List ISO 8601 date and time components with minute precision, + e.g., ‘2020-03-30 23:45’. These timestamps are shorter than + ‘full-iso’ timestamps, and are usually good enough for + everyday work. This style is equivalent to ‘+%Y-%m-%d %H:%M’. + + ‘iso’ + List ISO 8601 dates for non-recent timestamps (e.g., + ‘2020-03-30 ’), and ISO 8601-like month, day, hour, and minute + for recent timestamps (e.g., ‘03-30 23:45’). These timestamps + are uglier than ‘long-iso’ timestamps, but they carry nearly + the same information in a smaller space and their brevity + helps ‘ls’ output fit within traditional 80-column output + lines. The following two ‘ls’ invocations are equivalent: + + newline=' + ' + ls -l --time-style="+%Y-%m-%d $newline%m-%d %H:%M" + ls -l --time-style="iso" + + ‘locale’ + List timestamps in a locale-dependent form. For example, a + French locale might list non-recent timestamps like ‘30 + mars 2020’ and recent timestamps like ‘30 mars 23:45’. + Locale-dependent timestamps typically consume more space than + ‘iso’ timestamps and are harder for programs to parse because + locale conventions vary so widely, but they are easier for + many people to read. + + The ‘LC_TIME’ locale category specifies the timestamp format. + The default POSIX locale uses timestamps like ‘Mar 30 2020’ + and ‘Mar 30 23:45’; in this locale, the following two ‘ls’ + invocations are equivalent: + + newline=' + ' + ls -l --time-style="+%b %e %Y$newline%b %e %H:%M" + ls -l --time-style="locale" + + Other locales behave differently. For example, in a German + locale, ‘--time-style="locale"’ might be equivalent to + ‘--time-style="+%e. %b %Y $newline%e. %b %H:%M"’ and might + generate timestamps like ‘30. Mär 2020 ’ and ‘30. Mär 23:45’. + + ‘posix-STYLE’ + List POSIX-locale timestamps if the ‘LC_TIME’ locale category + is POSIX, STYLE timestamps otherwise. For example, the + ‘posix-long-iso’ style lists timestamps like ‘Mar 30 2020’ + and ‘Mar 30 23:45’ when in the POSIX locale, and like + ‘2020-03-30 23:45’ otherwise. + + You can specify the default value of the ‘--time-style’ option with +the environment variable ‘TIME_STYLE’; if ‘TIME_STYLE’ is not set the +default style is ‘locale’. GNU Emacs 21.3 and later use the ‘--dired’ +option and therefore can parse any date format, but if you are using +Emacs 21.1 or 21.2 and specify a non-POSIX locale you may need to set +‘TIME_STYLE="posix-long-iso"’. + + To avoid certain denial-of-service attacks, timestamps that would be +longer than 1000 bytes may be treated as errors. + + +File: coreutils.info, Node: Formatting the file names, Prev: Formatting file timestamps, Up: ls invocation + +10.1.6 Formatting the file names +-------------------------------- + +These options change how file names themselves are printed. + +‘-b’ +‘--escape’ +‘--quoting-style=escape’ + Quote nongraphic characters in file names using alphabetic and + octal backslash sequences like those used in C. + +‘-N’ +‘--literal’ +‘--quoting-style=literal’ + Do not quote file names. However, with ‘ls’ nongraphic characters + are still printed as question marks if the output is a terminal and + you do not specify the ‘--show-control-chars’ option. + +‘-q’ +‘--hide-control-chars’ + Print question marks instead of nongraphic characters in file + names. This is the default if the output is a terminal and the + program is ‘ls’. + +‘-Q’ +‘--quote-name’ +‘--quoting-style=c’ + Enclose file names in double quotes and quote nongraphic characters + as in C. + +‘--quoting-style=WORD’ + Use style WORD to quote file names and other strings that may + contain arbitrary characters. The WORD should be one of the + following: + + ‘literal’ + Output strings as-is; this is the same as the ‘--literal’ + (‘-N’) option. + ‘shell’ + Quote strings for the shell if they contain shell + metacharacters or would cause ambiguous output. The quoting + is suitable for POSIX-compatible shells like ‘bash’, but it + does not always work for incompatible shells like ‘csh’. + ‘shell-always’ + Quote strings for the shell, even if they would normally not + require quoting. + ‘shell-escape’ + Like ‘shell’, but also quoting non-printable characters using + the POSIX proposed ‘$''’ syntax suitable for most shells. + ‘shell-escape-always’ + Like ‘shell-escape’, but quote strings even if they would + normally not require quoting. + ‘c’ + Quote strings as for C character string literals, including + the surrounding double-quote characters; this is the same as + the ‘--quote-name’ (‘-Q’) option. + ‘escape’ + Quote strings as for C character string literals, except omit + the surrounding double-quote characters; this is the same as + the ‘--escape’ (‘-b’) option. + ‘clocale’ + Quote strings as for C character string literals, except use + surrounding quotation marks appropriate for the locale. + ‘locale’ + Quote strings as for C character string literals, except use + surrounding quotation marks appropriate for the locale, and + quote 'like this' instead of "like this" in the default C + locale. This looks nicer on many displays. + + You can specify the default value of the ‘--quoting-style’ option + with the environment variable ‘QUOTING_STYLE’. If that environment + variable is not set, the default value is ‘shell-escape’ when the + output is a terminal, and ‘literal’ otherwise. + +‘--show-control-chars’ + Print nongraphic characters as-is in file names. This is the + default unless the output is a terminal and the program is ‘ls’. + + +File: coreutils.info, Node: dir invocation, Next: vdir invocation, Prev: ls invocation, Up: Directory listing + +10.2 ‘dir’: Briefly list directory contents +=========================================== + +‘dir’ is equivalent to ‘ls -C -b’; that is, by default files are listed +in columns, sorted vertically, and special characters are represented by +backslash escape sequences. + + *Note ‘ls’: ls invocation. + + +File: coreutils.info, Node: vdir invocation, Next: dircolors invocation, Prev: dir invocation, Up: Directory listing + +10.3 ‘vdir’: Verbosely list directory contents +============================================== + +‘vdir’ is equivalent to ‘ls -l -b’; that is, by default files are listed +in long format and special characters are represented by backslash +escape sequences. + + *Note ‘ls’: ls invocation. + + +File: coreutils.info, Node: dircolors invocation, Prev: vdir invocation, Up: Directory listing + +10.4 ‘dircolors’: Color setup for ‘ls’ +====================================== + +‘dircolors’ outputs a sequence of shell commands to set up the terminal +for color output from ‘ls’ (and ‘dir’, etc.). Typical usage: + + eval "$(dircolors [OPTION]... [FILE])" + + If FILE is specified, ‘dircolors’ reads it to determine which colors +to use for which file types and extensions. Otherwise, a precompiled +database is used. For details on the format of these files, run +‘dircolors --print-database’. + + To make ‘dircolors’ read a ‘~/.dircolors’ file if it exists, you can +put the following lines in your ‘~/.bashrc’ (or adapt them to your +favorite shell): + + d=.dircolors + test -r $d && eval "$(dircolors $d)" + + The output is a shell command to set the ‘LS_COLORS’ environment +variable. You can specify the shell syntax to use on the command line, +or ‘dircolors’ will guess it from the value of the ‘SHELL’ environment +variable. + + The program accepts the following options. Also see *note Common +options::. + +‘-b’ +‘--sh’ +‘--bourne-shell’ + Output Bourne shell commands. This is the default if the ‘SHELL’ + environment variable is set and does not end with ‘csh’ or ‘tcsh’. + +‘-c’ +‘--csh’ +‘--c-shell’ + Output C shell commands. This is the default if ‘SHELL’ ends with + ‘csh’ or ‘tcsh’. + +‘-p’ +‘--print-database’ + Print the (compiled-in) default color configuration database. This + output is itself a valid configuration file, and is fairly + descriptive of the possibilities. + +‘--print-ls-colors’ + Print the LS_COLORS entries on separate lines, each colored as per + the color they represent. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: Basic operations, Next: Special file types, Prev: Directory listing, Up: Top + +11 Basic operations +******************* + +This chapter describes the commands for basic file manipulation: +copying, moving (renaming), and deleting (removing). + +* Menu: + +* cp invocation:: Copy files. +* dd invocation:: Convert and copy a file. +* install invocation:: Copy files and set attributes. +* mv invocation:: Move (rename) files. +* rm invocation:: Remove files or directories. +* shred invocation:: Remove files more securely. + + +File: coreutils.info, Node: cp invocation, Next: dd invocation, Up: Basic operations + +11.1 ‘cp’: Copy files and directories +===================================== + +‘cp’ copies files (or, optionally, directories). The copy is completely +independent of the original. You can either copy one file to another, +or copy arbitrarily many files to a destination directory. Synopses: + + cp [OPTION]... [-T] SOURCE DEST + cp [OPTION]... SOURCE... DIRECTORY + cp [OPTION]... -t DIRECTORY SOURCE... + + • If two file names are given, ‘cp’ copies the first file to the + second. + + • If the ‘--target-directory’ (‘-t’) option is given, or failing that + if the last file is a directory and the ‘--no-target-directory’ + (‘-T’) option is not given, ‘cp’ copies each SOURCE file to the + specified directory, using the SOURCEs’ names. + + Generally, files are written just as they are read. For exceptions, +see the ‘--sparse’ option below. + + By default, ‘cp’ does not copy directories. However, the ‘-R’, ‘-a’, +and ‘-r’ options cause ‘cp’ to copy recursively by descending into +source directories and copying files to corresponding destination +directories. + + When copying from a symbolic link, ‘cp’ normally follows the link +only when not copying recursively or when ‘--link’ (‘-l’) is used. This +default can be overridden with the ‘--archive’ (‘-a’), ‘-d’, +‘--dereference’ (‘-L’), ‘--no-dereference’ (‘-P’), and ‘-H’ options. If +more than one of these options is specified, the last one silently +overrides the others. + + When copying to a symbolic link, ‘cp’ follows the link only when it +refers to an existing regular file. However, when copying to a dangling +symbolic link, ‘cp’ refuses by default, and fails with a diagnostic, +since the operation is inherently dangerous. This behavior is contrary +to historical practice and to POSIX. Set ‘POSIXLY_CORRECT’ to make ‘cp’ +attempt to create the target of a dangling destination symlink, in spite +of the possible risk. Also, when an option like ‘--backup’ or ‘--link’ +acts to rename or remove the destination before copying, ‘cp’ renames or +removes the symbolic link rather than the file it points to. + + By default, ‘cp’ copies the contents of special files only when not +copying recursively. This default can be overridden with the +‘--copy-contents’ option. + + ‘cp’ generally refuses to copy a file onto itself, with the following +exception: if ‘--force --backup’ is specified with SOURCE and DEST +identical, and referring to a regular file, ‘cp’ will make a backup +file, either regular or numbered, as specified in the usual ways (*note +Backup options::). This is useful when you simply want to make a backup +of an existing file before changing it. + + The program accepts the following options. Also see *note Common +options::. + +‘-a’ +‘--archive’ + Preserve as much as possible of the structure and attributes of the + original files in the copy (but do not attempt to preserve internal + directory structure; i.e., ‘ls -U’ may list the entries in a copied + directory in a different order). Try to preserve SELinux security + context and extended attributes (xattr), but ignore any failure to + do that and print no corresponding diagnostic. Equivalent to ‘-dR + --preserve=all’ with the reduced diagnostics. + +‘--attributes-only’ + Copy only the specified attributes of the source file to the + destination. If the destination already exists, do not alter its + contents. See the ‘--preserve’ option for controlling which + attributes to copy. + +‘-b’ +‘--backup[=METHOD]’ + *Note Backup options::. Make a backup of each file that would + otherwise be overwritten or removed. As a special case, ‘cp’ makes + a backup of SOURCE when the force and backup options are given and + SOURCE and DEST are the same name for an existing, regular file. + One useful application of this combination of options is this tiny + Bourne shell script: + + #!/bin/sh + # Usage: backup FILE... + # Create a GNU-style backup of each listed FILE. + fail=0 + for i; do + cp --backup --force --preserve=all -- "$i" "$i" || fail=1 + done + exit $fail + +‘--copy-contents’ + If copying recursively, copy the contents of any special files + (e.g., FIFOs and device files) as if they were regular files. This + means trying to read the data in each source file and writing it to + the destination. It is usually a mistake to use this option, as it + normally has undesirable effects on special files like FIFOs and + the ones typically found in the ‘/dev’ directory. In most cases, + ‘cp -R --copy-contents’ will hang indefinitely trying to read from + FIFOs and special files like ‘/dev/console’, and it will fill up + your destination file system if you use it to copy ‘/dev/zero’. + This option has no effect unless copying recursively, and it does + not affect the copying of symbolic links. + +‘-d’ + Copy symbolic links as symbolic links rather than copying the files + that they point to, and preserve hard links between source files in + the copies. Equivalent to ‘--no-dereference --preserve=links’. + +‘--debug’ + Print extra information to stdout, explaining how files are copied. + This option implies the ‘--verbose’ option. + +‘-f’ +‘--force’ + When copying without this option and an existing destination file + cannot be opened for writing, the copy fails. However, with + ‘--force’, when a destination file cannot be opened, ‘cp’ then + tries to recreate the file by first removing it. Note ‘--force’ + alone will not remove dangling symlinks. When this option is + combined with ‘--link’ (‘-l’) or ‘--symbolic-link’ (‘-s’), the + destination link is replaced, and unless ‘--backup’ (‘-b’) is also + given there is no brief moment when the destination does not exist. + Also see the description of ‘--remove-destination’. + + This option is independent of the ‘--interactive’ or ‘-i’ option: + neither cancels the effect of the other. + + This option is ignored when the ‘--no-clobber’ or ‘-n’ option is + also used. + +‘-H’ + If a command line argument specifies a symbolic link, then copy the + file it points to rather than the symbolic link itself. However, + copy (preserving its nature) any symbolic link that is encountered + via recursive traversal. + +‘-i’ +‘--interactive’ + When copying a file other than a directory, prompt whether to + overwrite an existing destination file, and fail if the response is + not affirmative. The ‘-i’ option overrides a previous ‘-n’ option. + +‘-l’ +‘--link’ + Make hard links instead of copies of non-directories. + +‘-L’ +‘--dereference’ + Follow symbolic links when copying from them. With this option, + ‘cp’ cannot create a symbolic link. For example, a symlink (to + regular file) in the source tree will be copied to a regular file + in the destination tree. + +‘-n’ +‘--no-clobber’ + Do not overwrite an existing file; silently fail instead. This + option overrides a previous ‘-i’ option. This option is mutually + exclusive with ‘-b’ or ‘--backup’ option. + +‘-P’ +‘--no-dereference’ + Copy symbolic links as symbolic links rather than copying the files + that they point to. This option affects only symbolic links in the + source; symbolic links in the destination are always followed if + possible. + +‘-p’ +‘--preserve[=ATTRIBUTE_LIST]’ + Preserve the specified attributes of the original files. If + specified, the ATTRIBUTE_LIST must be a comma-separated list of one + or more of the following strings: + + ‘mode’ + Preserve attributes relevant to access permissions, including + file mode bits and (if possible) access control lists (ACLs). + ACL preservation is system-dependent, and ACLs are not + necessarily translated when the source and destination are on + file systems with different ACL formats (e.g., NFSv4 versus + POSIX formats). + + ‘ownership’ + Preserve the owner and group. On most modern systems, only + users with appropriate privileges may change the owner of a + file, and ordinary users may preserve the group ownership of a + file only if they happen to be a member of the desired group. + ‘timestamps’ + Preserve the times of last access and last modification, when + possible. On older systems, it is not possible to preserve + these attributes when the affected file is a symbolic link. + However, many systems now provide the ‘utimensat’ function, + which makes it possible even for symbolic links. + ‘links’ + Preserve in the destination files any links between + corresponding source files. Note that with ‘-L’ or ‘-H’, this + option can convert symbolic links to hard links. For example, + $ mkdir c; : > a; ln -s a b; cp -aH a b c; ls -i1 c + 74161745 a + 74161745 b + Note the inputs: ‘b’ is a symlink to regular file ‘a’, yet the + files in destination directory, ‘c/’, are hard-linked. Since + ‘-a’ implies ‘--no-dereference’ it would copy the symlink, but + the later ‘-H’ tells ‘cp’ to dereference the command line + arguments where it then sees two files with the same inode + number. Then the ‘--preserve=links’ option also implied by + ‘-a’ will preserve the perceived hard link. + + Here is a similar example that exercises ‘cp’’s ‘-L’ option: + $ mkdir b c; (cd b; : > a; ln -s a b); cp -aL b c; ls -i1 c/b + 74163295 a + 74163295 b + + ‘context’ + Preserve SELinux security context of the file, or fail with + full diagnostics. + ‘xattr’ + Preserve extended attributes of the file, or fail with full + diagnostics. If ‘cp’ is built without xattr support, ignore + this option. If SELinux context, ACLs or Capabilities are + implemented using xattrs, they are preserved implicitly by + this option as well, i.e., even without specifying + ‘--preserve=mode’ or ‘--preserve=context’. + ‘all’ + Preserve all file attributes. Equivalent to specifying all of + the above, but with the difference that failure to preserve + SELinux security context or extended attributes does not + change ‘cp’’s exit status. In contrast to ‘-a’, all but + ‘Operation not supported’ warnings are output. + + Using ‘--preserve’ with no ATTRIBUTE_LIST is equivalent to + ‘--preserve=mode,ownership,timestamps’. + + In the absence of this option, the permissions of existing + destination files are unchanged. Each new file is created with the + mode of the corresponding source file minus the set-user-ID, + set-group-ID, and sticky bits as the create mode; the operating + system then applies either the umask or a default ACL, possibly + resulting in a more restrictive file mode. *Note File + permissions::. + +‘--no-preserve=ATTRIBUTE_LIST’ + Do not preserve the specified attributes. The ATTRIBUTE_LIST has + the same form as for ‘--preserve’. + +‘--parents’ + Form the name of each destination file by appending to the target + directory a slash and the specified name of the source file. The + last argument given to ‘cp’ must be the name of an existing + directory. For example, the command: + + cp --parents a/b/c existing_dir + + copies the file ‘a/b/c’ to ‘existing_dir/a/b/c’, creating any + missing intermediate directories. + +‘-R’ +‘-r’ +‘--recursive’ + Copy directories recursively. By default, do not follow symbolic + links in the source unless used together with the ‘--link’ (‘-l’) + option; see the ‘--archive’ (‘-a’), ‘-d’, ‘--dereference’ (‘-L’), + ‘--no-dereference’ (‘-P’), and ‘-H’ options. Special files are + copied by creating a destination file of the same type as the + source; see the ‘--copy-contents’ option. It is not portable to + use ‘-r’ to copy symbolic links or special files. On some non-GNU + systems, ‘-r’ implies the equivalent of ‘-L’ and ‘--copy-contents’ + for historical reasons. Also, it is not portable to use ‘-R’ to + copy symbolic links unless you also specify ‘-P’, as POSIX allows + implementations that dereference symbolic links by default. + +‘--reflink[=WHEN]’ + Perform a lightweight, copy-on-write (COW) copy, if supported by + the file system. Once it has succeeded, beware that the source and + destination files share the same data blocks as long as they remain + unmodified. Thus, if an I/O error affects data blocks of one of + the files, the other suffers the same fate. + + The WHEN value can be one of the following: + + ‘always’ + If the copy-on-write operation is not supported then report + the failure for each file and exit with a failure status. + Plain ‘--reflink’ is equivalent to ‘--reflink=always’. + + ‘auto’ + If the copy-on-write operation is not supported then fall back + to the standard copy behavior. This is the default if no + ‘--reflink’ option is given. + + ‘never’ + Disable copy-on-write operation and use the standard copy + behavior. + + This option is overridden by the ‘--link’, ‘--symbolic-link’ and + ‘--attributes-only’ options, thus allowing it to be used to + configure the default data copying behavior for ‘cp’. + +‘--remove-destination’ + Remove each existing destination file before attempting to open it + (contrast with ‘-f’ above). + +‘--sparse=WHEN’ + A “sparse file” contains “holes” – a sequence of zero bytes that + does not occupy any file system blocks; the ‘read’ system call + reads these as zeros. This can both save considerable space and + increase speed, since many binary files contain lots of consecutive + zero bytes. By default, ‘cp’ detects holes in input source files + via a crude heuristic and makes the corresponding output file + sparse as well. Only regular files may be sparse. + + The WHEN value can be one of the following: + + ‘auto’ + The default behavior: if the input file is sparse, attempt to + make the output file sparse, too. However, if an output file + exists but refers to a non-regular file, then do not attempt + to make it sparse. + + ‘always’ + For each sufficiently long sequence of zero bytes in the input + file, attempt to create a corresponding hole in the output + file, even if the input file does not appear to be sparse. + This is useful when the input file resides on a file system + that does not support sparse files (for example, ‘efs’ file + systems in SGI IRIX 5.3 and earlier), but the output file is + on a type of file system that does support them. Holes may be + created only in regular files, so if the destination file is + of some other type, ‘cp’ does not even try to make it sparse. + + ‘never’ + Never make the output file sparse. This is useful in creating + a file for use with the ‘mkswap’ command, since such a file + must not have any holes. + + For example, with the following alias, ‘cp’ will use the minimum + amount of space supported by the file system. (Older versions of + ‘cp’ can also benefit from ‘--reflink=auto’ here.) + + alias cp='cp --sparse=always' + +‘--strip-trailing-slashes’ + Remove any trailing slashes from each SOURCE argument. *Note + Trailing slashes::. + +‘-s’ +‘--symbolic-link’ + Make symbolic links instead of copies of non-directories. All + source file names must be absolute (starting with ‘/’) unless the + destination files are in the current directory. This option merely + results in an error message on systems that do not support symbolic + links. + +‘-S SUFFIX’ +‘--suffix=SUFFIX’ + Append SUFFIX to each backup file made with ‘-b’. *Note Backup + options::. + +‘-t DIRECTORY’ +‘--target-directory=DIRECTORY’ + Specify the destination DIRECTORY. *Note Target directory::. + +‘-T’ +‘--no-target-directory’ + Do not treat the last operand specially when it is a directory or a + symbolic link to a directory. *Note Target directory::. + +‘-u’ +‘--update[=WHICH]’ + Do not copy a non-directory that has an existing destination with + the same or newer modification timestamp; instead, silently skip + the file without failing. If timestamps are being preserved, the + comparison is to the source timestamp truncated to the resolutions + of the destination file system and of the system calls used to + update timestamps; this avoids duplicate work if several ‘cp -pu’ + commands are executed with the same source and destination. This + option is ignored if the ‘-n’ or ‘--no-clobber’ option is also + specified. Also, if ‘--preserve=links’ is also specified (like + with ‘cp -au’ for example), that will take precedence; + consequently, depending on the order that files are processed from + the source, newer files in the destination may be replaced, to + mirror hard links in the source. + + WHICH gives more control over which existing files in the + destination are replaced, and its value can be one of the + following: + + ‘all’ + This is the default operation when an ‘--update’ option is not + specified, and results in all existing files in the + destination being replaced. + + ‘none’ + This is similar to the ‘--no-clobber’ option, in that no files + in the destination are replaced, but also skipping a file does + not induce a failure. + + ‘older’ + This is the default operation when ‘--update’ is specified, + and results in files being replaced if they’re older than the + corresponding source file. + +‘-v’ +‘--verbose’ + Print the name of each file before copying it. + +‘-x’ +‘--one-file-system’ + Skip subdirectories that are on different file systems from the one + that the copy started on. However, mount point directories _are_ + copied. + +‘-Z’ +‘--context[=CONTEXT]’ + Without a specified CONTEXT, adjust the SELinux security context + according to the system default type for destination files, + similarly to the ‘restorecon’ command. The long form of this + option with a specific context specified, will set the context for + newly created files only. With a specified context, if both + SELinux and SMACK are disabled, a warning is issued. This option + is mutually exclusive with the ‘--preserve=context’ option, and + overrides the ‘--preserve=all’ and ‘-a’ options. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: dd invocation, Next: install invocation, Prev: cp invocation, Up: Basic operations + +11.2 ‘dd’: Convert and copy a file +================================== + +‘dd’ copies input to output with a changeable I/O block size, while +optionally performing conversions on the data. Synopses: + + dd [OPERAND]... + dd OPTION + + The only options are ‘--help’ and ‘--version’. *Note Common +options::. + + By default, ‘dd’ copies standard input to standard output. To copy, +‘dd’ repeatedly does the following steps in order: + + 1. Read an input block. + + 2. If converting via ‘sync’, pad as needed to meet the input block + size. Pad with spaces if converting via ‘block’ or ‘unblock’, NUL + bytes otherwise. + + 3. If ‘bs=’ is given and no conversion mentioned in steps (4) or (5) + is given, output the data as a single block and skip all remaining + steps. + + 4. If the ‘swab’ conversion is given, swap each pair of input bytes. + If the input data length is odd, preserve the last input byte + (since there is nothing to swap it with). + + 5. If any of the conversions ‘swab’, ‘block’, ‘unblock’, ‘lcase’, + ‘ucase’, ‘ascii’, ‘ebcdic’ and ‘ibm’ are given, do these + conversions. These conversions operate independently of input + blocking, and might deal with records that span block boundaries. + + 6. Aggregate the resulting data into output blocks of the specified + size, and output each output block in turn. Do not pad the last + output block; it can be shorter than usual. + + ‘dd’ accepts the following operands, whose syntax was inspired by the +DD (data definition) statement of OS/360 JCL. + +‘if=FILE’ + Read from FILE instead of standard input. + +‘of=FILE’ + Write to FILE instead of standard output. Unless ‘conv=notrunc’ is + given, truncate FILE before writing it. + +‘ibs=BYTES’ + Set the input block size to BYTES. This makes ‘dd’ read BYTES per + block. The default is 512 bytes. + +‘obs=BYTES’ + Set the output block size to BYTES. This makes ‘dd’ write BYTES + per block. The default is 512 bytes. + +‘bs=BYTES’ + Set both input and output block sizes to BYTES. This makes ‘dd’ + read and write BYTES per block, overriding any ‘ibs’ and ‘obs’ + settings. In addition, if no data-transforming ‘conv’ operand is + specified, input is copied to the output as soon as it’s read, even + if it is smaller than the block size. + +‘cbs=BYTES’ + Set the conversion block size to BYTES. When converting + variable-length records to fixed-length ones (‘conv=block’) or the + reverse (‘conv=unblock’), use BYTES as the fixed record length. + +‘skip=N’ +‘iseek=N’ + Skip N ‘ibs’-byte blocks in the input file before copying. If N + ends in the letter ‘B’, interpret N as a byte count rather than a + block count. (‘B’ and the ‘iseek=’ spelling are GNU extensions to + POSIX.) + +‘seek=N’ +‘oseek=N’ + Skip N ‘obs’-byte blocks in the output file before truncating or + copying. If N ends in the letter ‘B’, interpret N as a byte count + rather than a block count. (‘B’ and the ‘oseek=’ spelling are GNU + extensions to POSIX.) + +‘count=N’ + Copy N ‘ibs’-byte blocks from the input file, instead of everything + until the end of the file. If N ends in the letter ‘B’, interpret + N as a byte count rather than a block count; this is a GNU + extension to POSIX. If short reads occur, as could be the case when + reading from a pipe for example, ‘iflag=fullblock’ ensures that + ‘count=’ counts complete input blocks rather than input read + operations. As an extension to POSIX, ‘count=0’ copies zero blocks + instead of copying all blocks. + +‘status=LEVEL’ + Specify the amount of information printed. If this operand is + given multiple times, the last one takes precedence. The LEVEL + value can be one of the following: + + ‘none’ + Do not print any informational or warning messages to standard + error. Error messages are output as normal. + + ‘noxfer’ + Do not print the final transfer rate and volume statistics + that normally make up the last status line. + + ‘progress’ + Print the transfer rate and volume statistics on standard + error, when processing each input block. Statistics are + output on a single line at most once every second, but updates + can be delayed when waiting on I/O. + + Transfer information is normally output to standard error upon + receipt of the ‘INFO’ signal or when ‘dd’ exits, and defaults to + the following form in the C locale: + + 7287+1 records in + 116608+0 records out + 59703296 bytes (60 MB, 57 MiB) copied, 0.0427974 s, 1.4 GB/s + + The notation ‘W+P’ stands for W whole blocks and P partial blocks. + A partial block occurs when a read or write operation succeeds but + transfers less data than the block size. An additional line like + ‘1 truncated record’ or ‘10 truncated records’ is output after the + ‘records out’ line if ‘conv=block’ processing truncated one or more + input records. + + The ‘status=’ operand is a GNU extension to POSIX. + +‘conv=CONVERSION[,CONVERSION]...’ + Convert the file as specified by the CONVERSION argument(s). (No + spaces around any comma(s).) + + Conversions: + + ‘ascii’ + Convert EBCDIC to ASCII, using the conversion table specified + by POSIX. This provides a 1:1 translation for all 256 bytes. + This implies ‘conv=unblock’; input is converted to ASCII + before trailing spaces are deleted. + + ‘ebcdic’ + Convert ASCII to EBCDIC. This is the inverse of the ‘ascii’ + conversion. This implies ‘conv=block’; trailing spaces are + added before being converted to EBCDIC. + + ‘ibm’ + This acts like ‘conv=ebcdic’, except it uses the alternate + conversion table specified by POSIX. This is not a 1:1 + translation, but reflects common historical practice for ‘~’, + ‘[’, and ‘]’. + + The ‘ascii’, ‘ebcdic’, and ‘ibm’ conversions are mutually + exclusive. If you use any of these conversions, you should + also use the ‘cbs=’ operand. + + ‘block’ + For each line in the input, output ‘cbs’ bytes, replacing the + input newline with a space and truncating or padding input + lines with spaces as necessary. + + ‘unblock’ + Remove any trailing spaces in each ‘cbs’-sized input block, + and append a newline. + + The ‘block’ and ‘unblock’ conversions are mutually exclusive. + If you use either of these conversions, you should also use + the ‘cbs=’ operand. + + ‘lcase’ + Change uppercase letters to lowercase. + + ‘ucase’ + Change lowercase letters to uppercase. + + The ‘lcase’ and ‘ucase’ conversions are mutually exclusive. + + ‘sparse’ + Try to seek rather than write NUL output blocks. On a file + system that supports sparse files, this will create sparse + output when extending the output file. Be careful when using + this conversion in conjunction with ‘conv=notrunc’ or + ‘oflag=append’. With ‘conv=notrunc’, existing data in the + output file corresponding to NUL blocks from the input, will + be untouched. With ‘oflag=append’ the seeks performed will be + ineffective. Similarly, when the output is a device rather + than a file, NUL input blocks are not copied, and therefore + this conversion is most useful with virtual or pre zeroed + devices. + + The ‘sparse’ conversion is a GNU extension to POSIX. + + ‘swab’ + Swap every pair of input bytes. + + ‘sync’ + Pad every input block to size of ‘ibs’ with trailing zero + bytes. When used with ‘block’ or ‘unblock’, pad with spaces + instead of zero bytes. + + The following “conversions” are really file flags and don’t affect + internal processing: + + ‘excl’ + Fail if the output file already exists; ‘dd’ must create the + output file itself. + + ‘nocreat’ + Do not create the output file; the output file must already + exist. + + The ‘excl’ and ‘nocreat’ conversions are mutually exclusive, + and are GNU extensions to POSIX. + + ‘notrunc’ + Do not truncate the output file. + + ‘noerror’ + Continue after read errors. + + ‘fdatasync’ + Synchronize output data just before finishing, even if there + were write errors. This forces a physical write of output + data, so that even if power is lost the output data will be + preserved. If neither this nor ‘fsync’ are specified, output + is treated as usual with file systems, i.e., output data and + metadata may be cached in primary memory for some time before + the operating system physically writes it, and thus output + data and metadata may be lost if power is lost. *Note sync + invocation::. This conversion is a GNU extension to POSIX. + + ‘fsync’ + Synchronize output data and metadata just before finishing, + even if there were write errors. This acts like ‘fdatasync’ + except it also preserves output metadata, such as the + last-modified time of the output file; for this reason it may + be a bit slower than ‘fdatasync’ although the performance + difference is typically insignificant for ‘dd’. This + conversion is a GNU extension to POSIX. + +‘iflag=FLAG[,FLAG]...’ + Access the input file using the flags specified by the FLAG + argument(s). (No spaces around any comma(s).) + +‘oflag=FLAG[,FLAG]...’ + Access the output file using the flags specified by the FLAG + argument(s). (No spaces around any comma(s).) + + Here are the flags. + + ‘append’ + Write in append mode, so that even if some other process is + writing to this file, every ‘dd’ write will append to the + current contents of the file. This flag makes sense only for + output. If you combine this flag with the ‘of=FILE’ operand, + you should also specify ‘conv=notrunc’ unless you want the + output file to be truncated before being appended to. + + ‘cio’ + Use concurrent I/O mode for data. This mode performs direct + I/O and drops the POSIX requirement to serialize all I/O to + the same file. A file cannot be opened in CIO mode and with a + standard open at the same time. + + ‘direct’ + Use direct I/O for data, avoiding the buffer cache. Note that + the kernel may impose restrictions on read or write buffer + sizes. For example, with an ext4 destination file system and + a Linux-based kernel, using ‘oflag=direct’ will cause writes + to fail with ‘EINVAL’ if the output buffer size is not a + multiple of 512. + + ‘directory’ + + Fail unless the file is a directory. Most operating systems + do not allow I/O to a directory, so this flag has limited + utility. + + ‘dsync’ + Use synchronized I/O for data. For the output file, this + forces a physical write of output data on each write. For the + input file, this flag can matter when reading from a remote + file that has been written to synchronously by some other + process. Metadata (e.g., last-access and last-modified time) + is not necessarily synchronized. + + ‘sync’ + Use synchronized I/O for both data and metadata. + + ‘nocache’ + Request to discard the system data cache for a file. When + count=0 all cached data for the file is specified, otherwise + the cache is dropped for the processed portion of the file. + Also when count=0, failure to discard the cache is diagnosed + and reflected in the exit status. + + Note data that is not already persisted to storage will not be + discarded from cache, so note the use of the ‘sync’ + conversions in the examples below, which are used to maximize + the effectiveness of the ‘nocache’ flag. + + Here are some usage examples: + + # Advise to drop cache for whole file + dd if=ifile iflag=nocache count=0 + + # Ensure drop cache for the whole file + dd of=ofile oflag=nocache conv=notrunc,fdatasync count=0 + + # Advise to drop cache for part of file + # Note the kernel will only consider complete and + # already persisted pages. + dd if=ifile iflag=nocache skip=10 count=10 of=/dev/null + + # Stream data using just the read-ahead cache. + # See also the ‘direct’ flag. + dd if=ifile of=ofile iflag=nocache oflag=nocache,sync + + ‘nonblock’ + Use non-blocking I/O. + + ‘noatime’ + Do not update the file’s access timestamp. *Note File + timestamps::. Some older file systems silently ignore this + flag, so it is a good idea to test it on your files before + relying on it. + + ‘noctty’ + Do not assign the file to be a controlling terminal for ‘dd’. + This has no effect when the file is not a terminal. On many + hosts (e.g., GNU/Linux hosts), this flag has no effect at all. + + ‘nofollow’ + Do not follow symbolic links. + + ‘nolinks’ + Fail if the file has multiple hard links. + + ‘binary’ + Use binary I/O. This flag has an effect only on nonstandard + platforms that distinguish binary from text I/O. + + ‘text’ + Use text I/O. Like ‘binary’, this flag has no effect on + standard platforms. + + ‘fullblock’ + Accumulate full blocks from input. The ‘read’ system call may + return early if a full block is not available. When that + happens, continue calling ‘read’ to fill the remainder of the + block. This flag can be used only with ‘iflag’. This flag is + useful with pipes for example as they may return short reads. + In that case, this flag is needed to ensure that a ‘count=’ + argument is interpreted as a block count rather than a count + of read operations. + + These flags are all GNU extensions to POSIX. They are not supported + on all systems, and ‘dd’ rejects attempts to use them when they are + not supported. When reading from standard input or writing to + standard output, the ‘nofollow’ and ‘noctty’ flags should not be + specified, and the other flags (e.g., ‘nonblock’) can affect how + other processes behave with the affected file descriptors, even + after ‘dd’ exits. + + The behavior of ‘dd’ is unspecified if operands other than ‘conv=’, +‘iflag=’, ‘oflag=’, and ‘status=’ are specified more than once. + + The numeric-valued strings above (N and BYTES) are unsigned decimal +integers that can be followed by a multiplier: ‘b’=512, ‘c’=1, ‘w’=2, +‘xM’=M, or any of the standard block size suffixes like ‘k’=1024 (*note +Block size::). These multipliers are GNU extensions to POSIX, except +that POSIX allows BYTES to be followed by ‘k’, ‘b’, and ‘xM’. Note ‘xM’ +can be used more than once in a number. Block sizes (i.e., specified by +BYTES strings) must be nonzero. + + Any block size you specify via ‘bs=’, ‘ibs=’, ‘obs=’, ‘cbs=’ should +not be too large – values larger than a few megabytes are generally +wasteful or (as in the gigabyte..exabyte case) downright +counterproductive or error-inducing. + + To process data with offset or size that is not a multiple of the I/O +block size, you can use a numeric string N that ends in the letter ‘B’. +For example, the following shell commands copy data in 1 MiB blocks +between a flash drive and a tape, but do not save or restore a 512-byte +area at the start of the flash drive: + + flash=/dev/sda + tape=/dev/st0 + + # Copy all but the initial 512 bytes from flash to tape. + dd if=$flash iseek=512B bs=1MiB of=$tape + + # Copy from tape back to flash, leaving initial 512 bytes alone. + dd if=$tape bs=1MiB of=$flash oseek=512B + + For failing storage devices, other tools come with a great variety of +extra functionality to ease the saving of as much data as possible +before the device finally dies, e.g. GNU ‘ddrescue’ +(https://www.gnu.org/software/ddrescue/). However, in some cases such a +tool is not available or the administrator feels more comfortable with +the handling of ‘dd’. As a simple rescue method, call ‘dd’ as shown in +the following example: the operand ‘conv=noerror,sync’ is used to +continue after read errors and to pad out bad reads with NULs, while +‘iflag=fullblock’ caters for short reads (which traditionally never +occur on flash or similar devices): + + # Rescue data from an (unmounted!) partition of a failing device. + dd conv=noerror,sync iflag=fullblock </dev/sda1 > /mnt/rescue.img + + Sending an ‘INFO’ signal (or ‘USR1’ signal where that is unavailable) +to a running ‘dd’ process makes it print I/O statistics to standard +error and then resume copying. In the example below, ‘dd’ is run in the +background to copy 5GB of data. The ‘kill’ command makes it output +intermediate I/O statistics, and when ‘dd’ completes normally or is +killed by the ‘SIGINT’ signal, it outputs the final statistics. + + # Ignore the signal so we never inadvertently terminate the dd child. + # Note this is not needed when SIGINFO is available. + trap '' USR1 + + # Run dd with the fullblock iflag to avoid short reads + # which can be triggered by reception of signals. + dd iflag=fullblock if=/dev/zero of=/dev/null count=5000000 bs=1000 & pid=$! + + # Output stats every second. + while kill -s USR1 $pid 2>/dev/null; do sleep 1; done + + The above script will output in the following format: + + 3441325+0 records in + 3441325+0 records out + 3441325000 bytes (3.4 GB, 3.2 GiB) copied, 1.00036 s, 3.4 GB/s + 5000000+0 records in + 5000000+0 records out + 5000000000 bytes (5.0 GB, 4.7 GiB) copied, 1.44433 s, 3.5 GB/s + + The ‘status=progress’ operand periodically updates the last line of +the transfer statistics above. + + On systems lacking the ‘INFO’ signal ‘dd’ responds to the ‘USR1’ +signal instead, unless the ‘POSIXLY_CORRECT’ environment variable is +set. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: install invocation, Next: mv invocation, Prev: dd invocation, Up: Basic operations + +11.3 ‘install’: Copy files and set attributes +============================================= + +‘install’ copies files while setting their file mode bits and, if +possible, their owner and group. Synopses: + + install [OPTION]... [-T] SOURCE DEST + install [OPTION]... SOURCE... DIRECTORY + install [OPTION]... -t DIRECTORY SOURCE... + install [OPTION]... -d DIRECTORY... + + • If two file names are given, ‘install’ copies the first file to the + second. + + • If the ‘--target-directory’ (‘-t’) option is given, or failing that + if the last file is a directory and the ‘--no-target-directory’ + (‘-T’) option is not given, ‘install’ copies each SOURCE file to + the specified directory, using the SOURCEs’ names. + + • If the ‘--directory’ (‘-d’) option is given, ‘install’ creates each + DIRECTORY and any missing parent directories. Parent directories + are created with mode ‘u=rwx,go=rx’ (755), regardless of the ‘-m’ + option or the current umask. *Note Directory Setuid and Setgid::, + for how the set-user-ID and set-group-ID bits of parent directories + are inherited. + + ‘install’ is similar to ‘cp’, but allows you to control the +attributes of destination files. It is typically used in Makefiles to +copy programs into their destination directories. It refuses to copy +files onto themselves. + + ‘install’ never preserves extended attributes (xattr). + + The program accepts the following options. Also see *note Common +options::. + +‘-b’ +‘--backup[=METHOD]’ + *Note Backup options::. Make a backup of each file that would + otherwise be overwritten or removed. + +‘-C’ +‘--compare’ + Compare content of source and destination files, and if there would + be no change to the destination content, owner, group, permissions, + and possibly SELinux context, then do not modify the destination at + all. Note this option is best used in conjunction with ‘--user’, + ‘--group’ and ‘--mode’ options, lest ‘install’ incorrectly + determines the default attributes that installed files would have + (as it doesn’t consider setgid directories and POSIX default ACLs + for example). This could result in redundant copies or attributes + that are not reset to the correct defaults. + +‘-c’ + Ignored; for compatibility with old Unix versions of ‘install’. + +‘-D’ + Create any missing parent directories of DEST, then copy SOURCE to + DEST. Explicitly specifying the ‘--target-directory=DIR’ will + similarly ensure the presence of that hierarchy before copying + SOURCE arguments. + +‘-d’ +‘--directory’ + Create any missing parent directories, giving them the default + attributes. Then create each given directory, setting their owner, + group and mode as given on the command line or to the defaults. + +‘--debug’ + Print extra information to stdout, explaining how files are copied. + This option implies the ‘--verbose’ option. + +‘-g GROUP’ +‘--group=GROUP’ + Set the group ownership of installed files or directories to GROUP. + The default is the process’s current group. GROUP may be either a + group name or a numeric group ID. + +‘-m MODE’ +‘--mode=MODE’ + Set the file mode bits for the installed file or directory to MODE, + which can be either an octal number, or a symbolic mode as in + ‘chmod’, with ‘a=’ (no access allowed to anyone) as the point of + departure (*note File permissions::). The default mode is + ‘u=rwx,go=rx,a-s’ – read, write, and execute for the owner, read + and execute for group and other, and with set-user-ID and + set-group-ID disabled. This default is not quite the same as + ‘755’, since it disables instead of preserving set-user-ID and + set-group-ID on directories. *Note Directory Setuid and Setgid::. + +‘-o OWNER’ +‘--owner=OWNER’ + If ‘install’ has appropriate privileges (is run as root), set the + ownership of installed files or directories to OWNER. The default + is ‘root’. OWNER may be either a user name or a numeric user ID. + +‘--preserve-context’ + Preserve the SELinux security context of files and directories. + Failure to preserve the context in all of the files or directories + will result in an exit status of 1. If SELinux is disabled then + print a warning and ignore the option. + +‘-p’ +‘--preserve-timestamps’ + Set the time of last access and the time of last modification of + each installed file to match those of each corresponding original + file. When a file is installed without this option, its last + access and last modification timestamps are both set to the time of + installation. This option is useful if you want to use the last + modification timestamps of installed files to keep track of when + they were last built as opposed to when they were last installed. + +‘-s’ +‘--strip’ + Strip the symbol tables from installed binary executables. + +‘--strip-program=PROGRAM’ + Program used to strip binaries. + +‘-S SUFFIX’ +‘--suffix=SUFFIX’ + Append SUFFIX to each backup file made with ‘-b’. *Note Backup + options::. + +‘-t DIRECTORY’ +‘--target-directory=DIRECTORY’ + Specify the destination DIRECTORY. *Note Target directory::. Also + specifying the ‘-D’ option will ensure the directory is present. + +‘-T’ +‘--no-target-directory’ + Do not treat the last operand specially when it is a directory or a + symbolic link to a directory. *Note Target directory::. + +‘-v’ +‘--verbose’ + Print the name of each file before copying it. + +‘-Z’ +‘--context[=CONTEXT]’ + Without a specified CONTEXT, adjust the SELinux security context + according to the system default type for destination files, + similarly to the ‘restorecon’ command. The long form of this + option with a specific context specified, will set the context for + newly created files only. With a specified context, if both + SELinux and SMACK are disabled, a warning is issued. This option + is mutually exclusive with the ‘--preserve-context’ option. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: mv invocation, Next: rm invocation, Prev: install invocation, Up: Basic operations + +11.4 ‘mv’: Move (rename) files +============================== + +‘mv’ moves or renames files (or directories). Synopses: + + mv [OPTION]... [-T] SOURCE DEST + mv [OPTION]... SOURCE... DIRECTORY + mv [OPTION]... -t DIRECTORY SOURCE... + + • If two file names are given, ‘mv’ moves the first file to the + second. + + • If the ‘--target-directory’ (‘-t’) option is given, or failing that + if the last file is a directory and the ‘--no-target-directory’ + (‘-T’) option is not given, ‘mv’ moves each SOURCE file to the + specified directory, using the SOURCEs’ names. + + To move a file, ‘mv’ ordinarily simply renames it. However, if +renaming does not work because the destination’s file system differs, +‘mv’ falls back on copying as if by ‘cp -a’, then (assuming the copy +succeeded) it removes the original. If the copy fails, then ‘mv’ +removes any partially created copy in the destination. If you were to +copy three directories from one file system to another and the copy of +the first directory succeeded, but the second didn’t, the first would be +left on the destination file system and the second and third would be +left on the original file system. + + ‘mv’ always tries to copy extended attributes (xattr), which may +include SELinux context, ACLs or Capabilities. Upon failure all but +‘Operation not supported’ warnings are output. + + If a destination file exists but is normally unwritable, standard +input is a terminal, and the ‘-f’ or ‘--force’ option is not given, ‘mv’ +prompts the user for whether to replace the file. (You might own the +file, or have write permission on its directory.) If the response is +not affirmative, the file is skipped. + + _Warning_: Avoid specifying a source name with a trailing slash, when +it might be a symlink to a directory. Otherwise, ‘mv’ may do something +very surprising, since its behavior depends on the underlying rename +system call. On a system with a modern Linux-based kernel, it fails +with ‘errno=ENOTDIR’. However, on other systems (at least FreeBSD 6.1 +and Solaris 10) it silently renames not the symlink but rather the +directory referenced by the symlink. *Note Trailing slashes::. + + _Note_: ‘mv’ will only replace empty directories in the destination. +Conflicting populated directories are skipped with a diagnostic. + + The program accepts the following options. Also see *note Common +options::. + +‘-b’ +‘--backup[=METHOD]’ + *Note Backup options::. Make a backup of each file that would + otherwise be overwritten or removed. + +‘--debug’ + Print extra information to stdout, explaining how files are copied. + This option implies the ‘--verbose’ option. + +‘-f’ +‘--force’ + Do not prompt the user before removing a destination file. If you + specify more than one of the ‘-i’, ‘-f’, ‘-n’ options, only the + final one takes effect. + +‘-i’ +‘--interactive’ + Prompt whether to overwrite each existing destination file, + regardless of its permissions, and fail if the response is not + affirmative. If you specify more than one of the ‘-i’, ‘-f’, ‘-n’ + options, only the final one takes effect. + +‘-n’ +‘--no-clobber’ + Do not overwrite an existing file; silently fail instead. If you + specify more than one of the ‘-i’, ‘-f’, ‘-n’ options, only the + final one takes effect. This option is mutually exclusive with + ‘-b’ or ‘--backup’ option. See also the ‘--update=none’ option + which will skip existing files but not fail. + +‘--no-copy’ + If a file cannot be renamed because the destination file system + differs, fail with a diagnostic instead of copying and then + removing the file. + +‘-u’ +‘--update’ + Do not move a non-directory that has an existing destination with + the same or newer modification timestamp; instead, silently skip + the file without failing. If the move is across file system + boundaries, the comparison is to the source timestamp truncated to + the resolutions of the destination file system and of the system + calls used to update timestamps; this avoids duplicate work if + several ‘mv -u’ commands are executed with the same source and + destination. This option is ignored if the ‘-n’ or ‘--no-clobber’ + option is also specified. + + WHICH gives more control over which existing files in the + destination are replaced, and its value can be one of the + following: + + ‘all’ + This is the default operation when an ‘--update’ option is not + specified, and results in all existing files in the + destination being replaced. + + ‘none’ + This is similar to the ‘--no-clobber’ option, in that no files + in the destination are replaced, but also skipping a file does + not induce a failure. + + ‘older’ + This is the default operation when ‘--update’ is specified, + and results in files being replaced if they’re older than the + corresponding source file. + +‘-v’ +‘--verbose’ + Print the name of each file before moving it. + +‘--strip-trailing-slashes’ + Remove any trailing slashes from each SOURCE argument. *Note + Trailing slashes::. + +‘-S SUFFIX’ +‘--suffix=SUFFIX’ + Append SUFFIX to each backup file made with ‘-b’. *Note Backup + options::. + +‘-t DIRECTORY’ +‘--target-directory=DIRECTORY’ + Specify the destination DIRECTORY. *Note Target directory::. + +‘-T’ +‘--no-target-directory’ + Do not treat the last operand specially when it is a directory or a + symbolic link to a directory. *Note Target directory::. + +‘-Z’ +‘--context’ + This option functions similarly to the ‘restorecon’ command, by + adjusting the SELinux security context according to the system + default type for destination files and each created directory. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: rm invocation, Next: shred invocation, Prev: mv invocation, Up: Basic operations + +11.5 ‘rm’: Remove files or directories +====================================== + +‘rm’ removes each given FILE. By default, it does not remove +directories. Synopsis: + + rm [OPTION]... [FILE]... + + If the ‘-I’ or ‘--interactive=once’ option is given, and there are +more than three files or the ‘-r’, ‘-R’, or ‘--recursive’ are given, +then ‘rm’ prompts the user for whether to proceed with the entire +operation. If the response is not affirmative, the entire command is +aborted. + + Otherwise, if a file is unwritable, standard input is a terminal, and +the ‘-f’ or ‘--force’ option is not given, or the ‘-i’ or +‘--interactive=always’ option _is_ given, ‘rm’ prompts the user for +whether to remove the file. If the response is not affirmative, the +file is skipped. + + Any attempt to remove a file whose last file name component is ‘.’ or +‘..’ is rejected without any prompting, as mandated by POSIX. + + _Warning_: If you use ‘rm’ to remove a file, it is usually possible +to recover the contents of that file. If you want more assurance that +the contents are unrecoverable, consider using ‘shred’. + + The program accepts the following options. Also see *note Common +options::. + +‘-d’ +‘--dir’ + Remove the listed directories if they are empty. + +‘-f’ +‘--force’ + Ignore nonexistent files and missing operands, and never prompt the + user. Ignore any previous ‘--interactive’ (‘-i’) option. + +‘-i’ + Prompt whether to remove each file. If the response is not + affirmative, silently skip the file without failing. Ignore any + previous ‘--force’ (‘-f’) option. Equivalent to + ‘--interactive=always’. + +‘-I’ + Prompt once whether to proceed with the command, if more than three + files are named or if a recursive removal is requested. Ignore any + previous ‘--force’ (‘-f’) option. Equivalent to + ‘--interactive=once’. + +‘--interactive [=WHEN]’ + Specify when to issue an interactive prompt. WHEN may be omitted, + or one of: + • never - Do not prompt at all. + • once - Prompt once if more than three files are named or if a + recursive removal is requested. Equivalent to ‘-I’. + • always - Prompt for every file being removed. Equivalent to + ‘-i’. + ‘--interactive’ with no WHEN is equivalent to + ‘--interactive=always’. + +‘--one-file-system’ + When removing a hierarchy recursively, do not remove any directory + that is on a file system different from that of the corresponding + command line argument. This option is useful when removing a build + “chroot” hierarchy, which normally contains no valuable data. + However, it is not uncommon to bind-mount ‘/home’ into such a + hierarchy, to make it easier to use one’s start-up file. The catch + is that it’s easy to forget to unmount ‘/home’. Then, when you use + ‘rm -rf’ to remove your normally throw-away chroot, that command + will remove everything under ‘/home’, too. Use the + ‘--one-file-system’ option, and it will diagnose and skip + directories on other file systems. Of course, this will not save + your ‘/home’ if it and your chroot happen to be on the same file + system. See also ‘--preserve-root=all’ to protect command line + arguments themselves. + +‘--preserve-root [=all]’ + Fail upon any attempt to remove the root directory, ‘/’, when used + with the ‘--recursive’ option. This is the default behavior. + *Note Treating / specially::. When ‘all’ is specified, reject any + command line argument that is not on the same file system as its + parent. + +‘--no-preserve-root’ + Do not treat ‘/’ specially when removing recursively. This option + is not recommended unless you really want to remove all the files + on your computer. *Note Treating / specially::. + +‘-r’ +‘-R’ +‘--recursive’ + Remove the listed directories and their contents recursively. + +‘-v’ +‘--verbose’ + Print the name of each file before removing it. + + One common question is how to remove files whose names begin with a +‘-’. GNU ‘rm’, like every program that uses the ‘getopt’ function to +parse its arguments, lets you use the ‘--’ option to indicate that all +following arguments are non-options. To remove a file called ‘-f’ in +the current directory, you could type either: + + rm -- -f + +or: + + rm ./-f + + The Unix ‘rm’ program’s use of a single ‘-’ for this purpose predates +the development of the ‘getopt’ standard syntax. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: shred invocation, Prev: rm invocation, Up: Basic operations + +11.6 ‘shred’: Remove files more securely +======================================== + +‘shred’ overwrites devices or files, to help prevent even extensive +forensics from recovering the data. + + Ordinarily when you remove a file (*note rm invocation::), its data +and metadata are not actually destroyed. Only the file’s directory +entry is removed, and the file’s storage is reclaimed only when no +process has the file open and no other directory entry links to the +file. And even if file’s data and metadata’s storage space is freed for +further reuse, there are undelete utilities that will attempt to +reconstruct the file from the data in freed storage, and that can bring +the file back if the storage was not rewritten. + + On a busy system with a nearly-full device, space can get reused in a +few seconds. But there is no way to know for sure. And although the +undelete utilities and already-existing processes require insider or +superuser access, you may be wary of the superuser, of processes running +on your behalf, or of attackers that can physically access the storage +device. So if you have sensitive data, you may want to be sure that +recovery is not possible by plausible attacks like these. + + The best way to remove something irretrievably is to destroy the +media it’s on with acid, melt it down, or the like. For cheap removable +media this is often the preferred method. However, some storage devices +are expensive or are harder to destroy, so the ‘shred’ utility tries to +achieve a similar effect non-destructively, by overwriting the file with +non-sensitive data. + + *Please note* that ‘shred’ relies on a crucial assumption: that the +file system and hardware overwrite data in place. Although this is +common and is the traditional way to do things, many modern file system +designs do not satisfy this assumption. Exceptions include: + + • Log-structured or journaled file systems, such as ext3/ext4 (in + ‘data=journal’ mode), Btrfs, NTFS, ReiserFS, XFS, ZFS, file systems + supplied with AIX and Solaris, etc., when they are configured to + journal data. + + • File systems that write redundant data and carry on even if some + writes fail, such as RAID-based file systems. + + • File systems that make snapshots, such as Network Appliance’s NFS + server. + + • File systems that cache in temporary locations, such as NFS version + 3 clients. + + • Compressed file systems. + + For ext3 and ext4 file systems, ‘shred’ is less effective when the +file system is in ‘data=journal’ mode, which journals file data in +addition to just metadata. In both the ‘data=ordered’ (default) and +‘data=writeback’ modes, ‘shred’ works as usual. The ext3/ext4 +journaling modes can be changed by adding the ‘data=something’ option to +the mount options for a particular file system in the ‘/etc/fstab’ file, +as documented in the ‘mount’ man page (‘man mount’). Alternatively, if +you know how large the journal is, you can shred the journal by +shredding enough file data so that the journal cycles around and fills +up with shredded data. + + If you are not sure how your file system operates, then you should +assume that it does not overwrite data in place, which means ‘shred’ +cannot reliably operate on regular files in your file system. + + Generally speaking, it is more reliable to shred a device than a +file, since this bypasses file system design issues mentioned above. +However, devices are also problematic for shredding, for reasons such as +the following: + + • Solid-state storage devices (SSDs) typically do wear leveling to + prolong service life, and this means writes are distributed to + other blocks by the hardware, so “overwritten” data blocks are + still present in the underlying device. + + • Most storage devices map out bad blocks invisibly to the + application; if the bad blocks contain sensitive data, ‘shred’ + won’t be able to destroy it. + + • With some obsolete storage technologies, it may be possible to take + (say) a floppy disk back to a laboratory and use a lot of sensitive + (and expensive) equipment to look for the faint “echoes” of the + original data underneath the overwritten data. With these older + technologies, if the file has been overwritten only once, it’s + reputedly not even that hard. Luckily, this kind of data recovery + has become difficult, and there is no public evidence that today’s + higher-density storage devices can be analyzed in this way. + + The ‘shred’ command can use many overwrite passes, with data + patterns chosen to maximize the damage they do to the old data. By + default the patterns are designed for best effect on hard drives + using now-obsolete technology; for newer devices, a single pass + should suffice. For more details, see the source code and Peter + Gutmann’s paper ‘Secure Deletion of Data from Magnetic and + Solid-State Memory’ + (https://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html), from + the proceedings of the Sixth USENIX Security Symposium (San Jose, + California, July 22–25, 1996). + + ‘shred’ makes no attempt to detect or report these problems, just as +it makes no attempt to do anything about backups. However, since it is +more reliable to shred devices than files, ‘shred’ by default does not +deallocate or remove the output file. This default is more suitable for +devices, which typically cannot be deallocated and should not be +removed. + + Finally, consider the risk of backups and mirrors. File system +backups and remote mirrors may contain copies of the file that cannot be +removed, and that will allow a shredded file to be recovered later. So +if you keep any data you may later want to destroy using ‘shred’, be +sure that it is not backed up or mirrored. + + shred [OPTION]... FILE[...] + + The program accepts the following options. Also see *note Common +options::. + +‘-f’ +‘--force’ + Override file permissions if necessary to allow overwriting. + +‘-n NUMBER’ +‘--iterations=NUMBER’ + By default, ‘shred’ uses 3 passes of overwrite. You can reduce + this to save time, or increase it if you think it’s appropriate. + After 25 passes all of the internal overwrite patterns will have + been used at least once. + +‘--random-source=FILE’ + Use FILE as a source of random data used to overwrite and to choose + pass ordering. *Note Random sources::. + +‘-s BYTES’ +‘--size=BYTES’ + Shred the first BYTES bytes of the file. The default is to shred + the whole file. BYTES can be followed by a size specification like + ‘K’, ‘M’, or ‘G’ to specify a multiple. *Note Block size::. + +‘-u’ +‘--remove[=HOW]’ + After shredding a file, deallocate it (if possible) and then remove + it. If a file has multiple links, only the named links will be + removed. Often the file name is less sensitive than the file data, + in which case the optional HOW parameter, supported with the long + form option, gives control of how to more efficiently remove each + directory entry. The ‘unlink’ parameter will just use a standard + unlink call, ‘wipe’ will also first obfuscate bytes in the name, + and ‘wipesync’ will also sync each obfuscated byte in the name to + the file system. Note ‘wipesync’ is the default method, but can be + expensive, requiring a sync for every character in every file. + This can become significant with many files, or is redundant if + your file system provides synchronous metadata updates. + +‘-v’ +‘--verbose’ + Display to standard error all status updates as sterilization + proceeds. + +‘-x’ +‘--exact’ + By default, ‘shred’ rounds the size of a regular file up to the + next multiple of the file system block size to fully erase the + slack space in the last block of the file. This space may contain + portions of the current system memory on some systems for example. + Use ‘--exact’ to suppress that behavior. Thus, by default if you + shred a 10-byte regular file on a system with 512-byte blocks, the + resulting file will be 512 bytes long. With this option, shred + does not increase the apparent size of the file. + +‘-z’ +‘--zero’ + Normally, the last pass that ‘shred’ writes is made up of random + data. If this would be conspicuous on your storage device (for + example, because it looks like encrypted data), or you just think + it’s tidier, the ‘--zero’ option adds an additional overwrite pass + with all zero bits. This is in addition to the number of passes + specified by the ‘--iterations’ option. + + You might use the following command to erase the file system you +created on a USB flash drive. This command typically takes several +minutes, depending on the drive’s size and write speed. On modern +storage devices a single pass should be adequate, and will take one +third the time of the default three-pass approach. + + shred -v -n 1 /dev/sdd1 + + Similarly, to erase all data on a selected partition of your device, +you could give a command like the following. + + # 1 pass, write pseudo-random data; 3x faster than the default + shred -v -n1 /dev/sda5 + + To be on the safe side, use at least one pass that overwrites using +pseudo-random data. I.e., don’t be tempted to use ‘-n0 --zero’, in case +some device controller optimizes the process of writing blocks of all +zeros, and thereby does not clear all bytes in a block. Some SSDs may +do just that. + + A FILE of ‘-’ denotes standard output. The intended use of this is +to shred a removed temporary file. For example: + + i=$(mktemp) + exec 3<>"$i" + rm -- "$i" + echo "Hello, world" >&3 + shred - >&3 + exec 3>- + + However, the command ‘shred - >file’ does not shred the contents of +FILE, since the shell truncates FILE before invoking ‘shred’. Use the +command ‘shred file’ or (if using a Bourne-compatible shell) the command +‘shred - 1<>file’ instead. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: Special file types, Next: Changing file attributes, Prev: Basic operations, Up: Top + +12 Special file types +********************* + +This chapter describes commands which create special types of files (and +‘rmdir’, which removes directories, one special file type). + + Although Unix-like operating systems have markedly fewer special file +types than others, not _everything_ can be treated only as the +undifferentiated byte stream of “normal files”. For example, when a +file is created or removed, the system must record this information, +which it does in a “directory” – a special type of file. Although you +can read directories as normal files, if you’re curious, in order for +the system to do its job it must impose a structure, a certain order, on +the bytes of the file. Thus it is a “special” type of file. + + Besides directories, other special file types include named pipes +(FIFOs), symbolic links, sockets, and so-called “special files”. + +* Menu: + +* link invocation:: Make a hard link via the link syscall +* ln invocation:: Make links between files. +* mkdir invocation:: Make directories. +* mkfifo invocation:: Make FIFOs (named pipes). +* mknod invocation:: Make block or character special files. +* readlink invocation:: Print value of a symlink or canonical file name. +* rmdir invocation:: Remove empty directories. +* unlink invocation:: Remove files via the unlink syscall + + +File: coreutils.info, Node: link invocation, Next: ln invocation, Up: Special file types + +12.1 ‘link’: Make a hard link via the link syscall +================================================== + +‘link’ creates a single hard link at a time. It is a minimalist +interface to the system-provided ‘link’ function. *Note (libc)Hard +Links::. It avoids the bells and whistles of the more commonly-used +‘ln’ command (*note ln invocation::). Synopsis: + + link FILENAME LINKNAME + + FILENAME must specify an existing file, and LINKNAME must specify a +nonexistent entry in an existing directory. ‘link’ simply calls ‘link +(FILENAME, LINKNAME)’ to create the link. + + On a GNU system, this command acts like ‘ln --directory +--no-target-directory FILENAME LINKNAME’. However, the ‘--directory’ +and ‘--no-target-directory’ options are not specified by POSIX, and the +‘link’ command is more portable in practice. + + If FILENAME is a symbolic link, it is unspecified whether LINKNAME +will be a hard link to the symbolic link or to the target of the +symbolic link. Use ‘ln -P’ or ‘ln -L’ to specify which behavior is +desired. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: ln invocation, Next: mkdir invocation, Prev: link invocation, Up: Special file types + +12.2 ‘ln’: Make links between files +=================================== + +‘ln’ makes links between files. By default, it makes hard links; with +the ‘-s’ option, it makes symbolic (or “soft”) links. Synopses: + + ln [OPTION]... [-T] TARGET LINKNAME + ln [OPTION]... TARGET + ln [OPTION]... TARGET... DIRECTORY + ln [OPTION]... -t DIRECTORY TARGET... + + • If two file names are given, ‘ln’ creates a link to the first file + from the second. + + • If one TARGET is given, ‘ln’ creates a link to that file in the + current directory. + + • If the ‘--target-directory’ (‘-t’) option is given, or failing that + if the last file is a directory and the ‘--no-target-directory’ + (‘-T’) option is not given, ‘ln’ creates a link to each TARGET file + in the specified directory, using the TARGETs’ names. + + Normally ‘ln’ does not replace existing files. Use the ‘--force’ +(‘-f’) option to replace them unconditionally, the ‘--interactive’ +(‘-i’) option to replace them conditionally, and the ‘--backup’ (‘-b’) +option to rename them. Unless the ‘--backup’ (‘-b’) option is used +there is no brief moment when the destination does not exist; this is an +extension to POSIX. + + A “hard link” is another name for an existing file; the link and the +original are indistinguishable. Technically speaking, they share the +same inode, and the inode contains all the information about a file – +indeed, it is not incorrect to say that the inode _is_ the file. Most +systems prohibit making a hard link to a directory; on those where it is +allowed, only the super-user can do so (and with caution, since creating +a cycle will cause problems to many other utilities). Hard links cannot +cross file system boundaries. (These restrictions are not mandated by +POSIX, however.) + + “Symbolic links” (“symlinks” for short), on the other hand, are a +special file type (which not all kernels support: System V release 3 +(and older) systems lack symlinks) in which the link file actually +refers to a different file, by name. When most operations (opening, +reading, writing, and so on) are passed the symbolic link file, the +kernel automatically “dereferences” the link and operates on the target +of the link. But some operations (e.g., removing) work on the link file +itself, rather than on its target. The owner and group of a symlink are +not significant to file access performed through the link, but do have +implications on deleting a symbolic link from a directory with the +restricted deletion bit set. On the GNU system, the mode of a symlink +has no significance and cannot be changed, but on some BSD systems, the +mode can be changed and will affect whether the symlink will be +traversed in file name resolution. *Note (libc)Symbolic Links::. + + Symbolic links can contain arbitrary strings; a “dangling symlink” +occurs when the string in the symlink does not resolve to a file. There +are no restrictions against creating dangling symbolic links. There are +trade-offs to using absolute or relative symlinks. An absolute symlink +always points to the same file, even if the directory containing the +link is moved. However, if the symlink is visible from more than one +machine (such as on a networked file system), the file pointed to might +not always be the same. A relative symbolic link is resolved in +relation to the directory that contains the link, and is often useful in +referring to files on the same device without regards to what name that +device is mounted on when accessed via networked machines. + + When creating a relative symlink in a different location than the +current directory, the resolution of the symlink will be different than +the resolution of the same string from the current directory. +Therefore, many users prefer to first change directories to the location +where the relative symlink will be created, so that tab-completion or +other file resolution will find the same target as what will be placed +in the symlink. + + The program accepts the following options. Also see *note Common +options::. + +‘-b’ +‘--backup[=METHOD]’ + *Note Backup options::. Make a backup of each file that would + otherwise be overwritten or removed. + +‘-d’ +‘-F’ +‘--directory’ + Allow users with appropriate privileges to attempt to make hard + links to directories. However, note that this will probably fail + due to system restrictions, even for the super-user. + +‘-f’ +‘--force’ + Remove existing destination files. + +‘-i’ +‘--interactive’ + Prompt whether to remove existing destination files, and fail if + the response is not affirmative. + +‘-L’ +‘--logical’ + If ‘-s’ is not in effect, and the source file is a symbolic link, + create the hard link to the file referred to by the symbolic link, + rather than the symbolic link itself. + +‘-n’ +‘--no-dereference’ + Do not treat the last operand specially when it is a symbolic link + to a directory. Instead, treat it as if it were a normal file. + + When the destination is an actual directory (not a symlink to one), + there is no ambiguity. The link is created in that directory. But + when the specified destination is a symlink to a directory, there + are two ways to treat the user’s request. ‘ln’ can treat the + destination just as it would a normal directory and create the link + in it. On the other hand, the destination can be viewed as a + non-directory – as the symlink itself. In that case, ‘ln’ must + delete or backup that symlink before creating the new link. The + default is to treat a destination that is a symlink to a directory + just like a directory. + + This option is weaker than the ‘--no-target-directory’ (‘-T’) + option, so it has no effect if both options are given. + +‘-P’ +‘--physical’ + If ‘-s’ is not in effect, and the source file is a symbolic link, + create the hard link to the symbolic link itself. On platforms + where this is not supported by the kernel, this option creates a + symbolic link with identical contents; since symbolic link contents + cannot be edited, any file name resolution performed through either + link will be the same as if a hard link had been created. + +‘-r’ +‘--relative’ + Make symbolic links relative to the link location. This option is + only valid with the ‘--symbolic’ option. + + Example: + + ln -srv /a/file /tmp + '/tmp/file' -> '../a/file' + + Relative symbolic links are generated based on their canonicalized + containing directory, and canonicalized targets. I.e., all + symbolic links in these file names will be resolved. *Note + realpath invocation::, which gives greater control over relative + file name generation, as demonstrated in the following example: + + ln--relative() { + test "$1" = --no-symlinks && { nosym=$1; shift; } + target="$1"; + test -d "$2" && link="$2/." || link="$2" + rtarget="$(realpath $nosym -m "$target" \ + --relative-to "$(dirname "$link")")" + ln -s -v "$rtarget" "$link" + } + +‘-s’ +‘--symbolic’ + Make symbolic links instead of hard links. This option merely + produces an error message on systems that do not support symbolic + links. + +‘-S SUFFIX’ +‘--suffix=SUFFIX’ + Append SUFFIX to each backup file made with ‘-b’. *Note Backup + options::. + +‘-t DIRECTORY’ +‘--target-directory=DIRECTORY’ + Specify the destination DIRECTORY. *Note Target directory::. + +‘-T’ +‘--no-target-directory’ + Do not treat the last operand specially when it is a directory or a + symbolic link to a directory. *Note Target directory::. + +‘-v’ +‘--verbose’ + Print the name of each file after linking it successfully. + + If ‘-L’ and ‘-P’ are both given, the last one takes precedence. If +‘-s’ is also given, ‘-L’ and ‘-P’ are silently ignored. If neither +option is given, then this implementation defaults to ‘-P’ if the system +‘link’ supports hard links to symbolic links (such as the GNU system), +and ‘-L’ if ‘link’ follows symbolic links (such as on BSD). + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + Examples: + + Bad Example: + + # Create link ../a pointing to a in that directory. + # Not really useful because it points to itself. + ln -s a .. + + Better Example: + + # Change to the target before creating symlinks to avoid being confused. + cd .. + ln -s adir/a . + + Bad Example: + + # Hard coded file names don't move well. + ln -s $(pwd)/a /some/dir/ + + Better Example: + + # Relative file names survive directory moves and also + # work across networked file systems. + ln -s afile anotherfile + ln -s ../adir/afile yetanotherfile + + +File: coreutils.info, Node: mkdir invocation, Next: mkfifo invocation, Prev: ln invocation, Up: Special file types + +12.3 ‘mkdir’: Make directories +============================== + +‘mkdir’ creates directories with the specified names. Synopsis: + + mkdir [OPTION]... NAME... + + ‘mkdir’ creates each directory NAME in the order given. It reports +an error if NAME already exists, unless the ‘-p’ option is given and +NAME is a directory. + + The program accepts the following options. Also see *note Common +options::. + +‘-m MODE’ +‘--mode=MODE’ + Set the file permission bits of created directories to MODE, which + uses the same syntax as in ‘chmod’ and uses ‘a=rwx’ (read, write + and execute allowed for everyone) for the point of the departure. + *Note File permissions::. This option affects only directories + given on the command line; it does not affect any parents that may + be created via the ‘-p’ option. + + Normally the directory has the desired file mode bits at the moment + it is created. As a GNU extension, MODE may also mention special + mode bits, but in this case there may be a temporary window during + which the directory exists but its special mode bits are incorrect. + *Note Directory Setuid and Setgid::, for how the set-user-ID and + set-group-ID bits of directories are inherited unless overridden in + this way. + +‘-p’ +‘--parents’ + Make any missing parent directories for each argument, setting + their file permission bits to ‘=rwx,u+wx’, that is, with the umask + modified by ‘u+wx’. Ignore existing parent directories, and do not + change their file permission bits. + + If the ‘-m’ option is also given, it does not affect file + permission bits of any newly-created parent directories. To + control these bits, set the umask before invoking ‘mkdir’. For + example, if the shell command ‘(umask u=rwx,go=rx; mkdir -p P/Q)’ + creates the parent ‘P’ it sets the parent’s file permission bits to + ‘u=rwx,go=rx’. (The umask must include ‘u=wx’ for this method to + work.) To set a parent’s special mode bits as well, you can invoke + ‘chmod’ after ‘mkdir’. *Note Directory Setuid and Setgid::, for + how the set-user-ID and set-group-ID bits of newly-created parent + directories are inherited. + +‘-v’ +‘--verbose’ + Print a message for each created directory. This is most useful + with ‘--parents’. + +‘-Z’ +‘--context[=CONTEXT]’ + Without a specified CONTEXT, adjust the SELinux security context + according to the system default type for destination files, + similarly to the ‘restorecon’ command. The long form of this + option with a specific context specified, will set the context for + newly created files only. With a specified context, if both + SELinux and SMACK are disabled, a warning is issued. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: mkfifo invocation, Next: mknod invocation, Prev: mkdir invocation, Up: Special file types + +12.4 ‘mkfifo’: Make FIFOs (named pipes) +======================================= + +‘mkfifo’ creates FIFOs (also called “named pipes”) with the specified +names. Synopsis: + + mkfifo [OPTION] NAME... + + A “FIFO” is a special file type that permits independent processes to +communicate. One process opens the FIFO file for writing, and another +for reading, after which data can flow as with the usual anonymous pipe +in shells or elsewhere. + + The program accepts the following options. Also see *note Common +options::. + +‘-m MODE’ +‘--mode=MODE’ + Set the mode of created FIFOs to MODE, which is symbolic as in + ‘chmod’ and uses ‘a=rw’ (read and write allowed for everyone) for + the point of departure. MODE should specify only file permission + bits. *Note File permissions::. + +‘-Z’ +‘--context[=CONTEXT]’ + Without a specified CONTEXT, adjust the SELinux security context + according to the system default type for destination files, + similarly to the ‘restorecon’ command. The long form of this + option with a specific context specified, will set the context for + newly created files only. With a specified context, if both + SELinux and SMACK are disabled, a warning is issued. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: mknod invocation, Next: readlink invocation, Prev: mkfifo invocation, Up: Special file types + +12.5 ‘mknod’: Make block or character special files +=================================================== + +‘mknod’ creates a FIFO, character special file, or block special file +with the specified name. Synopsis: + + mknod [OPTION]... NAME TYPE [MAJOR MINOR] + + Unlike the phrase “special file type” above, the term “special file” +has a technical meaning on Unix: something that can generate or receive +data. Usually this corresponds to a physical piece of hardware, e.g., a +printer or a flash drive. (These files are typically created at +system-configuration time.) The ‘mknod’ command is what creates files +of this type. Such devices can be read either a character at a time or +a “block” (many characters) at a time, hence we say there are “block +special” files and “character special” files. + + Due to shell aliases and built-in ‘mknod’ functions, using an +unadorned ‘mknod’ interactively or in a script may get you different +functionality than that described here. Invoke it via ‘env’ (i.e., ‘env +mknod ...’) to avoid interference from the shell. + + The arguments after NAME specify the type of file to make: + +‘p’ + for a FIFO + +‘b’ + for a block special file + +‘c’ + for a character special file + + When making a block or character special file, the major and minor +device numbers must be given after the file type. If a major or minor +device number begins with ‘0x’ or ‘0X’, it is interpreted as +hexadecimal; otherwise, if it begins with ‘0’, as octal; otherwise, as +decimal. + + The program accepts the following options. Also see *note Common +options::. + +‘-m MODE’ +‘--mode=MODE’ + Set the mode of created files to MODE, which is symbolic as in + ‘chmod’ and uses ‘a=rw’ as the point of departure. MODE should + specify only file permission bits. *Note File permissions::. + +‘-Z’ +‘--context[=CONTEXT]’ + Without a specified CONTEXT, adjust the SELinux security context + according to the system default type for destination files, + similarly to the ‘restorecon’ command. The long form of this + option with a specific context specified, will set the context for + newly created files only. With a specified context, if both + SELinux and SMACK are disabled, a warning is issued. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: readlink invocation, Next: rmdir invocation, Prev: mknod invocation, Up: Special file types + +12.6 ‘readlink’: Print value of a symlink or canonical file name +================================================================ + +‘readlink’ may work in one of two supported modes: + +‘Readlink mode’ + + ‘readlink’ outputs the value of the given symbolic links. If + ‘readlink’ is invoked with an argument other than the name of a + symbolic link, it produces no output and exits with a nonzero exit + code. + +‘Canonicalize mode’ + + ‘readlink’ outputs the absolute name of the given files which + contain no ‘.’, ‘..’ components nor any repeated separators (‘/’) + or symbolic links. Note the ‘realpath’ command is the preferred + command to use for canonicalization. *Note realpath invocation::. + + readlink [OPTION]... FILE... + + By default, ‘readlink’ operates in readlink mode. + + The program accepts the following options. Also see *note Common +options::. + +‘-f’ +‘--canonicalize’ + Activate canonicalize mode. If any component of the file name + except the last one is missing or unavailable, ‘readlink’ produces + no output and exits with a nonzero exit code. A trailing slash is + ignored. + +‘-e’ +‘--canonicalize-existing’ + Activate canonicalize mode. If any component is missing or + unavailable, ‘readlink’ produces no output and exits with a nonzero + exit code. A trailing slash requires that the name resolve to a + directory. + +‘-m’ +‘--canonicalize-missing’ + Activate canonicalize mode. If any component is missing or + unavailable, ‘readlink’ treats it as a directory. + +‘-n’ +‘--no-newline’ + Do not print the output delimiter, when a single FILE is specified. + Print a warning if specified along with multiple FILEs. + +‘-s’ +‘-q’ +‘--silent’ +‘--quiet’ + Suppress most error messages. On by default. + +‘-v’ +‘--verbose’ + Report error messages. + +‘-z’ +‘--zero’ + Output a zero byte (ASCII NUL) at the end of each line, rather than + a newline. This option enables other programs to parse the output + even when that output would contain data with embedded newlines. + + The ‘readlink’ utility first appeared in OpenBSD 2.1. + + The ‘realpath’ command without options, operates like ‘readlink’ in +canonicalize mode. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: rmdir invocation, Next: unlink invocation, Prev: readlink invocation, Up: Special file types + +12.7 ‘rmdir’: Remove empty directories +====================================== + +‘rmdir’ removes empty directories. Synopsis: + + rmdir [OPTION]... DIRECTORY... + + If any DIRECTORY argument does not refer to an existing empty +directory, it is an error. + + The program accepts the following options. Also see *note Common +options::. + +‘--ignore-fail-on-non-empty’ + Ignore each failure to remove a directory that is non-empty. + +‘-p’ +‘--parents’ + Remove DIRECTORY, then try to remove each component of DIRECTORY. + So, for example, ‘rmdir -p a/b/c’ is similar to ‘rmdir a/b/c a/b + a’. As such, it fails if any of those directories turns out not to + be empty. Use the ‘--ignore-fail-on-non-empty’ option to make it + so such a failure does not evoke a diagnostic and does not cause + ‘rmdir’ to exit unsuccessfully. + +‘-v’ +‘--verbose’ + Give a diagnostic for each successful removal. DIRECTORY is + removed. + + *Note rm invocation::, for how to remove non-empty directories +recursively. + + To remove all empty directories under DIRNAME, including directories +that become empty because other directories are removed, you can use +either of the following commands: + + # This uses GNU extensions. + find DIRNAME -type d -empty -delete + + # This runs on any POSIX platform. + find DIRNAME -depth -type d -exec rmdir {} + + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: unlink invocation, Prev: rmdir invocation, Up: Special file types + +12.8 ‘unlink’: Remove files via the unlink syscall +================================================== + +‘unlink’ deletes a single specified file name. It is a minimalist +interface to the system-provided ‘unlink’ function. *Note +(libc)Deleting Files::. Synopsis: It avoids the bells and whistles of +the more commonly-used ‘rm’ command (*note rm invocation::). + + unlink FILENAME + + On some systems ‘unlink’ can be used to delete the name of a +directory. On others, it can be used that way only by a privileged +user. In the GNU system ‘unlink’ can never delete the name of a +directory. + + The ‘unlink’ command honors the ‘--help’ and ‘--version’ options. To +remove a file whose name begins with ‘-’, prefix the name with ‘./’, +e.g., ‘unlink ./--help’. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: Changing file attributes, Next: File space usage, Prev: Special file types, Up: Top + +13 Changing file attributes +*************************** + +A file is not merely its contents, a name, and a file type (*note +Special file types::). A file also has an owner (a user ID), a group (a +group ID), permissions (what the owner can do with the file, what people +in the group can do, and what everyone else can do), various timestamps, +and other information. Collectively, we call these a file’s +“attributes”. + + These commands change file attributes. + +* Menu: + +* chown invocation:: Change file owners and groups. +* chgrp invocation:: Change file groups. +* chmod invocation:: Change access permissions. +* touch invocation:: Change file timestamps. + + +File: coreutils.info, Node: chown invocation, Next: chgrp invocation, Up: Changing file attributes + +13.1 ‘chown’: Change file owner and group +========================================= + +‘chown’ changes the user and/or group ownership of each given FILE to +NEW-OWNER or to the user and group of an existing reference file. +Synopsis: + + chown [OPTION]... {NEW-OWNER | --reference=REF_FILE} FILE... + + If used, NEW-OWNER specifies the new owner and/or group as follows +(with no embedded white space): + + [OWNER] [ : [GROUP] ] + + Specifically: + +OWNER + If only an OWNER (a user name or numeric user ID) is given, that + user is made the owner of each given file, and the files’ group is + not changed. + +OWNER‘:’GROUP + If the OWNER is followed by a colon and a GROUP (a group name or + numeric group ID), with no spaces between them, the group ownership + of the files is changed as well (to GROUP). + +OWNER‘:’ + If a colon but no group name follows OWNER, that user is made the + owner of the files and the group of the files is changed to OWNER’s + login group. + +‘:’GROUP + If the colon and following GROUP are given, but the owner is + omitted, only the group of the files is changed; in this case, + ‘chown’ performs the same function as ‘chgrp’. + +‘:’ + If only a colon is given, or if NEW-OWNER is empty, neither the + owner nor the group is changed. + + If OWNER or GROUP is intended to represent a numeric user or group +ID, then you may specify it with a leading ‘+’. *Note Disambiguating +names and IDs::. + + Some older scripts may still use ‘.’ in place of the ‘:’ separator. +POSIX 1003.1-2001 (*note Standards conformance::) does not require +support for that, but for backward compatibility GNU ‘chown’ supports +‘.’ so long as no ambiguity results, although it issues a warning and +support may be removed in future versions. New scripts should avoid the +use of ‘.’ because it is not portable, and because it has undesirable +results if the entire OWNER‘.’GROUP happens to identify a user whose +name contains ‘.’. + + It is system dependent whether a user can change the group to an +arbitrary one, or the more portable behavior of being restricted to +setting a group of which the user is a member. + + The ‘chown’ command sometimes clears the set-user-ID or set-group-ID +permission bits. This behavior depends on the policy and functionality +of the underlying ‘chown’ system call, which may make system-dependent +file mode modifications outside the control of the ‘chown’ command. For +example, the ‘chown’ command might not affect those bits when invoked by +a user with appropriate privileges, or when the bits signify some +function other than executable permission (e.g., mandatory locking). +When in doubt, check the underlying system behavior. + + The program accepts the following options. Also see *note Common +options::. + +‘-c’ +‘--changes’ + Verbosely describe the action for each FILE whose ownership + actually changes. + +‘-f’ +‘--silent’ +‘--quiet’ + Do not print error messages about files whose ownership cannot be + changed. + +‘--from=OLD-OWNER’ + Change a FILE’s ownership only if it has current attributes + specified by OLD-OWNER. OLD-OWNER has the same form as NEW-OWNER + described above. This option is useful primarily from a security + standpoint in that it narrows considerably the window of potential + abuse. For example, to reflect a user ID numbering change for one + user’s files without an option like this, ‘root’ might run + + find / -owner OLDUSER -print0 | xargs -0 chown -h NEWUSER + + But that is dangerous because the interval between when the ‘find’ + tests the existing file’s owner and when the ‘chown’ is actually + run may be quite large. One way to narrow the gap would be to + invoke chown for each file as it is found: + + find / -owner OLDUSER -exec chown -h NEWUSER {} \; + + But that is very slow if there are many affected files. With this + option, it is safer (the gap is narrower still) though still not + perfect: + + chown -h -R --from=OLDUSER NEWUSER / + +‘--dereference’ + Do not act on symbolic links themselves but rather on what they + point to. This is the default when not operating recursively. + + Combining this dereferencing option with the ‘--recursive’ option + may create a security risk: During the traversal of the directory + tree, an attacker may be able to introduce a symlink to an + arbitrary target; when the tool reaches that, the operation will be + performed on the target of that symlink, possibly allowing the + attacker to escalate privileges. + +‘-h’ +‘--no-dereference’ + Act on symbolic links themselves instead of what they point to. + This mode relies on the ‘lchown’ system call. On systems that do + not provide the ‘lchown’ system call, ‘chown’ fails when a file + specified on the command line is a symbolic link. By default, no + diagnostic is issued for symbolic links encountered during a + recursive traversal, but see ‘--verbose’. + +‘--preserve-root’ + Fail upon any attempt to recursively change the root directory, + ‘/’. Without ‘--recursive’, this option has no effect. *Note + Treating / specially::. + +‘--no-preserve-root’ + Cancel the effect of any preceding ‘--preserve-root’ option. *Note + Treating / specially::. + +‘--reference=REF_FILE’ + Change the user and group of each FILE to be the same as those of + REF_FILE. If REF_FILE is a symbolic link, do not use the user and + group of the symbolic link, but rather those of the file it refers + to. + +‘-v’ +‘--verbose’ + Output a diagnostic for every file processed. If a symbolic link + is encountered during a recursive traversal on a system without the + ‘lchown’ system call, and ‘--no-dereference’ is in effect, then + issue a diagnostic saying neither the symbolic link nor its + referent is being changed. + +‘-R’ +‘--recursive’ + Recursively change ownership of directories and their contents. + +‘-H’ + If ‘--recursive’ (‘-R’) is specified and a command line argument is + a symbolic link to a directory, traverse it. *Note Traversing + symlinks::. + +‘-L’ + In a recursive traversal, traverse every symbolic link to a + directory that is encountered. + + Combining this dereferencing option with the ‘--recursive’ option + may create a security risk: During the traversal of the directory + tree, an attacker may be able to introduce a symlink to an + arbitrary target; when the tool reaches that, the operation will be + performed on the target of that symlink, possibly allowing the + attacker to escalate privileges. + + *Note Traversing symlinks::. + +‘-P’ + Do not traverse any symbolic links. This is the default if none of + ‘-H’, ‘-L’, or ‘-P’ is specified. *Note Traversing symlinks::. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + Examples: + + # Change the owner of /u to "root". + chown root /u + + # Likewise, but also change its group to "staff". + chown root:staff /u + + # Change the owner of /u and subfiles to "root". + chown -hR root /u + + +File: coreutils.info, Node: chgrp invocation, Next: chmod invocation, Prev: chown invocation, Up: Changing file attributes + +13.2 ‘chgrp’: Change group ownership +==================================== + +‘chgrp’ changes the group ownership of each given FILE to GROUP (which +can be either a group name or a numeric group ID) or to the group of an +existing reference file. *Note chown invocation::. Synopsis: + + chgrp [OPTION]... {GROUP | --reference=REF_FILE} FILE... + + If GROUP is intended to represent a numeric group ID, then you may +specify it with a leading ‘+’. *Note Disambiguating names and IDs::. + + It is system dependent whether a user can change the group to an +arbitrary one, or the more portable behavior of being restricted to +setting a group of which the user is a member. + + The program accepts the following options. Also see *note Common +options::. + +‘-c’ +‘--changes’ + Verbosely describe the action for each FILE whose group actually + changes. + +‘-f’ +‘--silent’ +‘--quiet’ + Do not print error messages about files whose group cannot be + changed. + +‘--dereference’ + Do not act on symbolic links themselves but rather on what they + point to. This is the default when not operating recursively. + + Combining this dereferencing option with the ‘--recursive’ option + may create a security risk: During the traversal of the directory + tree, an attacker may be able to introduce a symlink to an + arbitrary target; when the tool reaches that, the operation will be + performed on the target of that symlink, possibly allowing the + attacker to escalate privileges. + +‘-h’ +‘--no-dereference’ + Act on symbolic links themselves instead of what they point to. + This mode relies on the ‘lchown’ system call. On systems that do + not provide the ‘lchown’ system call, ‘chgrp’ fails when a file + specified on the command line is a symbolic link. By default, no + diagnostic is issued for symbolic links encountered during a + recursive traversal, but see ‘--verbose’. + +‘--preserve-root’ + Fail upon any attempt to recursively change the root directory, + ‘/’. Without ‘--recursive’, this option has no effect. *Note + Treating / specially::. + +‘--no-preserve-root’ + Cancel the effect of any preceding ‘--preserve-root’ option. *Note + Treating / specially::. + +‘--reference=REF_FILE’ + Change the group of each FILE to be the same as that of REF_FILE. + If REF_FILE is a symbolic link, do not use the group of the + symbolic link, but rather that of the file it refers to. + +‘-v’ +‘--verbose’ + Output a diagnostic for every file processed. If a symbolic link + is encountered during a recursive traversal on a system without the + ‘lchown’ system call, and ‘--no-dereference’ is in effect, then + issue a diagnostic saying neither the symbolic link nor its + referent is being changed. + +‘-R’ +‘--recursive’ + Recursively change the group ownership of directories and their + contents. + +‘-H’ + If ‘--recursive’ (‘-R’) is specified and a command line argument is + a symbolic link to a directory, traverse it. *Note Traversing + symlinks::. + +‘-L’ + In a recursive traversal, traverse every symbolic link to a + directory that is encountered. + + Combining this dereferencing option with the ‘--recursive’ option + may create a security risk: During the traversal of the directory + tree, an attacker may be able to introduce a symlink to an + arbitrary target; when the tool reaches that, the operation will be + performed on the target of that symlink, possibly allowing the + attacker to escalate privileges. + + *Note Traversing symlinks::. + +‘-P’ + Do not traverse any symbolic links. This is the default if none of + ‘-H’, ‘-L’, or ‘-P’ is specified. *Note Traversing symlinks::. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + Examples: + + # Change the group of /u to "staff". + chgrp staff /u + + # Change the group of /u and subfiles to "staff". + chgrp -hR staff /u + + +File: coreutils.info, Node: chmod invocation, Next: touch invocation, Prev: chgrp invocation, Up: Changing file attributes + +13.3 ‘chmod’: Change access permissions +======================================= + +‘chmod’ changes the access permissions of the named files. Synopsis: + + chmod [OPTION]... {MODE | --reference=REF_FILE} FILE... + + ‘chmod’ never changes the permissions of symbolic links, since the +‘chmod’ system call cannot change their permissions. This is not a +problem since the permissions of symbolic links are never used. +However, for each symbolic link listed on the command line, ‘chmod’ +changes the permissions of the pointed-to file. In contrast, ‘chmod’ +ignores symbolic links encountered during recursive directory +traversals. + + Only a process whose effective user ID matches the user ID of the +file, or a process with appropriate privileges, is permitted to change +the file mode bits of a file. + + A successful use of ‘chmod’ clears the set-group-ID bit of a regular +file if the file’s group ID does not match the user’s effective group ID +or one of the user’s supplementary group IDs, unless the user has +appropriate privileges. Additional restrictions may cause the +set-user-ID and set-group-ID bits of MODE or REF_FILE to be ignored. +This behavior depends on the policy and functionality of the underlying +‘chmod’ system call. When in doubt, check the underlying system +behavior. + + If used, MODE specifies the new file mode bits. For details, see the +section on *note File permissions::. If you really want MODE to have a +leading ‘-’, you should use ‘--’ first, e.g., ‘chmod -- -w file’. +Typically, though, ‘chmod a-w file’ is preferable, and ‘chmod -w file’ +(without the ‘--’) complains if it behaves differently from what ‘chmod +a-w file’ would do. + + The program accepts the following options. Also see *note Common +options::. + +‘-c’ +‘--changes’ + Verbosely describe the action for each FILE whose permissions + actually change. + +‘-f’ +‘--silent’ +‘--quiet’ + Do not print error messages about files whose permissions cannot be + changed. + +‘--preserve-root’ + Fail upon any attempt to recursively change the root directory, + ‘/’. Without ‘--recursive’, this option has no effect. *Note + Treating / specially::. + +‘--no-preserve-root’ + Cancel the effect of any preceding ‘--preserve-root’ option. *Note + Treating / specially::. + +‘-v’ +‘--verbose’ + Verbosely describe the action or non-action taken for every FILE. + +‘--reference=REF_FILE’ + Change the mode of each FILE to be the same as that of REF_FILE. + *Note File permissions::. If REF_FILE is a symbolic link, do not + use the mode of the symbolic link, but rather that of the file it + refers to. + +‘-R’ +‘--recursive’ + Recursively change permissions of directories and their contents. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + Examples: + + # Change file permissions of FOO to be world readable + # and user writable, with no other permissions. + chmod 644 foo + chmod a=r,u+w foo + + # Add user and group execute permissions to FOO. + chmod +110 file + chmod ug+x file + + # Set file permissions of DIR and subsidiary files to + # be the umask default, assuming execute permissions for + # directories and for files already executable. + chmod -R a=,+rwX dir + + +File: coreutils.info, Node: touch invocation, Prev: chmod invocation, Up: Changing file attributes + +13.4 ‘touch’: Change file timestamps +==================================== + +‘touch’ changes the access and/or modification timestamps of the +specified files. Synopsis: + + touch [OPTION]... FILE... + + Any FILE argument that does not exist is created empty, unless option +‘--no-create’ (‘-c’) or ‘--no-dereference’ (‘-h’) was in effect. + + A FILE argument string of ‘-’ is handled specially and causes ‘touch’ +to change the times of the file associated with standard output. + + By default, ‘touch’ sets file timestamps to the current time. +Because ‘touch’ acts on its operands left to right, the resulting +timestamps of earlier and later operands may disagree. + + When setting file timestamps to the current time, ‘touch’ can change +the timestamps for files that the user does not own but has write +permission for. Otherwise, the user must own the files. Some older +systems have a further restriction: the user must own the files unless +both the access and modification timestamps are being set to the current +time. + + The ‘touch’ command cannot set a file’s status change timestamp to a +user-specified value, and cannot change the file’s birth time (if +supported) at all. Also, ‘touch’ has issues similar to those affecting +all programs that update file timestamps. For example, ‘touch’ may set +a file’s timestamp to a value that differs slightly from the requested +time. *Note File timestamps::. + + Timestamps assume the time zone rules specified by the ‘TZ’ +environment variable, or by the system default rules if ‘TZ’ is not set. +*Note Specifying the Time Zone with ‘TZ’: (libc)TZ Variable. You can +avoid ambiguities during daylight saving transitions by using UTC +timestamps. + + The program accepts the following options. Also see *note Common +options::. + +‘-a’ +‘--time=atime’ +‘--time=access’ +‘--time=use’ + Change the access timestamp only. *Note File timestamps::. + +‘-c’ +‘--no-create’ + Do not warn about or create files that do not exist. + +‘-d TIME’ +‘--date=TIME’ + Use TIME instead of the current time. It can contain month names, + time zones, ‘am’ and ‘pm’, ‘yesterday’, etc. For example, + ‘--date="2020-07-21 14:19:13.489392193 +0530"’ specifies the + instant of time that is 489,392,193 nanoseconds after July 21, 2020 + at 2:19:13 PM in a time zone that is 5 hours and 30 minutes east of + UTC. *Note Date input formats::. File systems that do not support + high-resolution timestamps silently ignore any excess precision + here. + +‘-f’ + Ignored; for compatibility with BSD versions of ‘touch’. + +‘-h’ +‘--no-dereference’ + Attempt to change the timestamps of a symbolic link, rather than + what the link refers to. When using this option, empty files are + not created, but option ‘-c’ must also be used to avoid warning + about files that do not exist. Not all systems support changing + the timestamps of symlinks, since underlying system support for + this action was not required until POSIX 2008. Also, on some + systems, the mere act of examining a symbolic link changes the + access timestamp, such that only changes to the modification + timestamp will persist long enough to be observable. When coupled + with option ‘-r’, a reference timestamp is taken from a symbolic + link rather than the file it refers to. + +‘-m’ +‘--time=mtime’ +‘--time=modify’ + Change the modification timestamp only. + +‘-r FILE’ +‘--reference=FILE’ + Use the times of the reference FILE instead of the current time. + If this option is combined with the ‘--date=TIME’ (‘-d TIME’) + option, the reference FILE’s time is the origin for any relative + TIMEs given, but is otherwise ignored. For example, ‘-r foo -d '-5 + seconds'’ specifies a timestamp equal to five seconds before the + corresponding timestamp for ‘foo’. If FILE is a symbolic link, the + reference timestamp is taken from the target of the symlink, unless + ‘-h’ was also in effect. + +‘-t [[CC]YY]MMDDHHMM[.SS]’ + Use the argument (optional four-digit or two-digit years, months, + days, hours, minutes, optional seconds) instead of the current + time. If the year is specified with only two digits, then CC is 20 + for years in the range 0 ... 68, and 19 for years in 69 ... 99. If + no digits of the year are specified, the argument is interpreted as + a date in the current year. On the atypical systems that support + leap seconds, SS may be ‘60’. + + On systems predating POSIX 1003.1-2001, ‘touch’ supports an obsolete +syntax, as follows. If no timestamp is given with any of the ‘-d’, +‘-r’, or ‘-t’ options, and if there are two or more FILEs and the first +FILE is of the form ‘MMDDHHMM[YY]’ and this would be a valid argument to +the ‘-t’ option (if the YY, if any, were moved to the front), and if the +represented year is in the range 1969–1999, that argument is interpreted +as the time for the other files instead of as a file name. Although +this obsolete behavior can be controlled with the ‘_POSIX2_VERSION’ +environment variable (*note Standards conformance::), portable scripts +should avoid commands whose behavior depends on this variable. For +example, use ‘touch ./12312359 main.c’ or ‘touch -t 12312359 main.c’ +rather than the ambiguous ‘touch 12312359 main.c’. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: File space usage, Next: Printing text, Prev: Changing file attributes, Up: Top + +14 File space usage +******************* + +No file system can hold an infinite amount of data. These commands +report how much storage is in use or available, report other file and +file status information, and write buffers to file systems. + +* Menu: + +* df invocation:: Report file system space usage. +* du invocation:: Estimate file space usage. +* stat invocation:: Report file or file system status. +* sync invocation:: Synchronize cached writes to persistent storage. +* truncate invocation:: Shrink or extend the size of a file. + + +File: coreutils.info, Node: df invocation, Next: du invocation, Up: File space usage + +14.1 ‘df’: Report file system space usage +========================================= + +‘df’ reports the amount of space used and available on file systems. +Synopsis: + + df [OPTION]... [FILE]... + + With no arguments, ‘df’ reports the space used and available on all +currently mounted file systems (of all types). Otherwise, ‘df’ reports +on the file system containing each argument FILE. + + Normally the space is printed in units of 1024 bytes, but this can be +overridden (*note Block size::). Non-integer quantities are rounded up +to the next higher unit. + + For bind mounts and without arguments, ‘df’ only outputs the +statistics for that device with the shortest mount point name in the +list of file systems (MTAB), i.e., it hides duplicate entries, unless +the ‘-a’ option is specified. + + With the same logic, ‘df’ elides a mount entry of a dummy pseudo +device if there is another mount entry of a real block device for that +mount point with the same device number, e.g. the early-boot pseudo +file system ‘rootfs’ is not shown per default when already the real root +device has been mounted. + + If an argument FILE resolves to a special file containing a mounted +file system, ‘df’ shows the space available on that file system rather +than on the file system containing the device node. GNU ‘df’ does not +attempt to determine the usage on unmounted file systems, because on +most kinds of systems doing so requires extremely non-portable intimate +knowledge of file system structures. + + The program accepts the following options. Also see *note Common +options::. + +‘-a’ +‘--all’ + Include in the listing dummy, duplicate, or inaccessible file + systems, which are omitted by default. Dummy file systems are + typically special purpose pseudo file systems such as ‘/proc’, with + no associated storage. Duplicate file systems are local or remote + file systems that are mounted at separate locations in the local + file hierarchy, or bind mounted locations. Inaccessible file + systems are those which are mounted but subsequently over-mounted + by another file system at that point, or otherwise inaccessible due + to permissions of the mount point etc. + +‘-B SIZE’ +‘--block-size=SIZE’ + Scale sizes by SIZE before printing them (*note Block size::). For + example, ‘-BG’ prints sizes in units of 1,073,741,824 bytes. + +‘-h’ +‘--human-readable’ + Append a size letter to each size, such as ‘M’ for mebibytes. + Powers of 1024 are used, not 1000; ‘M’ stands for 1,048,576 bytes. + This option is equivalent to ‘--block-size=human-readable’. Use + the ‘--si’ option if you prefer powers of 1000. + +‘-H’ + Equivalent to ‘--si’. + +‘-i’ +‘--inodes’ + List inode usage information instead of block usage. An inode + (short for index node) contains information about a file such as + its owner, permissions, timestamps, and location on the file + system. + +‘-k’ + Print sizes in 1024-byte blocks, overriding the default block size + (*note Block size::). This option is equivalent to + ‘--block-size=1K’. + +‘-l’ +‘--local’ + Limit the listing to local file systems. By default, remote file + systems are also listed. + +‘--no-sync’ + Do not invoke the ‘sync’ system call before getting any usage data. + This may make ‘df’ run significantly faster on systems with many + file systems, but on some systems (notably Solaris) the results may + be slightly out of date. This is the default. + +‘--output’ +‘--output[=FIELD_LIST]’ + Use the output format defined by FIELD_LIST, or print all fields if + FIELD_LIST is omitted. In the latter case, the order of the + columns conforms to the order of the field descriptions below. + + The use of the ‘--output’ together with each of the options ‘-i’, + ‘-P’, and ‘-T’ is mutually exclusive. + + FIELD_LIST is a comma-separated list of columns to be included in + ‘df’’s output and therefore effectively controls the order of + output columns. Each field can thus be used at the place of + choice, but yet must only be used once. + + Valid field names in the FIELD_LIST are: + ‘source’ + The source of the mount point, usually a device. + ‘fstype’ + File system type. + + ‘itotal’ + Total number of inodes. + ‘iused’ + Number of used inodes. + ‘iavail’ + Number of available inodes. + ‘ipcent’ + Percentage of IUSED divided by ITOTAL. + + ‘size’ + Total number of blocks. + ‘used’ + Number of used blocks. + ‘avail’ + Number of available blocks. + ‘pcent’ + Percentage of USED divided by SIZE. + + ‘file’ + The file name if specified on the command line. + ‘target’ + The mount point. + + The fields for block and inodes statistics are affected by the + scaling options like ‘-h’ as usual. + + The definition of the FIELD_LIST can even be split among several + ‘--output’ uses. + + #!/bin/sh + # Print the TARGET (i.e., the mount point) along with their percentage + # statistic regarding the blocks and the inodes. + df --out=target --output=pcent,ipcent + + # Print all available fields. + df --o + +‘-P’ +‘--portability’ + Use the POSIX output format. This is like the default format + except for the following: + + 1. The information about each file system is always printed on + exactly one line; a mount device is never put on a line by + itself. This means that if the mount device name is more than + 20 characters long (e.g., for some network mounts), the + columns are misaligned. + + 2. The labels in the header output line are changed to conform to + POSIX. + + 3. The default block size and output format are unaffected by the + ‘DF_BLOCK_SIZE’, ‘BLOCK_SIZE’ and ‘BLOCKSIZE’ environment + variables. However, the default block size is still affected + by ‘POSIXLY_CORRECT’: it is 512 if ‘POSIXLY_CORRECT’ is set, + 1024 otherwise. *Note Block size::. + +‘--si’ + Append an SI-style abbreviation to each size, such as ‘M’ for + megabytes. Powers of 1000 are used, not 1024; ‘M’ stands for + 1,000,000 bytes. This option is equivalent to ‘--block-size=si’. + Use the ‘-h’ or ‘--human-readable’ option if you prefer powers of + 1024. + +‘--sync’ + Invoke the ‘sync’ system call before getting any usage data. On + some systems (notably Solaris), doing this yields more up to date + results, but in general this option makes ‘df’ much slower, + especially when there are many or very busy file systems. + +‘--total’ + Print a grand total of all arguments after all arguments have been + processed. This can be used to find out the total size, usage and + available space of all listed devices. If no arguments are + specified df will try harder to elide file systems insignificant to + the total available space, by suppressing duplicate remote file + systems. + + For the grand total line, ‘df’ prints ‘"total"’ into the SOURCE + column, and ‘"-"’ into the TARGET column. If there is no SOURCE + column (see ‘--output’), then ‘df’ prints ‘"total"’ into the TARGET + column, if present. + +‘-t FSTYPE’ +‘--type=FSTYPE’ + Limit the listing to file systems of type FSTYPE. Multiple file + system types can be specified by giving multiple ‘-t’ options. By + default, nothing is omitted. + +‘-T’ +‘--print-type’ + Print each file system’s type. The types printed here are the same + ones you can include or exclude with ‘-t’ and ‘-x’. The particular + types printed are whatever is supported by the system. Here are + some of the common names (this list is certainly not exhaustive): + + ‘nfs’ + An NFS file system, i.e., one mounted over a network from + another machine. This is the one type name which seems to be + used uniformly by all systems. + + ‘ext2, ext3, ext4, xfs, btrfs...’ + A file system on a locally-mounted device. (The system might + even support more than one type here; GNU/Linux does.) + + ‘iso9660, cdfs’ + A file system on a CD or DVD drive. HP-UX uses ‘cdfs’, most + other systems use ‘iso9660’. + + ‘ntfs,fat’ + File systems used by MS-Windows / MS-DOS. + +‘-x FSTYPE’ +‘--exclude-type=FSTYPE’ + Limit the listing to file systems not of type FSTYPE. Multiple + file system types can be eliminated by giving multiple ‘-x’ + options. By default, no file system types are omitted. + +‘-v’ + Ignored; for compatibility with System V versions of ‘df’. + + ‘df’ is installed only on systems that have usable mount tables, so +portable scripts should not rely on its existence. + + An exit status of zero indicates success, and a nonzero value +indicates failure. Failure includes the case where no output is +generated, so you can inspect the exit status of a command like ‘df -t +ext3 -t reiserfs DIR’ to test whether DIR is on a file system of type +‘ext3’ or ‘reiserfs’. + + Since the list of file systems (MTAB) is needed to determine the file +system type, failure includes the cases when that list cannot be read +and one or more of the options ‘-a’, ‘-l’, ‘-t’ or ‘-x’ is used together +with a file name argument. + + +File: coreutils.info, Node: du invocation, Next: stat invocation, Prev: df invocation, Up: File space usage + +14.2 ‘du’: Estimate file space usage +==================================== + +‘du’ reports the space needed to represent a set of files. Synopsis: + + du [OPTION]... [FILE]... + + With no arguments, ‘du’ reports the space needed to represent the +files at or under the current directory. Normally the space is printed +in units of 1024 bytes, but this can be overridden (*note Block size::). +Non-integer quantities are rounded up to the next higher unit. + + If two or more hard links point to the same file, only one of the +hard links is counted. The FILE argument order affects which links are +counted, and changing the argument order may change the numbers and +entries that ‘du’ outputs. + + The program accepts the following options. Also see *note Common +options::. + +‘-0’ +‘--null’ + Output a zero byte (ASCII NUL) at the end of each line, rather than + a newline. This option enables other programs to parse the output + even when that output would contain data with embedded newlines. + +‘-a’ +‘--all’ + Show counts for all files, not just directories. + +‘--apparent-size’ + Print apparent sizes, rather than file system usage. The apparent + size of a file is the number of bytes reported by ‘wc -c’ on + regular files, or more generally, ‘ls -l --block-size=1’ or ‘stat + --format=%s’. For example, a file containing the word ‘zoo’ with + no newline would, of course, have an apparent size of 3. Such a + small file may require anywhere from 0 to 16 KiB or more of file + system space, depending on the type and configuration of the file + system on which the file resides. However, a sparse file created + with this command: + + dd bs=1 seek=2GiB if=/dev/null of=big + + has an apparent size of 2 GiB, yet on most modern file systems, it + actually uses almost no space. + + Apparent sizes are meaningful only for regular files and symbolic + links. Other file types do not contribute to apparent size. + +‘-B SIZE’ +‘--block-size=SIZE’ + Scale sizes by SIZE before printing them (*note Block size::). For + example, ‘-BG’ prints sizes in units of 1,073,741,824 bytes. + +‘-b’ +‘--bytes’ + Equivalent to ‘--apparent-size --block-size=1’. + +‘-c’ +‘--total’ + Print a grand total of all arguments after all arguments have been + processed. This can be used to find out the total file system + usage of a given set of files or directories. + +‘-D’ +‘--dereference-args’ + Dereference symbolic links that are command line arguments. Does + not affect other symbolic links. This is helpful for finding out + the file system usage of directories, such as ‘/usr/tmp’, which are + often symbolic links. + +‘-d DEPTH’ +‘--max-depth=DEPTH’ + Show the total for each directory (and file if ‘--all’) that is at + most MAX_DEPTH levels down from the root of the hierarchy. The + root is at level 0, so ‘du --max-depth=0’ is equivalent to ‘du -s’. + +‘--files0-from=FILE’ + Disallow processing files named on the command line, and instead + process those named in file FILE; each name being terminated by a + zero byte (ASCII NUL). This is useful when the list of file names + is so long that it may exceed a command line length limitation. In + such cases, running ‘du’ via ‘xargs’ is undesirable because it + splits the list into pieces and makes ‘du’ print with the ‘--total’ + (‘-c’) option for each sublist rather than for the entire list. + One way to produce a list of ASCII NUL terminated file names is + with GNU ‘find’, using its ‘-print0’ predicate. If FILE is ‘-’ + then the ASCII NUL terminated file names are read from standard + input. + +‘-H’ + Equivalent to ‘--dereference-args’ (‘-D’). + +‘-h’ +‘--human-readable’ + Append a size letter to each size, such as ‘M’ for mebibytes. + Powers of 1024 are used, not 1000; ‘M’ stands for 1,048,576 bytes. + This option is equivalent to ‘--block-size=human-readable’. Use + the ‘--si’ option if you prefer powers of 1000. + +‘--inodes’ + List inode usage information instead of block usage. This option + is useful for finding directories which contain many files, and + therefore eat up most of the inodes space of a file system (see + ‘df’, option ‘--inodes’). It can well be combined with the options + ‘-a’, ‘-c’, ‘-h’, ‘-l’, ‘-s’, ‘-S’, ‘-t’ and ‘-x’; however, passing + other options regarding the block size, for example ‘-b’, ‘-m’ and + ‘--apparent-size’, is ignored. + +‘-k’ + Print sizes in 1024-byte blocks, overriding the default block size + (*note Block size::). This option is equivalent to + ‘--block-size=1K’. + +‘-L’ +‘--dereference’ + Dereference symbolic links (show the file system space used by the + file or directory that the link points to instead of the space used + by the link). + +‘-l’ +‘--count-links’ + Count the size of all files, even if they have appeared already (as + a hard link). + +‘-m’ + Print sizes in 1,048,576-byte blocks, overriding the default block + size (*note Block size::). This option is equivalent to + ‘--block-size=1M’. + +‘-P’ +‘--no-dereference’ + For each symbolic link encountered by ‘du’, consider the file + system space used by the symbolic link itself. + +‘-S’ +‘--separate-dirs’ + Normally, in the output of ‘du’ (when not using ‘--summarize’), the + size listed next to a directory name, D, represents the sum of + sizes of all entries beneath D as well as the size of D itself. + With ‘--separate-dirs’, the size reported for a directory name, D, + will exclude the size of any subdirectories. + +‘--si’ + Append an SI-style abbreviation to each size, such as ‘M’ for + megabytes. Powers of 1000 are used, not 1024; ‘M’ stands for + 1,000,000 bytes. This option is equivalent to ‘--block-size=si’. + Use the ‘-h’ or ‘--human-readable’ option if you prefer powers of + 1024. + +‘-s’ +‘--summarize’ + Display only a total for each argument. + +‘-t SIZE’ +‘--threshold=SIZE’ + Exclude entries based on a given SIZE. The SIZE refers to used + blocks in normal mode (*note Block size::), or inodes count in + conjunction with the ‘--inodes’ option. + + If SIZE is positive, then ‘du’ will only print entries with a size + greater than or equal to that. + + If SIZE is negative, then ‘du’ will only print entries with a size + smaller than or equal to that. + + Although GNU ‘find’ can be used to find files of a certain size, + ‘du’’s ‘--threshold’ option can be used to also filter directories + based on a given size. + + When combined with the ‘--apparent-size’ option, the ‘--threshold’ + option elides entries based on apparent size. When combined with + the ‘--inodes’ option, it elides entries based on inode counts. + + Here’s how you would use ‘--threshold’ to find directories with a + size greater than or equal to 200 megabytes: + + du --threshold=200MB + + Here’s how you would use ‘--threshold’ to find directories and + files – note the ‘-a’ – with an apparent size smaller than or equal + to 500 bytes: + + du -a -t -500 --apparent-size + + Here’s how you would use ‘--threshold’ to find directories on the + root file system with more than 20000 inodes used in the directory + tree below: + + du --inodes -x --threshold=20000 / + +‘--time’ + Show the most recent modification timestamp (mtime) of any file in + the directory, or any of its subdirectories. *Note File + timestamps::. + +‘--time=ctime’ +‘--time=status’ +‘--time=use’ + Show the most recent status change timestamp (ctime) of any file in + the directory, or any of its subdirectories. *Note File + timestamps::. + +‘--time=atime’ +‘--time=access’ + Show the most recent access timestamp (atime) of any file in the + directory, or any of its subdirectories. *Note File timestamps::. + +‘--time-style=STYLE’ + List timestamps in style STYLE. This option has an effect only if + the ‘--time’ option is also specified. The STYLE should be one of + the following: + + ‘+FORMAT’ + List timestamps using FORMAT, where FORMAT is interpreted like + the format argument of ‘date’ (*note date invocation::). For + example, ‘--time-style="+%Y-%m-%d %H:%M:%S"’ causes ‘du’ to + list timestamps like ‘2020-07-21 23:45:56’. As with ‘date’, + FORMAT’s interpretation is affected by the ‘LC_TIME’ locale + category. + + ‘full-iso’ + List timestamps in full using ISO 8601-like date, time, and + time zone components with nanosecond precision, e.g., + ‘2020-07-21 23:45:56.477817180 -0400’. This style is + equivalent to ‘+%Y-%m-%d %H:%M:%S.%N %z’. + + ‘long-iso’ + List ISO 8601 date and time components with minute precision, + e.g., ‘2020-07-21 23:45’. These timestamps are shorter than + ‘full-iso’ timestamps, and are usually good enough for + everyday work. This style is equivalent to ‘+%Y-%m-%d %H:%M’. + + ‘iso’ + List ISO 8601 dates for timestamps, e.g., ‘2020-07-21’. This + style is equivalent to ‘+%Y-%m-%d’. + + You can specify the default value of the ‘--time-style’ option with + the environment variable ‘TIME_STYLE’; if ‘TIME_STYLE’ is not set + the default style is ‘long-iso’. For compatibility with ‘ls’, if + ‘TIME_STYLE’ begins with ‘+’ and contains a newline, the newline + and any later characters are ignored; if ‘TIME_STYLE’ begins with + ‘posix-’ the ‘posix-’ is ignored; and if ‘TIME_STYLE’ is ‘locale’ + it is ignored. + +‘-X FILE’ +‘--exclude-from=FILE’ + Like ‘--exclude’, except take the patterns to exclude from FILE, + one per line. If FILE is ‘-’, take the patterns from standard + input. + +‘--exclude=PATTERN’ + When recursing, skip subdirectories or files matching PATTERN. For + example, ‘du --exclude='*.o'’ excludes files whose names end in + ‘.o’. + +‘-x’ +‘--one-file-system’ + Skip directories that are on different file systems from the one + that the argument being processed is on. + + Since ‘du’ relies on information reported by the operating system, +its output might not reflect the space consumed in the underlying +devices. For example; + + • Operating systems normally do not report device space consumed by + duplicate or backup blocks, error correction bits, and so forth. + This causes ‘du’ to underestimate the device space actually used. + + • In file systems that use copy-on-write, if two distinct files share + space the output of ‘du’ typically counts the space that would be + consumed if all files’ non-holes were rewritten, not the space + currently consumed. + + • In file systems that use compression, the operating system might + report the uncompressed space. (If it does report the compressed + space, that report might change after one merely overwrites + existing file data.) + + • Networked file systems historically have had difficulty + communicating accurate file system information from server to + client. + +For these reasons ‘du’ might better be thought of as an estimate of the +size of a ‘tar’ or other conventional backup for a set of files, rather +than as a measure of space consumed in the underlying devices. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: stat invocation, Next: sync invocation, Prev: du invocation, Up: File space usage + +14.3 ‘stat’: Report file or file system status +============================================== + +‘stat’ displays information about the specified file(s). Synopsis: + + stat [OPTION]... [FILE]... + + With no option, ‘stat’ reports all information about the given files. +But it also can be used to report the information of the file systems +the given files are located on. If the files are links, ‘stat’ can also +give information about the files the links point to. + + Due to shell aliases and built-in ‘stat’ functions, using an +unadorned ‘stat’ interactively or in a script may get you different +functionality than that described here. Invoke it via ‘env’ (i.e., ‘env +stat ...’) to avoid interference from the shell. + +‘-L’ +‘--dereference’ + Change how ‘stat’ treats symbolic links. With this option, ‘stat’ + acts on the file referenced by each symbolic link argument. + Without it, ‘stat’ acts on any symbolic link argument directly. + +‘-f’ +‘--file-system’ + Report information about the file systems where the given files are + located instead of information about the files themselves. This + option implies the ‘-L’ option. + +‘--cached=MODE’ + Control how attributes are read from the file system; if supported + by the system. This allows one to control the trade-off between + freshness and efficiency of attribute access, especially useful + with remote file systems. MODE can be: + + ‘always’ + Always read the already cached attributes if available. + + ‘never’ + Always synchronize with the latest file system attributes. + This also mounts automounted files. + + ‘default’ + Leave the caching behavior to the underlying file system. + +‘-c’ +‘--format=FORMAT’ + Use FORMAT rather than the default format. FORMAT is automatically + newline-terminated, so running a command like the following with + two or more FILE operands produces a line of output for each + operand: + $ stat --format=%d:%i / /usr + 2050:2 + 2057:2 + +‘--printf=FORMAT’ + Use FORMAT rather than the default format. Like ‘--format’, but + interpret backslash escapes, and do not output a mandatory trailing + newline. If you want a newline, include ‘\n’ in the FORMAT. + Here’s how you would use ‘--printf’ to print the device and inode + numbers of ‘/’ and ‘/usr’: + $ stat --printf='%d:%i\n' / /usr + 2050:2 + 2057:2 + +‘-t’ +‘--terse’ + Print the information in terse form, suitable for parsing by other + programs. + + The output of the following commands are identical and the + ‘--format’ also identifies the items printed (in fuller form) in + the default format. Note the format string would include another + ‘%C’ at the end with an active SELinux security context. + $ stat --format="%n %s %b %f %u %g %D %i %h %t %T %X %Y %Z %W %o" ... + $ stat --terse ... + + The same illustrating terse output in ‘--file-system’ mode: + $ stat -f --format="%n %i %l %t %s %S %b %f %a %c %d" ... + $ stat -f --terse ... + + The valid FORMAT directives for files with ‘--format’ and ‘--printf’ +are: + + • %a – Permission bits in octal (note ‘#’ and ‘0’ printf flags) + • %A – Permission bits in symbolic form (similar to ‘ls -ld’) + • %b – Number of blocks allocated (see ‘%B’) + • %B – The size in bytes of each block reported by ‘%b’ + • %C – The SELinux security context of a file, if available + • %d – Device number in decimal (st_dev) + • %D – Device number in hex (st_dev) + • %Hd – Major device number in decimal + • %Ld – Minor device number in decimal + • %f – Raw mode in hex + • %F – File type + • %g – Group ID of owner + • %G – Group name of owner + • %h – Number of hard links + • %i – Inode number + • %m – Mount point (See note below) + • %n – File name + • %N – Quoted file name with dereference if symbolic link (see below) + • %o – Optimal I/O transfer size hint + • %s – Total size, in bytes + • %r – Device type in decimal (st_rdev) + • %R – Device type in hex (st_rdev) + • %Hr – Major device type in decimal (see below) + • %Lr – Minor device type in decimal (see below) + • %t – Major device type in hex (see below) + • %T – Minor device type in hex (see below) + • %u – User ID of owner + • %U – User name of owner + • %w – Time of file birth, or ‘-’ if unknown + • %W – Time of file birth as seconds since Epoch, or ‘0’ + • %x – Time of last access + • %X – Time of last access as seconds since Epoch + • %y – Time of last data modification + • %Y – Time of last data modification as seconds since Epoch + • %z – Time of last status change + • %Z – Time of last status change as seconds since Epoch + + The ‘%a’ format prints the octal mode, and so it is useful to control +the zero padding of the output with the ‘#’ and ‘0’ printf flags. For +example to pad to at least 3 wide while making larger numbers +unambiguously octal, you can use ‘%#03a’. + + The ‘%N’ format can be set with the environment variable +‘QUOTING_STYLE’. If that environment variable is not set, the default +value is ‘shell-escape-always’. Valid quoting styles are: +‘literal’ + Output strings as-is; this is the same as the ‘--literal’ (‘-N’) + option. +‘shell’ + Quote strings for the shell if they contain shell metacharacters or + would cause ambiguous output. The quoting is suitable for + POSIX-compatible shells like ‘bash’, but it does not always work + for incompatible shells like ‘csh’. +‘shell-always’ + Quote strings for the shell, even if they would normally not + require quoting. +‘shell-escape’ + Like ‘shell’, but also quoting non-printable characters using the + POSIX proposed ‘$''’ syntax suitable for most shells. +‘shell-escape-always’ + Like ‘shell-escape’, but quote strings even if they would normally + not require quoting. +‘c’ + Quote strings as for C character string literals, including the + surrounding double-quote characters; this is the same as the + ‘--quote-name’ (‘-Q’) option. +‘escape’ + Quote strings as for C character string literals, except omit the + surrounding double-quote characters; this is the same as the + ‘--escape’ (‘-b’) option. +‘clocale’ + Quote strings as for C character string literals, except use + surrounding quotation marks appropriate for the locale. +‘locale’ + Quote strings as for C character string literals, except use + surrounding quotation marks appropriate for the locale, and quote + 'like this' instead of "like this" in the default C locale. This + looks nicer on many displays. + + The ‘r’, ‘R’, ‘%t’, and ‘%T’ formats operate on the st_rdev member of +the stat(2) structure, i.e., the represented device rather than the +containing device, and so are only defined for character and block +special files. On some systems or file types, st_rdev may be used to +represent other quantities. + + The ‘%W’, ‘%X’, ‘%Y’, and ‘%Z’ formats accept a precision preceded by +a period to specify the number of digits to print after the decimal +point. For example, ‘%.3X’ outputs the access timestamp to millisecond +precision. If a period is given but no precision, ‘stat’ uses 9 digits, +so ‘%.X’ is equivalent to ‘%.9X’. When discarding excess precision, +timestamps are truncated toward minus infinity. + + zero pad: + $ stat -c '[%015Y]' /usr + [000001288929712] + space align: + $ stat -c '[%15Y]' /usr + [ 1288929712] + $ stat -c '[%-15Y]' /usr + [1288929712 ] + precision: + $ stat -c '[%.3Y]' /usr + [1288929712.114] + $ stat -c '[%.Y]' /usr + [1288929712.114951834] + + The mount point printed by ‘%m’ is similar to that output by ‘df’, +except that: + • stat does not dereference symlinks by default (unless ‘-L’ is + specified) + • stat does not search for specified device nodes in the file system + list, instead operating on them directly + • stat outputs the alias for a bind mounted file, rather than the + initial mount point of its backing device. One can recursively + call stat until there is no change in output, to get the current + base mount point + + When listing file system information (‘--file-system’ (‘-f’)), you +must use a different set of FORMAT directives: + + • %a – Free blocks available to non-super-user + • %b – Total data blocks in file system + • %c – Total file nodes in file system + • %d – Free file nodes in file system + • %f – Free blocks in file system + • %i – File System ID in hex + • %l – Maximum length of file names + • %n – File name + • %s – Block size (for faster transfers) + • %S – Fundamental block size (for block counts) + • %t – Type in hex + • %T – Type in human readable form + + Timestamps are listed according to the time zone rules specified by +the ‘TZ’ environment variable, or by the system default rules if ‘TZ’ is +not set. *Note Specifying the Time Zone with ‘TZ’: (libc)TZ Variable. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: sync invocation, Next: truncate invocation, Prev: stat invocation, Up: File space usage + +14.4 ‘sync’: Synchronize cached writes to persistent storage +============================================================ + +‘sync’ synchronizes in memory files or file systems to persistent +storage. Synopsis: + + sync [OPTION] [FILE]... + + ‘sync’ writes any data buffered in memory out to the storage device. +This can include (but is not limited to) modified superblocks, modified +inodes, and delayed reads and writes. This must be implemented by the +kernel; The ‘sync’ program does nothing but exercise the ‘sync’, +‘syncfs’, ‘fsync’, and ‘fdatasync’ system calls. + + The kernel keeps data in memory to avoid doing (relatively slow) +device reads and writes. This improves performance, but if the computer +crashes, data may be lost or the file system corrupted as a result. The +‘sync’ command instructs the kernel to write data in memory to +persistent storage. + + If any argument is specified then only those files will be +synchronized using the fsync(2) syscall by default. + + If at least one file is specified, it is possible to change the +synchronization method with the following options. Also see *note +Common options::. + +‘-d’ +‘--data’ + Use fdatasync(2) to sync only the data for the file, and any + metadata required to maintain file system consistency. + +‘-f’ +‘--file-system’ + Synchronize all the I/O waiting for the file systems that contain + the file, using the syscall syncfs(2). Note you would usually + _not_ specify this option if passing a device node like ‘/dev/sda’ + for example, as that would sync the containing file system rather + than the referenced one. Note also that depending on the system, + passing individual device nodes or files may have different sync + characteristics than using no arguments. I.e., arguments passed to + fsync(2) may provide greater guarantees through write barriers, + than a global sync(2) used when no arguments are provided. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: truncate invocation, Prev: sync invocation, Up: File space usage + +14.5 ‘truncate’: Shrink or extend the size of a file +==================================================== + +‘truncate’ shrinks or extends the size of each FILE to the specified +size. Synopsis: + + truncate OPTION... FILE... + + Any FILE that does not exist is created. + + If a FILE is larger than the specified size, the extra data is lost. +If a FILE is shorter, it is extended and the sparse extended part (or +hole) reads as zero bytes. + + The program accepts the following options. Also see *note Common +options::. + +‘-c’ +‘--no-create’ + Do not create files that do not exist. + +‘-o’ +‘--io-blocks’ + Treat SIZE as number of I/O blocks of the FILE rather than bytes. + +‘-r RFILE’ +‘--reference=RFILE’ + Base the size of each FILE on the size of RFILE. + +‘-s SIZE’ +‘--size=SIZE’ + Set or adjust the size of each FILE according to SIZE. SIZE is in + bytes unless ‘--io-blocks’ is specified. SIZE may be, or may be an + integer optionally followed by, one of the following multiplicative + suffixes: + ‘KB’ => 1000 (KiloBytes) + ‘K’ => 1024 (KibiBytes) + ‘MB’ => 1000*1000 (MegaBytes) + ‘M’ => 1024*1024 (MebiBytes) + ‘GB’ => 1000*1000*1000 (GigaBytes) + ‘G’ => 1024*1024*1024 (GibiBytes) + and so on for ‘T’, ‘P’, ‘E’, ‘Z’, ‘Y’, ‘R’, and ‘Q’. Binary + prefixes can be used, too: ‘KiB’=‘K’, ‘MiB’=‘M’, and so on. + + SIZE may also be prefixed by one of the following to adjust the + size of each FILE based on its current size: + ‘+’ => extend by + ‘-’ => reduce by + ‘<’ => at most + ‘>’ => at least + ‘/’ => round down to multiple of + ‘%’ => round up to multiple of + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: Printing text, Next: Conditions, Prev: File space usage, Up: Top + +15 Printing text +**************** + +This section describes commands that display text strings. + +* Menu: + +* echo invocation:: Print a line of text. +* printf invocation:: Format and print data. +* yes invocation:: Print a string until interrupted. + + +File: coreutils.info, Node: echo invocation, Next: printf invocation, Up: Printing text + +15.1 ‘echo’: Print a line of text +================================= + +‘echo’ writes each given STRING to standard output, with a space between +each and a newline after the last one. Synopsis: + + echo [OPTION]... [STRING]... + + Due to shell aliases and built-in ‘echo’ functions, using an +unadorned ‘echo’ interactively or in a script may get you different +functionality than that described here. Invoke it via ‘env’ (i.e., ‘env +echo ...’) to avoid interference from the shell. + + Due to historical and backwards compatibility reasons, certain bare +option-like strings cannot be passed to ‘echo’ as non-option arguments. +It is therefore not advisable to use ‘echo’ for printing unknown or +variable arguments. The ‘printf’ command is recommended as a more +portable and flexible replacement for tasks historically performed by +‘echo’. *Note printf invocation::. + + The program accepts the following options. Also see *note Common +options::. Options must precede operands, and the normally-special +argument ‘--’ has no special meaning and is treated like any other +STRING. + +‘-n’ + Do not output the trailing newline. + +‘-e’ + Enable interpretation of the following backslash-escaped characters + in each STRING: + + ‘\a’ + alert (bell) + ‘\b’ + backspace + ‘\c’ + produce no further output + ‘\e’ + escape + ‘\f’ + form feed + ‘\n’ + newline + ‘\r’ + carriage return + ‘\t’ + horizontal tab + ‘\v’ + vertical tab + ‘\\’ + backslash + ‘\0NNN’ + the eight-bit value that is the octal number NNN (zero to + three octal digits), if NNN is a nine-bit value, the ninth bit + is ignored + ‘\NNN’ + the eight-bit value that is the octal number NNN (one to three + octal digits), if NNN is a nine-bit value, the ninth bit is + ignored + ‘\xHH’ + the eight-bit value that is the hexadecimal number HH (one or + two hexadecimal digits) + +‘-E’ + Disable interpretation of backslash escapes in each STRING. This + is the default. If ‘-e’ and ‘-E’ are both specified, the last one + given takes effect. + + If the ‘POSIXLY_CORRECT’ environment variable is set, then when +‘echo’’s first argument is not ‘-n’ it outputs option-like arguments +instead of treating them as options. For example, ‘echo -ne hello’ +outputs ‘-ne hello’ instead of plain ‘hello’. Also backslash escapes +are always enabled. Note to echo the string ‘-n’, one of the characters +can be escaped in either octal or hexadecimal representation. For +example, ‘echo -e '\x2dn'’. + + POSIX does not require support for any options, and says that the +behavior of ‘echo’ is implementation-defined if any STRING contains a +backslash or if the first argument is ‘-n’. Portable programs should +use the ‘printf’ command instead. *Note printf invocation::. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: printf invocation, Next: yes invocation, Prev: echo invocation, Up: Printing text + +15.2 ‘printf’: Format and print data +==================================== + +‘printf’ does formatted printing of text. Synopsis: + + printf FORMAT [ARGUMENT]... + + ‘printf’ prints the FORMAT string, interpreting ‘%’ directives and +‘\’ escapes to format numeric and string arguments in a way that is +mostly similar to the C ‘printf’ function. *Note ‘printf’ format +directives: (libc)Output Conversion Syntax, for details. The +differences are listed below. + + Due to shell aliases and built-in ‘printf’ functions, using an +unadorned ‘printf’ interactively or in a script may get you different +functionality than that described here. Invoke it via ‘env’ (i.e., ‘env +printf ...’) to avoid interference from the shell. + + • The FORMAT argument is reused as necessary to convert all the given + ARGUMENTs. For example, the command ‘printf %s a b’ outputs ‘ab’. + + • Missing ARGUMENTs are treated as null strings or as zeros, + depending on whether the context expects a string or a number. For + example, the command ‘printf %sx%d’ prints ‘x0’. + + • An additional escape, ‘\c’, causes ‘printf’ to produce no further + output. For example, the command ‘printf 'A%sC\cD%sF' B E’ prints + ‘ABC’. + + • The hexadecimal escape sequence ‘\xHH’ has at most two digits, as + opposed to C where it can have an unlimited number of digits. For + example, the command ‘printf '\x07e'’ prints two bytes, whereas the + C statement ‘printf ("\x07e")’ prints just one. + + • An additional directive ‘%b’, prints its argument string with ‘\’ + escapes interpreted in the same way as in the FORMAT string, except + that octal escapes are of the form ‘\0OOO’ where OOO is 0 to 3 + octal digits. If ‘\OOO’ is nine-bit value, ignore the ninth bit. + If a precision is also given, it limits the number of bytes printed + from the converted string. + + • An additional directive ‘%q’, prints its argument string in a + format that can be reused as input by most shells. Non-printable + characters are escaped with the POSIX proposed ‘$''’ syntax, and + shell metacharacters are quoted appropriately. This is an + equivalent format to ‘ls --quoting=shell-escape’ output. + + • Numeric arguments must be single C constants, possibly with leading + ‘+’ or ‘-’. For example, ‘printf %.4d -3’ outputs ‘-0003’. + + • If the leading character of a numeric argument is ‘"’ or ‘'’ then + its value is the numeric value of the immediately following + character. Any remaining characters are silently ignored if the + ‘POSIXLY_CORRECT’ environment variable is set; otherwise, a warning + is printed. For example, ‘printf "%d" "'a"’ outputs ‘97’ on hosts + that use the ASCII character set, since ‘a’ has the numeric value + 97 in ASCII. + + A floating point argument is interpreted according to the +‘LC_NUMERIC’ category of either the current or the C locale, and is +printed according to the current locale. For example, in a locale whose +decimal point character is a comma, the command ‘printf '%g %g' 2,5 2.5’ +outputs ‘2,5 2,5’. *Note Floating point::. + + ‘printf’ interprets ‘\OOO’ in FORMAT as an octal number (if OOO is 1 +to 3 octal digits) specifying a byte to print, and ‘\xHH’ as a +hexadecimal number (if HH is 1 to 2 hex digits) specifying a character +to print. Note however that when ‘\OOO’ specifies a number larger than +255, ‘printf’ ignores the ninth bit. For example, ‘printf '\400'’ is +equivalent to ‘printf '\0'’. + + ‘printf’ interprets two syntax forms for specifying Unicode (ISO/IEC +10646) characters. ‘\u’ for 16-bit Unicode characters, specified as +four hexadecimal digits HHHH, and ‘\U’ for 32-bit Unicode characters, +specified as eight hexadecimal digits HHHHHHHH. ‘printf’ outputs the +Unicode characters according to the ‘LC_CTYPE’ locale. Unicode +characters in the range U+D800...U+DFFF cannot be specified by this +syntax. This syntax fully supports the universal character subset +introduced in ISO C 99. + + The processing of ‘\u’ and ‘\U’ requires a full-featured ‘iconv’ +facility. It is activated on systems with glibc 2.2 (or newer), or when +‘libiconv’ is installed prior to this package. Otherwise ‘\u’ and ‘\U’ +will print as-is. + + Unicode character syntax is useful for writing strings in a locale +independent way. For example, a string containing the Euro currency +symbol + + $ env printf '\u20AC 14.95' + +will be output correctly in all locales supporting the Euro symbol +(ISO-8859-15, UTF-8, and others). Similarly, a Chinese string + + $ env printf '\u4e2d\u6587' + +will be output correctly in all Chinese locales (GB2312, BIG5, UTF-8, +etc). + + Note that in these examples, the ‘printf’ command has been invoked +via ‘env’ to ensure that we run the program found via your shell’s +search path, and not a shell alias or a built-in function. + + For larger strings, you don’t need to look up the hexadecimal code +values of each character one by one. ASCII characters mixed with \u +escape sequences is also known as the JAVA source file encoding. You +can use GNU recode 3.5c (or newer) to convert strings to this encoding. +Here is how to convert a piece of text into a shell script which will +output this text in a locale-independent way: + + $ LC_CTYPE=zh_TW.big5 env printf \ + '\u4e2d\u6587\n' > sample.txt + $ recode BIG5..JAVA < sample.txt \ + | sed -e "s|^|env printf '|" -e "s|%|%%|g" -e "s|$|\\\\n'|" \ + > sample.sh + + The only options are a lone ‘--help’ or ‘--version’. *Note Common +options::. Options must precede operands. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: yes invocation, Prev: printf invocation, Up: Printing text + +15.3 ‘yes’: Print a string until interrupted +============================================ + +‘yes’ prints the command line arguments, separated by spaces and +followed by a newline, forever until it is killed. If no arguments are +given, it prints ‘y’ followed by a newline forever until killed. + + Upon a write error, ‘yes’ exits with status ‘1’. + + The only options are a lone ‘--help’ or ‘--version’. To output an +argument that begins with ‘-’, precede it with ‘--’, e.g., ‘yes -- +--help’. *Note Common options::. + + +File: coreutils.info, Node: Conditions, Next: Redirection, Prev: Printing text, Up: Top + +16 Conditions +************* + +This section describes commands that are primarily useful for their exit +status, rather than their output. Thus, they are often used as the +condition of shell ‘if’ statements, or as the last command in a +pipeline. + +* Menu: + +* false invocation:: Do nothing, unsuccessfully. +* true invocation:: Do nothing, successfully. +* test invocation:: Check file types and compare values. +* expr invocation:: Evaluate expressions. + + +File: coreutils.info, Node: false invocation, Next: true invocation, Up: Conditions + +16.1 ‘false’: Do nothing, unsuccessfully +======================================== + +‘false’ does nothing except return an exit status of 1, meaning +“failure”. It can be used as a place holder in shell scripts where an +unsuccessful command is needed. In most modern shells, ‘false’ is a +built-in command, so when you use ‘false’ in a script, you’re probably +using the built-in command, not the one documented here. + + ‘false’ honors the ‘--help’ and ‘--version’ options. + + This version of ‘false’ is implemented as a C program, and is thus +more secure and faster than a shell script implementation, and may +safely be used as a dummy shell for the purpose of disabling accounts. + + Note that ‘false’ (unlike all other programs documented herein) exits +unsuccessfully, even when invoked with ‘--help’ or ‘--version’. + + Portable programs should not assume that the exit status of ‘false’ +is 1, as it is greater than 1 on some non-GNU hosts. + + +File: coreutils.info, Node: true invocation, Next: test invocation, Prev: false invocation, Up: Conditions + +16.2 ‘true’: Do nothing, successfully +===================================== + +‘true’ does nothing except return an exit status of 0, meaning +“success”. It can be used as a place holder in shell scripts where a +successful command is needed, although the shell built-in command ‘:’ +(colon) may do the same thing faster. In most modern shells, ‘true’ is +a built-in command, so when you use ‘true’ in a script, you’re probably +using the built-in command, not the one documented here. + + ‘true’ honors the ‘--help’ and ‘--version’ options. + + Note, however, that it is possible to cause ‘true’ to exit with +nonzero status: with the ‘--help’ or ‘--version’ option, and with +standard output already closed or redirected to a file that evokes an +I/O error. For example, using a Bourne-compatible shell: + + $ ./true --version >&- + ./true: write error: Bad file number + $ ./true --version > /dev/full + ./true: write error: No space left on device + + This version of ‘true’ is implemented as a C program, and is thus +more secure and faster than a shell script implementation, and may +safely be used as a dummy shell for the purpose of disabling accounts. + + +File: coreutils.info, Node: test invocation, Next: expr invocation, Prev: true invocation, Up: Conditions + +16.3 ‘test’: Check file types and compare values +================================================ + +‘test’ returns a status of 0 (true) or 1 (false) depending on the +evaluation of the conditional expression EXPR. Each part of the +expression must be a separate argument. + + ‘test’ has file status checks, string operators, and numeric +comparison operators. + + ‘test’ has an alternate form that uses opening and closing square +brackets instead a leading ‘test’. For example, instead of ‘test -d /’, +you can write ‘[ -d / ]’. The square brackets must be separate +arguments; for example, ‘[-d /]’ does not have the desired effect. +Since ‘test EXPR’ and ‘[ EXPR ]’ have the same meaning, only the former +form is discussed below. + + Synopses: + + test EXPRESSION + test + [ EXPRESSION ] + [ ] + [ OPTION + + Due to shell aliases and built-in ‘test’ functions, using an +unadorned ‘test’ interactively or in a script may get you different +functionality than that described here. Invoke it via ‘env’ (i.e., ‘env +test ...’) to avoid interference from the shell. + + If EXPRESSION is omitted, ‘test’ returns false. If EXPRESSION is a +single argument, ‘test’ returns false if the argument is null and true +otherwise. The argument can be any string, including strings like ‘-d’, +‘-1’, ‘--’, ‘--help’, and ‘--version’ that most other programs would +treat as options. To get help and version information, invoke the +commands ‘[ --help’ and ‘[ --version’, without the usual closing +brackets. *Note Common options::. + + Exit status: + + 0 if the expression is true, + 1 if the expression is false, + 2 if an error occurred. + +* Menu: + +* File type tests:: ‘-[bcdfhLpSt]’ +* Access permission tests:: ‘-[gkruwxOG]’ +* File characteristic tests:: ‘-e -s -nt -ot -ef’ +* String tests:: ‘-z -n = == !=’ +* Numeric tests:: ‘-eq -ne -lt -le -gt -ge’ +* Connectives for test:: ‘! -a -o’ + + +File: coreutils.info, Node: File type tests, Next: Access permission tests, Up: test invocation + +16.3.1 File type tests +---------------------- + +These options test for particular types of files. (Everything’s a file, +but not all files are the same!) + +‘-b FILE’ + True if FILE exists and is a block special device. + +‘-c FILE’ + True if FILE exists and is a character special device. + +‘-d FILE’ + True if FILE exists and is a directory. + +‘-f FILE’ + True if FILE exists and is a regular file. + +‘-h FILE’ +‘-L FILE’ + True if FILE exists and is a symbolic link. Unlike all other + file-related tests, this test does not dereference FILE if it is a + symbolic link. + +‘-p FILE’ + True if FILE exists and is a named pipe. + +‘-S FILE’ + True if FILE exists and is a socket. + +‘-t FD’ + True if FD is a file descriptor that is associated with a terminal. + + +File: coreutils.info, Node: Access permission tests, Next: File characteristic tests, Prev: File type tests, Up: test invocation + +16.3.2 Access permission tests +------------------------------ + +These options test for particular access permissions. + +‘-g FILE’ + True if FILE exists and has its set-group-ID bit set. + +‘-k FILE’ + True if FILE exists and has its “sticky” bit set. + +‘-r FILE’ + True if FILE exists and the user has read access. + +‘-u FILE’ + True if FILE exists and has its set-user-ID bit set. + +‘-w FILE’ + True if FILE exists and the user has write access. + +‘-x FILE’ + True if FILE exists and the user has execute access (or search + permission, if it is a directory). + +‘-O FILE’ + True if FILE exists and is owned by the current effective user ID. + +‘-G FILE’ + True if FILE exists and is owned by the current effective group ID. + + +File: coreutils.info, Node: File characteristic tests, Next: String tests, Prev: Access permission tests, Up: test invocation + +16.3.3 File characteristic tests +-------------------------------- + +These options test other file characteristics. + +‘-e FILE’ + True if FILE exists. + +‘-s FILE’ + True if FILE exists and has a size greater than zero. + +‘FILE1 -nt FILE2’ + True if FILE1 is newer (according to modification date) than FILE2, + or if FILE1 exists and FILE2 does not. + +‘FILE1 -ot FILE2’ + True if FILE1 is older (according to modification date) than FILE2, + or if FILE2 exists and FILE1 does not. + +‘FILE1 -ef FILE2’ + True if FILE1 and FILE2 have the same device and inode numbers, + i.e., if they are hard links to each other. + +‘-N FILE’ + True if FILE exists and has been modified (mtime) since it was last + read (atime). + + +File: coreutils.info, Node: String tests, Next: Numeric tests, Prev: File characteristic tests, Up: test invocation + +16.3.4 String tests +------------------- + +These options test string characteristics. You may need to quote STRING +arguments for the shell. For example: + + test -n "$V" + + The quotes here prevent the wrong arguments from being passed to +‘test’ if ‘$V’ is empty or contains special characters. + +‘-z STRING’ + True if the length of STRING is zero. + +‘-n STRING’ +‘STRING’ + True if the length of STRING is nonzero. + +‘STRING1 = STRING2’ + True if the strings are equal. + +‘STRING1 == STRING2’ + True if the strings are equal (synonym for =). Note this form is + not as portable to other shells and systems. + +‘STRING1 != STRING2’ + True if the strings are not equal. + + +File: coreutils.info, Node: Numeric tests, Next: Connectives for test, Prev: String tests, Up: test invocation + +16.3.5 Numeric tests +-------------------- + +Numeric relational operators. The arguments must be entirely numeric +(possibly negative), or the special expression ‘-l STRING’, which +evaluates to the length of STRING. + +‘ARG1 -eq ARG2’ +‘ARG1 -ne ARG2’ +‘ARG1 -lt ARG2’ +‘ARG1 -le ARG2’ +‘ARG1 -gt ARG2’ +‘ARG1 -ge ARG2’ + These arithmetic binary operators return true if ARG1 is equal, + not-equal, less-than, less-than-or-equal, greater-than, or + greater-than-or-equal than ARG2, respectively. + + For example: + + test -1 -gt -2 && echo yes + ⇒ yes + test -l abc -gt 1 && echo yes + ⇒ yes + test 0x100 -eq 1 + error→ test: integer expression expected before -eq + + +File: coreutils.info, Node: Connectives for test, Prev: Numeric tests, Up: test invocation + +16.3.6 Connectives for ‘test’ +----------------------------- + +Note it’s preferred to use shell logical primitives rather than these +logical connectives internal to ‘test’, because an expression may become +ambiguous depending on the expansion of its parameters. + + For example, this becomes ambiguous when ‘$1’ is set to ‘'!'’ and +‘$2’ to the empty string ‘''’: + + test "$1" -a "$2" + + and should be written as: + + test "$1" && test "$2" + + Note the shell logical primitives also benefit from short circuit +operation, which can be significant for file attribute tests. + +‘! EXPR’ + True if EXPR is false. ‘!’ has lower precedence than all parts of + EXPR. Note ‘!’ needs to be specified to the left of a binary + expression, I.e., ‘'!' 1 -gt 2’ rather than ‘1 '!' -gt 2’. Also + ‘!’ is often a shell special character and is best used quoted. + +‘EXPR1 -a EXPR2’ + True if both EXPR1 and EXPR2 are true. ‘-a’ is left associative, + and has a higher precedence than ‘-o’. + +‘EXPR1 -o EXPR2’ + True if either EXPR1 or EXPR2 is true. ‘-o’ is left associative. + + +File: coreutils.info, Node: expr invocation, Prev: test invocation, Up: Conditions + +16.4 ‘expr’: Evaluate expressions +================================= + +‘expr’ evaluates an expression and writes the result on standard output. +Each token of the expression must be a separate argument. + + Operands are either integers or strings. Integers consist of one or +more decimal digits, with an optional leading ‘-’. ‘expr’ converts +anything appearing in an operand position to an integer or a string +depending on the operation being applied to it. + + Strings are not quoted for ‘expr’ itself, though you may need to +quote them to protect characters with special meaning to the shell, +e.g., spaces. However, regardless of whether it is quoted, a string +operand should not be a parenthesis or any of ‘expr’’s operators like +‘+’, so you cannot safely pass an arbitrary string ‘$str’ to expr merely +by quoting it to the shell. One way to work around this is to use the +GNU extension ‘+’, (e.g., ‘+ "$str" = foo’); a more portable way is to +use ‘" $str"’ and to adjust the rest of the expression to take the +leading space into account (e.g., ‘" $str" = " foo"’). + + You should not pass a negative integer or a string with leading ‘-’ +as ‘expr’’s first argument, as it might be misinterpreted as an option; +this can be avoided by parenthesization. Also, portable scripts should +not use a string operand that happens to take the form of an integer; +this can be worked around by inserting leading spaces as mentioned +above. + + Operators may be given as infix symbols or prefix keywords. +Parentheses may be used for grouping in the usual manner. You must +quote parentheses and many operators to avoid the shell evaluating them, +however. + + Because ‘expr’ uses multiple-precision arithmetic, it works with +integers wider than those of machine registers. + + The only options are ‘--help’ and ‘--version’. *Note Common +options::. Options must precede operands. + + Exit status: + + 0 if the expression is neither null nor 0, + 1 if the expression is null or 0, + 2 if the expression is invalid, + 3 if an internal error occurred (e.g., arithmetic overflow). + +* Menu: + +* String expressions:: ‘+ : match substr index length’ +* Numeric expressions:: ‘+ - * / %’ +* Relations for expr:: ‘| & < <= = == != >= >’ +* Examples of expr:: Examples. + + +File: coreutils.info, Node: String expressions, Next: Numeric expressions, Up: expr invocation + +16.4.1 String expressions +------------------------- + +‘expr’ supports pattern matching and other string operators. These have +higher precedence than both the numeric and relational operators (in the +next sections). + +‘STRING : REGEX’ + Perform pattern matching. The arguments are converted to strings + and the second is considered to be a (basic, a la GNU ‘grep’) + regular expression, with a ‘^’ implicitly prepended. The first + argument is then matched against this regular expression. + + If REGEX does not use ‘\(’ and ‘\)’, the ‘:’ expression returns the + number of characters matched, or 0 if the match fails. + + If REGEX uses ‘\(’ and ‘\)’, the ‘:’ expression returns the part of + STRING that matched the subexpression, or the null string if the + match failed or the subexpression did not contribute to the match. + + Only the first ‘\( ... \)’ pair is relevant to the return value; + additional pairs are meaningful only for grouping the regular + expression operators. + + In the regular expression, ‘\+’, ‘\?’, and ‘\|’ are operators which + respectively match one or more, zero or one, or separate + alternatives. These operators are GNU extensions. *Note Regular + Expressions: (grep)Regular Expressions, for details of regular + expression syntax. Some examples are in *note Examples of expr::. + +‘match STRING REGEX’ + An alternative way to do pattern matching. This is the same as + ‘STRING : REGEX’. + +‘substr STRING POSITION LENGTH’ + Returns the substring of STRING beginning at POSITION with length + at most LENGTH. If either POSITION or LENGTH is negative, zero, or + non-numeric, returns the null string. + +‘index STRING CHARSET’ + Returns the first position in STRING where the first character in + CHARSET was found. If no character in CHARSET is found in STRING, + return 0. + +‘length STRING’ + Returns the length of STRING. + +‘+ TOKEN’ + Interpret TOKEN as a string, even if it is a keyword like MATCH or + an operator like ‘/’. This makes it possible to test ‘expr length + + "$x"’ or ‘expr + "$x" : '.*/\(.\)'’ and have it do the right + thing even if the value of $X happens to be (for example) ‘/’ or + ‘index’. This operator is a GNU extension. Portable shell scripts + should use ‘" $token" : ' \(.*\)'’ instead of ‘+ "$token"’. + + To make ‘expr’ interpret keywords as strings, you must use the +‘quote’ operator. + + +File: coreutils.info, Node: Numeric expressions, Next: Relations for expr, Prev: String expressions, Up: expr invocation + +16.4.2 Numeric expressions +-------------------------- + +‘expr’ supports the usual numeric operators, in order of increasing +precedence. These numeric operators have lower precedence than the +string operators described in the previous section, and higher +precedence than the connectives (next section). + +‘+ -’ + Addition and subtraction. Both arguments are converted to + integers; an error occurs if this cannot be done. + +‘* / %’ + Multiplication, division, remainder. Both arguments are converted + to integers; an error occurs if this cannot be done. + + +File: coreutils.info, Node: Relations for expr, Next: Examples of expr, Prev: Numeric expressions, Up: expr invocation + +16.4.3 Relations for ‘expr’ +--------------------------- + +‘expr’ supports the usual logical connectives and relations. These have +lower precedence than the string and numeric operators (previous +sections). Here is the list, lowest-precedence operator first. + +‘|’ + Returns its first argument if that is neither null nor zero, + otherwise its second argument if it is neither null nor zero, + otherwise 0. It does not evaluate its second argument if its first + argument is neither null nor zero. + +‘&’ + Return its first argument if neither argument is null or zero, + otherwise 0. It does not evaluate its second argument if its first + argument is null or zero. + +‘< <= = == != >= >’ + Compare the arguments and return 1 if the relation is true, 0 + otherwise. ‘==’ is a synonym for ‘=’. ‘expr’ first tries to + convert both arguments to integers and do a numeric comparison; if + either conversion fails, it does a lexicographic comparison using + the character collating sequence specified by the ‘LC_COLLATE’ + locale. + + +File: coreutils.info, Node: Examples of expr, Prev: Relations for expr, Up: expr invocation + +16.4.4 Examples of using ‘expr’ +------------------------------- + +Here are a few examples, including quoting for shell metacharacters. + + To add 1 to the shell variable ‘foo’, in Bourne-compatible shells: + + foo=$(expr $foo + 1) + + To print the non-directory part of the file name stored in ‘$fname’, +which need not contain a ‘/’: + + expr $fname : '.*/\(.*\)' '|' $fname + + An example showing that ‘\+’ is an operator: + + expr aaa : 'a\+' + ⇒ 3 + + expr abc : 'a\(.\)c' + ⇒ b + expr index abcdef cz + ⇒ 3 + expr index index a + error→ expr: syntax error + expr index + index a + ⇒ 0 + + +File: coreutils.info, Node: Redirection, Next: File name manipulation, Prev: Conditions, Up: Top + +17 Redirection +************** + +Unix shells commonly provide several forms of “redirection” – ways to +change the input source or output destination of a command. But one +useful redirection is performed by a separate command, not by the shell; +it’s described here. + +* Menu: + +* tee invocation:: Redirect output to multiple files or processes. + + +File: coreutils.info, Node: tee invocation, Up: Redirection + +17.1 ‘tee’: Redirect output to multiple files or processes +========================================================== + +The ‘tee’ command copies standard input to standard output and also to +any files given as arguments. This is useful when you want not only to +send some data down a pipe, but also to save a copy. Synopsis: + + tee [OPTION]... [FILE]... + + If a file being written to does not already exist, it is created. If +a file being written to already exists, the data it previously contained +is overwritten unless the ‘-a’ option is used. + + In previous versions of GNU Coreutils (5.3.0–8.23), a FILE of ‘-’ +caused ‘tee’ to send another copy of input to standard output. However, +as the interleaved output was not very useful, ‘tee’ now conforms to +POSIX and treats ‘-’ as a file name. + + The program accepts the following options. Also see *note Common +options::. + +‘-a’ +‘--append’ + Append standard input to the given files rather than overwriting + them. + +‘-i’ +‘--ignore-interrupts’ + Ignore interrupt signals. + +‘-p’ +‘--output-error[=MODE]’ + Adjust the behavior with errors on the outputs. In summary ‘-p’ + allows ‘tee’ to operate in a more appropriate manner with pipes, + and to continue to process data to any remaining outputs, if any + pipe outputs exit early. The default operation when + ‘--output-error’ is _not_ specified is to exit immediately on error + writing to a pipe, and diagnose errors writing to a non-pipe. The + long form ‘--output-error’ option supports selection between the + following MODEs: + + ‘warn’ + Warn on error opening or writing any output, including pipes. + Writing is continued to still open files/pipes. Exit status + indicates failure if any output has an error. + + ‘warn-nopipe’ + This is the default MODE when not specified, or when the short + form ‘-p’ is used. Warn on error opening or writing any + output, except pipes. Writing is continued to still open + files/pipes. Exit immediately if all remaining outputs become + broken pipes. Exit status indicates failure if any non pipe + output had an error. + + ‘exit’ + Exit on error opening or writing any output, including pipes. + + ‘exit-nopipe’ + Exit on error opening or writing any output, except pipes. + Exit immediately if all remaining outputs become broken pipes. + + The ‘tee’ command is useful when you happen to be transferring a +large amount of data and also want to summarize that data without +reading it a second time. For example, when you are downloading a DVD +image, you often want to verify its signature or checksum right away. +The inefficient way to do it is simply: + + wget https://example.com/some.iso && sha1sum some.iso + + One problem with the above is that it makes you wait for the download +to complete before starting the time-consuming SHA1 computation. +Perhaps even more importantly, the above requires reading the DVD image +a second time (the first was from the network). + + The efficient way to do it is to interleave the download and SHA1 +computation. Then, you’ll get the checksum for free, because the entire +process parallelizes so well: + + # slightly contrived, to demonstrate process substitution + wget -O - https://example.com/dvd.iso \ + | tee >(sha1sum > dvd.sha1) > dvd.iso + + That makes ‘tee’ write not just to the expected output file, but also +to a pipe running ‘sha1sum’ and saving the final checksum in a file +named ‘dvd.sha1’. + + Note, however, that this example relies on a feature of modern shells +called “process substitution” (the ‘>(command)’ syntax, above; *Note +Process Substitution: (bash)Process Substitution.), so it works with +‘zsh’, ‘bash’, and ‘ksh’, but not with ‘/bin/sh’. So if you write code +like this in a shell script, be sure to start the script with +‘#!/bin/bash’. + + Note also that if any of the process substitutions (or piped standard +output) might exit early without consuming all the data, the ‘-p’ option +is needed to allow ‘tee’ to continue to process the input to any +remaining outputs. + + Since the above example writes to one file and one process, a more +conventional and portable use of ‘tee’ is even better: + + wget -O - https://example.com/dvd.iso \ + | tee dvd.iso | sha1sum > dvd.sha1 + + You can extend this example to make ‘tee’ write to two processes, +computing MD5 and SHA1 checksums in parallel. In this case, process +substitution is required: + + wget -O - https://example.com/dvd.iso \ + | tee >(sha1sum > dvd.sha1) \ + >(md5sum > dvd.md5) \ + > dvd.iso + + This technique is also useful when you want to make a _compressed_ +copy of the contents of a pipe. Consider a tool to graphically +summarize file system usage data from ‘du -ak’. For a large hierarchy, +‘du -ak’ can run for a long time, and can easily produce terabytes of +data, so you won’t want to rerun the command unnecessarily. Nor will +you want to save the uncompressed output. + + Doing it the inefficient way, you can’t even start the GUI until +after you’ve compressed all of the ‘du’ output: + + du -ak | gzip -9 > /tmp/du.gz + gzip -d /tmp/du.gz | checkspace -a + + With ‘tee’ and process substitution, you start the GUI right away and +eliminate the decompression completely: + + du -ak | tee >(gzip -9 > /tmp/du.gz) | checkspace -a + + Finally, if you regularly create more than one type of compressed +tarball at once, for example when ‘make dist’ creates both +‘gzip’-compressed and ‘bzip2’-compressed tarballs, there may be a better +way. Typical ‘automake’-generated ‘Makefile’ rules create the two +compressed tar archives with commands in sequence, like this (slightly +simplified): + + tardir=your-pkg-M.N + tar chof - "$tardir" | gzip -9 -c > your-pkg-M.N.tar.gz + tar chof - "$tardir" | bzip2 -9 -c > your-pkg-M.N.tar.bz2 + + However, if the hierarchy you are archiving and compressing is larger +than a couple megabytes, and especially if you are using a +multi-processor system with plenty of memory, then you can do much +better by reading the directory contents only once and running the +compression programs in parallel: + + tardir=your-pkg-M.N + tar chof - "$tardir" \ + | tee >(gzip -9 -c > your-pkg-M.N.tar.gz) \ + | bzip2 -9 -c > your-pkg-M.N.tar.bz2 + + If you want to further process the output from process substitutions, +and those processes write atomically (i.e., write less than the system’s +PIPE_BUF size at a time), that’s possible with a construct like: + + tardir=your-pkg-M.N + tar chof - "$tardir" \ + | tee >(md5sum --tag) > >(sha256sum --tag) \ + | sort | gpg --clearsign > your-pkg-M.N.tar.sig + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: File name manipulation, Next: Working context, Prev: Redirection, Up: Top + +18 File name manipulation +************************* + +This section describes commands that manipulate file names. + +* Menu: + +* basename invocation:: Strip directory and suffix from a file name. +* dirname invocation:: Strip last file name component. +* pathchk invocation:: Check file name validity and portability. +* mktemp invocation:: Create temporary file or directory. +* realpath invocation:: Print resolved file names. + + +File: coreutils.info, Node: basename invocation, Next: dirname invocation, Up: File name manipulation + +18.1 ‘basename’: Strip directory and suffix from a file name +============================================================ + +‘basename’ removes any leading directory components from NAME. +Synopsis: + + basename NAME [SUFFIX] + basename OPTION... NAME... + + If SUFFIX is specified and is identical to the end of NAME, it is +removed from NAME as well. Note that since trailing slashes are removed +prior to suffix matching, SUFFIX will do nothing if it contains slashes. +‘basename’ prints the result on standard output. + + Together, ‘basename’ and ‘dirname’ are designed such that if ‘ls +"$name"’ succeeds, then the command sequence ‘cd "$(dirname "$name")"; +ls "$(basename "$name")"’ will, too. This works for everything except +file names containing a trailing newline. + + POSIX allows the implementation to define the results if NAME is +empty or ‘//’. In the former case, GNU ‘basename’ returns the empty +string. In the latter case, the result is ‘//’ on platforms where // is +distinct from /, and ‘/’ on platforms where there is no difference. + + The program accepts the following options. Also see *note Common +options::. Options must precede operands. + +‘-a’ +‘--multiple’ + Support more than one argument. Treat every argument as a NAME. + With this, an optional SUFFIX must be specified using the ‘-s’ + option. + +‘-s SUFFIX’ +‘--suffix=SUFFIX’ + Remove a trailing SUFFIX. This option implies the ‘-a’ option. + +‘-z’ +‘--zero’ + Output a zero byte (ASCII NUL) at the end of each line, rather than + a newline. This option enables other programs to parse the output + even when that output would contain data with embedded newlines. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + Examples: + + # Output "sort". + basename /usr/bin/sort + + # Output "stdio". + basename include/stdio.h .h + + # Output "stdio". + basename -s .h include/stdio.h + + # Output "stdio" followed by "stdlib" + basename -a -s .h include/stdio.h include/stdlib.h + + +File: coreutils.info, Node: dirname invocation, Next: pathchk invocation, Prev: basename invocation, Up: File name manipulation + +18.2 ‘dirname’: Strip last file name component +============================================== + +‘dirname’ prints all but the final slash-delimited component of each +NAME. Slashes on either side of the final component are also removed. +If the string contains no slash, ‘dirname’ prints ‘.’ (meaning the +current directory). Synopsis: + + dirname [OPTION] NAME... + + NAME need not be a file name, but if it is, this operation +effectively lists the directory that contains the final component, +including the case when the final component is itself a directory. + + Together, ‘basename’ and ‘dirname’ are designed such that if ‘ls +"$name"’ succeeds, then the command sequence ‘cd "$(dirname "$name")"; +ls "$(basename "$name")"’ will, too. This works for everything except +file names containing a trailing newline. + + POSIX allows the implementation to define the results if NAME is +‘//’. With GNU ‘dirname’, the result is ‘//’ on platforms where // is +distinct from /, and ‘/’ on platforms where there is no difference. + + The program accepts the following option. Also see *note Common +options::. + +‘-z’ +‘--zero’ + Output a zero byte (ASCII NUL) at the end of each line, rather than + a newline. This option enables other programs to parse the output + even when that output would contain data with embedded newlines. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + Examples: + + # Output "/usr/bin". + dirname /usr/bin/sort + dirname /usr/bin//.// + + # Output "dir1" followed by "dir2" + dirname dir1/str dir2/str + + # Output ".". + dirname stdio.h + + +File: coreutils.info, Node: pathchk invocation, Next: mktemp invocation, Prev: dirname invocation, Up: File name manipulation + +18.3 ‘pathchk’: Check file name validity and portability +======================================================== + +‘pathchk’ checks validity and portability of file names. Synopsis: + + pathchk [OPTION]... NAME... + + For each NAME, ‘pathchk’ prints an error message if any of these +conditions is true: + + 1. One of the existing directories in NAME does not have search + (execute) permission, + 2. The length of NAME is larger than the maximum supported by the + operating system. + 3. The length of one component of NAME is longer than its file + system’s maximum. + + A nonexistent NAME is not an error, so long as a file with that name +could be created under the above conditions. + + The program accepts the following options. Also see *note Common +options::. Options must precede operands. + +‘-p’ + Instead of performing checks based on the underlying file system, + print an error message if any of these conditions is true: + + 1. A file name is empty. + + 2. A file name contains a character outside the POSIX portable + file name character set, namely, the ASCII letters and digits, + ‘.’, ‘_’, ‘-’, and ‘/’. + + 3. The length of a file name or one of its components exceeds the + POSIX minimum limits for portability. + +‘-P’ + Print an error message if a file name is empty, or if it contains a + component that begins with ‘-’. + +‘--portability’ + Print an error message if a file name is not portable to all POSIX + hosts. This option is equivalent to ‘-p -P’. + + Exit status: + + 0 if all specified file names passed all checks, + 1 otherwise. + + +File: coreutils.info, Node: mktemp invocation, Next: realpath invocation, Prev: pathchk invocation, Up: File name manipulation + +18.4 ‘mktemp’: Create temporary file or directory +================================================= + +‘mktemp’ manages the creation of temporary files and directories. +Synopsis: + + mktemp [OPTION]... [TEMPLATE] + + Safely create a temporary file or directory based on TEMPLATE, and +print its name. If given, TEMPLATE must include at least three +consecutive ‘X’s in the last component. If omitted, the template +‘tmp.XXXXXXXXXX’ is used, and option ‘--tmpdir’ is implied. The final +run of ‘X’s in the TEMPLATE will be replaced by alpha-numeric +characters; thus, on a case-sensitive file system, and with a TEMPLATE +including a run of N instances of ‘X’, there are ‘62**N’ potential file +names. + + Older scripts used to create temporary files by simply joining the +name of the program with the process id (‘$$’) as a suffix. However, +that naming scheme is easily predictable, and suffers from a race +condition where the attacker can create an appropriately named symbolic +link, such that when the script then opens a handle to what it thought +was an unused file, it is instead modifying an existing file. Using the +same scheme to create a directory is slightly safer, since the ‘mkdir’ +will fail if the target already exists, but it is still inferior because +it allows for denial of service attacks. Therefore, modern scripts +should use the ‘mktemp’ command to guarantee that the generated name +will be unpredictable, and that knowledge of the temporary file name +implies that the file was created by the current script and cannot be +modified by other users. + + When creating a file, the resulting file has read and write +permissions for the current user, but no permissions for the group or +others; these permissions are reduced if the current umask is more +restrictive. + + Here are some examples (although note that if you repeat them, you +will most likely get different file names): + + • Create a temporary file in the current directory. + $ mktemp file.XXXX + file.H47c + + • Create a temporary file with a known suffix. + $ mktemp --suffix=.txt file-XXXX + file-H08W.txt + $ mktemp file-XXXX-XXXX.txt + file-XXXX-eI9L.txt + + • Create a secure fifo relative to the user’s choice of ‘TMPDIR’, but + falling back to the current directory rather than ‘/tmp’. Note + that ‘mktemp’ does not create fifos, but can create a secure + directory in which the fifo can live. Exit the shell if the + directory or fifo could not be created. + $ dir=$(mktemp -p "${TMPDIR:-.}" -d dir-XXXX) || exit 1 + $ fifo=$dir/fifo + $ mkfifo "$fifo" || { rmdir "$dir"; exit 1; } + + • Create and use a temporary file if possible, but ignore failure. + The file will reside in the directory named by ‘TMPDIR’, if + specified, or else in ‘/tmp’. + $ file=$(mktemp -q) && { + > # Safe to use $file only within this block. Use quotes, + > # since $TMPDIR, and thus $file, may contain whitespace. + > echo ... > "$file" + > rm "$file" + > } + + • Act as a semi-random character generator (it is not fully random, + since it is impacted by the contents of the current directory). To + avoid security holes, do not use the resulting names to create a + file. + $ mktemp -u XXX + Gb9 + $ mktemp -u XXX + nzC + + The program accepts the following options. Also see *note Common +options::. + +‘-d’ +‘--directory’ + Create a directory rather than a file. The directory will have + read, write, and search permissions for the current user, but no + permissions for the group or others; these permissions are reduced + if the current umask is more restrictive. + +‘-q’ +‘--quiet’ + Suppress diagnostics about failure to create a file or directory. + The exit status will still reflect whether a file was created. + +‘-u’ +‘--dry-run’ + Generate a temporary name that does not name an existing file, + without changing the file system contents. Using the output of + this command to create a new file is inherently unsafe, as there is + a window of time between generating the name and using it where + another process can create an object by the same name. + +‘-p DIR’ +‘--tmpdir[=DIR]’ + Treat TEMPLATE relative to the directory DIR. If DIR is not + specified (only possible with the long option ‘--tmpdir’) or is the + empty string, use the value of ‘TMPDIR’ if available, otherwise use + ‘/tmp’. If this is specified, TEMPLATE must not be absolute. + However, TEMPLATE can still contain slashes, although intermediate + directories must already exist. + +‘--suffix=SUFFIX’ + Append SUFFIX to the TEMPLATE. SUFFIX must not contain slash. If + ‘--suffix’ is specified, TEMPLATE must end in ‘X’; if it is not + specified, then an appropriate ‘--suffix’ is inferred by finding + the last ‘X’ in TEMPLATE. This option exists for use with the + default TEMPLATE and for the creation of a SUFFIX that starts with + ‘X’. + +‘-t’ + Treat TEMPLATE as a single file relative to the value of ‘TMPDIR’ + if available, or to the directory specified by ‘-p’, otherwise to + ‘/tmp’. TEMPLATE must not contain slashes. This option is + deprecated; the use of ‘-p’ without ‘-t’ offers better defaults (by + favoring the command line over ‘TMPDIR’) and more flexibility (by + allowing intermediate directories). + + Exit status: + + 0 if the file was created, + 1 otherwise. + + +File: coreutils.info, Node: realpath invocation, Prev: mktemp invocation, Up: File name manipulation + +18.5 ‘realpath’: Print the resolved file name. +============================================== + +‘realpath’ expands all symbolic links and resolves references to ‘/./’, +‘/../’ and extra ‘/’ characters. By default, all but the last component +of the specified files must exist. Synopsis: + + realpath [OPTION]... FILE... + + The file name canonicalization functionality overlaps with that of +the ‘readlink’ command. This is the preferred command for +canonicalization as it’s a more suitable and standard name. In addition +this command supports relative file name processing functionality. + + The program accepts the following options. Also see *note Common +options::. + +‘-e’ +‘--canonicalize-existing’ + Ensure that all components of the specified file names exist. If + any component is missing or unavailable, ‘realpath’ will output a + diagnostic unless the ‘-q’ option is specified, and exit with a + nonzero exit code. A trailing slash requires that the name resolve + to a directory. + +‘-m’ +‘--canonicalize-missing’ + If any component of a specified file name is missing or + unavailable, treat it as a directory. + +‘-L’ +‘--logical’ + Symbolic links are resolved in the specified file names, but they + are resolved after any subsequent ‘..’ components are processed. + +‘-P’ +‘--physical’ + Symbolic links are resolved in the specified file names, and they + are resolved before any subsequent ‘..’ components are processed. + This is the default mode of operation. + +‘-q’ +‘--quiet’ + Suppress diagnostic messages for specified file names. + +‘--relative-to=DIR’ + Print the resolved file names relative to the specified directory. + Note this option honors the ‘-m’ and ‘-e’ options pertaining to + file existence. + +‘--relative-base=DIR’ + Print the resolved file names as relative _if_ the files are + descendants of DIR. Otherwise, print the resolved file names as + absolute. Note this option honors the ‘-m’ and ‘-e’ options + pertaining to file existence. For details about combining + ‘--relative-to’ and ‘--relative-base’, *note Realpath usage + examples::. + +‘-s’ +‘--strip’ +‘--no-symlinks’ + Do not resolve symbolic links. Only resolve references to ‘/./’, + ‘/../’ and remove extra ‘/’ characters. When combined with the + ‘-m’ option, realpath operates only on the file name, and does not + touch any actual file. + +‘-z’ +‘--zero’ + Output a zero byte (ASCII NUL) at the end of each line, rather than + a newline. This option enables other programs to parse the output + even when that output would contain data with embedded newlines. + + Exit status: + + 0 if all file names were printed without issue. + 1 otherwise. + +* Menu: + +* Realpath usage examples:: Realpath usage examples. + + +File: coreutils.info, Node: Realpath usage examples, Up: realpath invocation + +18.5.1 Realpath usage examples +------------------------------ + +By default, ‘realpath’ prints the absolute file name of given files +(symlinks are resolved, ‘words’ is resolved to ‘american-english’): + + cd /home/user + realpath /usr/bin/sort /tmp/foo /usr/share/dict/words 1.txt + ⇒ /usr/bin/sort + ⇒ /tmp/foo + ⇒ /usr/share/dict/american-english + ⇒ /home/user/1.txt + + With ‘--relative-to’, file names are printed relative to the given +directory: + + realpath --relative-to=/usr/bin \ + /usr/bin/sort /tmp/foo /usr/share/dict/words 1.txt + ⇒ sort + ⇒ ../../tmp/foo + ⇒ ../share/dict/american-english + ⇒ ../../home/user/1.txt + + With ‘--relative-base’, relative file names are printed _if_ the +resolved file name is below the given base directory. For files outside +the base directory absolute file names are printed: + + realpath --relative-base=/usr \ + /usr/bin/sort /tmp/foo /usr/share/dict/words 1.txt + ⇒ bin/sort + ⇒ /tmp/foo + ⇒ share/dict/american-english + ⇒ /home/user/1.txt + + When both ‘--relative-to=DIR1’ and ‘--relative-base=DIR2’ are used, +file names are printed relative to DIR1 _if_ they are located below +DIR2. If the files are not below DIR2, they are printed as absolute +file names: + + realpath --relative-to=/usr/bin --relative-base=/usr \ + /usr/bin/sort /tmp/foo /usr/share/dict/words 1.txt + ⇒ sort + ⇒ /tmp/foo + ⇒ ../share/dict/american-english + ⇒ /home/user/1.txt + + When both ‘--relative-to=DIR1’ and ‘--relative-base=DIR2’ are used, +DIR1 _must_ be a subdirectory of DIR2. Otherwise, ‘realpath’ prints +absolutes file names. + + +File: coreutils.info, Node: Working context, Next: User information, Prev: File name manipulation, Up: Top + +19 Working context +****************** + +This section describes commands that display or alter the context in +which you are working: the current directory, the terminal settings, and +so forth. See also the user-related commands in the next section. + +* Menu: + +* pwd invocation:: Print working directory. +* stty invocation:: Print or change terminal characteristics. +* printenv invocation:: Print environment variables. +* tty invocation:: Print file name of terminal on standard input. + + +File: coreutils.info, Node: pwd invocation, Next: stty invocation, Up: Working context + +19.1 ‘pwd’: Print working directory +=================================== + +‘pwd’ prints the name of the current directory. Synopsis: + + pwd [OPTION]... + + The program accepts the following options. Also see *note Common +options::. + +‘-L’ +‘--logical’ + If the contents of the environment variable ‘PWD’ provide an + absolute name of the current directory with no ‘.’ or ‘..’ + components, but possibly with symbolic links, then output those + contents. Otherwise, fall back to default ‘-P’ handling. + +‘-P’ +‘--physical’ + Print a fully resolved name for the current directory. That is, + all components of the printed name will be actual directory names – + none will be symbolic links. + + If ‘-L’ and ‘-P’ are both given, the last one takes precedence. If +neither option is given, then this implementation uses ‘-P’ as the +default unless the ‘POSIXLY_CORRECT’ environment variable is set. + + Due to shell aliases and built-in ‘pwd’ functions, using an unadorned +‘pwd’ interactively or in a script may get you different functionality +than that described here. Invoke it via ‘env’ (i.e., ‘env pwd ...’) to +avoid interference from the shell. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: stty invocation, Next: printenv invocation, Prev: pwd invocation, Up: Working context + +19.2 ‘stty’: Print or change terminal characteristics +===================================================== + +‘stty’ prints or changes terminal characteristics, such as baud rate. +Synopses: + + stty [OPTION] [SETTING]... + stty [OPTION] + + If given no line settings, ‘stty’ prints the baud rate, line +discipline number (on systems that support it), and line settings that +have been changed from the values set by ‘stty sane’. By default, mode +reading and setting are performed on the tty line connected to standard +input, although this can be modified by the ‘--file’ option. + + ‘stty’ accepts many non-option arguments that change aspects of the +terminal line operation, as described below. + + The program accepts the following options. Also see *note Common +options::. + +‘-a’ +‘--all’ + Print all current settings in human-readable form. This option may + not be used in combination with any line settings. + +‘-F DEVICE’ +‘--file=DEVICE’ + Set the line opened by the file name specified in DEVICE instead of + the tty line connected to standard input. This option is necessary + because opening a POSIX tty requires use of the ‘O_NONDELAY’ flag + to prevent a POSIX tty from blocking until the carrier detect line + is high if the ‘clocal’ flag is not set. Hence, it is not always + possible to allow the shell to open the device in the traditional + manner. + +‘-g’ +‘--save’ + Print all current settings in a form that can be used as an + argument to another ‘stty’ command to restore the current settings. + This option may not be used in combination with any line settings. + + Many settings can be turned off by preceding them with a ‘-’. Such +arguments are marked below with “May be negated” in their description. +The descriptions themselves refer to the positive case, that is, when +_not_ negated (unless stated otherwise, of course). + + Some settings are not available on all POSIX systems, since they use +extensions. Such arguments are marked below with “Non-POSIX” in their +description. On non-POSIX systems, those or other settings also may not +be available, but it’s not feasible to document all the variations: just +try it and see. + + ‘stty’ is installed only on platforms with the POSIX terminal +interface, so portable scripts should not rely on its existence on +non-POSIX platforms. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + +* Menu: + +* Control:: Control settings +* Input:: Input settings +* Output:: Output settings +* Local:: Local settings +* Combination:: Combination settings +* Characters:: Special characters +* Special:: Special settings + + +File: coreutils.info, Node: Control, Next: Input, Up: stty invocation + +19.2.1 Control settings +----------------------- + +Control settings: + +‘parenb’ + Generate parity bit in output and expect parity bit in input. May + be negated. + +‘parodd’ + Set odd parity (even if negated). May be negated. + +‘cmspar’ + Use "stick" (mark/space) parity. If parodd is set, the parity bit + is always 1; if parodd is not set, the parity bit is always zero. + Non-POSIX. May be negated. + +‘cs5’ +‘cs6’ +‘cs7’ +‘cs8’ + Set character size to 5, 6, 7, or 8 bits. + +‘hup’ +‘hupcl’ + Send a hangup signal when the last process closes the tty. May be + negated. + +‘cstopb’ + Use two stop bits per character (one if negated). May be negated. + +‘cread’ + Allow input to be received. May be negated. + +‘clocal’ + Disable modem control signals. May be negated. + +‘crtscts’ + Enable RTS/CTS flow control. Non-POSIX. May be negated. + +‘cdtrdsr’ + Enable DTR/DSR flow control. Non-POSIX. May be negated. + + +File: coreutils.info, Node: Input, Next: Output, Prev: Control, Up: stty invocation + +19.2.2 Input settings +--------------------- + +These settings control operations on data received from the terminal. + +‘ignbrk’ + Ignore break characters. May be negated. + +‘brkint’ + Make breaks cause an interrupt signal. May be negated. + +‘ignpar’ + Ignore characters with parity errors. May be negated. + +‘parmrk’ + Mark parity errors (with a 255-0-character sequence). May be + negated. + +‘inpck’ + Enable input parity checking. May be negated. + +‘istrip’ + Clear high (8th) bit of input characters. May be negated. + +‘inlcr’ + Translate newline to carriage return. May be negated. + +‘igncr’ + Ignore carriage return. May be negated. + +‘icrnl’ + Translate carriage return to newline. May be negated. + +‘iutf8’ + Assume input characters are UTF-8 encoded. May be negated. + +‘ixon’ + Enable XON/XOFF flow control (that is, ‘Ctrl-S’/‘Ctrl-Q’). May be + negated. + +‘ixoff’ +‘tandem’ + Enable sending of ‘stop’ character when the system input buffer is + almost full, and ‘start’ character when it becomes almost empty + again. May be negated. + +‘iuclc’ + Translate uppercase characters to lowercase. Non-POSIX. May be + negated. Note ilcuc is not implemented, as one would not be able + to issue almost any (lowercase) Unix command, after invoking it. + +‘ixany’ + Allow any character to restart output (only the start character if + negated). Non-POSIX. May be negated. + +‘imaxbel’ + Enable beeping and not flushing input buffer if a character arrives + when the input buffer is full. Non-POSIX. May be negated. + + +File: coreutils.info, Node: Output, Next: Local, Prev: Input, Up: stty invocation + +19.2.3 Output settings +---------------------- + +These settings control operations on data sent to the terminal. + +‘opost’ + Postprocess output. May be negated. + +‘olcuc’ + Translate lowercase characters to uppercase. Non-POSIX. May be + negated. (Note ouclc is not currently implemented.) + +‘ocrnl’ + Translate carriage return to newline. Non-POSIX. May be negated. + +‘onlcr’ + Translate newline to carriage return-newline. Non-POSIX. May be + negated. + +‘onocr’ + Do not print carriage returns in the first column. Non-POSIX. May + be negated. + +‘onlret’ + Newline performs a carriage return. Non-POSIX. May be negated. + +‘ofill’ + Use fill (padding) characters instead of timing for delays. + Non-POSIX. May be negated. + +‘ofdel’ + Use ASCII DEL characters for fill instead of ASCII NUL characters. + Non-POSIX. May be negated. + +‘nl1’ +‘nl0’ + Newline delay style. Non-POSIX. + +‘cr3’ +‘cr2’ +‘cr1’ +‘cr0’ + Carriage return delay style. Non-POSIX. + +‘tab3’ +‘tab2’ +‘tab1’ +‘tab0’ + Horizontal tab delay style. Non-POSIX. + +‘bs1’ +‘bs0’ + Backspace delay style. Non-POSIX. + +‘vt1’ +‘vt0’ + Vertical tab delay style. Non-POSIX. + +‘ff1’ +‘ff0’ + Form feed delay style. Non-POSIX. + + +File: coreutils.info, Node: Local, Next: Combination, Prev: Output, Up: stty invocation + +19.2.4 Local settings +--------------------- + +‘isig’ + Enable ‘interrupt’, ‘quit’, and ‘suspend’ special characters. May + be negated. + +‘icanon’ + Enable ‘erase’, ‘kill’, ‘werase’, and ‘rprnt’ special characters. + May be negated. + +‘iexten’ + Enable non-POSIX special characters. May be negated. + +‘echo’ + Echo input characters. May be negated. + +‘echoe’ +‘crterase’ + Echo ‘erase’ characters as backspace-space-backspace. May be + negated. + +‘echok’ + Echo a newline after a ‘kill’ character. May be negated. + +‘echonl’ + Echo newline even if not echoing other characters. May be negated. + +‘noflsh’ + Disable flushing after ‘interrupt’ and ‘quit’ special characters. + May be negated. + +‘xcase’ + Enable input and output of uppercase characters by preceding their + lowercase equivalents with ‘\’, when ‘icanon’ is set. Non-POSIX. + May be negated. + +‘tostop’ + Stop background jobs that try to write to the terminal. Non-POSIX. + May be negated. + +‘echoprt’ +‘prterase’ + Echo erased characters backward, between ‘\’ and ‘/’. Non-POSIX. + May be negated. + +‘echoctl’ +‘ctlecho’ + Echo control characters in hat notation (‘^C’) instead of + literally. Non-POSIX. May be negated. + +‘echoke’ +‘crtkill’ + Echo the ‘kill’ special character by erasing each character on the + line as indicated by the ‘echoprt’ and ‘echoe’ settings, instead of + by the ‘echoctl’ and ‘echok’ settings. Non-POSIX. May be negated. + +‘extproc’ + Enable ‘LINEMODE’, which is used to avoid echoing each character + over high latency links. See also Internet RFC 1116 + (https://tools.ietf.org/search/rfc1116). Non-POSIX. May be + negated. + +‘flusho’ + Discard output. Note this setting is currently ignored on + GNU/Linux systems. Non-POSIX. May be negated. + + +File: coreutils.info, Node: Combination, Next: Characters, Prev: Local, Up: stty invocation + +19.2.5 Combination settings +--------------------------- + +Combination settings: + +‘evenp’ +‘parity’ + Same as ‘parenb -parodd cs7’. May be negated. If negated, same as + ‘-parenb cs8’. + +‘oddp’ + Same as ‘parenb parodd cs7’. May be negated. If negated, same as + ‘-parenb cs8’. + +‘nl’ + Same as ‘-icrnl -onlcr’. May be negated. If negated, same as + ‘icrnl -inlcr -igncr onlcr -ocrnl -onlret’. + +‘ek’ + Reset the ‘erase’ and ‘kill’ special characters to their default + values. + +‘sane’ + Same as: + + cread -ignbrk brkint -inlcr -igncr icrnl + icanon iexten echo echoe echok -echonl -noflsh + -ixoff -iutf8 -iuclc -ixany imaxbel -xcase -olcuc -ocrnl + opost -ofill onlcr -onocr -onlret nl0 cr0 tab0 bs0 vt0 ff0 + isig -tostop -ofdel -echoprt echoctl echoke -extproc + + and also sets all special characters to their default values. + +‘cooked’ + Same as ‘brkint ignpar istrip icrnl ixon opost isig icanon’, plus + sets the ‘eof’ and ‘eol’ characters to their default values if they + are the same as the ‘min’ and ‘time’ characters. May be negated. + If negated, same as ‘raw’. + +‘raw’ + Same as: + + -ignbrk -brkint -ignpar -parmrk -inpck -istrip + -inlcr -igncr -icrnl -ixon -ixoff -icanon -opost + -isig -iuclc -ixany -imaxbel -xcase min 1 time 0 + + May be negated. If negated, same as ‘cooked’. + +‘cbreak’ + Same as ‘-icanon’. May be negated. If negated, same as ‘icanon’. + +‘pass8’ + Same as ‘-parenb -istrip cs8’. May be negated. If negated, same + as ‘parenb istrip cs7’. + +‘litout’ + Same as ‘-parenb -istrip -opost cs8’. May be negated. If negated, + same as ‘parenb istrip opost cs7’. + +‘decctlq’ + Same as ‘-ixany’. Non-POSIX. May be negated. + +‘tabs’ + Same as ‘tab0’. Non-POSIX. May be negated. If negated, same as + ‘tab3’. + +‘lcase’ +‘LCASE’ + Same as ‘xcase iuclc olcuc’. Non-POSIX. May be negated. (Used + for terminals with uppercase characters only.) + +‘crt’ + Same as ‘echoe echoctl echoke’. + +‘dec’ + Same as ‘echoe echoctl echoke -ixany intr ^C erase ^? kill C-u’. + + +File: coreutils.info, Node: Characters, Next: Special, Prev: Combination, Up: stty invocation + +19.2.6 Special characters +------------------------- + +The special characters’ default values vary from system to system. They +are set with the syntax ‘name value’, where the names are listed below +and the value can be given either literally, in hat notation (‘^C’), or +as an integer which may start with ‘0x’ to indicate hexadecimal, ‘0’ to +indicate octal, or any other digit to indicate decimal. + + For GNU stty, giving a value of ‘^-’ or ‘undef’ disables that special +character. (This is incompatible with Ultrix ‘stty’, which uses a value +of ‘u’ to disable a special character. GNU ‘stty’ treats a value ‘u’ +like any other, namely to set that special character to <U>.) + +‘intr’ + Send an interrupt signal. + +‘quit’ + Send a quit signal. + +‘erase’ + Erase the last character typed. + +‘kill’ + Erase the current line. + +‘eof’ + Send an end of file (terminate the input). + +‘eol’ + End the line. + +‘eol2’ + Alternate character to end the line. Non-POSIX. + +‘discard’ + Alternate character to toggle discarding of output. Non-POSIX. + +‘swtch’ + Switch to a different shell layer. Non-POSIX. + +‘status’ + Send an info signal. Not currently supported on GNU/Linux. + Non-POSIX. + +‘start’ + Restart the output after stopping it. + +‘stop’ + Stop the output. + +‘susp’ + Send a terminal stop signal. + +‘dsusp’ + Send a terminal stop signal after flushing the input. Non-POSIX. + +‘rprnt’ + Redraw the current line. Non-POSIX. + +‘werase’ + Erase the last word typed. Non-POSIX. + +‘lnext’ + Enter the next character typed literally, even if it is a special + character. Non-POSIX. + + +File: coreutils.info, Node: Special, Prev: Characters, Up: stty invocation + +19.2.7 Special settings +----------------------- + +‘min N’ + Set the minimum number of characters that will satisfy a read until + the time value has expired, when ‘-icanon’ is set. + +‘time N’ + Set the number of tenths of a second before reads time out if the + minimum number of characters have not been read, when ‘-icanon’ is + set. + +‘ispeed N’ + Set the input speed to N. + +‘ospeed N’ + Set the output speed to N. + +‘rows N’ + Tell the tty kernel driver that the terminal has N rows. + Non-POSIX. + +‘cols N’ +‘columns N’ + Tell the kernel that the terminal has N columns. Non-POSIX. + +‘drain’ + Apply settings after first waiting for pending output to be + transmitted. This is enabled by default for GNU ‘stty’. Note this + is treated as an option rather than a line setting, and will follow + the option processing rules described in the summary above. It is + useful to disable this option in cases where the system may be in a + state where serial transmission is not possible. For example, if + the system has received the ‘DC3’ character with ‘ixon’ (software + flow control) enabled, then ‘stty’ would block without ‘-drain’ + being specified. May be negated. Non-POSIX. + +‘size’ + Print the number of rows and columns that the kernel thinks the + terminal has. (Systems that don’t support rows and columns in the + kernel typically use the environment variables ‘LINES’ and + ‘COLUMNS’ instead; however, GNU ‘stty’ does not know anything about + them.) Non-POSIX. + +‘line N’ + Use line discipline N. Non-POSIX. + +‘speed’ + Print the terminal speed. + +‘N’ + Set the input and output speeds to N. N can be one of: 0 50 75 110 + 134 134.5 150 200 300 600 1200 1800 2400 4800 9600 19200 38400 + ‘exta’ ‘extb’. ‘exta’ is the same as 19200; ‘extb’ is the same as + 38400. Many systems, including GNU/Linux, support higher speeds. + The ‘stty’ command includes support for speeds of 57600, 115200, + 230400, 460800, 500000, 576000, 921600, 1000000, 1152000, 1500000, + 2000000, 2500000, 3000000, 3500000, or 4000000 where the system + supports these. 0 hangs up the line if ‘-clocal’ is set. + + +File: coreutils.info, Node: printenv invocation, Next: tty invocation, Prev: stty invocation, Up: Working context + +19.3 ‘printenv’: Print all or some environment variables +======================================================== + +‘printenv’ prints environment variable values. Synopsis: + + printenv [OPTION] [VARIABLE]... + + If no VARIABLEs are specified, ‘printenv’ prints the value of every +environment variable. Otherwise, it prints the value of each VARIABLE +that is set, and nothing for those that are not set. + + The program accepts the following option. Also see *note Common +options::. + +‘-0’ +‘--null’ + Output a zero byte (ASCII NUL) at the end of each line, rather than + a newline. This option enables other programs to parse the output + even when that output would contain data with embedded newlines. + + Exit status: + + 0 if all variables specified were found + 1 if at least one specified variable was not found + 2 if a write error occurred + + +File: coreutils.info, Node: tty invocation, Prev: printenv invocation, Up: Working context + +19.4 ‘tty’: Print file name of terminal on standard input +========================================================= + +‘tty’ prints the file name of the terminal connected to its standard +input. It prints ‘not a tty’ if standard input is not a terminal. +Synopsis: + + tty [OPTION]... + + The program accepts the following option. Also see *note Common +options::. + +‘-s’ +‘--silent’ +‘--quiet’ + Print nothing; only return an exit status. + + Exit status: + + 0 if standard input is a terminal + 1 if standard input is a non-terminal file + 2 if given incorrect arguments + 3 if a write error occurs + + +File: coreutils.info, Node: User information, Next: System context, Prev: Working context, Up: Top + +20 User information +******************* + +This section describes commands that print user-related information: +logins, groups, and so forth. + +* Menu: + +* id invocation:: Print user identity. +* logname invocation:: Print current login name. +* whoami invocation:: Print effective user ID. +* groups invocation:: Print group names a user is in. +* users invocation:: Print login names of users currently logged in. +* who invocation:: Print who is currently logged in. + + +File: coreutils.info, Node: id invocation, Next: logname invocation, Up: User information + +20.1 ‘id’: Print user identity +============================== + +‘id’ prints information about the given user, or the process running it +if no user is specified. Synopsis: + + id [OPTION]... [USER]... + + USER can be either a user ID or a name, with name look-up taking +precedence unless the ID is specified with a leading ‘+’. *Note +Disambiguating names and IDs::. + + By default, it prints the real user ID, real group ID, effective user +ID if different from the real user ID, effective group ID if different +from the real group ID, and supplemental group IDs. In addition, if +SELinux is enabled and the ‘POSIXLY_CORRECT’ environment variable is not +set, then print ‘context=C’, where C is the security context. + + Each of these numeric values is preceded by an identifying string and +followed by the corresponding user or group name in parentheses. + + The options cause ‘id’ to print only part of the above information. +Also see *note Common options::. + +‘-g’ +‘--group’ + Print only the group ID. + +‘-G’ +‘--groups’ + Print only the group ID and the supplementary groups. + +‘-n’ +‘--name’ + Print the user or group name instead of the ID number. Requires + ‘-u’, ‘-g’, or ‘-G’. + +‘-r’ +‘--real’ + Print the real, instead of effective, user or group ID. Requires + ‘-u’, ‘-g’, or ‘-G’. + +‘-u’ +‘--user’ + Print only the user ID. + +‘-Z’ +‘--context’ + Print only the security context of the process, which is generally + the user’s security context inherited from the parent process. If + neither SELinux or SMACK is enabled then print a warning and set + the exit status to 1. + +‘-z’ +‘--zero’ + Delimit output items with ASCII NUL characters. This option is not + permitted when using the default format. When multiple users are + specified, and the ‘--groups’ option is also in effect, groups are + delimited with a single NUL character, while users are delimited + with two NUL characters. + + Example: + $ id -Gn --zero + users <NUL> devs <NUL> + + Primary and supplementary groups for a process are normally inherited +from its parent and are usually unchanged since login. This means that +if you change the group database after logging in, ‘id’ will not reflect +your changes within your existing login session. Running ‘id’ with a +user argument causes the user and group database to be consulted afresh, +and so will give a different result. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: logname invocation, Next: whoami invocation, Prev: id invocation, Up: User information + +20.2 ‘logname’: Print current login name +======================================== + +‘logname’ prints the calling user’s name, as found in a +system-maintained file (often ‘/var/run/utmp’ or ‘/etc/utmp’), and exits +with a status of 0. If there is no entry for the calling process, +‘logname’ prints an error message and exits with a status of 1. + + The only options are ‘--help’ and ‘--version’. *Note Common +options::. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: whoami invocation, Next: groups invocation, Prev: logname invocation, Up: User information + +20.3 ‘whoami’: Print effective user name +======================================== + +‘whoami’ prints the user name associated with the current effective user +ID. It is equivalent to the command ‘id -un’. + + The only options are ‘--help’ and ‘--version’. *Note Common +options::. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: groups invocation, Next: users invocation, Prev: whoami invocation, Up: User information + +20.4 ‘groups’: Print group names a user is in +============================================= + +‘groups’ prints the names of the primary and any supplementary groups +for each given USERNAME, or the current process if no names are given. +If more than one name is given, the name of each user is printed before +the list of that user’s groups and the user name is separated from the +group list by a colon. Synopsis: + + groups [USERNAME]... + + The group lists are equivalent to the output of the command ‘id -Gn’. + + The only options are ‘--help’ and ‘--version’. *Note Common +options::. + + Primary and supplementary groups for a process are normally inherited +from its parent and are usually unchanged since login. This means that +if you change the group database after logging in, ‘groups’ will not +reflect your changes within your existing login session. Running +‘groups’ with a list of users causes the user and group database to be +consulted afresh, and so will give a different result. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: users invocation, Next: who invocation, Prev: groups invocation, Up: User information + +20.5 ‘users’: Print login names of users currently logged in +============================================================ + +‘users’ prints on a single line a blank-separated list of user names of +users currently logged in to the current host. Each user name +corresponds to a login session, so if a user has more than one login +session, that user’s name will appear the same number of times in the +output. Synopsis: + + users [FILE] + + With no FILE argument, ‘users’ extracts its information from a +system-maintained file (often ‘/var/run/utmp’ or ‘/etc/utmp’). If a +file argument is given, ‘users’ uses that file instead. A common choice +is ‘/var/log/wtmp’. + + The only options are ‘--help’ and ‘--version’. *Note Common +options::. + + The ‘users’ command is installed only on platforms with the POSIX +‘<utmpx.h>’ include file or equivalent, so portable scripts should not +rely on its existence on non-POSIX platforms. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: who invocation, Prev: users invocation, Up: User information + +20.6 ‘who’: Print who is currently logged in +============================================ + +‘who’ prints information about users who are currently logged on. +Synopsis: + + who [OPTION] [FILE] [am i] + + If given no non-option arguments, ‘who’ prints the following +information for each user currently logged on: login name, terminal +line, login time, and remote hostname or X display. + + If given one non-option argument, ‘who’ uses that instead of a +default system-maintained file (often ‘/var/run/utmp’ or ‘/etc/utmp’) as +the name of the file containing the record of users logged on. +‘/var/log/wtmp’ is commonly given as an argument to ‘who’ to look at who +has previously logged on. + + If given two non-option arguments, ‘who’ prints only the entry for +the user running it (determined from its standard input), preceded by +the hostname. Traditionally, the two arguments given are ‘am i’, as in +‘who am i’. + + Timestamps are listed according to the time zone rules specified by +the ‘TZ’ environment variable, or by the system default rules if ‘TZ’ is +not set. *Note Specifying the Time Zone with ‘TZ’: (libc)TZ Variable. + + The program accepts the following options. Also see *note Common +options::. + +‘-a’ +‘--all’ + Same as ‘-b -d --login -p -r -t -T -u’. + +‘-b’ +‘--boot’ + Print the date and time of last system boot. + +‘-d’ +‘--dead’ + Print information corresponding to dead processes. + +‘-H’ +‘--heading’ + Print a line of column headings. + +‘-l’ +‘--login’ + List only the entries that correspond to processes via which the + system is waiting for a user to login. The user name is always + ‘LOGIN’. + +‘--lookup’ + Attempt to canonicalize hostnames found in utmp through a DNS + lookup. This is not the default because it can cause significant + delays on systems with automatic dial-up internet access. + +‘-m’ + Same as ‘who am i’. + +‘-p’ +‘--process’ + List active processes spawned by init. + +‘-q’ +‘--count’ + Print only the login names and the number of users logged on. + Overrides all other options. + +‘-r’ +‘--runlevel’ + Print the current (and maybe previous) run-level of the init + process. + +‘-s’ + Ignored; for compatibility with other versions of ‘who’. + +‘-t’ +‘--time’ + Print last system clock change. + +‘-u’ + After the login time, print the number of hours and minutes that + the user has been idle. ‘.’ means the user was active in the last + minute. ‘old’ means the user has been idle for more than 24 hours. + +‘-w’ +‘-T’ +‘--mesg’ +‘--message’ +‘--writable’ + After each login name print a character indicating the user’s + message status: + + ‘+’ allowing ‘write’ messages + ‘-’ disallowing ‘write’ messages + ‘?’ cannot find terminal device + + The ‘who’ command is installed only on platforms with the POSIX +‘<utmpx.h>’ include file or equivalent, so portable scripts should not +rely on its existence on non-POSIX platforms. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: System context, Next: SELinux context, Prev: User information, Up: Top + +21 System context +***************** + +This section describes commands that print or change system-wide +information. + +* Menu: + +* date invocation:: Print or set system date and time. +* arch invocation:: Print machine hardware name. +* nproc invocation:: Print the number of processors. +* uname invocation:: Print system information. +* hostname invocation:: Print or set system name. +* hostid invocation:: Print numeric host identifier. +* uptime invocation:: Print system uptime and load. + + +File: coreutils.info, Node: date invocation, Next: arch invocation, Up: System context + +21.1 ‘date’: Print or set system date and time +============================================== + +Synopses: + + date [OPTION]... [+FORMAT] + date [-u|--utc|--universal] [ MMDDhhmm[[CC]YY][.ss] ] + + The ‘date’ command displays the date and time. With the ‘--set’ +(‘-s’) option, or with ‘MMDDhhmm[[CC]YY][.ss]’, it sets the date and +time. + + Invoking ‘date’ with no FORMAT argument is equivalent to invoking it +with a default format that depends on the ‘LC_TIME’ locale category. In +the default C locale, this format is ‘'+%a %b %e %H:%M:%S %Z %Y'’, so +the output looks like ‘Thu Jul 9 17:00:00 EDT 2020’. + + Normally, ‘date’ uses the time zone rules indicated by the ‘TZ’ +environment variable, or the system default rules if ‘TZ’ is not set. +*Note Specifying the Time Zone with ‘TZ’: (libc)TZ Variable. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + +* Menu: + +* Date format specifiers:: Used in ‘date '+...'’ +* Setting the time:: Changing the system clock. +* Options for date:: Instead of the current time. +* Date input formats:: Specifying date strings. +* Examples of date:: Examples. + + +File: coreutils.info, Node: Date format specifiers, Next: Setting the time, Up: date invocation + +21.1.1 Specifying the format of ‘date’ output +--------------------------------------------- + +If given an argument that starts with a ‘+’, ‘date’ prints the current +date and time (or the date and time specified by the ‘--date’ option, +see below) in the format defined by that argument, which is similar to +that of the ‘strftime’ function. Except for conversion specifiers, +which start with ‘%’, characters in the format string are printed +unchanged. The conversion specifiers are described below. + +* Menu: + +* Time conversion specifiers:: %[HIklMNpPrRsSTXzZ] +* Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY] +* Literal conversion specifiers:: %[%nt] +* Padding and other flags:: Pad with zeros, spaces, etc. + + +File: coreutils.info, Node: Time conversion specifiers, Next: Date conversion specifiers, Up: Date format specifiers + +21.1.1.1 Time conversion specifiers +................................... + +‘date’ conversion specifiers related to times. + +‘%H’ + hour (‘00’...‘23’) +‘%I’ + hour (‘01’...‘12’) +‘%k’ + hour, space padded (‘ 0’...‘23’); equivalent to ‘%_H’. This is a + GNU extension. +‘%l’ + hour, space padded (‘ 1’...‘12’); equivalent to ‘%_I’. This is a + GNU extension. +‘%M’ + minute (‘00’...‘59’) +‘%N’ + nanoseconds (‘000000000’...‘999999999’). This is a GNU extension. +‘%p’ + locale’s equivalent of either ‘AM’ or ‘PM’; blank in many locales. + Noon is treated as ‘PM’ and midnight as ‘AM’. +‘%P’ + like ‘%p’, except lower case. This is a GNU extension. +‘%r’ + locale’s 12-hour clock time (e.g., ‘11:11:04 PM’) +‘%R’ + 24-hour hour and minute. Same as ‘%H:%M’. +‘%s’ + seconds since the Epoch, i.e., since 1970-01-01 00:00 UTC. Leap + seconds are not counted unless leap second support is available. + *Note %s-examples::, for examples. This is a GNU extension. +‘%S’ + second (‘00’...‘60’). This may be ‘60’ if leap seconds are + supported. +‘%T’ + 24-hour hour, minute, and second. Same as ‘%H:%M:%S’. +‘%X’ + locale’s time representation (e.g., ‘23:13:48’) +‘%z’ + Four-digit numeric time zone, e.g., ‘-0600’ or ‘+0530’, or ‘-0000’ + if no time zone is determinable. This value reflects the numeric + time zone appropriate for the current time, using the time zone + rules specified by the ‘TZ’ environment variable. A time zone is + not determinable if its numeric offset is zero and its abbreviation + begins with ‘-’. The time (and optionally, the time zone rules) + can be overridden by the ‘--date’ option. +‘%:z’ + Numeric time zone with ‘:’, e.g., ‘-06:00’ or ‘+05:30’), or + ‘-00:00’ if no time zone is determinable. This is a GNU extension. +‘%::z’ + Numeric time zone to the nearest second with ‘:’ (e.g., ‘-06:00:00’ + or ‘+05:30:00’), or ‘-00:00:00’ if no time zone is determinable. + This is a GNU extension. +‘%:::z’ + Numeric time zone with ‘:’ using the minimum necessary precision + (e.g., ‘-06’, ‘+05:30’, or ‘-04:56:02’), or ‘-00’ if no time zone + is determinable. This is a GNU extension. +‘%Z’ + alphabetic time zone abbreviation (e.g., ‘EDT’), or nothing if no + time zone is determinable. See ‘%z’ for how it is determined. + + +File: coreutils.info, Node: Date conversion specifiers, Next: Literal conversion specifiers, Prev: Time conversion specifiers, Up: Date format specifiers + +21.1.1.2 Date conversion specifiers +................................... + +‘date’ conversion specifiers related to dates. + +‘%a’ + locale’s abbreviated weekday name (e.g., ‘Sun’) +‘%A’ + locale’s full weekday name, variable length (e.g., ‘Sunday’) +‘%b’ + locale’s abbreviated month name (e.g., ‘Jan’) +‘%B’ + locale’s full month name, variable length (e.g., ‘January’) +‘%c’ + locale’s date and time (e.g., ‘Thu Mar 3 23:05:25 2020’) +‘%C’ + century. This is like ‘%Y’, except the last two digits are + omitted. For example, it is ‘20’ if ‘%Y’ is ‘2019’, and is ‘-0’ if + ‘%Y’ is ‘-001’. It is normally at least two characters, but it may + be more. +‘%d’ + day of month (e.g., ‘01’) +‘%D’ + date; same as ‘%m/%d/%y’ +‘%e’ + day of month, space padded; same as ‘%_d’ +‘%F’ + full date in ISO 8601 format; like ‘%+4Y-%m-%d’ except that any + flags or field width override the ‘+’ and (after subtracting 6) the + ‘4’. This is a good choice for a date format, as it is standard + and is easy to sort in the usual case where years are in the range + 0000...9999. +‘%g’ + year corresponding to the ISO week number, but without the century + (range ‘00’ through ‘99’). This has the same format and value as + ‘%y’, except that if the ISO week number (see ‘%V’) belongs to the + previous or next year, that year is used instead. +‘%G’ + year corresponding to the ISO week number. This has the same + format and value as ‘%Y’, except that if the ISO week number (see + ‘%V’) belongs to the previous or next year, that year is used + instead. It is normally useful only if ‘%V’ is also used; for + example, the format ‘%G-%m-%d’ is probably a mistake, since it + combines the ISO week number year with the conventional month and + day. +‘%h’ + same as ‘%b’ +‘%j’ + day of year (‘001’...‘366’) +‘%m’ + month (‘01’...‘12’) +‘%q’ + quarter of year (‘1’...‘4’) +‘%u’ + day of week (‘1’...‘7’) with ‘1’ corresponding to Monday +‘%U’ + week number of year, with Sunday as the first day of the week + (‘00’...‘53’). Days in a new year preceding the first Sunday are + in week zero. +‘%V’ + ISO week number, that is, the week number of year, with Monday as + the first day of the week (‘01’...‘53’). If the week containing + January 1 has four or more days in the new year, then it is + considered week 1; otherwise, it is week 53 of the previous year, + and the next week is week 1. (See the ISO 8601 standard.) +‘%w’ + day of week (‘0’...‘6’) with 0 corresponding to Sunday +‘%W’ + week number of year, with Monday as first day of week + (‘00’...‘53’). Days in a new year preceding the first Monday are + in week zero. +‘%x’ + locale’s date representation (e.g., ‘12/31/99’) +‘%y’ + last two digits of year (‘00’...‘99’) +‘%Y’ + year. This is normally at least four characters, but it may be + more. Year ‘0000’ precedes year ‘0001’, and year ‘-001’ precedes + year ‘0000’. + + +File: coreutils.info, Node: Literal conversion specifiers, Next: Padding and other flags, Prev: Date conversion specifiers, Up: Date format specifiers + +21.1.1.3 Literal conversion specifiers +...................................... + +‘date’ conversion specifiers that produce literal strings. + +‘%%’ + a literal % +‘%n’ + a newline +‘%t’ + a horizontal tab + + +File: coreutils.info, Node: Padding and other flags, Prev: Literal conversion specifiers, Up: Date format specifiers + +21.1.1.4 Padding and other flags +................................ + +Unless otherwise specified, ‘date’ normally pads numeric fields with +zeros, so that, for example, numeric months are always output as two +digits. Most numeric fields are padded on the left. However, +nanoseconds are padded on the right since they are commonly used after +decimal points in formats like ‘%s.%-N’. Also, seconds since the Epoch +are not padded since there is no natural width for them. + + The following optional flags can appear after the ‘%’: + +‘-’ + (hyphen) Do not pad the field; useful if the output is intended for + human consumption. This is a GNU extension. As a special case, + ‘%-N’ outputs only enough trailing digits to not lose information, + assuming that the timestamp’s resolution is the same as the current + hardware clock. For example, if the hardware clock resolution is 1 + microsecond, ‘%s.%-N’ outputs something like ‘1640890100.395710’. + +‘_’ + (underscore) Pad with spaces; useful if you need a fixed number of + characters in the output, but zeros are too distracting. This is a + GNU extension. +‘0’ + (zero) Pad with zeros even if the conversion specifier would + normally pad with spaces. +‘+’ + Pad with zeros, like ‘0’. In addition, precede any year number + with ‘+’ if it exceeds 9999 or if its field width exceeds 4; + similarly, precede any century number with ‘+’ if it exceeds 99 or + if its field width exceeds 2. This supports ISO 8601 formats for + dates far in the future; for example, the command ‘date + --date=12019-02-25 +%+13F’ outputs the string ‘+012019-02-25’. +‘^’ + Use upper case characters if possible. This is a GNU extension. +‘#’ + Use opposite case characters if possible. A field that is normally + upper case becomes lower case, and vice versa. This is a GNU + extension. + +Here are some examples of padding: + + date +%d/%m -d "Feb 1" + ⇒ 01/02 + date +%-d/%-m -d "Feb 1" + ⇒ 1/2 + date +%_d/%_m -d "Feb 1" + ⇒ 1/ 2 + + You can optionally specify the field width (after any flag, if +present) as a decimal number. If the natural size of the output of the +field has less than the specified number of characters, the result is +normally written right adjusted and padded to the given size. For +example, ‘%9B’ prints the right adjusted month name in a field of width +9. Nanoseconds are left adjusted, and are truncated or padded to the +field width. + + An optional modifier can follow the optional flag and width +specification. The modifiers are: + +‘E’ + Use the locale’s alternate representation for date and time. This + modifier applies to the ‘%c’, ‘%C’, ‘%x’, ‘%X’, ‘%y’ and ‘%Y’ + conversion specifiers. In a Japanese locale, for example, ‘%Ex’ + might yield a date format based on the Japanese Emperors’ reigns. + +‘O’ + Use the locale’s alternate numeric symbols for numbers. This + modifier applies only to numeric conversion specifiers. + + If the format supports the modifier but no alternate representation +is available, it is ignored. + + POSIX specifies the behavior of flags and field widths only for ‘%C’, +‘%F’, ‘%G’, and ‘%Y’ (all without modifiers), and requires a flag to be +present if and only if a field width is also present. Other +combinations of flags, field widths and modifiers are GNU extensions. + + +File: coreutils.info, Node: Setting the time, Next: Options for date, Prev: Date format specifiers, Up: date invocation + +21.1.2 Setting the time +----------------------- + +You must have appropriate privileges to set the system clock. For +changes to persist across a reboot, the hardware clock may need to be +updated from the system clock, which might not happen automatically on +your system. + + To set the clock, you can use the ‘--set’ (‘-s’) option (*note +Options for date::). To set the clock without using GNU extensions, you +can give ‘date’ an argument of the form ‘MMDDhhmm[[CC]YY][.ss]’ where +each two-letter component stands for two digits with the following +meanings: + +MM + month +DD + day within month +HH + hour +MM + minute +CC + first two digits of year (optional) +YY + last two digits of year (optional) +SS + second (optional) + + Note, the ‘--date’ and ‘--set’ options may not be used with an +argument in the above format. The ‘--universal’ option may be used with +such an argument to indicate that the specified date and time are +relative to Universal Time rather than to the local time zone. + + +File: coreutils.info, Node: Options for date, Next: Examples of date, Prev: Setting the time, Up: date invocation + +21.1.3 Options for ‘date’ +------------------------- + +The program accepts the following options. Also see *note Common +options::. Except for ‘-u’, these options are all GNU extensions to +POSIX. + + All options that specify the date to display are mutually exclusive. +I.e.: ‘--date’, ‘--file’, ‘--reference’, ‘--resolution’. + +‘-d DATESTR’ +‘--date=DATESTR’ + Display the date and time specified in DATESTR instead of the + current date and time. DATESTR can be in almost any common format. + It can contain month names, time zones, ‘am’ and ‘pm’, ‘yesterday’, + etc. For example, ‘--date="2020-07-21 14:19:13.489392193 +0530"’ + specifies the instant of time that is 489,392,193 nanoseconds after + July 21, 2020 at 2:19:13 PM in a time zone that is 5 hours and 30 + minutes east of UTC. + Note: input currently must be in locale independent format. E.g., + the LC_TIME=C below is needed to print back the correct date in + many locales: + date -d "$(LC_TIME=C date)" + *Note Date input formats::. + +‘--debug’ + Annotate the parsed date, display the effective time zone, and warn + about potential misuse. + +‘-f DATEFILE’ +‘--file=DATEFILE’ + Parse each line in DATEFILE as with ‘-d’ and display the resulting + date and time. If DATEFILE is ‘-’, use standard input. This is + useful when you have many dates to process, because the system + overhead of starting up the ‘date’ executable many times can be + considerable. + +‘-I[TIMESPEC]’ +‘--iso-8601[=TIMESPEC]’ + Display the date using an ISO 8601 format, ‘%Y-%m-%d’. + + The argument TIMESPEC specifies the number of additional terms of + the time to include. It can be one of the following: + ‘auto’ + Print just the date. This is the default if TIMESPEC is + omitted. This is like the format ‘%Y-%m-%d’. + + ‘hours’ + Also print hours and time zone. This is like the format + ‘%Y-%m-%dT%H%:z’. + + ‘minutes’ + Also print minutes. This is like the format + ‘%Y-%m-%dT%H:%M%:z’. + + ‘seconds’ + Also print seconds. This is like the format + ‘%Y-%m-%dT%H:%M:%S%:z’. + + ‘ns’ + Also print nanoseconds. This is like the format + ‘%Y-%m-%dT%H:%M:%S,%N%:z’. + + This format is always suitable as input for the ‘--date’ (‘-d’) and + ‘--file’ (‘-f’) options, regardless of the current locale. + +‘-r FILE’ +‘--reference=FILE’ + Display the date and time of the last modification of FILE, instead + of the current date and time. + +‘--resolution’ + Display the timestamp resolution instead of the time. Current + clock timestamps that are output by ‘date’ are integer multiples of + the timestamp resolution. With this option, the format defaults to + ‘%s.%N’. For example, if the clock resolution is 1 millisecond, + the output is: + + 0.001000000 + +‘-R’ +‘--rfc-email’ + Display the date and time using the format ‘%a, %d %b %Y %H:%M:%S + %z’, evaluated in the C locale so abbreviations are always in + English. For example: + + Mon, 09 Jul 2020 17:00:00 -0400 + + This format conforms to Internet RFCs 5322 + (https://tools.ietf.org/search/rfc5322), 2822 + (https://tools.ietf.org/search/rfc2822) and 822 + (https://tools.ietf.org/search/rfc822), the current and previous + standards for Internet email. For compatibility with older + versions of ‘date’, ‘--rfc-2822’ and ‘--rfc-822’ are aliases for + ‘--rfc-email’. + +‘--rfc-3339=TIMESPEC’ + Display the date using a format specified by Internet RFC 3339 + (https://tools.ietf.org/search/rfc3339). This is like + ‘--iso-8601’, except that a space rather than a ‘T’ separates dates + from times, and a period rather than a comma separates seconds from + subseconds. This format is always suitable as input for the + ‘--date’ (‘-d’) and ‘--file’ (‘-f’) options, regardless of the + current locale. + + The argument TIMESPEC specifies how much of the time to include. + It can be one of the following: + + ‘date’ + Print just the full-date, e.g., ‘2020-07-21’. This is like + the format ‘%Y-%m-%d’. + + ‘seconds’ + Print the full-date and full-time separated by a space, e.g., + ‘2020-07-21 04:30:37+05:30’. The output ends with a numeric + time-offset; here the ‘+05:30’ means that local time is five + hours and thirty minutes east of UTC. This is like the format + ‘%Y-%m-%d %H:%M:%S%:z’. + + ‘ns’ + Like ‘seconds’, but also print nanoseconds, e.g., ‘2020-07-21 + 04:30:37.998458565+05:30’. This is like the format ‘%Y-%m-%d + %H:%M:%S.%N%:z’. + +‘-s DATESTR’ +‘--set=DATESTR’ + Set the date and time to DATESTR. See ‘-d’ above. See also *note + Setting the time::. + +‘-u’ +‘--utc’ +‘--universal’ + Use Universal Time by operating as if the ‘TZ’ environment variable + were set to the string ‘UTC0’. UTC stands for Coordinated + Universal Time, established in 1960. Universal Time is often + called “Greenwich Mean Time” (GMT) for historical reasons. + Typically, systems ignore leap seconds and thus implement an + approximation to UTC rather than true UTC. + + +File: coreutils.info, Node: Examples of date, Prev: Options for date, Up: date invocation + +21.1.4 Examples of ‘date’ +------------------------- + +Here are a few examples. Also see the documentation for the ‘-d’ option +in the previous section. + + • To print the date of the day before yesterday: + + date --date='2 days ago' + + • To print the date of the day three months and one day hence: + + date --date='3 months 1 day' + + • To print the day of year of Christmas in the current year: + + date --date='25 Dec' +%j + + • To print the current full month name and the day of the month: + + date '+%B %d' + + But this may not be what you want because for the first nine days + of the month, the ‘%d’ expands to a zero-padded two-digit field, + for example ‘date -d 1may '+%B %d'’ will print ‘May 01’. + + • To print a date without the leading zero for one-digit days of the + month, you can use the (GNU extension) ‘-’ flag to suppress the + padding altogether: + + date -d 1may '+%B %-d' + + • To print the current date and time in the format required by many + non-GNU versions of ‘date’ when setting the system clock: + + date +%m%d%H%M%Y.%S + + • To set the system clock forward by two minutes: + + date --set='+2 minutes' + + • To print the date in Internet RFC 5322 format, use ‘date + --rfc-email’. Here is some example output: + + Tue, 09 Jul 2020 19:00:37 -0400 + + • To convert a date string to the number of seconds since the Epoch + (which is 1970-01-01 00:00 UTC), use the ‘--date’ option with the + ‘%s’ format. That can be useful in sorting and/or graphing and/or + comparing data by date. The following command outputs the number + of the seconds since the Epoch for the time two minutes after the + Epoch: + + date --date='1970-01-01 00:02:00 +0000' +%s + 120 + + To convert a date string from one time zone FROM to another TO, + specify ‘TZ="FROM"’ in the environment and ‘TZ="TO"’ in the + ‘--date’ option. *Note Specifying time zone rules::. For example: + + TZ="Asia/Tokyo" date --date='TZ="America/New_York" 2023-05-07 12:23' + Mon May 8 01:23:00 JST 2023 + + If you do not specify time zone information in the date string, + ‘date’ uses your computer’s idea of the time zone when interpreting + the string. For example, if your computer’s time zone is that of + Cambridge, Massachusetts, which was then 5 hours (i.e., 18,000 + seconds) behind UTC: + + # local time zone used + date --date='1970-01-01 00:02:00' +%s + 18120 + + • If you’re sorting or graphing dated data, your raw date values may + be represented as seconds since the Epoch. But few people can look + at the date ‘1577836800’ and casually note “Oh, that’s the first + second of the year 2020 in Greenwich, England.” + + date --date='2020-01-01 UTC' +%s + 1577836800 + + An alternative is to use the ‘--utc’ (‘-u’) option. Then you may + omit ‘UTC’ from the date string. Although this produces the same + result for ‘%s’ and many other format sequences, with a time zone + offset different from zero, it would give a different result for + zone-dependent formats like ‘%z’. + + date -u --date=2020-07-21 +%s + 1595289600 + + To convert such an unwieldy number of seconds back to a more + readable form, use a command like this: + + date -d @1595289600 +"%F %T %z" + 2020-07-20 20:00:00 -0400 + + Often it is better to output UTC-relative date and time: + + date -u -d @1595289600 +"%F %T %z" + 2020-07-21 00:00:00 +0000 + + • Typically the seconds count omits leap seconds, but some systems + are exceptions. Because leap seconds are not predictable, the + mapping between the seconds count and a future timestamp is not + reliable on the atypical systems that include leap seconds in their + counts. + + Here is how the two kinds of systems handle the leap second at the + end of the year 2016: + + # Typical systems ignore leap seconds: + date --date='2016-12-31 23:59:59 +0000' +%s + 1483228799 + date --date='2016-12-31 23:59:60 +0000' +%s + date: invalid date '2016-12-31 23:59:60 +0000' + date --date='2017-01-01 00:00:00 +0000' +%s + 1483228800 + + # Atypical systems count leap seconds: + date --date='2016-12-31 23:59:59 +0000' +%s + 1483228825 + date --date='2016-12-31 23:59:60 +0000' +%s + 1483228826 + date --date='2017-01-01 00:00:00 +0000' +%s + 1483228827 + + +File: coreutils.info, Node: arch invocation, Next: nproc invocation, Prev: date invocation, Up: System context + +21.2 ‘arch’: Print machine hardware name +======================================== + +‘arch’ prints the machine hardware name, and is equivalent to ‘uname +-m’. Synopsis: + + arch [OPTION] + + The program accepts the *note Common options:: only. + + ‘arch’ is not installed by default, so portable scripts should not +rely on its existence. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: nproc invocation, Next: uname invocation, Prev: arch invocation, Up: System context + +21.3 ‘nproc’: Print the number of available processors +====================================================== + +Print the number of processing units available to the current process, +which may be less than the number of online processors. If this +information is not accessible, then print the number of processors +installed. If the ‘OMP_NUM_THREADS’ or ‘OMP_THREAD_LIMIT’ environment +variables are set, then they will determine the minimum and maximum +returned value respectively. The result is guaranteed to be greater +than zero. Synopsis: + + nproc [OPTION] + + The program accepts the following options. Also see *note Common +options::. + +‘--all’ + Print the number of installed processors on the system, which may + be greater than the number online or available to the current + process. The ‘OMP_NUM_THREADS’ or ‘OMP_THREAD_LIMIT’ environment + variables are not honored in this case. + +‘--ignore=NUMBER’ + If possible, exclude this NUMBER of processing units. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: uname invocation, Next: hostname invocation, Prev: nproc invocation, Up: System context + +21.4 ‘uname’: Print system information +====================================== + +‘uname’ prints information about the machine and operating system it is +run on. If no options are given, ‘uname’ acts as if the ‘-s’ option +were given. Synopsis: + + uname [OPTION]... + + If multiple options or ‘-a’ are given, the selected information is +printed in this order: + + KERNEL-NAME NODENAME KERNEL-RELEASE KERNEL-VERSION + MACHINE PROCESSOR HARDWARE-PLATFORM OPERATING-SYSTEM + + The information may contain internal spaces, so such output cannot be +parsed reliably. In the following example, KERNEL-VERSION is ‘#1 SMP +Fri Jul 17 17:18:38 UTC 2020’: + + uname -a + ⇒ Linux dumdum.example.org 5.9.16-200.fc33.x86_64 #1 SMP Mon Dec 21 14:08:22 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux + + The program accepts the following options. Also see *note Common +options::. + +‘-a’ +‘--all’ + Print all of the below information, except omit the processor type + and the hardware platform name if they are unknown. + +‘-i’ +‘--hardware-platform’ + Print the hardware platform name (sometimes called the hardware + implementation). Print ‘unknown’ if this information is not + available. Note this is non-portable (even across GNU/Linux + distributions). + +‘-m’ +‘--machine’ + Print the machine hardware name (sometimes called the hardware + class or hardware type). + +‘-n’ +‘--nodename’ + Print the network node hostname. + +‘-p’ +‘--processor’ + Print the processor type (sometimes called the instruction set + architecture or ISA). Print ‘unknown’ if this information is not + available. Note this is non-portable (even across GNU/Linux + distributions). + +‘-o’ +‘--operating-system’ + Print the name of the operating system. + +‘-r’ +‘--kernel-release’ + Print the kernel release. + +‘-s’ +‘--kernel-name’ + Print the kernel name. POSIX 1003.1-2001 (*note Standards + conformance::) calls this “the implementation of the operating + system”, because the POSIX specification itself has no notion of + “kernel”. The kernel name might be the same as the operating + system name printed by the ‘-o’ or ‘--operating-system’ option, but + it might differ. Some operating systems (e.g., FreeBSD, HP-UX) + have the same name as their underlying kernels; others (e.g., + GNU/Linux, Solaris) do not. + +‘-v’ +‘--kernel-version’ + Print the kernel version. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: hostname invocation, Next: hostid invocation, Prev: uname invocation, Up: System context + +21.5 ‘hostname’: Print or set system name +========================================= + +With no arguments, ‘hostname’ prints the name of the current host +system. With one argument, it sets the current host name to the +specified string. You must have appropriate privileges to set the host +name. Synopsis: + + hostname [NAME] + + The only options are ‘--help’ and ‘--version’. *Note Common +options::. + + ‘hostname’ is not installed by default, and other packages also +supply a ‘hostname’ command, so portable scripts should not rely on its +existence or on the exact behavior documented above. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: hostid invocation, Next: uptime invocation, Prev: hostname invocation, Up: System context + +21.6 ‘hostid’: Print numeric host identifier +============================================ + +‘hostid’ prints the numeric identifier of the current host in +hexadecimal. This command accepts no arguments. The only options are +‘--help’ and ‘--version’. *Note Common options::. + + For example, here’s what it prints on one system I use: + + $ hostid + 1bac013d + + On that system, the 32-bit quantity happens to be closely related to +the system’s Internet address, but that isn’t always the case. + + ‘hostid’ is installed only on systems that have the ‘gethostid’ +function, so portable scripts should not rely on its existence. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: uptime invocation, Prev: hostid invocation, Up: System context + +21.7 ‘uptime’: Print system uptime and load +=========================================== + +‘uptime’ prints the current time, the system’s uptime, the number of +logged-in users and the current load average. + + If an argument is specified, it is used as the file to be read to +discover how many users are logged in. If no argument is specified, a +system default is used (‘uptime --help’ indicates the default setting). + + The only options are ‘--help’ and ‘--version’. *Note Common +options::. + + For example, here’s what it prints right now on one system I use: + + $ uptime + 14:07 up 3:35, 3 users, load average: 1.39, 1.15, 1.04 + + The precise method of calculation of load average varies somewhat +between systems. Some systems calculate it as the average number of +runnable processes over the last 1, 5 and 15 minutes, but some systems +also include processes in the uninterruptible sleep state (that is, +those processes which are waiting for device I/O). The Linux kernel +includes uninterruptible processes. + + ‘uptime’ is installed only on platforms with infrastructure for +obtaining the boot time, and other packages also supply an ‘uptime’ +command, so portable scripts should not rely on its existence or on the +exact behavior documented above. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: SELinux context, Next: Modified command invocation, Prev: System context, Up: Top + +22 SELinux context +****************** + +This section describes commands for operations with SELinux contexts. + +* Menu: + +* chcon invocation:: Change SELinux context of file +* runcon invocation:: Run a command in specified SELinux context + + +File: coreutils.info, Node: chcon invocation, Next: runcon invocation, Up: SELinux context + +22.1 ‘chcon’: Change SELinux context of file +============================================ + +‘chcon’ changes the SELinux security context of the selected files. +Synopses: + + chcon [OPTION]... CONTEXT FILE... + chcon [OPTION]... [-u USER] [-r ROLE] [-l RANGE] [-t TYPE] FILE... + chcon [OPTION]... --reference=RFILE FILE... + + Change the SELinux security context of each FILE to CONTEXT. With +‘--reference’, change the security context of each FILE to that of +RFILE. + + The program accepts the following options. Also see *note Common +options::. + +‘--dereference’ + Do not affect symbolic links but what they refer to; this is the + default. + +‘-h’ +‘--no-dereference’ + Affect the symbolic links themselves instead of any referenced + file. + +‘--reference=RFILE’ + Use RFILE’s security context rather than specifying a CONTEXT + value. + +‘-R’ +‘--recursive’ + Operate on files and directories recursively. + +‘--preserve-root’ + Refuse to operate recursively on the root directory, ‘/’, when used + together with the ‘--recursive’ option. *Note Treating / + specially::. + +‘--no-preserve-root’ + Do not treat the root directory, ‘/’, specially when operating + recursively; this is the default. *Note Treating / specially::. + +‘-H’ + If ‘--recursive’ (‘-R’) is specified and a command line argument is + a symbolic link to a directory, traverse it. *Note Traversing + symlinks::. + +‘-L’ + In a recursive traversal, traverse every symbolic link to a + directory that is encountered. *Note Traversing symlinks::. + +‘-P’ + Do not traverse any symbolic links. This is the default if none of + ‘-H’, ‘-L’, or ‘-P’ is specified. *Note Traversing symlinks::. + +‘-v’ +‘--verbose’ + Output a diagnostic for every file processed. + +‘-u USER’ +‘--user=USER’ + Set user USER in the target security context. + +‘-r ROLE’ +‘--role=ROLE’ + Set role ROLE in the target security context. + +‘-t TYPE’ +‘--type=TYPE’ + Set type TYPE in the target security context. + +‘-l RANGE’ +‘--range=RANGE’ + Set range RANGE in the target security context. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: runcon invocation, Prev: chcon invocation, Up: SELinux context + +22.2 ‘runcon’: Run a command in specified SELinux context +========================================================= + +‘runcon’ runs file in specified SELinux security context. + + Synopses: + runcon CONTEXT COMMAND [ARGS] + runcon [ -c ] [-u USER] [-r ROLE] [-t TYPE] [-l RANGE] COMMAND [ARGS] + + Run COMMAND with completely-specified CONTEXT, or with current or +transitioned security context modified by one or more of LEVEL, ROLE, +TYPE and USER. + + If none of ‘-c’, ‘-t’, ‘-u’, ‘-r’, or ‘-l’ is specified, the first +argument is used as the complete context. Any additional arguments +after COMMAND are interpreted as arguments to the command. + + With neither CONTEXT nor COMMAND, print the current security context. + + Note also the ‘setpriv’ command which can be used to set the +NO_NEW_PRIVS bit using ‘setpriv --no-new-privs runcon ...’, thus +disallowing usage of a security context with more privileges than the +process would normally have. + + ‘runcon’ accepts the following options. Also see *note Common +options::. + +‘-c’ +‘--compute’ + Compute process transition context before modifying. + +‘-u USER’ +‘--user=USER’ + Set user USER in the target security context. + +‘-r ROLE’ +‘--role=ROLE’ + Set role ROLE in the target security context. + +‘-t TYPE’ +‘--type=TYPE’ + Set type TYPE in the target security context. + +‘-l RANGE’ +‘--range=RANGE’ + Set range RANGE in the target security context. + + Exit status: + + 125 if ‘runcon’ itself fails + 126 if COMMAND is found but cannot be invoked + 127 if COMMAND cannot be found + the exit status of COMMAND otherwise + + +File: coreutils.info, Node: Modified command invocation, Next: Process control, Prev: SELinux context, Up: Top + +23 Modified command invocation +****************************** + +This section describes commands that run other commands in some context +different than the current one: a modified environment, as a different +user, etc. + +* Menu: + +* chroot invocation:: Modify the root directory. +* env invocation:: Modify environment variables. +* nice invocation:: Modify niceness. +* nohup invocation:: Immunize to hangups. +* stdbuf invocation:: Modify buffering of standard streams. +* timeout invocation:: Run with time limit. + + +File: coreutils.info, Node: chroot invocation, Next: env invocation, Up: Modified command invocation + +23.1 ‘chroot’: Run a command with a different root directory +============================================================ + +‘chroot’ runs a command with a specified root directory. On many +systems, only the super-user can do this.(1). Synopses: + + chroot OPTION NEWROOT [COMMAND [ARGS]...] + chroot OPTION + + Ordinarily, file names are looked up starting at the root of the +directory structure, i.e., ‘/’. ‘chroot’ changes the root to the +directory NEWROOT (which must exist), then changes the working directory +to ‘/’, and finally runs COMMAND with optional ARGS. If COMMAND is not +specified, the default is the value of the ‘SHELL’ environment variable +or ‘/bin/sh’ if not set, invoked with the ‘-i’ option. COMMAND must not +be a special built-in utility (*note Special built-in utilities::). + + The program accepts the following options. Also see *note Common +options::. Options must precede operands. + +‘--groups=GROUPS’ + Use this option to override the supplementary GROUPS to be used by + the new process. The items in the list (names or numeric IDs) must + be separated by commas. Use ‘--groups=''’ to disable the + supplementary group look-up implicit in the ‘--userspec’ option. + +‘--userspec=USER[:GROUP]’ + By default, COMMAND is run with the same credentials as the + invoking process. Use this option to run it as a different USER + and/or with a different primary GROUP. If a USER is specified then + the supplementary groups are set according to the system defined + list for that user, unless overridden with the ‘--groups’ option. + +‘--skip-chdir’ + Use this option to not change the working directory to ‘/’ after + changing the root directory to NEWROOT, i.e., inside the chroot. + This option is only permitted when NEWROOT is the old ‘/’ + directory, and therefore is mostly useful together with the + ‘--groups’ and ‘--userspec’ options to retain the previous working + directory. + + The user and group name look-up performed by the ‘--userspec’ and +‘--groups’ options, is done both outside and inside the chroot, with +successful look-ups inside the chroot taking precedence. If the +specified user or group items are intended to represent a numeric ID, +then a name to ID resolving step is avoided by specifying a leading ‘+’. +*Note Disambiguating names and IDs::. + + Here are a few tips to help avoid common problems in using chroot. +To start with a simple example, make COMMAND refer to a statically +linked binary. If you were to use a dynamically linked executable, then +you’d have to arrange to have the shared libraries in the right place +under your new root directory. + + For example, if you create a statically linked ‘ls’ executable, and +put it in ‘/tmp/empty’, you can run this command as root: + + $ chroot /tmp/empty /ls -Rl / + + Then you’ll see output like this: + + /: + total 1023 + -rwxr-xr-x 1 0 0 1041745 Aug 16 11:17 ls + + If you want to use a dynamically linked executable, say ‘bash’, then +first run ‘ldd bash’ to see what shared objects it needs. Then, in +addition to copying the actual binary, also copy the listed files to the +required positions under your intended new root directory. Finally, if +the executable requires any other files (e.g., data, state, device +files), copy them into place, too. + + ‘chroot’ is installed only on systems that have the ‘chroot’ +function, so portable scripts should not rely on its existence. + + Exit status: + + 125 if ‘chroot’ itself fails + 126 if COMMAND is found but cannot be invoked + 127 if COMMAND cannot be found + the exit status of COMMAND otherwise + + ---------- Footnotes ---------- + + (1) However, some systems (e.g., FreeBSD) can be configured to allow +certain regular users to use the ‘chroot’ system call, and hence to run +this program. Also, on Cygwin, anyone can run the ‘chroot’ command, +because the underlying function is non-privileged due to lack of support +in MS-Windows. Furthermore, the ‘chroot’ command avoids the ‘chroot’ +system call when NEWROOT is identical to the old ‘/’ directory for +consistency with systems where this is allowed for non-privileged users. + + +File: coreutils.info, Node: env invocation, Next: nice invocation, Prev: chroot invocation, Up: Modified command invocation + +23.2 ‘env’: Run a command in a modified environment +=================================================== + +‘env’ runs a command with a modified environment. Synopses: + + env [OPTION]... [NAME=VALUE]... [COMMAND [ARGS]...] + env -[v]S'[OPTION]... [NAME=VALUE]... [COMMAND [ARGS]...]' + env + + ‘env’ is commonly used on first line of scripts (shebang line): + #!/usr/bin/env COMMAND + #!/usr/bin/env -[v]S[OPTION]... [NAME=VALUE]... COMMAND [ARGS]... + + Operands of the form ‘VARIABLE=VALUE’ set the environment variable +VARIABLE to value VALUE. VALUE may be empty (‘VARIABLE=’). Setting a +variable to an empty value is different from unsetting it. These +operands are evaluated left-to-right, so if two operands mention the +same variable the earlier is ignored. + + Environment variable names can be empty, and can contain any +characters other than ‘=’ and ASCII NUL. However, it is wise to limit +yourself to names that consist solely of underscores, digits, and ASCII +letters, and that begin with a non-digit, as applications like the shell +do not work well with other names. + + The first operand that does not contain the character ‘=’ specifies +the program to invoke; it is searched for according to the ‘PATH’ +environment variable. Any remaining arguments are passed as arguments +to that program. The program should not be a special built-in utility +(*note Special built-in utilities::). + + Modifications to ‘PATH’ take effect prior to searching for COMMAND. +Use caution when reducing ‘PATH’; behavior is not portable when ‘PATH’ +is undefined or omits key directories such as ‘/bin’. + + In the rare case that a utility contains a ‘=’ in the name, the only +way to disambiguate it from a variable assignment is to use an +intermediate command for COMMAND, and pass the problematic program name +via ARGS. For example, if ‘./prog=’ is an executable in the current +‘PATH’: + + env prog= true # runs 'true', with prog= in environment + env ./prog= true # runs 'true', with ./prog= in environment + env -- prog= true # runs 'true', with prog= in environment + env sh -c '\prog= true' # runs 'prog=' with argument 'true' + env sh -c 'exec "$@"' sh prog= true # also runs 'prog=' + + If no command name is specified following the environment +specifications, the resulting environment is printed. This is like +specifying the ‘printenv’ program. + + For some examples, suppose the environment passed to ‘env’ contains +‘LOGNAME=rms’, ‘EDITOR=emacs’, and ‘PATH=.:/gnubin:/hacks’: + + • Output the current environment. + $ env | LC_ALL=C sort + EDITOR=emacs + LOGNAME=rms + PATH=.:/gnubin:/hacks + + • Run ‘foo’ with a reduced environment, preserving only the original + ‘PATH’ to avoid problems in locating ‘foo’. + env - PATH="$PATH" foo + + • Run ‘foo’ with the environment containing ‘LOGNAME=rms’, + ‘EDITOR=emacs’, and ‘PATH=.:/gnubin:/hacks’, and guarantees that + ‘foo’ was found in the file system rather than as a shell built-in. + env foo + + • Run ‘nemacs’ with the environment containing ‘LOGNAME=foo’, + ‘EDITOR=emacs’, ‘PATH=.:/gnubin:/hacks’, and ‘DISPLAY=gnu:0’. + env DISPLAY=gnu:0 LOGNAME=foo nemacs + + • Attempt to run the program ‘/energy/--’ (as that is the only + possible path search result); if the command exists, the + environment will contain ‘LOGNAME=rms’ and ‘PATH=/energy’, and the + arguments will be ‘e=mc2’, ‘bar’, and ‘baz’. + env -u EDITOR PATH=/energy -- e=mc2 bar baz + +23.2.1 General options +---------------------- + +The program accepts the following options. Also see *note Common +options::. Options must precede operands. + +‘-0’ +‘--null’ + Output a zero byte (ASCII NUL) at the end of each line, rather than + a newline. This option enables other programs to parse the output + even when that output would contain data with embedded newlines. + +‘-u NAME’ +‘--unset=NAME’ + Remove variable NAME from the environment, if it was in the + environment. + +‘-’ +‘-i’ +‘--ignore-environment’ + Start with an empty environment, ignoring the inherited + environment. + +‘-C DIR’ +‘--chdir=DIR’ + Change the working directory to DIR before invoking COMMAND. This + differs from the shell built-in ‘cd’ in that it starts COMMAND as a + subprocess rather than altering the shell’s own working directory; + this allows it to be chained with other commands that run commands + in a different context. For example: + + # Run 'true' with /chroot as its root directory and /srv as its working + # directory. + chroot /chroot env --chdir=/srv true + # Run 'true' with /build as its working directory, FOO=bar in its + # environment, and a time limit of five seconds. + env --chdir=/build FOO=bar timeout 5 true + +‘--default-signal[=SIG]’ + Unblock and reset signal SIG to its default signal handler. + Without SIG all known signals are unblocked and reset to their + defaults. Multiple signals can be comma-separated. An empty SIG + argument is a no-op. The following command runs ‘seq’ with SIGINT + and SIGPIPE set to their default (which is to terminate the + program): + + env --default-signal=PIPE,INT seq 1000 | head -n1 + + In the following example, we see how this is not possible to do + with traditional shells. Here the first trap command sets SIGPIPE + to ignore. The second trap command ostensibly sets it back to its + default, but POSIX mandates that the shell must not change + inherited state of the signal – so it is a no-op. + + trap '' PIPE && sh -c 'trap - PIPE ; seq inf | head -n1' + + Using ‘--default-signal=PIPE’ we can ensure the signal handling is + set to its default behavior: + + trap '' PIPE && sh -c 'env --default-signal=PIPE seq inf | head -n1' + +‘--ignore-signal[=SIG]’ + Ignore signal SIG when running a program. Without SIG all known + signals are set to ignore. Multiple signals can be + comma-separated. An empty SIG argument is a no-op. The following + command runs ‘seq’ with SIGINT set to be ignored – pressing + ‘Ctrl-C’ will not terminate it: + + env --ignore-signal=INT seq inf > /dev/null + + ‘SIGCHLD’ is special, in that ‘--ignore-signal=CHLD’ might have no + effect (POSIX says it’s unspecified). + + Most operating systems do not allow ignoring ‘SIGKILL’, ‘SIGSTOP’ + (and possibly other signals). Attempting to ignore these signals + will fail. + + Multiple (and contradictory) ‘--default-signal=SIG’ and + ‘--ignore-signal=SIG’ options are processed left-to-right, with the + latter taking precedence. In the following example, ‘SIGPIPE’ is + set to default while ‘SIGINT’ is ignored: + + env --default-signal=INT,PIPE --ignore-signal=INT + +‘--block-signal[=SIG]’ + Block signal(s) SIG from being delivered. Without SIG all known + signals are set to blocked. Multiple signals can be + comma-separated. An empty SIG argument is a no-op. + +‘--list-signal-handling’ + List blocked or ignored signals to standard error, before executing + a command. + +‘-v’ +‘--debug’ + Show verbose information for each processing step. + + $ env -v -uTERM A=B uname -s + unset: TERM + setenv: A=B + executing: uname + arg[0]= 'uname' + arg[1]= '-s' + Linux + + When combined with ‘-S’ it is recommended to list ‘-v’ first, e.g. + ‘env -vS'string'’. + +‘-S STRING’ +‘--split-string=STRING’ + process and split STRING into separate arguments used to pass + multiple arguments on shebang lines. ‘env’ supports FreeBSD’s + syntax of several escape sequences and environment variable + expansions. See below for details and examples. + + Exit status: + + 0 if no COMMAND is specified and the environment is output + 125 if ‘env’ itself fails + 126 if COMMAND is found but cannot be invoked + 127 if COMMAND cannot be found + the exit status of COMMAND otherwise + +23.2.2 ‘-S’/‘--split-string’ usage in scripts +--------------------------------------------- + +The ‘-S’/‘--split-string’ option enables use of multiple arguments on +the first line of scripts (the shebang line, ‘#!’). + + When a script’s interpreter is in a known location, scripts typically +contain the absolute file name in their first line: + +Shell script: #!/bin/sh + echo hello + +Perl script: #!/usr/bin/perl + print "hello\n"; + +Python script: #!/usr/bin/python3 + print("hello") + + + When a script’s interpreter is in a non-standard location in the +‘PATH’ environment variable, it is recommended to use ‘env’ on the first +line of the script to find the executable and run it: + +Shell script: #!/usr/bin/env bash + echo hello + +Perl script: #!/usr/bin/env perl + print "hello\n"; + +Python script: #!/usr/bin/env python3 + print("hello") + + + Most operating systems (e.g. GNU/Linux, BSDs) treat all text after +the first space as a single argument. When using ‘env’ in a script it +is thus not possible to specify multiple arguments. + + In the following example: + #!/usr/bin/env perl -T -w + print "hello\n"; + + The operating system treats ‘perl -T -w’ as one argument (the +program’s name), and executing the script fails with: + + /usr/bin/env: 'perl -T -w': No such file or directory + + The ‘-S’ option instructs ‘env’ to split the single string into +multiple arguments. The following example works as expected: + + $ cat hello.pl + #!/usr/bin/env -S perl -T -w + print "hello\n"; + + $ chmod a+x hello.pl + $ ./hello.pl + hello + + And is equivalent to running ‘perl -T -w hello.pl’ on the command +line prompt. + +Testing and troubleshooting +........................... + +To test ‘env -S’ on the command line, use single quotes for the ‘-S’ +string to emulate a single parameter. Single quotes are not needed when +using ‘env -S’ in a shebang line on the first line of a script (the +operating system already treats it as one argument). + + The following command is equivalent to the ‘hello.pl’ script above: + + $ env -S'perl -T -w' hello.pl + + To troubleshoot ‘-S’ usage add the ‘-v’ as the first argument (before +‘-S’). + + Using ‘-vS’ on a shebang line in a script: + + $ cat hello-debug.pl + #!/usr/bin/env -vS perl -T -w + print "hello\n"; + + $ chmod a+x hello-debug.pl + $ ./hello-debug.pl + split -S: 'perl -T -w' + into: 'perl' + & '-T' + & '-w' + executing: perl + arg[0]= 'perl' + arg[1]= '-T' + arg[2]= '-w' + arg[3]= './hello-debug.pl' + hello + + Using ‘-vS’ on the command line prompt (adding single quotes): + + $ env -vS'perl -T -w' hello-debug.pl + split -S: 'perl -T -w' + into: 'perl' + & '-T' + & '-w' + executing: perl + arg[0]= 'perl' + arg[1]= '-T' + arg[2]= '-w' + arg[3]= 'hello-debug.pl' + hello + +23.2.3 ‘-S’/‘--split-string’ syntax +----------------------------------- + +Splitting arguments by whitespace +................................. + +Running ‘env -Sstring’ splits the STRING into arguments based on +unquoted spaces or tab characters. (Newlines, carriage returns, +vertical tabs and form feeds are treated like spaces and tabs.) + + In the following contrived example the ‘awk’ variable ‘OFS’ will be +‘<space>xyz<space>’ as these spaces are inside double quotes. The other +space characters are used as argument separators: + + $ cat one.awk + #!/usr/bin/env -S awk -v OFS=" xyz " -f + BEGIN {print 1,2,3} + + $ chmod a+x one.awk + $ ./one.awk + 1 xyz 2 xyz 3 + + When using ‘-S’ on the command line prompt, remember to add single +quotes around the entire string: + + $ env -S'awk -v OFS=" xyz " -f' one.awk + 1 xyz 2 xyz 3 + +Escape sequences +................ + +‘env’ supports several escape sequences. These sequences are processed +when unquoted or inside double quotes (unless otherwise noted). Single +quotes disable escape sequences except ‘\'’ and ‘\\’. + +‘\c’ Ignore the remaining characters in the string. Cannot be used + inside double quotes. + +‘\f’ form-feed character (ASCII 0x0C) + +‘\n’ new-line character (ASCII 0x0A) + +‘\r’ carriage-return character (ASCII 0x0D) + +‘\t’ tab character (ASCII 0x09) + +‘\v’ vertical tab character (ASCII 0x0B) + +‘\#’ A hash ‘#’ character. Used when a ‘#’ character is needed as + the first character of an argument (see ’comments’ section + below). + +‘\$’ A dollar-sign character ‘$’. Unescaped ‘$’ characters are used + to expand environment variables (see ’variables’ section + below). + +‘\_’ Inside double-quotes, replaced with a single space character. + Outside quotes, treated as an argument separator. ‘\_’ can be + used to avoid space characters in a shebang line (see examples + below). + +‘\"’ A double-quote character. + +‘\'’ A single-quote character. This escape sequence works inside + single-quoted strings. + +‘\\’ A backslash character. This escape sequence works inside + single-quoted strings. + + + The following ‘awk’ script will use tab character as input and output +field separator (instead of spaces and tabs): + + $ cat tabs.awk + #!/usr/bin/env -S awk -v FS="\t" -v OFS="\t" -f + ... + +Comments +........ + +The escape sequence ‘\c’ (used outside single/double quotes) causes +‘env’ to ignore the rest of the string. + + The ‘#’ character causes ‘env’ to ignore the rest of the string when +it appears as the first character of an argument. Use ‘\#’ to reverse +this behavior. + + $ env -S'printf %s\n A B C' + A + B + C + + $ env -S'printf %s\n A# B C' + A# + B + C + + $ env -S'printf %s\n A #B C' + A + + $ env -S'printf %s\n A \#B C' + A + #B + C + + $ env -S'printf %s\n A\cB C' + A + + NOTE: The above examples use single quotes as they are executed on +the command-line. + +Environment variable expansion +.............................. + +The pattern ‘${VARNAME}’ is used to substitute a value from the +environment variable. The pattern must include the curly braces +(‘{’,‘}’). Without them ‘env’ will reject the string. Special shell +variables (such as ‘$@’, ‘$*’, ‘$$’) are not supported. + + If the environment variable is empty or not set, the pattern will be +replaced by an empty string. The value of ‘${VARNAME}’ will be that of +the executed ‘env’, before any modifications using +‘-i’/‘--ignore-environment’/‘-u’/‘--unset’ or setting new values using +‘VAR=VALUE’. + + The following python script prepends ‘/opt/custom/modules’ to the +python module search path environment variable (‘PYTHONPATH’): + + $ cat custom.py + #!/usr/bin/env -S PYTHONPATH=/opt/custom/modules/:${PYTHONPATH} python + print "hello" + ... + + The expansion of ‘${PYTHONPATH}’ is performed by ‘env’, not by a +shell. If the curly braces are omitted, ‘env’ will fail: + + $ cat custom.py + #!/usr/bin/env -S PYTHONPATH=/opt/custom/modules/:$PYTHONPATH python + print "hello" + ... + + $ chmod a+x custom.py + $ custom.py + /usr/bin/env: only ${VARNAME} expansion is supported, error at: $PYTHONPATH python + + Environment variable expansion happens before clearing the +environment (with ‘-i’) or unsetting specific variables (with ‘-u’): + + $ env -S'-i OLDUSER=${USER} env' + OLDUSER=gordon + + Use ‘-v’ to diagnose the operations step-by-step: + + $ env -vS'-i OLDUSER=${USER} env' + expanding ${USER} into 'gordon' + split -S: '-i OLDUSER=${USER} env' + into: '-i' + & 'OLDUSER=gordon' + & 'env' + cleaning environ + setenv: OLDUSER=gordon + executing: env + arg[0]= 'env' + OLDUSER=gordon + + +File: coreutils.info, Node: nice invocation, Next: nohup invocation, Prev: env invocation, Up: Modified command invocation + +23.3 ‘nice’: Run a command with modified niceness +================================================= + +‘nice’ prints a process’s “niceness”, or runs a command with modified +niceness. “niceness” affects how favorably the process is scheduled in +the system. Synopsis: + + nice [OPTION]... [COMMAND [ARG]...] + + If no arguments are given, ‘nice’ prints the current niceness. +Otherwise, ‘nice’ runs the given COMMAND with its niceness adjusted. By +default, its niceness is incremented by 10. + + Niceness values range at least from −20 (process has high priority +and gets more resources, thus slowing down other processes) through 19 +(process has lower priority and runs slowly itself, but has less impact +on the speed of other running processes). Some systems may have a wider +range of niceness values; conversely, other systems may enforce more +restrictive limits. An attempt to set the niceness outside the +supported range is treated as an attempt to use the minimum or maximum +supported value. + + A niceness should not be confused with a scheduling priority, which +lets applications determine the order in which threads are scheduled to +run. Unlike a priority, a niceness is merely advice to the scheduler, +which the scheduler is free to ignore. Also, as a point of terminology, +POSIX defines the behavior of ‘nice’ in terms of a “nice value”, which +is the non-negative difference between a niceness and the minimum +niceness. Though ‘nice’ conforms to POSIX, its documentation and +diagnostics use the term “niceness” for compatibility with historical +practice. + + COMMAND must not be a special built-in utility (*note Special +built-in utilities::). + + Due to shell aliases and built-in ‘nice’ functions, using an +unadorned ‘nice’ interactively or in a script may get you different +functionality than that described here. Invoke it via ‘env’ (i.e., ‘env +nice ...’) to avoid interference from the shell. + + Note to change the “niceness” of an existing process, one needs to +use the ‘renice’ command. + + The program accepts the following option. Also see *note Common +options::. Options must precede operands. + +‘-n ADJUSTMENT’ +‘--adjustment=ADJUSTMENT’ + Add ADJUSTMENT instead of 10 to the command’s niceness. If + ADJUSTMENT is negative and you lack appropriate privileges, ‘nice’ + issues a warning but otherwise acts as if you specified a zero + adjustment. + + For compatibility ‘nice’ also supports an obsolete option syntax + ‘-ADJUSTMENT’. New scripts should use ‘-n ADJUSTMENT’ instead. + + ‘nice’ is installed only on systems that have the POSIX ‘setpriority’ +function, so portable scripts should not rely on its existence on +non-POSIX platforms. + + Exit status: + + 0 if no COMMAND is specified and the niceness is output + 125 if ‘nice’ itself fails + 126 if COMMAND is found but cannot be invoked + 127 if COMMAND cannot be found + the exit status of COMMAND otherwise + + It is sometimes useful to run a non-interactive program with reduced +niceness. + + $ nice factor 4611686018427387903 + + Since ‘nice’ prints the current niceness, you can invoke it through +itself to demonstrate how it works. + + The default behavior is to increase the niceness by ‘10’: + + $ nice + 0 + $ nice nice + 10 + $ nice -n 10 nice + 10 + + The ADJUSTMENT is relative to the current niceness. In the next +example, the first ‘nice’ invocation runs the second one with niceness +10, and it in turn runs the final one with a niceness that is 3 more: + + $ nice nice -n 3 nice + 13 + + Specifying a niceness larger than the supported range is the same as +specifying the maximum supported value: + + $ nice -n 10000000000 nice + 19 + + Only a privileged user may run a process with lower niceness: + + $ nice -n -1 nice + nice: cannot set niceness: Permission denied + 0 + $ sudo nice -n -1 nice + -1 + + +File: coreutils.info, Node: nohup invocation, Next: stdbuf invocation, Prev: nice invocation, Up: Modified command invocation + +23.4 ‘nohup’: Run a command immune to hangups +============================================= + +‘nohup’ runs the given COMMAND with hangup signals ignored, so that the +command can continue running in the background after you log out. +Synopsis: + + nohup COMMAND [ARG]... + + If standard input is a terminal, redirect it so that terminal +sessions do not mistakenly consider the terminal to be used by the +command. Make the substitute file descriptor unreadable, so that +commands that mistakenly attempt to read from standard input can report +an error. This redirection is a GNU extension; programs intended to be +portable to non-GNU hosts can use ‘nohup COMMAND [ARG]... 0>/dev/null’ +instead. + + If standard output is a terminal, the command’s standard output is +appended to the file ‘nohup.out’; if that cannot be written to, it is +appended to the file ‘$HOME/nohup.out’; and if that cannot be written +to, the command is not run. Any ‘nohup.out’ or ‘$HOME/nohup.out’ file +created by ‘nohup’ is made readable and writable only to the user, +regardless of the current umask settings. + + If standard error is a terminal, it is normally redirected to the +same file descriptor as the (possibly-redirected) standard output. +However, if standard output is closed, standard error terminal output is +instead appended to the file ‘nohup.out’ or ‘$HOME/nohup.out’ as above. + + To capture the command’s output to a file other than ‘nohup.out’ you +can redirect it. For example, to capture the output of ‘make’: + + nohup make > make.log + + ‘nohup’ does not automatically put the command it runs in the +background; you must do that explicitly, by ending the command line with +an ‘&’. Also, ‘nohup’ does not alter the niceness of COMMAND; use +‘nice’ for that, e.g., ‘nohup nice COMMAND’. + + COMMAND must not be a special built-in utility (*note Special +built-in utilities::). + + The only options are ‘--help’ and ‘--version’. *Note Common +options::. Options must precede operands. + + Exit status: + + 125 if ‘nohup’ itself fails, and ‘POSIXLY_CORRECT’ is not set + 126 if COMMAND is found but cannot be invoked + 127 if COMMAND cannot be found + the exit status of COMMAND otherwise + + If ‘POSIXLY_CORRECT’ is set, internal failures give status 127 +instead of 125. + + +File: coreutils.info, Node: stdbuf invocation, Next: timeout invocation, Prev: nohup invocation, Up: Modified command invocation + +23.5 ‘stdbuf’: Run a command with modified I/O stream buffering +=============================================================== + +‘stdbuf’ allows one to modify the buffering operations of the three +standard I/O streams associated with a program. Synopsis: + + stdbuf OPTION... COMMAND + + COMMAND must start with the name of a program that + 1. uses the ISO C ‘FILE’ streams for input/output (note the programs + ‘dd’ and ‘cat’ don’t do that), + + 2. does not adjust the buffering of its standard streams (note the + program ‘tee’ is not in this category). + + Any additional ARGs are passed as additional arguments to the +COMMAND. + + The program accepts the following options. Also see *note Common +options::. + +‘-i MODE’ +‘--input=MODE’ + Adjust the standard input stream buffering. + +‘-o MODE’ +‘--output=MODE’ + Adjust the standard output stream buffering. + +‘-e MODE’ +‘--error=MODE’ + Adjust the standard error stream buffering. + + The MODE can be specified as follows: + +‘L’ + Set the stream to line buffered mode. In this mode data is + coalesced until a newline is output or input is read from any + stream attached to a terminal device. This option is invalid with + standard input. + +‘0’ + Disable buffering of the selected stream. In this mode, data is + output immediately and only the amount of data requested is read + from input. Note the difference in function for input and output. + Disabling buffering for input will not influence the responsiveness + or blocking behavior of the stream input functions. For example + ‘fread’ will still block until ‘EOF’ or error, even if the + underlying ‘read’ returns less data than requested. + +‘SIZE’ + Specify the size of the buffer to use in fully buffered mode. SIZE + may be, or may be an integer optionally followed by, one of the + following multiplicative suffixes: + ‘KB’ => 1000 (KiloBytes) + ‘K’ => 1024 (KibiBytes) + ‘MB’ => 1000*1000 (MegaBytes) + ‘M’ => 1024*1024 (MebiBytes) + ‘GB’ => 1000*1000*1000 (GigaBytes) + ‘G’ => 1024*1024*1024 (GibiBytes) + and so on for ‘T’, ‘P’, ‘E’, ‘Z’, ‘Y’, ‘R’, and ‘Q’. Binary + prefixes can be used, too: ‘KiB’=‘K’, ‘MiB’=‘M’, and so on. + + ‘stdbuf’ is installed only on platforms that use the Executable and +Linkable Format (ELF) and support the ‘constructor’ attribute, so +portable scripts should not rely on its existence. + + Exit status: + + 125 if ‘stdbuf’ itself fails + 126 if COMMAND is found but cannot be invoked + 127 if COMMAND cannot be found + the exit status of COMMAND otherwise + + +File: coreutils.info, Node: timeout invocation, Prev: stdbuf invocation, Up: Modified command invocation + +23.6 ‘timeout’: Run a command with a time limit +=============================================== + +‘timeout’ runs the given COMMAND and kills it if it is still running +after the specified time interval. Synopsis: + + timeout [OPTION] DURATION COMMAND [ARG]... + + COMMAND must not be a special built-in utility (*note Special +built-in utilities::). + + The program accepts the following options. Also see *note Common +options::. Options must precede operands. + +‘--preserve-status’ + Return the exit status of the managed COMMAND on timeout, rather + than a specific exit status indicating a timeout. This is useful + if the managed COMMAND supports running for an indeterminate amount + of time. + +‘--foreground’ + Don’t create a separate background program group, so that the + managed COMMAND can use the foreground TTY normally. This is + needed to support two situations when timing out commands, when not + invoking ‘timeout’ from an interactive shell. + 1. COMMAND is interactive and needs to read from the terminal for + example + 2. the user wants to support sending signals directly to COMMAND + from the terminal (like Ctrl-C for example) + + Note in this mode of operation, any children of COMMAND will not be + timed out. Also SIGCONT will not be sent to COMMAND, as it’s + generally not needed with foreground processes, and can cause + intermittent signal delivery issues with programs that are monitors + themselves (like GDB for example). + +‘-k DURATION’ +‘--kill-after=DURATION’ + Ensure the monitored COMMAND is killed by also sending a ‘KILL’ + signal. + + The specified DURATION starts from the point in time when ‘timeout’ + sends the initial signal to COMMAND, i.e., not from the beginning + when the COMMAND is started. + + This option has no effect if either the main DURATION of the + ‘timeout’ command, or the DURATION specified to this option, is 0. + + This option may be useful if the selected signal did not kill the + COMMAND, either because the signal was blocked or ignored, or if + the COMMAND takes too long (e.g. for cleanup work) to terminate + itself within a certain amount of time. + +‘-s SIGNAL’ +‘--signal=SIGNAL’ + Send this SIGNAL to COMMAND on timeout, rather than the default + ‘TERM’ signal. SIGNAL may be a name like ‘HUP’ or a number. *Note + Signal specifications::. + +‘-v’ +‘--verbose’ + Diagnose to standard error, any signal sent upon timeout. + + DURATION is a floating point number in either the current or the C +locale (*note Floating point::) followed by an optional unit: + ‘s’ for seconds (the default) + ‘m’ for minutes + ‘h’ for hours + ‘d’ for days + A duration of 0 disables the associated timeout. Note that the +actual timeout duration is dependent on system conditions, which should +be especially considered when specifying sub-second timeouts. + + Exit status: + + 124 if COMMAND times out, and ‘--preserve-status’ is not specified + 125 if ‘timeout’ itself fails + 126 if COMMAND is found but cannot be invoked + 127 if COMMAND cannot be found + 137 if COMMAND or ‘timeout’ is sent the KILL(9) signal (128+9) + the exit status of COMMAND otherwise + + In the case of the ‘KILL(9)’ signal, ‘timeout’ returns with exit +status 137, regardless of whether that signal is sent to COMMAND or to +‘timeout’ itself, i.e., these cases cannot be distinguished. In the +latter case, the COMMAND process may still be alive after ‘timeout’ has +forcefully been terminated. + + Examples: + + # Send the default TERM signal after 20s to a short-living 'sleep 1'. + # As that terminates long before the given duration, 'timeout' returns + # with the same exit status as the command, 0 in this case. + timeout 20 sleep 1 + + # Send the INT signal after 5s to the 'sleep' command. Returns after + # 5 seconds with exit status 124 to indicate the sending of the signal. + timeout -s INT 5 sleep 20 + + # Likewise, but the command ignoring the INT signal due to being started + # via 'env --ignore-signal'. Thus, 'sleep' terminates regularly after + # the full 20 seconds, still 'timeout' returns with exit status 124. + timeout -s INT 5s env --ignore-signal=INT sleep 20 + + # Likewise, but sending the KILL signal 3 seconds after the initial + # INT signal. Hence, 'sleep' is forcefully terminated after about + # 8 seconds (5+3), and 'timeout' returns with an exit status of 137. + timeout -s INT -k 3s 5s env --ignore-signal=INT sleep 20 + + +File: coreutils.info, Node: Process control, Next: Delaying, Prev: Modified command invocation, Up: Top + +24 Process control +****************** + +* Menu: + +* kill invocation:: Sending a signal to processes. + + +File: coreutils.info, Node: kill invocation, Up: Process control + +24.1 ‘kill’: Send a signal to processes +======================================= + +The ‘kill’ command sends a signal to processes, causing them to +terminate or otherwise act upon receiving the signal in some way. +Alternatively, it lists information about signals. Synopses: + + kill [-s SIGNAL | --signal SIGNAL | -SIGNAL] PID... + kill [-l | --list | -t | --table] [SIGNAL]... + + Due to shell aliases and built-in ‘kill’ functions, using an +unadorned ‘kill’ interactively or in a script may get you different +functionality than that described here. Invoke it via ‘env’ (i.e., ‘env +kill ...’) to avoid interference from the shell. + + The first form of the ‘kill’ command sends a signal to all PID +arguments. The default signal to send if none is specified is ‘TERM’. +The special signal number ‘0’ does not denote a valid signal, but can be +used to test whether the PID arguments specify processes to which a +signal could be sent. + + If PID is positive, the signal is sent to the process with the +process ID PID. If PID is zero, the signal is sent to all processes in +the process group of the current process. If PID is −1, the signal is +sent to all processes for which the user has permission to send a +signal. If PID is less than −1, the signal is sent to all processes in +the process group that equals the absolute value of PID. + + If PID is not positive, a system-dependent set of system processes is +excluded from the list of processes to which the signal is sent. + + If a negative PID argument is desired as the first one, it should be +preceded by ‘--’. However, as a common extension to POSIX, ‘--’ is not +required with ‘kill -SIGNAL -PID’. The following commands are +equivalent: + + kill -15 -1 + kill -TERM -1 + kill -s TERM -- -1 + kill -- -1 + + The first form of the ‘kill’ command succeeds if every PID argument +specifies at least one process that the signal was sent to. + + The second form of the ‘kill’ command lists signal information. +Either the ‘-l’ or ‘--list’ option, or the ‘-t’ or ‘--table’ option must +be specified. Without any SIGNAL argument, all supported signals are +listed. The output of ‘-l’ or ‘--list’ is a list of the signal names, +one per line; if SIGNAL is already a name, the signal number is printed +instead. The output of ‘-t’ or ‘--table’ is a table of signal numbers, +names, and descriptions. This form of the ‘kill’ command succeeds if +all SIGNAL arguments are valid and if there is no output error. + + The ‘kill’ command also supports the ‘--help’ and ‘--version’ +options. *Note Common options::. + + A SIGNAL may be a signal name like ‘HUP’, or a signal number like +‘1’, or an exit status of a process terminated by the signal. A signal +name can be given in canonical form or prefixed by ‘SIG’. The case of +the letters is ignored, except for the ‘-SIGNAL’ option which must use +upper case to avoid ambiguity with lower case option letters. *Note +Signal specifications::, for a list of supported signal names and +numbers. + + +File: coreutils.info, Node: Delaying, Next: Numeric operations, Prev: Process control, Up: Top + +25 Delaying +*********** + +* Menu: + +* sleep invocation:: Delay for a specified time. + + +File: coreutils.info, Node: sleep invocation, Up: Delaying + +25.1 ‘sleep’: Delay for a specified time +======================================== + +‘sleep’ pauses for an amount of time specified by the sum of the values +of the command line arguments. Synopsis: + + sleep NUMBER[smhd]... + + Each argument is a non-negative number followed by an optional unit; +the default is seconds. The units are: + +‘s’ + seconds +‘m’ + minutes +‘h’ + hours +‘d’ + days + + Although portable POSIX scripts must give ‘sleep’ a single +non-negative integer argument without a suffix, GNU ‘sleep’ also accepts +two or more arguments, unit suffixes, and floating-point numbers in +either the current or the C locale. *Note Floating point::. + + For instance, the following could be used to ‘sleep’ for 1 second, +234 milli-, 567 micro- and 890 nanoseconds: + + sleep 1234e-3 567.89e-6 + + Also one could sleep indefinitely like: + + sleep inf + + The only options are ‘--help’ and ‘--version’. *Note Common +options::. + + Due to shell aliases and built-in ‘sleep’ functions, using an +unadorned ‘sleep’ interactively or in a script may get you different +functionality than that described here. Invoke it via ‘env’ (i.e., ‘env +sleep ...’) to avoid interference from the shell. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: Numeric operations, Next: File permissions, Prev: Delaying, Up: Top + +26 Numeric operations +********************* + +These programs do numerically-related operations. + +* Menu: + +* factor invocation:: Show factors of numbers. +* numfmt invocation:: Reformat numbers. +* seq invocation:: Print sequences of numbers. + + +File: coreutils.info, Node: factor invocation, Next: numfmt invocation, Up: Numeric operations + +26.1 ‘factor’: Print prime factors +================================== + +‘factor’ prints prime factors. Synopsis: + + factor [OPTION]... [NUMBER]... + + If no NUMBER is specified on the command line, ‘factor’ reads numbers +from standard input, delimited by newlines, tabs, or spaces. + + The program accepts the following options. Also see *note Common +options::. + +‘-h’ +‘--exponents’ + print factors in the form p^e, rather than repeating the prime ‘p’, + ‘e’ times. If the exponent ‘e’ is 1, then it is omitted. + + $ factor --exponents 3000 + 3000: 2^3 3 5^3 + + If the number to be factored is small (less than 2^{127} on typical +machines), ‘factor’ uses a faster algorithm. For example, on a +circa-2017 Intel Xeon Silver 4116, factoring the product of the eighth +and ninth Mersenne primes (approximately 2^{92}) takes about 4 ms of CPU +time: + + $ M8=$(echo 2^31-1 | bc) + $ M9=$(echo 2^61-1 | bc) + $ n=$(echo "$M8 * $M9" | bc) + $ bash -c "time factor $n" + 4951760154835678088235319297: 2147483647 2305843009213693951 + + real 0m0.004s + user 0m0.004s + sys 0m0.000s + + For larger numbers, ‘factor’ uses a slower algorithm. On the same +platform, factoring the eighth Fermat number 2^{256} + 1 takes about 14 +seconds, and the slower algorithm would have taken about 750 ms to +factor 2^{127} - 3 instead of the 50 ms needed by the faster algorithm. + + Factoring large numbers is, in general, hard. The Pollard-Brent rho +algorithm used by ‘factor’ is particularly effective for numbers with +relatively small factors. If you wish to factor large numbers which do +not have small factors (for example, numbers which are the product of +two large primes), other methods are far better. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: numfmt invocation, Next: seq invocation, Prev: factor invocation, Up: Numeric operations + +26.2 ‘numfmt’: Reformat numbers +=============================== + +‘numfmt’ reads numbers in various representations and reformats them as +requested. The most common usage is converting numbers to/from _human_ +representation (e.g. ‘4G’ ↦ ‘4,000,000,000’). + + numfmt [OPTION]... [NUMBER] + + ‘numfmt’ converts each NUMBER on the command-line according to the +specified options (see below). If no NUMBERs are given, it reads +numbers from standard input. ‘numfmt’ can optionally extract numbers +from specific columns, maintaining proper line padding and alignment. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + See ‘--invalid’ for additional information regarding exit status. + +26.2.1 General options +---------------------- + +The program accepts the following options. Also see *note Common +options::. + +‘--debug’ + Print (to standard error) warning messages about possible erroneous + usage. + +‘-d D’ +‘--delimiter=D’ + Use the character D as input field separator (default: whitespace). + _Note_: Using non-default delimiter turns off automatic padding. + +‘--field=FIELDS’ + Convert the number in input field FIELDS (default: 1). FIELDS + supports ‘cut’ style field ranges: + + N N'th field, counted from 1 + N- from N'th field, to end of line + N-M from N'th to M'th field (inclusive) + -M from first to M'th field (inclusive) + - all fields + +‘--format=FORMAT’ + Use printf-style floating FORMAT string. The FORMAT string must + contain one ‘%f’ directive, optionally with ‘'’, ‘-’, ‘0’, width or + precision modifiers. The ‘'’ modifier will enable ‘--grouping’, + the ‘-’ modifier will enable left-aligned ‘--padding’ and the width + modifier will enable right-aligned ‘--padding’. The ‘0’ width + modifier (without the ‘-’ modifier) will generate leading zeros on + the number, up to the specified width. A precision specification + like ‘%.1f’ will override the precision determined from the input + data or set due to ‘--to’ option auto scaling. + +‘--from=UNIT’ + Auto-scales input numbers according to UNIT. See UNITS below. The + default is no scaling, meaning suffixes (e.g. ‘M’, ‘G’) will + trigger an error. + +‘--from-unit=N’ + Specify the input unit size (instead of the default 1). Use this + option when the input numbers represent other units (e.g. if the + input number ‘10’ represents 10 units of 512 bytes, use + ‘--from-unit=512’). Suffixes are handled as with ‘--from=auto’. + +‘--grouping’ + Group digits in output numbers according to the current locale’s + grouping rules (e.g _Thousands Separator_ character, commonly ‘.’ + (dot) or ‘,’ comma). This option has no effect in ‘POSIX/C’ + locale. + +‘--header[=N]’ + Print the first N (default: 1) lines without any conversion. + +‘--invalid=MODE’ + The default action on input errors is to exit immediately with + status code 2. ‘--invalid=‘abort’’ explicitly specifies this + default mode. With a MODE of ‘fail’, print a warning for _each_ + conversion error, and exit with status 2. With a MODE of ‘warn’, + exit with status 0, even in the presence of conversion errors, and + with a MODE of ‘ignore’ do not even print diagnostics. + +‘--padding=N’ + Pad the output numbers to N characters, by adding spaces. If N is + a positive number, numbers will be right-aligned. If N is a + negative number, numbers will be left-aligned. By default, numbers + are automatically aligned based on the input line’s width (only + with the default delimiter). + +‘--round=METHOD’ + When converting number representations, round the number according + to METHOD, which can be ‘up’, ‘down’, ‘from-zero’ (the default), + ‘towards-zero’, ‘nearest’. + +‘--suffix=SUFFIX’ + Add ‘SUFFIX’ to the output numbers, and accept optional ‘SUFFIX’ in + input numbers. + +‘--to=UNIT’ + Auto-scales output numbers according to UNIT. See _Units_ below. + The default is no scaling, meaning all the digits of the number are + printed. + +‘--to-unit=N’ + Specify the output unit size (instead of the default 1). Use this + option when the output numbers represent other units (e.g. to + represent ‘4,000,000’ bytes in blocks of 1KB, use ‘--to=si + --to-unit=1000’). Suffixes are handled as with ‘--from=auto’. + +‘-z’ +‘--zero-terminated’ + Delimit items with a zero byte rather than a newline (ASCII LF). + I.e., treat input as items separated by ASCII NUL and terminate + output items with ASCII NUL. This option can be useful in + conjunction with ‘perl -0’ or ‘find -print0’ and ‘xargs -0’ which + do the same in order to reliably handle arbitrary file names (even + those containing blanks or other special characters). Note with + ‘-z’ the newline character is treated as a field separator. + +26.2.2 Possible UNITs: +---------------------- + +The following are the possible UNIT options with ‘--from=UNITS’ and +‘--to=UNITS’: + +NONE + No scaling is performed. For input numbers, no suffixes are + accepted, and any trailing characters following the number will + trigger an error. For output numbers, all digits of the numbers + will be printed. + +SI + Auto-scale numbers according to the _International System of Units + (SI)_ standard. For input numbers, accept one of the following + suffixes. For output numbers, values larger than 1000 will be + rounded, and printed with one of the following suffixes: + + ‘K’ => 1000^1 = 10^3 (Kilo) + ‘M’ => 1000^2 = 10^6 (Mega) + ‘G’ => 1000^3 = 10^9 (Giga) + ‘T’ => 1000^4 = 10^{12} (Tera) + ‘P’ => 1000^5 = 10^{15} (Peta) + ‘E’ => 1000^6 = 10^{18} (Exa) + ‘Z’ => 1000^7 = 10^{21} (Zetta) + ‘Y’ => 1000^8 = 10^{24} (Yotta) + ‘R’ => 1000^9 = 10^{27} (Ronna) + ‘Q’ => 1000^{10} = 10^{30} (Quetta) + +IEC + Auto-scale numbers according to the _International Electrotechnical + Commission (IEC)_ standard. For input numbers, accept one of the + following suffixes. For output numbers, values larger than 1024 + will be rounded, and printed with one of the following suffixes: + + ‘K’ => 1024^1 = 2^{10} (Kibi) + ‘M’ => 1024^2 = 2^{20} (Mebi) + ‘G’ => 1024^3 = 2^{30} (Gibi) + ‘T’ => 1024^4 = 2^{40} (Tebi) + ‘P’ => 1024^5 = 2^{50} (Pebi) + ‘E’ => 1024^6 = 2^{60} (Exbi) + ‘Z’ => 1024^7 = 2^{70} (Zebi) + ‘Y’ => 1024^8 = 2^{80} (Yobi) + ‘R’ => 1024^9 = 2^{90} (Robi) + ‘Q’ => 1024^{10} = 2^{100} (Quebi) + + The ‘iec’ option uses a single letter suffix (e.g. ‘G’), which is + not fully standard, as the _iec_ standard recommends a two-letter + symbol (e.g ‘Gi’) – but in practice, this method is common. + Compare with the ‘iec-i’ option. + +IEC-I + Auto-scale numbers according to the _International Electrotechnical + Commission (IEC)_ standard. For input numbers, accept one of the + following suffixes. For output numbers, values larger than 1024 + will be rounded, and printed with one of the following suffixes: + + ‘Ki’ => 1024^1 = 2^{10} (Kibi) + ‘Mi’ => 1024^2 = 2^{20} (Mebi) + ‘Gi’ => 1024^3 = 2^{30} (Gibi) + ‘Ti’ => 1024^4 = 2^{40} (Tebi) + ‘Pi’ => 1024^5 = 2^{50} (Pebi) + ‘Ei’ => 1024^6 = 2^{60} (Exbi) + ‘Zi’ => 1024^7 = 2^{70} (Zebi) + ‘Yi’ => 1024^8 = 2^{80} (Yobi) + ‘Ri’ => 1024^9 = 2^{90} (Robi) + ‘Qi’ => 1024^{10} = 2^{100} (Quebi) + + The ‘iec-i’ option uses a two-letter suffix symbol (e.g. ‘Gi’), as + the _iec_ standard recommends, but this is not always common in + practice. Compare with the ‘iec’ option. + +AUTO + ‘auto’ can only be used with ‘--from’. With this method, numbers + with single-letter suffixes like ‘K’ suffixes are interpreted as + _SI_ values, and numbers with two-letter suffixes like ‘Ki’ are + interpreted as _IEC_ values. + +26.2.3 Examples of using ‘numfmt’ +--------------------------------- + +Converting a single number from/to _human_ representation: + $ numfmt --to=si 500000 + 500K + + $ numfmt --to=iec 500000 + 489K + + $ numfmt --to=iec-i 500000 + 489Ki + + $ numfmt --from=si 1M + 1000000 + + $ numfmt --from=iec 1M + 1048576 + + # with '--from=auto', M=Mega, Mi=Mebi + $ numfmt --from=auto 1M + 1000000 + $ numfmt --from=auto 1Mi + 1048576 + + Converting from ‘SI’ to ‘IEC’ scales (e.g. when a drive’s capacity +is advertised as ‘1TB’, while checking the drive’s capacity gives lower +values): + + $ numfmt --from=si --to=iec 1T + 932G + + With both input and output scales specified, the largest defined +prefixes are supported: + + $ numfmt --from=si --to=iec-i 2000R + 1.6Qi + + Converting a single field from an input file / piped input (these +contrived examples are for demonstration purposes only, as both ‘ls’ and +‘df’ support the ‘--human-readable’ option to output sizes in +human-readable format): + + # Third field (file size) will be shown in SI representation + $ ls -log | numfmt --field 3 --header --to=si | head -n4 + -rw-r--r-- 1 94K Aug 23 2011 ABOUT-NLS + -rw-r--r-- 1 3.7K Jan 7 16:15 AUTHORS + -rw-r--r-- 1 36K Jun 1 2011 COPYING + -rw-r--r-- 1 0 Jan 7 15:15 ChangeLog + + # Second field (size) will be shown in IEC representation + $ df --block-size=1 | numfmt --field 2 --header --to=iec | head -n4 + File system 1B-blocks Used Available Use% Mounted on + rootfs 132G 104741408 26554036 80% / + tmpfs 794M 7580 804960 1% /run/shm + /dev/sdb1 694G 651424756 46074696 94% /home + + Output can be tweaked using ‘--padding’ or ‘--format’: + + # Pad to 10 characters, right-aligned + $ du -s * | numfmt --to=si --padding=10 + 2.5K config.log + 108 config.status + 1.7K configure + 20 configure.ac + + # Pad to 10 characters, left-aligned + $ du -s * | numfmt --to=si --padding=-10 + 2.5K config.log + 108 config.status + 1.7K configure + 20 configure.ac + + # Pad to 10 characters, left-aligned, using 'format' + $ du -s * | numfmt --to=si --format="%10f" + 2.5K config.log + 108 config.status + 1.7K configure + 20 configure.ac + + # Pad to 10 characters, left-aligned, using 'format' + $ du -s * | numfmt --to=si --padding="%-10f" + 2.5K config.log + 108 config.status + 1.7K configure + 20 configure.ac + + With locales that support grouping digits, using ‘--grouping’ or +‘--format’ enables grouping. In ‘POSIX’ locale, grouping is silently +ignored: + + $ LC_ALL=C numfmt --from=iec --grouping 2G + 2147483648 + + $ LC_ALL=en_US.utf8 numfmt --from=iec --grouping 2G + 2,147,483,648 + + $ LC_ALL=ta_IN numfmt --from=iec --grouping 2G + 2,14,74,83,648 + + $ LC_ALL=C numfmt --from=iec --format="==%'15f==" 2G + == 2147483648== + + $ LC_ALL=en_US.utf8 numfmt --from=iec --format="==%'15f==" 2G + == 2,147,483,648== + + $ LC_ALL=en_US.utf8 numfmt --from=iec --format="==%'-15f==" 2G + ==2,147,483,648 == + + $ LC_ALL=ta_IN numfmt --from=iec --format="==%'15f==" 2G + == 2,14,74,83,648== + + +File: coreutils.info, Node: seq invocation, Prev: numfmt invocation, Up: Numeric operations + +26.3 ‘seq’: Print numeric sequences +=================================== + +‘seq’ prints a sequence of numbers to standard output. Synopses: + + seq [OPTION]... LAST + seq [OPTION]... FIRST LAST + seq [OPTION]... FIRST INCREMENT LAST + + ‘seq’ prints the numbers from FIRST to LAST by INCREMENT. By +default, each number is printed on a separate line. When INCREMENT is +not specified, it defaults to ‘1’, even when FIRST is larger than LAST. +FIRST also defaults to ‘1’. So ‘seq 1’ prints ‘1’, but ‘seq 0’ and ‘seq +10 5’ produce no output. The sequence of numbers ends when the sum of +the current number and INCREMENT would become greater than LAST, so ‘seq +1 10 10’ only produces ‘1’. INCREMENT must not be ‘0’; use the tool +‘yes’ to get repeated output of a constant number. FIRST, INCREMENT and +LAST must not be ‘NaN’, but ‘inf’ is supported. Floating-point numbers +may be specified in either the current or the C locale. *Note Floating +point::. + + The program accepts the following options. Also see *note Common +options::. Options must precede operands. + +‘-f FORMAT’ +‘--format=FORMAT’ + Print all numbers using FORMAT. FORMAT must contain exactly one of + the ‘printf’-style floating point conversion specifications ‘%a’, + ‘%e’, ‘%f’, ‘%g’, ‘%A’, ‘%E’, ‘%F’, ‘%G’. The ‘%’ may be followed + by zero or more flags taken from the set ‘-+#0 '’, then an optional + width containing one or more digits, then an optional precision + consisting of a ‘.’ followed by zero or more digits. FORMAT may + also contain any number of ‘%%’ conversion specifications. All + conversion specifications have the same meaning as with ‘printf’. + + The default format is derived from FIRST, STEP, and LAST. If these + all use a fixed point decimal representation, the default format is + ‘%.Pf’, where P is the minimum precision that can represent the + output numbers exactly. Otherwise, the default format is ‘%g’. + +‘-s STRING’ +‘--separator=STRING’ + Separate numbers with STRING; default is a newline. The output + always terminates with a newline. + +‘-w’ +‘--equal-width’ + Print all numbers with the same width, by padding with leading + zeros. FIRST, STEP, and LAST should all use a fixed point decimal + representation. (To have other kinds of padding, use ‘--format’). + + You can get finer-grained control over output with ‘-f’: + + $ seq -f '(%9.2E)' -9e5 1.1e6 1.3e6 + (-9.00E+05) + ( 2.00E+05) + ( 1.30E+06) + + If you want hexadecimal integer output, you can use ‘printf’ to +perform the conversion: + + $ printf '%x\n' $(seq 1048575 1024 1050623) + fffff + 1003ff + 1007ff + + For very long lists of numbers, use xargs to avoid system limitations +on the length of an argument list: + + $ seq 1000000 | xargs printf '%x\n' | tail -n 3 + f423e + f423f + f4240 + + To generate octal output, use the printf ‘%o’ format instead of ‘%x’. + + On most systems, seq can produce whole-number output for values up to +at least 2^{53}. Larger integers are approximated. The details differ +depending on your floating-point implementation. *Note Floating +point::. A common case is that ‘seq’ works with integers through +2^{64}, and larger integers may not be numerically correct: + + $ seq 50000000000000000000 2 50000000000000000004 + 50000000000000000000 + 50000000000000000000 + 50000000000000000004 + + However, note that when limited to non-negative whole numbers, an +increment of less than 200, and no format-specifying option, seq can +print arbitrarily large numbers. Therefore ‘seq inf’ can be used to +generate an infinite sequence of numbers. + + Be careful when using ‘seq’ with outlandish values: otherwise you may +see surprising results, as ‘seq’ uses floating point internally. For +example, on the x86 platform, where the internal representation uses a +64-bit fraction, the command: + + seq 1 0.0000000000000000001 1.0000000000000000009 + + outputs 1.0000000000000000007 twice and skips 1.0000000000000000008. + + An exit status of zero indicates success, and a nonzero value +indicates failure. + + +File: coreutils.info, Node: File permissions, Next: File timestamps, Prev: Numeric operations, Up: Top + +27 File permissions +******************* + +Each file has a set of “file mode bits” that control the kinds of access +that users have to that file. They can be represented either in +symbolic form or as an octal number. + +* Menu: + +* Mode Structure:: Structure of file mode bits. +* Symbolic Modes:: Mnemonic representation of file mode bits. +* Numeric Modes:: File mode bits as octal numbers. +* Operator Numeric Modes:: ANDing, ORing, and setting modes octally. +* Directory Setuid and Setgid:: Set-user-ID and set-group-ID on directories. + + +File: coreutils.info, Node: Mode Structure, Next: Symbolic Modes, Up: File permissions + +27.1 Structure of File Mode Bits +================================ + +The file mode bits have two parts: the “file permission bits”, which +control ordinary access to the file, and “special mode bits”, which +affect only some files. + + There are three kinds of permissions that a user can have for a file: + + 1. permission to read the file. For directories, this means + permission to list the contents of the directory. + 2. permission to write to (change) the file. For directories, this + means permission to create and remove files in the directory. + 3. permission to execute the file (run it as a program). For + directories, this means permission to access files in the + directory. + + There are three categories of users who may have different +permissions to perform any of the above operations on a file: + + 1. the file’s owner; + 2. other users who are in the file’s group; + 3. everyone else. + + Files are given an owner and group when they are created. Usually +the owner is the current user and the group is the group of the +directory the file is in, but this varies with the operating system, the +file system the file is created on, and the way the file is created. +You can change the owner and group of a file by using the ‘chown’ and +‘chgrp’ commands. + + In addition to the three sets of three permissions listed above, the +file mode bits have three special components, which affect only +executable files (programs) and, on most systems, directories: + +The “set-user-ID bit” (“setuid bit”). + On execution, set the process’s effective user ID to that of the + file. For directories on a few systems, give files created in the + directory the same owner as the directory, no matter who creates + them, and set the set-user-ID bit of newly-created subdirectories. + +The “set-group-ID bit” (“setgid bit”). + On execution, set the process’s effective group ID to that of the + file. For directories on most systems, give files created in the + directory the same group as the directory, no matter what group the + user who creates them is in, and set the set-group-ID bit of + newly-created subdirectories. + +The “restricted deletion flag” or “sticky bit”. + Prevent unprivileged users from removing or renaming a file in a + directory unless they own the file or the directory; this is + commonly found on world-writable directories like ‘/tmp’. For + regular files on some older systems, save the program’s text image + on the swap device so it will load more quickly when run, so that + the image is “sticky”. + + In addition to the file mode bits listed above, there may be file +attributes specific to the file system, e.g., access control lists +(ACLs), whether a file is compressed, whether a file can be modified +(immutability), and whether a file can be dumped. These are usually set +using programs specific to the file system. For example: + +ext2 + On GNU and GNU/Linux the file attributes specific to the ext2 file + system are set using ‘chattr’. + +FFS + On FreeBSD the file flags specific to the FFS file system are set + using ‘chflags’. + + Even if a file’s mode bits allow an operation on that file, that +operation may still fail, because: + + • the file-system-specific attributes or flags do not permit it; or + + • the file system is mounted as read-only. + + For example, if the immutable attribute is set on a file, it cannot +be modified, regardless of the fact that you may have just run ‘chmod +a+w FILE’. + + +File: coreutils.info, Node: Symbolic Modes, Next: Numeric Modes, Prev: Mode Structure, Up: File permissions + +27.2 Symbolic Modes +=================== + +“Symbolic modes” represent changes to files’ mode bits as operations on +single-character symbols. They allow you to modify either all or +selected parts of files’ mode bits, optionally based on their previous +values, and perhaps on the current ‘umask’ as well (*note Umask and +Protection::). + + The format of symbolic modes is: + + [ugoa...][-+=]PERMS...[,...] + +where PERMS is either zero or more letters from the set ‘rwxXst’, or a +single letter from the set ‘ugo’. + + The following sections describe the operators and other details of +symbolic modes. + +* Menu: + +* Setting Permissions:: Basic operations on permissions. +* Copying Permissions:: Copying existing permissions. +* Changing Special Mode Bits:: Special mode bits. +* Conditional Executability:: Conditionally affecting executability. +* Multiple Changes:: Making multiple changes. +* Umask and Protection:: The effect of the umask. + + +File: coreutils.info, Node: Setting Permissions, Next: Copying Permissions, Up: Symbolic Modes + +27.2.1 Setting Permissions +-------------------------- + +The basic symbolic operations on a file’s permissions are adding, +removing, and setting the permission that certain users have to read, +write, and execute or search the file. These operations have the +following format: + + USERS OPERATION PERMISSIONS + +The spaces between the three parts above are shown for readability only; +symbolic modes cannot contain spaces. + + The USERS part tells which users’ access to the file is changed. It +consists of one or more of the following letters (or it can be empty; +*note Umask and Protection::, for a description of what happens then). +When more than one of these letters is given, the order that they are in +does not matter. + +‘u’ + the user who owns the file; +‘g’ + other users who are in the file’s group; +‘o’ + all other users; +‘a’ + all users; the same as ‘ugo’. + + The OPERATION part tells how to change the affected users’ access to +the file, and is one of the following symbols: + +‘+’ + to add the PERMISSIONS to whatever permissions the USERS already + have for the file; +‘-’ + to remove the PERMISSIONS from whatever permissions the USERS + already have for the file; +‘=’ + to make the PERMISSIONS the only permissions that the USERS have + for the file. + + The PERMISSIONS part tells what kind of access to the file should be +changed; it is normally zero or more of the following letters. As with +the USERS part, the order does not matter when more than one letter is +given. Omitting the PERMISSIONS part is useful only with the ‘=’ +operation, where it gives the specified USERS no access at all to the +file. + +‘r’ + the permission the USERS have to read the file; +‘w’ + the permission the USERS have to write to the file; +‘x’ + the permission the USERS have to execute the file, or search it if + it is a directory. + + For example, to give everyone permission to read and write a regular +file, but not to execute it, use: + + a=rw + + To remove write permission for all users other than the file’s owner, +use: + + go-w + +The above command does not affect the access that the owner of the file +has to it, nor does it affect whether other users can read or execute +the file. + + To give everyone except a file’s owner no permission to do anything +with that file, use the mode below. Other users could still remove the +file, if they have write permission on the directory it is in. + + go= + +Another way to specify the same thing is: + + og-rwx + + +File: coreutils.info, Node: Copying Permissions, Next: Changing Special Mode Bits, Prev: Setting Permissions, Up: Symbolic Modes + +27.2.2 Copying Existing Permissions +----------------------------------- + +You can base a file’s permissions on its existing permissions. To do +this, instead of using a series of ‘r’, ‘w’, or ‘x’ letters after the +operator, you use the letter ‘u’, ‘g’, or ‘o’. For example, the mode + + o+g + +adds the permissions for users who are in a file’s group to the +permissions that other users have for the file. Thus, if the file +started out as mode 664 (‘rw-rw-r--’), the above mode would change it to +mode 666 (‘rw-rw-rw-’). If the file had started out as mode 741 +(‘rwxr----x’), the above mode would change it to mode 745 (‘rwxr--r-x’). +The ‘-’ and ‘=’ operations work analogously. + + +File: coreutils.info, Node: Changing Special Mode Bits, Next: Conditional Executability, Prev: Copying Permissions, Up: Symbolic Modes + +27.2.3 Changing Special Mode Bits +--------------------------------- + +In addition to changing a file’s read, write, and execute/search +permissions, you can change its special mode bits. *Note Mode +Structure::, for a summary of these special mode bits. + + To change the file mode bits to set the user ID on execution, use ‘u’ +in the USERS part of the symbolic mode and ‘s’ in the PERMISSIONS part. + + To change the file mode bits to set the group ID on execution, use +‘g’ in the USERS part of the symbolic mode and ‘s’ in the PERMISSIONS +part. + + To set both user and group ID on execution, omit the USERS part of +the symbolic mode (or use ‘a’) and use ‘s’ in the PERMISSIONS part. + + To change the file mode bits to set the restricted deletion flag or +sticky bit, omit the USERS part of the symbolic mode (or use ‘a’) and +use ‘t’ in the PERMISSIONS part. + + For example, to set the set-user-ID mode bit of a program, you can +use the mode: + + u+s + + To remove both set-user-ID and set-group-ID mode bits from it, you +can use the mode: + + a-s + + To set the restricted deletion flag or sticky bit, you can use the +mode: + + +t + + The combination ‘o+s’ has no effect. On GNU systems the combinations +‘u+t’ and ‘g+t’ have no effect, and ‘o+t’ acts like plain ‘+t’. + + The ‘=’ operator is not very useful with special mode bits. For +example, the mode: + + o=t + +does set the restricted deletion flag or sticky bit, but it also removes +all read, write, and execute/search permissions that users not in the +file’s group might have had for it. + + *Note Directory Setuid and Setgid::, for additional rules concerning +set-user-ID and set-group-ID bits and directories. + + +File: coreutils.info, Node: Conditional Executability, Next: Multiple Changes, Prev: Changing Special Mode Bits, Up: Symbolic Modes + +27.2.4 Conditional Executability +-------------------------------- + +There is one more special type of symbolic permission: if you use ‘X’ +instead of ‘x’, execute/search permission is affected only if the file +is a directory or already had execute permission. + + For example, this mode: + + a+X + +gives all users permission to search directories, or to execute files if +anyone could execute them before. + + +File: coreutils.info, Node: Multiple Changes, Next: Umask and Protection, Prev: Conditional Executability, Up: Symbolic Modes + +27.2.5 Making Multiple Changes +------------------------------ + +The format of symbolic modes is actually more complex than described +above (*note Setting Permissions::). It provides two ways to make +multiple changes to files’ mode bits. + + The first way is to specify multiple OPERATION and PERMISSIONS parts +after a USERS part in the symbolic mode. + + For example, the mode: + + og+rX-w + +gives users other than the owner of the file read permission and, if it +is a directory or if someone already had execute permission to it, gives +them execute/search permission; and it also denies them write permission +to the file. It does not affect the permission that the owner of the +file has for it. The above mode is equivalent to the two modes: + + og+rX + og-w + + The second way to make multiple changes is to specify more than one +simple symbolic mode, separated by commas. For example, the mode: + + a+r,go-w + +gives everyone permission to read the file and removes write permission +on it for all users except its owner. Another example: + + u=rwx,g=rx,o= + +sets all of the permission bits for the file explicitly. (It gives +users who are not in the file’s group no permission at all for it.) + + The two methods can be combined. The mode: + + a+r,g+x-w + +gives all users permission to read the file, and gives users who are in +the file’s group permission to execute/search it as well, but not +permission to write to it. The above mode could be written in several +different ways; another is: + + u+r,g+rx,o+r,g-w + + +File: coreutils.info, Node: Umask and Protection, Prev: Multiple Changes, Up: Symbolic Modes + +27.2.6 The Umask and Protection +------------------------------- + +If the USERS part of a symbolic mode is omitted, it defaults to ‘a’ +(affect all users), except that any permissions that are _set_ in the +system variable ‘umask’ are _not affected_. The value of ‘umask’ can be +set using the ‘umask’ command. Its default value varies from system to +system. + + Omitting the USERS part of a symbolic mode is generally not useful +with operations other than ‘+’. It is useful with ‘+’ because it allows +you to use ‘umask’ as an easily customizable protection against giving +away more permission to files than you intended to. + + As an example, if ‘umask’ has the value 2, which removes write +permission for users who are not in the file’s group, then the mode: + + +w + +adds permission to write to the file to its owner and to other users who +are in the file’s group, but _not_ to other users. In contrast, the +mode: + + a+w + +ignores ‘umask’, and _does_ give write permission for the file to all +users. + + +File: coreutils.info, Node: Numeric Modes, Next: Operator Numeric Modes, Prev: Symbolic Modes, Up: File permissions + +27.3 Numeric Modes +================== + +As an alternative to giving a symbolic mode, you can give an octal (base +8) number that represents the mode. + + The permissions granted to the user, to other users in the file’s +group, and to other users not in the file’s group each require three +bits: one bit for read, one for write, and one for execute/search +permission. These three bits are represented as one octal digit; for +example, if all three are present, the resulting 111 (in binary) is +represented as the digit 7 (in octal). The three special mode bits also +require one bit each, and they are as a group represented as another +octal digit. Here is how the bits are arranged, starting with the +highest valued bit: + + Value in Corresponding + Mode Mode Bit + + Special mode bits: + 4000 Set user ID + 2000 Set group ID + 1000 Restricted deletion flag or sticky bit + + The file's owner: + 400 Read + 200 Write + 100 Execute/search + + Other users in the file's group: + 40 Read + 20 Write + 10 Execute/search + + Other users not in the file's group: + 4 Read + 2 Write + 1 Execute/search + + For example, numeric mode ‘4751’ corresponds to symbolic mode +‘u=srwx,g=rx,o=x’, and numeric mode ‘664’ corresponds to symbolic mode +‘ug=rw,o=r’. Numeric mode ‘0’ corresponds to symbolic mode ‘a=’. + + A numeric mode is usually shorter than the corresponding symbolic +mode, but it is limited in that normally it cannot take into account the +previous file mode bits; it can only set them absolutely. The +set-user-ID and set-group-ID bits of directories are an exception to +this general limitation. *Note Directory Setuid and Setgid::. Also, +operator numeric modes can take previous file mode bits into account. +*Note Operator Numeric Modes::. + + Numeric modes are always interpreted in octal; you do not have to add +a leading ‘0’, as you do in C. Mode ‘0055’ is the same as mode ‘55’. +However, modes of five digits or more, such as ‘00055’, are sometimes +special (*note Directory Setuid and Setgid::). + + +File: coreutils.info, Node: Operator Numeric Modes, Next: Directory Setuid and Setgid, Prev: Numeric Modes, Up: File permissions + +27.4 Operator Numeric Modes +=========================== + +An operator numeric mode is a numeric mode that is prefixed by a ‘-’, +‘+’, or ‘=’ operator, which has the same interpretation as in symbolic +modes. For example, ‘+440’ enables read permission for the file’s owner +and group, ‘-1’ disables execute permission for other users, and ‘=600’ +clears all permissions except for enabling read-write permissions for +the file’s owner. Operator numeric modes can be combined with symbolic +modes by separating them with a comma; for example, ‘=0,u+r’ clears all +permissions except for enabling read permission for the file’s owner. + + The commands ‘chmod =755 DIR’ and ‘chmod 755 DIR’ differ in that the +former clears the directory DIR’s setuid and setgid bits, whereas the +latter preserves them. *Note Directory Setuid and Setgid::. + + Operator numeric modes are a GNU extension. + + +File: coreutils.info, Node: Directory Setuid and Setgid, Prev: Operator Numeric Modes, Up: File permissions + +27.5 Directories and the Set-User-ID and Set-Group-ID Bits +========================================================== + +On most systems, if a directory’s set-group-ID bit is set, newly created +subfiles inherit the same group as the directory, and newly created +subdirectories inherit the set-group-ID bit of the parent directory. On +a few systems, a directory’s set-user-ID bit has a similar effect on the +ownership of new subfiles and the set-user-ID bits of new +subdirectories. These mechanisms let users share files more easily, by +lessening the need to use ‘chmod’ or ‘chown’ to share new files. + + These convenience mechanisms rely on the set-user-ID and set-group-ID +bits of directories. If commands like ‘chmod’ and ‘mkdir’ routinely +cleared these bits on directories, the mechanisms would be less +convenient and it would be harder to share files. Therefore, a command +like ‘chmod’ does not affect the set-user-ID or set-group-ID bits of a +directory unless the user specifically mentions them in a symbolic mode, +or uses an operator numeric mode such as ‘=755’, or sets them in a +numeric mode, or clears them in a numeric mode that has five or more +octal digits. For example, on systems that support set-group-ID +inheritance: + + # These commands leave the set-user-ID and + # set-group-ID bits of the subdirectories alone, + # so that they retain their default values. + mkdir A B C + chmod 755 A + chmod 0755 B + chmod u=rwx,go=rx C + mkdir -m 755 D + mkdir -m 0755 E + mkdir -m u=rwx,go=rx F + + If you want to try to set these bits, you must mention them +explicitly in the symbolic or numeric modes, e.g.: + + # These commands try to set the set-user-ID + # and set-group-ID bits of the subdirectories. + mkdir G + chmod 6755 G + chmod +6000 G + chmod u=rwx,go=rx,a+s G + mkdir -m 6755 H + mkdir -m +6000 I + mkdir -m u=rwx,go=rx,a+s J + + If you want to try to clear these bits, you must mention them +explicitly in a symbolic mode, or use an operator numeric mode, or +specify a numeric mode with five or more octal digits, e.g.: + + # These commands try to clear the set-user-ID + # and set-group-ID bits of the directory D. + chmod a-s D + chmod -6000 D + chmod =755 D + chmod 00755 D + + This behavior is a GNU extension. Portable scripts should not rely +on requests to set or clear these bits on directories, as POSIX allows +implementations to ignore these requests. The GNU behavior with numeric +modes of four or fewer digits is intended for scripts portable to +systems that preserve these bits; the behavior with numeric modes of +five or more digits is for scripts portable to systems that do not +preserve the bits. + + +File: coreutils.info, Node: File timestamps, Next: Date input formats, Prev: File permissions, Up: Top + +28 File timestamps +****************** + +Standard POSIX files have three timestamps: the access timestamp (atime) +of the last read, the modification timestamp (mtime) of the last write, +and the status change timestamp (ctime) of the last change to the file’s +meta-information. Some file systems support a fourth time: the birth +timestamp (birthtime) of when the file was created; by definition, +birthtime never changes. + + One common example of a ctime change is when the permissions of a +file change. Changing the permissions doesn’t access the file, so atime +doesn’t change, nor does it modify the file, so the mtime doesn’t +change. Yet, something about the file itself has changed, and this must +be noted somewhere. This is the job of the ctime field. This is +necessary, so that, for example, a backup program can make a fresh copy +of the file, including the new permissions value. Another operation +that modifies a file’s ctime without affecting the others is renaming. + + Naively, a file’s atime, mtime, and ctime are set to the current time +whenever you read, write, or change the attributes of the file +respectively, and searching a directory counts as reading it. A file’s +atime and mtime can also be set directly, via the ‘touch’ command (*note +touch invocation::). In practice, though, timestamps are not updated +quite that way. + + For efficiency reasons, many systems are lazy about updating atimes: +when a program accesses a file, they may delay updating the file’s +atime, or may not update the file’s atime if the file has been accessed +recently, or may not update the atime at all. Similar laziness, though +typically not quite so extreme, applies to mtimes and ctimes. + + Some systems emulate timestamps instead of supporting them directly, +and these emulations may disagree with the naive interpretation. For +example, a system may fake an atime or ctime by using the mtime. + + The determination of what time is “current” depends on the platform. +Platforms with network file systems often use different clocks for the +operating system and for file systems; because updates typically uses +file systems’ clocks by default, clock skew can cause the resulting file +timestamps to appear to be in a program’s “future” or “past”. + + When the system updates a file timestamp to a desired time T (which +is either the current time, or a time specified via the ‘touch’ +command), there are several reasons the file’s timestamp may be set to a +value that differs from T. First, T may have a higher resolution than +supported. Second, a file system may use different resolutions for +different types of times. Third, file timestamps may use a different +resolution than operating system timestamps. Fourth, the operating +system primitives used to update timestamps may employ yet a different +resolution. For example, in theory a file system might use +10-microsecond resolution for access timestamp and 100-nanosecond +resolution for modification timestamp, and the operating system might +use nanosecond resolution for the current time and microsecond +resolution for the primitive that ‘touch’ uses to set a file’s timestamp +to an arbitrary value. + + +File: coreutils.info, Node: Date input formats, Next: Version sort ordering, Prev: File timestamps, Up: Top + +29 Date input formats +********************* + +First, a quote: + + Our units of temporal measurement, from seconds on up to months, + are so complicated, asymmetrical and disjunctive so as to make + coherent mental reckoning in time all but impossible. Indeed, had + some tyrannical god contrived to enslave our minds to time, to make + it all but impossible for us to escape subjection to sodden + routines and unpleasant surprises, he could hardly have done better + than handing down our present system. It is like a set of + trapezoidal building blocks, with no vertical or horizontal + surfaces, like a language in which the simplest thought demands + ornate constructions, useless particles and lengthy + circumlocutions. Unlike the more successful patterns of language + and science, which enable us to face experience boldly or at least + level-headedly, our system of temporal calculation silently and + persistently encourages our terror of time. + + ... It is as though architects had to measure length in feet, width + in meters and height in ells; as though basic instruction manuals + demanded a knowledge of five different languages. It is no wonder + then that we often look into our own immediate past or future, last + Tuesday or a week from Sunday, with feelings of helpless confusion. + ... + + —Robert Grudin, ‘Time and the Art of Living’. + + This section describes the textual date representations that GNU +programs accept. These are the strings you, as a user, can supply as +arguments to the various programs. The C interface (via the +‘parse_datetime’ function) is not described here. + +* Menu: + +* General date syntax:: Common rules +* Calendar date items:: ‘14 Nov 2022’ +* Time of day items:: ‘9:02pm’ +* Time zone items:: ‘UTC’, ‘-0700’, ‘+0900’, ... +* Combined date and time of day items:: ‘2022-11-14T21:02:42,000000-0500’ +* Day of week items:: ‘Monday’ and others +* Relative items in date strings:: ‘next tuesday, 2 years ago’ +* Pure numbers in date strings:: ‘20221114’, ‘2102’ +* Seconds since the Epoch:: ‘@1668477762’ +* Specifying time zone rules:: ‘TZ="America/New_York"’, ‘TZ="UTC0"’ +* Authors of parse_datetime:: Bellovin, Eggert, Salz, Berets, et al. + + +File: coreutils.info, Node: General date syntax, Next: Calendar date items, Up: Date input formats + +29.1 General date syntax +======================== + +A “date” is a string, possibly empty, containing many items separated by +whitespace. The whitespace may be omitted when no ambiguity arises. +The empty string means the beginning of today (i.e., midnight). Order +of the items is immaterial. A date string may contain many flavors of +items: + + • calendar date items + • time of day items + • time zone items + • combined date and time of day items + • day of the week items + • relative items + • pure numbers. + +We describe each of these item types in turn, below. + + A few ordinal numbers may be written out in words in some contexts. +This is most useful for specifying day of the week items or relative +items (see below). Among the most commonly used ordinal numbers, the +word ‘last’ stands for -1, ‘this’ stands for 0, and ‘first’ and ‘next’ +both stand for 1. Because the word ‘second’ stands for the unit of time +there is no way to write the ordinal number 2, but for convenience +‘third’ stands for 3, ‘fourth’ for 4, ‘fifth’ for 5, ‘sixth’ for 6, +‘seventh’ for 7, ‘eighth’ for 8, ‘ninth’ for 9, ‘tenth’ for 10, +‘eleventh’ for 11 and ‘twelfth’ for 12. + + When a month is written this way, it is still considered to be +written numerically, instead of being “spelled in full”; this changes +the allowed strings. + + In the current implementation, only English is supported for words +and abbreviations like ‘AM’, ‘DST’, ‘EST’, ‘first’, ‘January’, ‘Sunday’, +‘tomorrow’, and ‘year’. + + The output of the ‘date’ command is not always acceptable as a date +string, not only because of the language problem, but also because there +is no standard meaning for time zone items like ‘IST’. When using +‘date’ to generate a date string intended to be parsed later, specify a +date format that is independent of language and that does not use time +zone items other than ‘UTC’ and ‘Z’. Here are some ways to do this: + + $ LC_ALL=C TZ=UTC0 date + Tue Nov 15 02:02:42 UTC 2022 + $ TZ=UTC0 date +'%Y-%m-%d %H:%M:%SZ' + 2022-11-15 02:02:42Z + $ date --rfc-3339=ns # --rfc-3339 is a GNU extension. + 2022-11-14 21:02:42.000000000-05:00 + $ date --rfc-email # a GNU extension + Mon, 14 Nov 2022 21:02:42 -0500 + $ date +'%Y-%m-%d %H:%M:%S %z' # %z is a GNU extension. + 2022-11-14 21:02:42 -0500 + $ date +'@%s.%N' # %s and %N are GNU extensions. + @1668477762.692722128 + + Alphabetic case is completely ignored in dates. Comments may be +introduced between round parentheses, as long as included parentheses +are properly nested. Hyphens not followed by a digit are currently +ignored. Leading zeros on numbers are ignored. + + Invalid dates like ‘2022-02-29’ or times like ‘24:00’ are rejected. +In the typical case of a host that does not support leap seconds, a time +like ‘23:59:60’ is rejected even if it corresponds to a valid leap +second. + + +File: coreutils.info, Node: Calendar date items, Next: Time of day items, Prev: General date syntax, Up: Date input formats + +29.2 Calendar date items +======================== + +A “calendar date item” specifies a day of the year. It is specified +differently, depending on whether the month is specified numerically or +literally. All these strings specify the same calendar date: + + 2022-11-14 # ISO 8601. + 22-11-14 # Assume 19xx for 69 through 99, + # 20xx for 00 through 68 (not recommended). + 11/14/2022 # Common U.S. writing. + 14 November 2022 + 14 Nov 2022 # Three-letter abbreviations always allowed. + November 14, 2022 + 14-nov-2022 + 14nov2022 + + The year can also be omitted. In this case, the last specified year +is used, or the current year if none. For example: + + 11/14 + nov 14 + + Here are the rules. + + For numeric months, the ISO 8601 format ‘YEAR-MONTH-DAY’ is allowed, +where YEAR is any positive number, MONTH is a number between 01 and 12, +and DAY is a number between 01 and 31. A leading zero must be present +if a number is less than ten. If YEAR is 68 or smaller, then 2000 is +added to it; otherwise, if YEAR is less than 100, then 1900 is added to +it. The construct ‘MONTH/DAY/YEAR’, popular in the United States, is +accepted. Also ‘MONTH/DAY’, omitting the year. + + Literal months may be spelled out in full: ‘January’, ‘February’, +‘March’, ‘April’, ‘May’, ‘June’, ‘July’, ‘August’, ‘September’, +‘October’, ‘November’ or ‘December’. Literal months may be abbreviated +to their first three letters, possibly followed by an abbreviating dot. +It is also permitted to write ‘Sept’ instead of ‘September’. + + When months are written literally, the calendar date may be given as +any of the following: + + DAY MONTH YEAR + DAY MONTH + MONTH DAY YEAR + DAY-MONTH-YEAR + + Or, omitting the year: + + MONTH DAY + + +File: coreutils.info, Node: Time of day items, Next: Time zone items, Prev: Calendar date items, Up: Date input formats + +29.3 Time of day items +====================== + +A “time of day item” in date strings specifies the time on a given day. +Here are some examples, all of which represent the same time: + + 20:02:00.000000 + 20:02 + 8:02pm + 20:02-0500 # In EST (U.S. Eastern Standard Time). + + More generally, the time of day may be given as ‘HOUR:MINUTE:SECOND’, +where HOUR is a number between 0 and 23, MINUTE is a number between 0 +and 59, and SECOND is a number between 0 and 59 possibly followed by ‘.’ +or ‘,’ and a fraction containing one or more digits. Alternatively, +‘:SECOND’ can be omitted, in which case it is taken to be zero. On the +rare hosts that support leap seconds, SECOND may be 60. + + If the time is followed by ‘am’ or ‘pm’ (or ‘a.m.’ or ‘p.m.’), HOUR +is restricted to run from 1 to 12, and ‘:MINUTE’ may be omitted (taken +to be zero). ‘am’ indicates the first half of the day, ‘pm’ indicates +the second half of the day. In this notation, 12 is the predecessor of +1: midnight is ‘12am’ while noon is ‘12pm’. (This is the zero-oriented +interpretation of ‘12am’ and ‘12pm’, as opposed to the old tradition +derived from Latin which uses ‘12m’ for noon and ‘12pm’ for midnight.) + + The time may alternatively be followed by a time zone correction, +expressed as ‘SHHMM’, where S is ‘+’ or ‘-’, HH is a number of zone +hours and MM is a number of zone minutes. The zone minutes term, MM, +may be omitted, in which case the one- or two-digit correction is +interpreted as a number of hours. You can also separate HH from MM with +a colon. When a time zone correction is given this way, it forces +interpretation of the time relative to Coordinated Universal Time (UTC), +overriding any previous specification for the time zone or the local +time zone. For example, ‘+0530’ and ‘+05:30’ both stand for the time +zone 5.5 hours ahead of UTC (e.g., India). This is the best way to +specify a time zone correction by fractional parts of an hour. The +maximum zone correction is 24 hours. + + Either ‘am’/‘pm’ or a time zone correction may be specified, but not +both. + + +File: coreutils.info, Node: Time zone items, Next: Combined date and time of day items, Prev: Time of day items, Up: Date input formats + +29.4 Time zone items +==================== + +A “time zone item” specifies an international time zone, indicated by a +small set of letters, e.g., ‘UTC’ or ‘Z’ for Coordinated Universal Time. +Any included periods are ignored. By following a non-daylight-saving +time zone by the string ‘DST’ in a separate word (that is, separated by +some white space), the corresponding daylight saving time zone may be +specified. Alternatively, a non-daylight-saving time zone can be +followed by a time zone correction, to add the two values. This is +normally done only for ‘UTC’; for example, ‘UTC+05:30’ is equivalent to +‘+05:30’. + + Time zone items other than ‘UTC’ and ‘Z’ are obsolescent and are not +recommended, because they are ambiguous; for example, ‘EST’ has a +different meaning in Australia than in the United States, and ‘A’ has +different meaning as a military time zone than as an obsolete RFC 822 +time zone. Instead, it’s better to use unambiguous numeric time zone +corrections like ‘-0500’, as described in the previous section. + + If neither a time zone item nor a time zone correction is supplied, +timestamps are interpreted using the rules of the default time zone +(*note Specifying time zone rules::). + + +File: coreutils.info, Node: Combined date and time of day items, Next: Day of week items, Prev: Time zone items, Up: Date input formats + +29.5 Combined date and time of day items +======================================== + +The ISO 8601 date and time of day extended format consists of an ISO +8601 date, a ‘T’ character separator, and an ISO 8601 time of day. This +format is also recognized if the ‘T’ is replaced by a space. + + In this format, the time of day should use 24-hour notation. +Fractional seconds are allowed, with either comma or period preceding +the fraction. ISO 8601 fractional minutes and hours are not supported. +Typically, hosts support nanosecond timestamp resolution; excess +precision is silently discarded. + + Here are some examples: + + 2022-09-24T20:02:00.052-05:00 + 2022-12-31T23:59:59,999999999+11:00 + 1970-01-01 00:00Z + + +File: coreutils.info, Node: Day of week items, Next: Relative items in date strings, Prev: Combined date and time of day items, Up: Date input formats + +29.6 Day of week items +====================== + +The explicit mention of a day of the week will forward the date (only if +necessary) to reach that day of the week in the future. + + Days of the week may be spelled out in full: ‘Sunday’, ‘Monday’, +‘Tuesday’, ‘Wednesday’, ‘Thursday’, ‘Friday’ or ‘Saturday’. Days may be +abbreviated to their first three letters, optionally followed by a +period. The special abbreviations ‘Tues’ for ‘Tuesday’, ‘Wednes’ for +‘Wednesday’ and ‘Thur’ or ‘Thurs’ for ‘Thursday’ are also allowed. + + A number may precede a day of the week item to move forward +supplementary weeks. It is best used in expression like ‘third monday’. +In this context, ‘last DAY’ or ‘next DAY’ is also acceptable; they move +one week before or after the day that DAY by itself would represent. + + A comma following a day of the week item is ignored. + + +File: coreutils.info, Node: Relative items in date strings, Next: Pure numbers in date strings, Prev: Day of week items, Up: Date input formats + +29.7 Relative items in date strings +=================================== + +“Relative items” adjust a date (or the current date if none) forward or +backward. The effects of relative items accumulate. Here are some +examples: + + 1 year + 1 year ago + 3 years + 2 days + + The unit of time displacement may be selected by the string ‘year’ or +‘month’ for moving by whole years or months. These are fuzzy units, as +years and months are not all of equal duration. More precise units are +‘fortnight’ which is worth 14 days, ‘week’ worth 7 days, ‘day’ worth 24 +hours, ‘hour’ worth 60 minutes, ‘minute’ or ‘min’ worth 60 seconds, and +‘second’ or ‘sec’ worth one second. An ‘s’ suffix on these units is +accepted and ignored. + + The unit of time may be preceded by a multiplier, given as an +optionally signed number. Unsigned numbers are taken as positively +signed. No number at all implies 1 for a multiplier. Following a +relative item by the string ‘ago’ is equivalent to preceding the unit by +a multiplier with value -1. + + The string ‘tomorrow’ is worth one day in the future (equivalent to +‘day’), the string ‘yesterday’ is worth one day in the past (equivalent +to ‘day ago’). + + The strings ‘now’ or ‘today’ are relative items corresponding to +zero-valued time displacement, these strings come from the fact a +zero-valued time displacement represents the current time when not +otherwise changed by previous items. They may be used to stress other +items, like in ‘12:00 today’. The string ‘this’ also has the meaning of +a zero-valued time displacement, but is preferred in date strings like +‘this thursday’. + + When a relative item causes the resulting date to cross a boundary +where the clocks were adjusted, typically for daylight saving time, the +resulting date and time are adjusted accordingly. + + The fuzz in units can cause problems with relative items. For +example, ‘2022-12-31 -1 month’ might evaluate to 2022-12-01, because +2022-11-31 is an invalid date. To determine the previous month more +reliably, you can ask for the month before the 15th of the current +month. For example: + + $ date -R + Thu, 31 Dec 2022 13:02:39 -0400 + $ date --date='-1 month' +'Last month was %B?' + Last month was December? + $ date --date="$(date +%Y-%m-15) -1 month" +'Last month was %B!' + Last month was November! + + Also, take care when manipulating dates around clock changes such as +daylight saving leaps. In a few cases these have added or subtracted as +much as 24 hours from the clock, so it is often wise to adopt universal +time by setting the ‘TZ’ environment variable to ‘UTC0’ before embarking +on calendrical calculations. + + +File: coreutils.info, Node: Pure numbers in date strings, Next: Seconds since the Epoch, Prev: Relative items in date strings, Up: Date input formats + +29.8 Pure numbers in date strings +================================= + +The precise interpretation of a pure decimal number depends on the +context in the date string. + + If the decimal number is of the form YYYYMMDD and no other calendar +date item (*note Calendar date items::) appears before it in the date +string, then YYYY is read as the year, MM as the month number and DD as +the day of the month, for the specified calendar date. + + If the decimal number is of the form HHMM and no other time of day +item appears before it in the date string, then HH is read as the hour +of the day and MM as the minute of the hour, for the specified time of +day. MM can also be omitted. + + If both a calendar date and a time of day appear to the left of a +number in the date string, but no relative item, then the number +overrides the year. + + +File: coreutils.info, Node: Seconds since the Epoch, Next: Specifying time zone rules, Prev: Pure numbers in date strings, Up: Date input formats + +29.9 Seconds since the Epoch +============================ + +If you precede a number with ‘@’, it represents an internal timestamp as +a count of seconds. The number can contain an internal decimal point +(either ‘.’ or ‘,’); any excess precision not supported by the internal +representation is truncated toward minus infinity. Such a number cannot +be combined with any other date item, as it specifies a complete +timestamp. + + Internally, computer times are represented as a count of seconds +since an Epoch—a well-defined point of time. On GNU and POSIX systems, +the Epoch is 1970-01-01 00:00:00 UTC, so ‘@0’ represents this time, ‘@1’ +represents 1970-01-01 00:00:01 UTC, and so forth. GNU and most other +POSIX-compliant systems support such times as an extension to POSIX, +using negative counts, so that ‘@-1’ represents 1969-12-31 23:59:59 UTC. + + Most modern systems count seconds with 64-bit two’s-complement +integers of seconds with nanosecond subcounts, which is a range that +includes the known lifetime of the universe with nanosecond resolution. +Some obsolescent systems count seconds with 32-bit two’s-complement +integers and can represent times from 1901-12-13 20:45:52 through +2038-01-19 03:14:07 UTC. A few systems sport other time ranges. + + On most hosts, these counts ignore the presence of leap seconds. For +example, on most hosts ‘@1483228799’ represents 2016-12-31 23:59:59 UTC, +‘@1483228800’ represents 2017-01-01 00:00:00 UTC, and there is no way to +represent the intervening leap second 2016-12-31 23:59:60 UTC. + + +File: coreutils.info, Node: Specifying time zone rules, Next: Authors of parse_datetime, Prev: Seconds since the Epoch, Up: Date input formats + +29.10 Specifying time zone rules +================================ + +Normally, dates are interpreted using the rules of the current time +zone, which in turn are specified by the ‘TZ’ environment variable, or +by a system default if ‘TZ’ is not set. To specify a different set of +default time zone rules that apply just to one date, start the date with +a string of the form ‘TZ="RULE"’. The two quote characters (‘"’) must +be present in the date, and any quotes or backslashes within RULE must +be escaped by a backslash. + + For example, with the GNU ‘date’ command you can answer the question +“What time is it in New York when a Paris clock shows 6:30am on October +31, 2022?” by using a date beginning with ‘TZ="Europe/Paris"’ as shown +in the following shell transcript: + + $ export TZ="America/New_York" + $ date --date='TZ="Europe/Paris" 2022-10-31 06:30' + Mon Oct 31 01:30:00 EDT 2022 + + In this example, the ‘--date’ operand begins with its own ‘TZ’ +setting, so the rest of that operand is processed according to +‘Europe/Paris’ rules, treating the string ‘2022-11-14 06:30’ as if it +were in Paris. However, since the output of the ‘date’ command is +processed according to the overall time zone rules, it uses New York +time. (Paris was normally six hours ahead of New York in 2022, but this +example refers to a brief Halloween period when the gap was five hours.) + + A ‘TZ’ value is a rule that typically names a location in the ‘tz’ +database (https://www.iana.org/time-zones). A recent catalog of +location names appears in the TWiki Date and Time Gateway +(https://twiki.org/cgi-bin/xtra/tzdatepick.html). A few non-GNU hosts +require a colon before a location name in a ‘TZ’ setting, e.g., +‘TZ=":America/New_York"’. + + The ‘tz’ database includes a wide variety of locations ranging from +‘Africa/Abidjan’ to ‘Pacific/Tongatapu’, but if you are at sea and have +your own private time zone, or if you are using a non-GNU host that does +not support the ‘tz’ database, you may need to use a POSIX rule instead. +The previously-mentioned POSIX rule ‘UTC0’ says that the time zone +abbreviation is ‘UTC’, the zone is zero hours away from Greenwich, and +there is no daylight saving time. POSIX rules can also specify nonzero +Greenwich offsets. For example, the following shell transcript answers +the question “What time is it five and a half hours east of Greenwich +when a clock seven hours west of Greenwich shows 9:50pm on July 12, +2022?” + + $ TZ="<+0530>-5:30" date --date='TZ="<-07>+7" 2022-07-12 21:50' + Wed Jul 13 10:20:00 +0530 2022 + +This example uses the somewhat-confusing POSIX convention for rules. +‘TZ="<-07>+7"’ says that the time zone abbreviation is ‘-07’ and the +time zone is 7 hours west of Greenwich, and ‘TZ="<+0530>-5:30"’ says +that the time zone abbreviation is ‘+0530’ and the time zone is 5 hours +30 minutes east of Greenwich. (One should never use a setting like +‘TZ="UTC-5"’, since this would incorrectly imply that local time is five +hours east of Greenwich and the time zone is called “UTC”.) Although +trickier POSIX ‘TZ’ settings like ‘TZ="<-05>+5<-04>,M3.2.0/2,M11.1.0/2"’ +can specify some daylight saving regimes, location-based settings like +‘TZ="America/New_York"’ are typically simpler and more accurate +historically. *Note Specifying the Time Zone with ‘TZ’: (libc)TZ +Variable. + + +File: coreutils.info, Node: Authors of parse_datetime, Prev: Specifying time zone rules, Up: Date input formats + +29.11 Authors of ‘parse_datetime’ +================================= + +‘parse_datetime’ started life as ‘getdate’, as originally implemented by +Steven M. Bellovin (<smb@research.att.com>) while at the University of +North Carolina at Chapel Hill. The code was later tweaked by a couple +of people on Usenet, then completely overhauled by Rich $alz +(<rsalz@bbn.com>) and Jim Berets (<jberets@bbn.com>) in August, 1990. +Various revisions for the GNU system were made by David MacKenzie, Jim +Meyering, Paul Eggert and others, including renaming it to ‘get_date’ to +avoid a conflict with the alternative Posix function ‘getdate’, and a +later rename to ‘parse_datetime’. The Posix function ‘getdate’ can +parse more locale-specific dates using ‘strptime’, but relies on an +environment variable and external file, and lacks the thread-safety of +‘parse_datetime’. + + This chapter was originally produced by François Pinard +(<pinard@iro.umontreal.ca>) from the ‘parse_datetime.y’ source code, and +then edited by K. Berry (<kb@cs.umb.edu>). + + +File: coreutils.info, Node: Version sort ordering, Next: Opening the software toolbox, Prev: Date input formats, Up: Top + +30 Version sort ordering +************************ + +* Menu: + +* Version sort overview:: +* Version sort implementation:: +* Differences from Debian version sort:: +* Advanced version sort topics:: + + +File: coreutils.info, Node: Version sort overview, Next: Version sort implementation, Up: Version sort ordering + +30.1 Version sort overview +========================== + +“Version sort” puts items such as file names and lines of text in an +order that feels natural to people, when the text contains a mixture of +letters and digits. + + Lexicographic sorting usually does not produce the order that one +expects because comparisons are made on a character-by-character basis. + + Compare the sorting of the following items: + + Lexicographic sort: Version Sort: + + a1 a1 + a120 a2 + a13 a13 + a2 a120 + + Version sort functionality in GNU Coreutils is available in the ‘ls +-v’, ‘ls --sort=version’, ‘sort -V’, and ‘sort --version-sort’ commands. + +* Menu: + +* Using version sort in GNU Coreutils:: +* Version sort and natural sort:: +* Variations in version sort order:: + + +File: coreutils.info, Node: Using version sort in GNU Coreutils, Next: Version sort and natural sort, Up: Version sort overview + +30.1.1 Using version sort in GNU Coreutils +------------------------------------------ + +Two GNU Coreutils programs use version sort: ‘ls’ and ‘sort’. + + To list files in version sort order, use ‘ls’ with the ‘-v’ or +‘--sort=version’ option: + + default sort: version sort: + + $ ls -1 $ ls -1 -v + a1 a1 + a100 a1.4 + a1.13 a1.13 + a1.4 a1.40 + a1.40 a2 + a2 a100 + + To sort text files in version sort order, use ‘sort’ with the ‘-V’ or +‘--version-sort’ option: + + $ cat input + b3 + b11 + b1 + b20 + + + lexicographic order: version sort order: + + $ sort input $ sort -V input + b1 b1 + b11 b3 + b20 b11 + b3 b20 + + To sort a specific field in a file, use ‘-k/--key’ with ‘V’ type +sorting, which is often combined with ‘b’ to ignore leading blanks in +the field: + + $ cat input2 + 100 b3 apples + 2000 b11 oranges + 3000 b1 potatoes + 4000 b20 bananas + $ sort -k 2bV,2 input2 + 3000 b1 potatoes + 100 b3 apples + 2000 b11 oranges + 4000 b20 bananas + + +File: coreutils.info, Node: Version sort and natural sort, Next: Variations in version sort order, Prev: Using version sort in GNU Coreutils, Up: Version sort overview + +30.1.2 Version sort and natural sort +------------------------------------ + +In GNU Coreutils, the name “version sort” was chosen because it is based +on Debian GNU/Linux’s algorithm of sorting packages’ versions. + + Its goal is to answer questions like “Which package is newer, +‘firefox-60.7.2’ or ‘firefox-60.12.3’?” + + In Coreutils this algorithm was slightly modified to work on more +general input such as textual strings and file names (see *note +Differences from Debian version sort::). + + In other contexts, such as other programs and other programming +languages, a similar sorting functionality is called natural sort +(https://en.wikipedia.org/wiki/Natural_sort_order). + + +File: coreutils.info, Node: Variations in version sort order, Prev: Version sort and natural sort, Up: Version sort overview + +30.1.3 Variations in version sort order +--------------------------------------- + +Currently there is no standard for version sort. + + That is: there is no one correct way or universally agreed-upon way +to order items. Each program and each programming language can decide +its own ordering algorithm and call it “version sort”, “natural sort”, +or other names. + + See *note Other version/natural sort implementations:: for many +examples of differing sorting possibilities, each with its own rules and +variations. + + If you find a bug in the Coreutils implementation of version-sort, +please report it. *Note Reporting version sort bugs::. + + +File: coreutils.info, Node: Version sort implementation, Next: Differences from Debian version sort, Prev: Version sort overview, Up: Version sort ordering + +30.2 Version sort implementation +================================ + +GNU Coreutils version sort is based on the “upstream version” part of +Debian’s versioning scheme +(https://www.debian.org/doc/debian-policy/ch-controlfields.html#version). + + This section describes the GNU Coreutils sort ordering rules. + + The next section (*note Differences from Debian version sort::) +describes some differences between GNU Coreutils and Debian version +sort. + +* Menu: + +* Version-sort ordering rules:: +* Version sort is not the same as numeric sort:: +* Version sort punctuation:: +* Punctuation vs letters:: +* The tilde ~:: +* Version sort ignores locale:: + + +File: coreutils.info, Node: Version-sort ordering rules, Next: Version sort is not the same as numeric sort, Up: Version sort implementation + +30.2.1 Version-sort ordering rules +---------------------------------- + +The version sort ordering rules are: + + 1. The strings are compared from left to right. + + 2. First the initial part of each string consisting entirely of + non-digit bytes is determined. + + A. These two parts (either of which may be empty) are compared + lexically. If a difference is found it is returned. + + B. The lexical comparison is a lexicographic comparison of byte + strings, except that: + + a. ASCII letters sort before other bytes. + b. A tilde sorts before anything, even an empty string. + + 3. Then the initial part of the remainder of each string that contains + all the leading digits is determined. The numerical values + represented by these two parts are compared, and any difference + found is returned as the result of the comparison. + + A. For these purposes an empty string (which can only occur at + the end of one or both version strings being compared) counts + as zero. + + B. Because the numerical value is used, non-identical strings can + compare equal. For example, ‘123’ compares equal to ‘00123’, + and the empty string compares equal to ‘0’. + + 4. These two steps (comparing and removing initial non-digit strings + and initial digit strings) are repeated until a difference is found + or both strings are exhausted. + + Consider the version-sort comparison of two file names: ‘foo07.7z’ +and ‘foo7a.7z’. The two strings will be broken down to the following +parts, and the parts compared respectively from each string: + + foo vs foo (rule 2, non-digits) + 07 vs 7 (rule 3, digits) + . vs a. (rule 2) + 7 vs 7 (rule 3) + z vs z (rule 2) + + Comparison flow based on above algorithm: + + 1. The first parts (‘foo’) are identical. + + 2. The second parts (‘07’ and ‘7’) are compared numerically, and + compare equal. + + 3. The third parts (‘.’ vs ‘a.’) are compared lexically by ASCII value + (rule 2.B). + + 4. The first byte of the first string (‘.’) is compared to the first + byte of the second string (‘a’). + + 5. Rule 2.B.a says letters sorts before non-letters. Hence, ‘a’ comes + before ‘.’. + + 6. The returned result is that ‘foo7a.7z’ comes before ‘foo07.7z’. + + Result when using sort: + + $ cat input3 + foo07.7z + foo7a.7z + $ sort -V input3 + foo7a.7z + foo07.7z + + See *note Differences from Debian version sort:: for additional rules +that extend the Debian algorithm in Coreutils. + + +File: coreutils.info, Node: Version sort is not the same as numeric sort, Next: Version sort punctuation, Prev: Version-sort ordering rules, Up: Version sort implementation + +30.2.2 Version sort is not the same as numeric sort +--------------------------------------------------- + +Consider the following text file: + + $ cat input4 + 8.10 + 8.5 + 8.1 + 8.01 + 8.010 + 8.100 + 8.49 + + Numerical Sort: Version Sort: + + $ sort -n input4 $ sort -V input4 + 8.01 8.01 + 8.010 8.1 + 8.1 8.5 + 8.10 8.010 + 8.100 8.10 + 8.49 8.49 + 8.5 8.100 + + Numeric sort (‘sort -n’) treats the entire string as a single numeric +value, and compares it to other values. For example, ‘8.1’, ‘8.10’ and +‘8.100’ are numerically equivalent, and are ordered together. +Similarly, ‘8.49’ is numerically less than ‘8.5’, and appears before +first. + + Version sort (‘sort -V’) first breaks down the string into digit and +non-digit parts, and only then compares each part (see annotated example +in *note Version-sort ordering rules::). + + Comparing the string ‘8.1’ to ‘8.01’, first the ‘8’s are compared +(and are identical), then the dots (‘.’) are compared and are identical, +and lastly the remaining digits are compared numerically (‘1’ and ‘01’) +– which are numerically equal. Hence, ‘8.01’ and ‘8.1’ are grouped +together. + + Similarly, comparing ‘8.5’ to ‘8.49’ – the ‘8’ and ‘.’ parts are +identical, then the numeric values ‘5’ and ‘49’ are compared. The +resulting ‘5’ appears before ‘49’. + + This sorting order (where ‘8.5’ comes before ‘8.49’) is common when +assigning versions to computer programs (while perhaps not intuitive or +“natural” for people). + + +File: coreutils.info, Node: Version sort punctuation, Next: Punctuation vs letters, Prev: Version sort is not the same as numeric sort, Up: Version sort implementation + +30.2.3 Version sort punctuation +------------------------------- + +Punctuation is sorted by ASCII order (rule 2.B). + + $ touch 1.0.5_src.tar.gz 1.0_src.tar.gz + $ ls -v -1 + 1.0.5_src.tar.gz + 1.0_src.tar.gz + + Why is ‘1.0.5_src.tar.gz’ listed before ‘1.0_src.tar.gz’? + + Based on the version-sort ordering rules, the strings are broken down +into the following parts: + + 1 vs 1 (rule 3, all digits) + . vs . (rule 2, all non-digits) + 0 vs 0 (rule 3) + . vs _src.tar.gz (rule 2) + 5 vs empty string (no more bytes in the file name) + _src.tar.gz vs empty string + + The fourth parts (‘.’ and ‘_src.tar.gz’) are compared lexically by +ASCII order. The ‘.’ (ASCII value 46) is less than ‘_’ (ASCII value 95) +– and should be listed before it. + + Hence, ‘1.0.5_src.tar.gz’ is listed first. + + If a different byte appears instead of the underscore (for example, +percent sign ‘%’ ASCII value 37, which is less than dot’s ASCII value of +46), that file will be listed first: + + $ touch 1.0.5_src.tar.gz 1.0%zzzzz.gz + 1.0%zzzzz.gz + 1.0.5_src.tar.gz + + The same reasoning applies to the following example, as ‘.’ with +ASCII value 46 is less than ‘/’ with ASCII value 47: + + $ cat input5 + 3.0/ + 3.0.5 + $ sort -V input5 + 3.0.5 + 3.0/ + + +File: coreutils.info, Node: Punctuation vs letters, Next: The tilde ~, Prev: Version sort punctuation, Up: Version sort implementation + +30.2.4 Punctuation vs letters +----------------------------- + +Rule 2.B.a says letters sort before non-letters (after breaking down a +string to digit and non-digit parts). + + $ cat input6 + a% + az + $ sort -V input6 + az + a% + + The input strings consist entirely of non-digits, and based on the +above algorithm have only one part, all non-digits (‘a%’ vs ‘az’). + + Each part is then compared lexically, byte-by-byte; ‘a’ compares +identically in both strings. + + Rule 2.B.a says a letter like ‘z’ sorts before a non-letter like ‘%’ +– hence ‘az’ appears first (despite ‘z’ having ASCII value of 122, much +larger than ‘%’ with ASCII value 37). + + +File: coreutils.info, Node: The tilde ~, Next: Version sort ignores locale, Prev: Punctuation vs letters, Up: Version sort implementation + +30.2.5 The tilde ‘~’ +-------------------- + +Rule 2.B.b says the tilde ‘~’ (ASCII 126) sorts before other bytes, and +before an empty string. + + $ cat input7 + 1 + 1% + 1.2 + 1~ + ~ + $ sort -V input7 + ~ + 1~ + 1 + 1% + 1.2 + + The sorting algorithm starts by breaking down the string into +non-digit (rule 2) and digit parts (rule 3). + + In the above input file, only the last line in the input file starts +with a non-digit (‘~’). This is the first part. All other lines in the +input file start with a digit – their first non-digit part is empty. + + Based on rule 2.B.b, tilde ‘~’ sorts before other bytes and before +the empty string – hence it comes before all other strings, and is +listed first in the sorted output. + + The remaining lines (‘1’, ‘1%’, ‘1.2’, ‘1~’) follow similar logic: +The digit part is extracted (1 for all strings) and compares equal. The +following extracted parts for the remaining input lines are: empty part, +‘%’, ‘.’, ‘~’. + + Tilde sorts before all others, hence the line ‘1~’ appears next. + + The remaining lines (‘1’, ‘1%’, ‘1.2’) are sorted based on previously +explained rules. + + +File: coreutils.info, Node: Version sort ignores locale, Prev: The tilde ~, Up: Version sort implementation + +30.2.6 Version sort ignores locale +---------------------------------- + +In version sort, Unicode characters are compared byte-by-byte according +to their binary representation, ignoring their Unicode value or the +current locale. + + Most commonly, Unicode characters are encoded as UTF-8 bytes; for +example, GREEK SMALL LETTER ALPHA (U+03B1, ‘α’) is encoded as the UTF-8 +sequence ‘0xCE 0xB1’). The encoding is compared byte-by-byte, e.g., +first ‘0xCE’ (decimal value 206) then ‘0xB1’ (decimal value 177). + + $ touch aa az "a%" "aα" + $ ls -1 -v + aa + az + a% + aα + + Ignoring the first letter (‘a’) which is identical in all strings, +the compared values are: + + ‘a’ and ‘z’ are letters, and sort before all other non-digits. + + Then, percent sign ‘%’ (ASCII value 37) is compared to the first byte +of the UTF-8 sequence of ‘α’, which is 0xCE or 206). The value 37 is +smaller, hence ‘a%’ is listed before ‘aα’. + + +File: coreutils.info, Node: Differences from Debian version sort, Next: Advanced version sort topics, Prev: Version sort implementation, Up: Version sort ordering + +30.3 Differences from Debian version sort +========================================= + +GNU Coreutils version sort differs slightly from the official Debian +algorithm, in order to accommodate more general usage and file name +listing. + +* Menu: + +* Hyphen-minus and colon:: +* Special priority in GNU Coreutils version sort:: +* Special handling of file extensions:: +* Comparing two strings using Debian's algorithm:: + + +File: coreutils.info, Node: Hyphen-minus and colon, Next: Special priority in GNU Coreutils version sort, Up: Differences from Debian version sort + +30.3.1 Hyphen-minus ‘-’ and colon ‘:’ +------------------------------------- + +In Debian’s version string syntax the version consists of three parts: + [epoch:]upstream_version[-debian_revision] + The ‘epoch’ and ‘debian_revision’ parts are optional. + + Example of such version strings: + + 60.7.2esr-1~deb9u1 + 52.9.0esr-1~deb9u1 + 1:2.3.4-1+b2 + 327-2 + 1:1.0.13-3 + 2:1.19.2-1+deb9u5 + + If the ‘debian_revision part’ is not present, hyphens ‘-’ are not +allowed. If epoch is not present, colons ‘:’ are not allowed. + + If these parts are present, hyphen and/or colons can appear only once +in valid Debian version strings. + + In GNU Coreutils, such restrictions are not reasonable (a file name +can have many hyphens, a line of text can have many colons). + + As a result, in GNU Coreutils hyphens and colons are treated exactly +like all other punctuation, i.e., they are sorted after letters. *Note +Version sort punctuation::. + + In Debian, these characters are treated differently than in +Coreutils: a version string with hyphen will sort before similar strings +without hyphens. + + Compare: + + $ touch 1ab-cd 1abb + $ ls -v -1 + 1abb + 1ab-cd + $ if dpkg --compare-versions 1abb lt 1ab-cd + > then echo sorted + > else echo out of order + > fi + out of order + + For further details, see *note Comparing two strings using Debian's +algorithm:: and GNU Bug 35939 (https://bugs.gnu.org/35939). + + +File: coreutils.info, Node: Special priority in GNU Coreutils version sort, Next: Special handling of file extensions, Prev: Hyphen-minus and colon, Up: Differences from Debian version sort + +30.3.2 Special priority in GNU Coreutils version sort +----------------------------------------------------- + +In GNU Coreutils version sort, the following items have special priority +and sort before all other strings (listed in order): + + 1. The empty string + + 2. The string ‘.’ (a single dot, ASCII 46) + + 3. The string ‘..’ (two dots) + + 4. Strings starting with dot (‘.’) sort before strings starting with + any other byte. + + Example: + + $ printf '%s\n' a "" b "." c ".." ".d20" ".d3" | sort -V + . + .. + .d3 + .d20 + a + b + c + + These priorities make perfect sense for ‘ls -v’: The special files +dot ‘.’ and dot-dot ‘..’ will be listed first, followed by any hidden +files (files starting with a dot), followed by non-hidden files. + + For ‘sort -V’ these priorities might seem arbitrary. However, +because the sorting code is shared between the ‘ls’ and ‘sort’ program, +the ordering rules are the same. + + +File: coreutils.info, Node: Special handling of file extensions, Next: Comparing two strings using Debian's algorithm, Prev: Special priority in GNU Coreutils version sort, Up: Differences from Debian version sort + +30.3.3 Special handling of file extensions +------------------------------------------ + +GNU Coreutils version sort implements specialized handling of strings +that look like file names with extensions. This enables slightly more +natural ordering of file names. + + The following additional rules apply when comparing two strings where +both begin with non-‘.’. They also apply when comparing two strings +where both begin with ‘.’ but neither is ‘.’ or ‘..’. + + 1. A suffix (i.e., a file extension) is defined as: a dot, followed by + an ASCII letter or tilde, followed by zero or more ASCII letters, + digits, or tildes; all repeated zero or more times, and ending at + string end. This is equivalent to matching the extended regular + expression ‘(\.[A-Za-z~][A-Za-z0-9~]*)*$’ in the C locale. The + longest such match is used, except that a suffix is not allowed to + match an entire nonempty string. + + 2. The suffixes are temporarily removed, and the strings are compared + without them, using version sort (see *note Version-sort ordering + rules::) without special priority (see *note Special priority in + GNU Coreutils version sort::). + + 3. If the suffix-less strings do not compare equal, this comparison + result is used and the suffixes are effectively ignored. + + 4. If the suffix-less strings compare equal, the suffixes are restored + and the entire strings are compared using version sort. + + Examples for rule 1: + + • ‘hello-8.txt’: the suffix is ‘.txt’ + + • ‘hello-8.2.txt’: the suffix is ‘.txt’ (‘.2’ is not included because + the dot is not followed by a letter) + + • ‘hello-8.0.12.tar.gz’: the suffix is ‘.tar.gz’ (‘.0.12’ is not + included) + + • ‘hello-8.2’: no suffix (suffix is an empty string) + + • ‘hello.foobar65’: the suffix is ‘.foobar65’ + + • ‘gcc-c++-10.8.12-0.7rc2.fc9.tar.bz2’: the suffix is ‘.fc9.tar.bz2’ + (‘.7rc2’ is not included as it begins with a digit) + + • ‘.autom4te.cfg’: the suffix is the entire string. + + Examples for rule 2: + + • Comparing ‘hello-8.txt’ to ‘hello-8.2.12.txt’, the ‘.txt’ suffix is + temporarily removed from both strings. + + • Comparing ‘foo-10.3.tar.gz’ to ‘foo-10.tar.xz’, the suffixes + ‘.tar.gz’ and ‘.tar.xz’ are temporarily removed from the strings. + + Example for rule 3: + + • Comparing ‘hello.foobar65’ to ‘hello.foobar4’, the suffixes + (‘.foobar65’ and ‘.foobar4’) are temporarily removed. The + remaining strings are identical (‘hello’). The suffixes are then + restored, and the entire strings are compared (‘hello.foobar4’ + comes first). + + Examples for rule 4: + + • When comparing the strings ‘hello-8.2.txt’ and ‘hello-8.10.txt’, + the suffixes (‘.txt’) are temporarily removed. The remaining + strings (‘hello-8.2’ and ‘hello-8.10’) are compared as previously + described (‘hello-8.2’ comes first). (In this case the suffix + removal algorithm does not have a noticeable effect on the + resulting order.) + + How does the suffix-removal algorithm effect ordering results? + + Consider the comparison of hello-8.txt and hello-8.2.txt. + + Without the suffix-removal algorithm, the strings will be broken down +to the following parts: + + hello- vs hello- (rule 2, all non-digits) + 8 vs 8 (rule 3, all digits) + .txt vs . (rule 2) + empty vs 2 + empty vs .txt + + The comparison of the third parts (‘.’ vs ‘.txt’) will determine that +the shorter string comes first – resulting in ‘hello-8.2.txt’ appearing +first. + + Indeed this is the order in which Debian’s ‘dpkg’ compares the +strings. + + A more natural result is that ‘hello-8.txt’ should come before +‘hello-8.2.txt’, and this is where the suffix-removal comes into play: + + The suffixes (‘.txt’) are removed, and the remaining strings are +broken down into the following parts: + + hello- vs hello- (rule 2, all non-digits) + 8 vs 8 (rule 3, all digits) + empty vs . (rule 2) + empty vs 2 + + As empty strings sort before non-empty strings, the result is +‘hello-8’ being first. + + A real-world example would be listing files such as: +‘gcc_10.fc9.tar.gz’ and ‘gcc_10.8.12.7rc2.fc9.tar.bz2’: Debian’s +algorithm would list ‘gcc_10.8.12.7rc2.fc9.tar.bz2’ first, while ‘ls -v’ +will list ‘gcc_10.fc9.tar.gz’ first. + + These priorities make sense for ‘ls -v’: Versioned files will be +listed in a more natural order. + + For ‘sort -V’ these priorities might seem arbitrary. However, +because the sorting code is shared between the ‘ls’ and ‘sort’ program, +the ordering rules are the same. + + +File: coreutils.info, Node: Comparing two strings using Debian's algorithm, Prev: Special handling of file extensions, Up: Differences from Debian version sort + +30.3.4 Comparing two strings using Debian’s algorithm +----------------------------------------------------- + +The Debian program ‘dpkg’ (available on all Debian and Ubuntu +installations) can compare two strings using the ‘--compare-versions’ +option. + + To use it, create a helper shell function (simply copy & paste the +following snippet to your shell command-prompt): + + compver() { + if dpkg --compare-versions "$1" lt "$2" + then printf '%s\n' "$1" "$2" + else printf '%s\n' "$2" "$1" + fi + } + + Then compare two strings by calling ‘compver’: + + $ compver 8.49 8.5 + 8.5 + 8.49 + + Note that ‘dpkg’ will warn if the strings have invalid syntax: + + $ compver "foo07.7z" "foo7a.7z" + dpkg: warning: version 'foo07.7z' has bad syntax: + version number does not start with digit + dpkg: warning: version 'foo7a.7z' has bad syntax: + version number does not start with digit + foo7a.7z + foo07.7z + $ compver "3.0/" "3.0.5" + dpkg: warning: version '3.0/' has bad syntax: + invalid character in version number + 3.0.5 + 3.0/ + + To illustrate the different handling of hyphens between Debian and +Coreutils algorithms (see *note Hyphen-minus and colon::): + + $ compver abb ab-cd 2>/dev/null $ printf 'abb\nab-cd\n' | sort -V + ab-cd abb + abb ab-cd + + To illustrate the different handling of file extension: (see *note +Special handling of file extensions::): + + $ compver hello-8.txt hello-8.2.txt 2>/dev/null + hello-8.2.txt + hello-8.txt + $ printf '%s\n' hello-8.txt hello-8.2.txt | sort -V + hello-8.txt + hello-8.2.txt + + +File: coreutils.info, Node: Advanced version sort topics, Prev: Differences from Debian version sort, Up: Version sort ordering + +30.4 Advanced Topics +==================== + +* Menu: + +* Reporting version sort bugs:: +* Other version/natural sort implementations:: +* Related source code:: + + +File: coreutils.info, Node: Reporting version sort bugs, Next: Other version/natural sort implementations, Up: Advanced version sort topics + +30.4.1 Reporting version sort bugs +---------------------------------- + +If you suspect a bug in GNU Coreutils version sort (i.e., in the output +of ‘ls -v’ or ‘sort -V’), please first check the following: + + 1. Is the result consistent with Debian’s own ordering (using ‘dpkg’, + see *note Comparing two strings using Debian's algorithm::)? If it + is, then this is not a bug – please do not report it. + + 2. If the result differs from Debian’s, is it explained by one of the + sections in *note Differences from Debian version sort::? If it + is, then this is not a bug – please do not report it. + + 3. If you have a question about specific ordering which is not + explained here, please write to <coreutils@gnu.org>, and provide a + concise example that will help us diagnose the issue. + + 4. If you still suspect a bug which is not explained by the above, + please write to <bug-coreutils@gnu.org> with a concrete example of + the suspected incorrect output, with details on why you think it is + incorrect. + + +File: coreutils.info, Node: Other version/natural sort implementations, Next: Related source code, Prev: Reporting version sort bugs, Up: Advanced version sort topics + +30.4.2 Other version/natural sort implementations +------------------------------------------------- + +As previously mentioned, there are multiple variations on +version/natural sort, each with its own rules. Some examples are: + + • Natural Sorting variants in Rosetta Code + (https://rosettacode.org/wiki/Natural_sorting). + + • Python’s natsort package (https://pypi.org/project/natsort/) + (includes detailed description of their sorting rules: natsort – + how it works + (https://natsort.readthedocs.io/en/master/howitworks.html)). + + • Ruby’s version_sorter (https://github.com/github/version_sorter). + + • Perl has multiple packages for natural and version sorts (each + likely with its own rules and nuances): Sort::Naturally + (https://metacpan.org/pod/Sort::Naturally), Sort::Versions + (https://metacpan.org/pod/Sort::Versions), CPAN::Version + (https://metacpan.org/pod/CPAN::Version). + + • PHP has a built-in function natsort + (https://www.php.net/manual/en/function.natsort.php). + + • NodeJS’s natural-sort package + (https://www.npmjs.com/package/natural-sort). + + • In zsh, the glob modifier + (http://zsh.sourceforge.net/Doc/Release/Expansion.html#Glob-Qualifiers) + ‘*(n)’ will expand to files in natural sort order. + + • When writing C programs, the GNU libc library (‘glibc’) provides + the strverscmp(3) + (https://man7.org/linux/man-pages/man3/strverscmp.3.html) function + to compare two strings, and versionsort(3) + (https://man7.org/linux/man-pages/man3/versionsort.3.html) function + to compare two directory entries (despite the names, they are not + identical to GNU Coreutils version sort ordering). + + • Using Debian’s sorting algorithm in: + + • python: Stack Overflow Example #4957741 + (https://stackoverflow.com/a/4957741). + + • NodeJS: deb-version-compare + (https://www.npmjs.com/package/deb-version-compare). + + +File: coreutils.info, Node: Related source code, Prev: Other version/natural sort implementations, Up: Advanced version sort topics + +30.4.3 Related source code +-------------------------- + + • Debian’s code which splits a version string into + ‘epoch/upstream_version/debian_revision’ parts: + parsehelp.c:parseversion() + (https://git.dpkg.org/cgit/dpkg/dpkg.git/tree/lib/dpkg/parsehelp.c#n191). + + • Debian’s code which performs the ‘upstream_version’ comparison: + version.c + (https://git.dpkg.org/cgit/dpkg/dpkg.git/tree/lib/dpkg/version.c#n140). + + • Gnulib code (used by GNU Coreutils) which performs the version + comparison: filevercmp.c + (https://git.savannah.gnu.org/cgit/gnulib.git/tree/lib/filevercmp.c). + + +File: coreutils.info, Node: Opening the software toolbox, Next: GNU Free Documentation License, Prev: Version sort ordering, Up: Top + +31 Opening the Software Toolbox +******************************* + +An earlier version of this chapter appeared in the ‘What’s GNU?’ column +of the June 1994 ‘Linux Journal’ +(https://www.linuxjournal.com/article.php?sid=2762). It was written by +Arnold Robbins. + +* Menu: + +* Toolbox introduction:: Toolbox introduction +* I/O redirection:: I/O redirection +* The who command:: The ‘who’ command +* The cut command:: The ‘cut’ command +* The sort command:: The ‘sort’ command +* The uniq command:: The ‘uniq’ command +* Putting the tools together:: Putting the tools together + + +File: coreutils.info, Node: Toolbox introduction, Next: I/O redirection, Up: Opening the software toolbox + +Toolbox Introduction +==================== + +This month’s column is only peripherally related to the GNU Project, in +that it describes a number of the GNU tools on your GNU/Linux system and +how they might be used. What it’s really about is the “Software Tools” +philosophy of program development and usage. + + The software tools philosophy was an important and integral concept +in the initial design and development of Unix (of which GNU/Linux and +GNU are essentially clones). Unfortunately, in the modern day press of +Internetworking and flashy GUIs, it seems to have fallen by the wayside. +This is a shame, since it provides a powerful mental model for solving +many kinds of problems. + + Many people carry a Swiss Army knife around in their pants pockets +(or purse). A Swiss Army knife is a handy tool to have: it has several +knife blades, a screwdriver, tweezers, toothpick, nail file, corkscrew, +and perhaps a number of other things on it. For the everyday, small +miscellaneous jobs where you need a simple, general purpose tool, it’s +just the thing. + + On the other hand, an experienced carpenter doesn’t build a house +using a Swiss Army knife. Instead, he has a toolbox chock full of +specialized tools – a saw, a hammer, a screwdriver, a plane, and so on. +And he knows exactly when and where to use each tool; you won’t catch +him hammering nails with the handle of his screwdriver. + + The Unix developers at Bell Labs were all professional programmers +and trained computer scientists. They had found that while a +one-size-fits-all program might appeal to a user because there’s only +one program to use, in practice such programs are + + a. difficult to write, + + b. difficult to maintain and debug, and + + c. difficult to extend to meet new situations. + + Instead, they felt that programs should be specialized tools. In +short, each program “should do one thing well.” No more and no less. +Such programs are simpler to design, write, and get right – they only do +one thing. + + Furthermore, they found that with the right machinery for hooking +programs together, that the whole was greater than the sum of the parts. +By combining several special purpose programs, you could accomplish a +specific task that none of the programs was designed for, and accomplish +it much more quickly and easily than if you had to write a special +purpose program. We will see some (classic) examples of this further on +in the column. (An important additional point was that, if necessary, +take a detour and build any software tools you may need first, if you +don’t already have something appropriate in the toolbox.) + + +File: coreutils.info, Node: I/O redirection, Next: The who command, Prev: Toolbox introduction, Up: Opening the software toolbox + +I/O Redirection +=============== + +Hopefully, you are familiar with the basics of I/O redirection in the +shell, in particular the concepts of “standard input,” “standard +output,” and “standard error”. Briefly, “standard input” is a data +source, where data comes from. A program should not need to either know +or care if the data source is a regular file, a keyboard, a magnetic +tape, or even a punched card reader. Similarly, “standard output” is a +data sink, where data goes to. The program should neither know nor care +where this might be. Programs that only read their standard input, do +something to the data, and then send it on, are called “filters”, by +analogy to filters in a water pipeline. + + With the Unix shell, it’s very easy to set up data pipelines: + + program_to_create_data | filter1 | ... | filterN > final.pretty.data + + We start out by creating the raw data; each filter applies some +successive transformation to the data, until by the time it comes out of +the pipeline, it is in the desired form. + + This is fine and good for standard input and standard output. Where +does the standard error come in to play? Well, think about ‘filter1’ in +the pipeline above. What happens if it encounters an error in the data +it sees? If it writes an error message to standard output, it will just +disappear down the pipeline into ‘filter2’’s input, and the user will +probably never see it. So programs need a place where they can send +error messages so that the user will notice them. This is standard +error, and it is usually connected to your console or window, even if +you have redirected standard output of your program away from your +screen. + + For filter programs to work together, the format of the data has to +be agreed upon. The most straightforward and easiest format to use is +simply lines of text. Unix data files are generally just streams of +bytes, with lines delimited by the ASCII LF (Line Feed) character, +conventionally called a “newline” in the Unix literature. (This is +‘'\n'’ if you’re a C programmer.) This is the format used by all the +traditional filtering programs. (Many earlier operating systems had +elaborate facilities and special purpose programs for managing binary +data. Unix has always shied away from such things, under the philosophy +that it’s easiest to simply be able to view and edit your data with a +text editor.) + + OK, enough introduction. Let’s take a look at some of the tools, and +then we’ll see how to hook them together in interesting ways. In the +following discussion, we will only present those command line options +that interest us. As you should always do, double check your system +documentation for the full story. + + +File: coreutils.info, Node: The who command, Next: The cut command, Prev: I/O redirection, Up: Opening the software toolbox + +The ‘who’ Command +================= + +The first program is the ‘who’ command. By itself, it generates a list +of the users who are currently logged in. Although I’m writing this on +a single-user system, we’ll pretend that several people are logged in: + + $ who + ⊣ arnold console Jan 22 19:57 + ⊣ miriam ttyp0 Jan 23 14:19(:0.0) + ⊣ bill ttyp1 Jan 21 09:32(:0.0) + ⊣ arnold ttyp2 Jan 23 20:48(:0.0) + + Here, the ‘$’ is the usual shell prompt, at which I typed ‘who’. +There are three people logged in, and I am logged in twice. On +traditional Unix systems, user names are never more than eight +characters long. This little bit of trivia will be useful later. The +output of ‘who’ is nice, but the data is not all that exciting. + + +File: coreutils.info, Node: The cut command, Next: The sort command, Prev: The who command, Up: Opening the software toolbox + +The ‘cut’ Command +================= + +The next program we’ll look at is the ‘cut’ command. This program cuts +out columns or fields of input data. For example, we can tell it to +print just the login name and full name from the ‘/etc/passwd’ file. +The ‘/etc/passwd’ file has seven fields, separated by colons: + + arnold:xyzzy:2076:10:Arnold D. Robbins:/home/arnold:/bin/bash + + To get the first and fifth fields, we would use ‘cut’ like this: + + $ cut -d: -f1,5 /etc/passwd + ⊣ root:Operator + ... + ⊣ arnold:Arnold D. Robbins + ⊣ miriam:Miriam A. Robbins + ... + + With the ‘-c’ option, ‘cut’ will cut out specific characters (i.e., +columns) in the input lines. This is useful for input data that has +fixed width fields, and does not have a field separator. For example, +list the Monday dates for the current month: + + $ cal | cut -c 3-5 + ⊣Mo + ⊣ + ⊣ 6 + ⊣ 13 + ⊣ 20 + ⊣ 27 + + +File: coreutils.info, Node: The sort command, Next: The uniq command, Prev: The cut command, Up: Opening the software toolbox + +The ‘sort’ Command +================== + +Next we’ll look at the ‘sort’ command. This is one of the most powerful +commands on a Unix-style system; one that you will often find yourself +using when setting up fancy data plumbing. + + The ‘sort’ command reads and sorts each file named on the command +line. It then merges the sorted data and writes it to standard output. +It will read standard input if no files are given on the command line +(thus making it into a filter). The sort is based on the character +collating sequence or based on user-supplied ordering criteria. + + +File: coreutils.info, Node: The uniq command, Next: Putting the tools together, Prev: The sort command, Up: Opening the software toolbox + +The ‘uniq’ Command +================== + +Finally (at least for now), we’ll look at the ‘uniq’ program. When +sorting data, you will often end up with duplicate lines, lines that are +identical. Usually, all you need is one instance of each line. This is +where ‘uniq’ comes in. The ‘uniq’ program reads its standard input. It +prints only one copy of each repeated line. It does have several +options. Later on, we’ll use the ‘-c’ option, which prints each unique +line, preceded by a count of the number of times that line occurred in +the input. + + +File: coreutils.info, Node: Putting the tools together, Prev: The uniq command, Up: Opening the software toolbox + +Putting the Tools Together +========================== + +Now, let’s suppose this is a large ISP server system with dozens of +users logged in. The management wants the system administrator to write +a program that will generate a sorted list of logged in users. +Furthermore, even if a user is logged in multiple times, his or her name +should only show up in the output once. + + The administrator could sit down with the system documentation and +write a C program that did this. It would take perhaps a couple of +hundred lines of code and about two hours to write it, test it, and +debug it. However, knowing the software toolbox, the administrator can +instead start out by generating just a list of logged on users: + + $ who | cut -c1-8 + ⊣ arnold + ⊣ miriam + ⊣ bill + ⊣ arnold + + Next, sort the list: + + $ who | cut -c1-8 | sort + ⊣ arnold + ⊣ arnold + ⊣ bill + ⊣ miriam + + Finally, run the sorted list through ‘uniq’, to weed out duplicates: + + $ who | cut -c1-8 | sort | uniq + ⊣ arnold + ⊣ bill + ⊣ miriam + + The ‘sort’ command actually has a ‘-u’ option that does what ‘uniq’ +does. However, ‘uniq’ has other uses for which one cannot substitute +‘sort -u’. + + The administrator puts this pipeline into a shell script, and makes +it available for all the users on the system (‘#’ is the system +administrator, or ‘root’, prompt): + + # cat > /usr/local/bin/listusers + who | cut -c1-8 | sort | uniq + ^D + # chmod +x /usr/local/bin/listusers + + There are four major points to note here. First, with just four +programs, on one command line, the administrator was able to save about +two hours worth of work. Furthermore, the shell pipeline is just about +as efficient as the C program would be, and it is much more efficient in +terms of programmer time. People time is much more expensive than +computer time, and in our modern “there’s never enough time to do +everything” society, saving two hours of programmer time is no mean +feat. + + Second, it is also important to emphasize that with the _combination_ +of the tools, it is possible to do a special purpose job never imagined +by the authors of the individual programs. + + Third, it is also valuable to build up your pipeline in stages, as we +did here. This allows you to view the data at each stage in the +pipeline, which helps you acquire the confidence that you are indeed +using these tools correctly. + + Finally, by bundling the pipeline in a shell script, other users can +use your command, without having to remember the fancy plumbing you set +up for them. In terms of how you run them, shell scripts and compiled +programs are indistinguishable. + + After the previous warm-up exercise, we’ll look at two additional, +more complicated pipelines. For them, we need to introduce two more +tools. + + The first is the ‘tr’ command, which stands for “transliterate.” The +‘tr’ command works on a character-by-character basis, changing +characters. Normally it is used for things like mapping upper case to +lower case: + + $ echo ThIs ExAmPlE HaS MIXED case! | tr '[:upper:]' '[:lower:]' + ⊣ this example has mixed case! + + There are several options of interest: + +‘-c’ + work on the complement of the listed characters, i.e., operations + apply to characters not in the given set + +‘-d’ + delete characters in the first set from the output + +‘-s’ + squeeze repeated characters in the output into just one character. + + We will be using all three options in a moment. + + The other command we’ll look at is ‘comm’. The ‘comm’ command takes +two sorted input files as input data, and prints out the files’ lines in +three columns. The output columns are the data lines unique to the +first file, the data lines unique to the second file, and the data lines +that are common to both. The ‘-1’, ‘-2’, and ‘-3’ command line options +_omit_ the respective columns. (This is non-intuitive and takes a +little getting used to.) For example: + + $ cat f1 + ⊣ 11111 + ⊣ 22222 + ⊣ 33333 + ⊣ 44444 + $ cat f2 + ⊣ 00000 + ⊣ 22222 + ⊣ 33333 + ⊣ 55555 + $ comm f1 f2 + ⊣ 00000 + ⊣ 11111 + ⊣ 22222 + ⊣ 33333 + ⊣ 44444 + ⊣ 55555 + + The file name ‘-’ tells ‘comm’ to read standard input instead of a +regular file. + + Now we’re ready to build a fancy pipeline. The first application is +a word frequency counter. This helps an author determine if he or she +is over-using certain words. + + The first step is to change the case of all the letters in our input +file to one case. “The” and “the” are the same word when doing +counting. + + $ tr '[:upper:]' '[:lower:]' < whats.gnu | ... + + The next step is to get rid of punctuation. Quoted words and +unquoted words should be treated identically; it’s easiest to just get +the punctuation out of the way. + + $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | ... + + The second ‘tr’ command operates on the complement of the listed +characters, which are all the letters, the digits, the underscore, and +the blank. The ‘\n’ represents the newline character; it has to be left +alone. (The ASCII tab character should also be included for good +measure in a production script.) + + At this point, we have data consisting of words separated by blank +space. The words only contain alphanumeric characters (and the +underscore). The next step is break the data apart so that we have one +word per line. This makes the counting operation much easier, as we +will see shortly. + + $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | + > tr -s ' ' '\n' | ... + + This command turns blanks into newlines. The ‘-s’ option squeezes +multiple newline characters in the output into just one, removing blank +lines. (The ‘>’ is the shell’s “secondary prompt.” This is what the +shell prints when it notices you haven’t finished typing in all of a +command.) + + We now have data consisting of one word per line, no punctuation, all +one case. We’re ready to count each word: + + $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | + > tr -s ' ' '\n' | sort | uniq -c | ... + + At this point, the data might look something like this: + + 60 a + 2 able + 6 about + 1 above + 2 accomplish + 1 acquire + 1 actually + 2 additional + + The output is sorted by word, not by count! What we want is the most +frequently used words first. Fortunately, this is easy to accomplish, +with the help of two more ‘sort’ options: + +‘-n’ + do a numeric sort, not a textual one + +‘-r’ + reverse the order of the sort + + The final pipeline looks like this: + + $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | + > tr -s ' ' '\n' | sort | uniq -c | sort -n -r + ⊣ 156 the + ⊣ 60 a + ⊣ 58 to + ⊣ 51 of + ⊣ 51 and + ... + + Whew! That’s a lot to digest. Yet, the same principles apply. With +six commands, on two lines (really one long one split for convenience), +we’ve created a program that does something interesting and useful, in +much less time than we could have written a C program to do the same +thing. + + A minor modification to the above pipeline can give us a simple +spelling checker! To determine if you’ve spelled a word correctly, all +you have to do is look it up in a dictionary. If it is not there, then +chances are that your spelling is incorrect. So, we need a dictionary. +The conventional location for a dictionary is ‘/usr/share/dict/words’. + + Now, how to compare our file with the dictionary? As before, we +generate a sorted list of words, one per line: + + $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | + > tr -s ' ' '\n' | sort -u | ... + + Now, all we need is a list of words that are _not_ in the dictionary. +Here is where the ‘comm’ command comes in. Unfortunately ‘comm’ +operates on sorted input and ‘/usr/share/dict/words’ is not sorted the +way that ‘sort’ and ‘comm’ normally use, so we first create a +properly-sorted copy of the dictionary and then run a pipeline that uses +the copy. + + $ sort /usr/share/dict/words > sorted-words + $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | + > tr -s ' ' '\n' | sort -u | + > comm -23 - sorted-words + + The ‘-2’ and ‘-3’ options eliminate lines that are only in the +dictionary (the second file), and lines that are in both files. Lines +only in the first file (standard input, our stream of words), are words +that are not in the dictionary. These are likely candidates for +spelling errors. This pipeline was the first cut at a production +spelling checker on Unix. + + There are some other tools that deserve brief mention. + +‘grep’ + search files for text that matches a regular expression + +‘wc’ + count lines, words, characters + +‘tee’ + a T-fitting for data pipes, copies data to files and to standard + output + +‘sed’ + the stream editor, an advanced tool + +‘awk’ + a data manipulation language, another advanced tool + + The software tools philosophy also espoused the following bit of +advice: “Let someone else do the hard part.” This means, take something +that gives you most of what you need, and then massage it the rest of +the way until it’s in the form that you want. + + To summarize: + + 1. Each program should do one thing well. No more, no less. + + 2. Combining programs with appropriate plumbing leads to results where + the whole is greater than the sum of the parts. It also leads to + novel uses of programs that the authors might never have imagined. + + 3. Programs should never print extraneous header or trailer data, + since these could get sent on down a pipeline. (A point we didn’t + mention earlier.) + + 4. Let someone else do the hard part. + + 5. Know your toolbox! Use each program appropriately. If you don’t + have an appropriate tool, build one. + + All the programs discussed are available as described in GNU core +utilities (https://www.gnu.org/software/coreutils/coreutils.html). + + None of what I have presented in this column is new. The Software +Tools philosophy was first introduced in the book ‘Software Tools’, by +Brian Kernighan and P.J. Plauger (Addison-Wesley, ISBN 0-201-03669-X). +This book showed how to write and use software tools. It was written in +1976, using a preprocessor for FORTRAN named ‘ratfor’ (RATional +FORtran). At the time, C was not as ubiquitous as it is now; FORTRAN +was. The last chapter presented a ‘ratfor’ to FORTRAN processor, +written in ‘ratfor’. ‘ratfor’ looks an awful lot like C; if you know C, +you won’t have any problem following the code. + + In 1981, the book was updated and made available as ‘Software Tools +in Pascal’ (Addison-Wesley, ISBN 0-201-10342-7). Both books are still +in print and are well worth reading if you’re a programmer. They +certainly made a major change in how I view programming. + + The programs in both books are available from Brian Kernighan’s home +page (https://www.cs.princeton.edu/~bwk/). For a number of years, there +was an active Software Tools Users Group, whose members had ported the +original ‘ratfor’ programs to essentially every computer system with a +FORTRAN compiler. The popularity of the group waned in the middle 1980s +as Unix began to spread beyond universities. + + With the current proliferation of GNU code and other clones of Unix +programs, these programs now receive little attention; modern C versions +are much more efficient and do more than these programs do. +Nevertheless, as exposition of good programming style, and evangelism +for a still-valuable philosophy, these books are unparalleled, and I +recommend them highly. + + Acknowledgment: I would like to express my gratitude to Brian +Kernighan of Bell Labs, the original Software Toolsmith, for reviewing +this column. + + +File: coreutils.info, Node: GNU Free Documentation License, Next: Concept index, Prev: Opening the software toolbox, Up: Top + +Appendix A GNU Free Documentation License +***************************************** + + Version 1.3, 3 November 2008 + + Copyright © 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc. + <https://fsf.org/> + + Everyone is permitted to copy and distribute verbatim copies + of this license document, but changing it is not allowed. + + 0. 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These + Warranty Disclaimers are considered to be included by reference in + this License, but only as regards disclaiming warranties: any other + implication that these Warranty Disclaimers may have is void and + has no effect on the meaning of this License. + + 2. VERBATIM COPYING + + You may copy and distribute the Document in any medium, either + commercially or noncommercially, provided that this License, the + copyright notices, and the license notice saying this License + applies to the Document are reproduced in all copies, and that you + add no other conditions whatsoever to those of this License. You + may not use technical measures to obstruct or control the reading + or further copying of the copies you make or distribute. However, + you may accept compensation in exchange for copies. If you + distribute a large enough number of copies you must also follow the + conditions in section 3. + + You may also lend copies, under the same conditions stated above, + and you may publicly display copies. + + 3. COPYING IN QUANTITY + + If you publish printed copies (or copies in media that commonly + have printed covers) of the Document, numbering more than 100, and + the Document’s license notice requires Cover Texts, you must + enclose the copies in covers that carry, clearly and legibly, all + these Cover Texts: Front-Cover Texts on the front cover, and + Back-Cover Texts on the back cover. Both covers must also clearly + and legibly identify you as the publisher of these copies. The + front cover must present the full title with all words of the title + equally prominent and visible. You may add other material on the + covers in addition. Copying with changes limited to the covers, as + long as they preserve the title of the Document and satisfy these + conditions, can be treated as verbatim copying in other respects. + + If the required texts for either cover are too voluminous to fit + legibly, you should put the first ones listed (as many as fit + reasonably) on the actual cover, and continue the rest onto + adjacent pages. + + If you publish or distribute Opaque copies of the Document + numbering more than 100, you must either include a machine-readable + Transparent copy along with each Opaque copy, or state in or with + each Opaque copy a computer-network location from which the general + network-using public has access to download using public-standard + network protocols a complete Transparent copy of the Document, free + of added material. If you use the latter option, you must take + reasonably prudent steps, when you begin distribution of Opaque + copies in quantity, to ensure that this Transparent copy will + remain thus accessible at the stated location until at least one + year after the last time you distribute an Opaque copy (directly or + through your agents or retailers) of that edition to the public. + + It is requested, but not required, that you contact the authors of + the Document well before redistributing any large number of copies, + to give them a chance to provide you with an updated version of the + Document. + + 4. MODIFICATIONS + + You may copy and distribute a Modified Version of the Document + under the conditions of sections 2 and 3 above, provided that you + release the Modified Version under precisely this License, with the + Modified Version filling the role of the Document, thus licensing + distribution and modification of the Modified Version to whoever + possesses a copy of it. In addition, you must do these things in + the Modified Version: + + A. Use in the Title Page (and on the covers, if any) a title + distinct from that of the Document, and from those of previous + versions (which should, if there were any, be listed in the + History section of the Document). You may use the same title + as a previous version if the original publisher of that + version gives permission. + + B. List on the Title Page, as authors, one or more persons or + entities responsible for authorship of the modifications in + the Modified Version, together with at least five of the + principal authors of the Document (all of its principal + authors, if it has fewer than five), unless they release you + from this requirement. + + C. State on the Title page the name of the publisher of the + Modified Version, as the publisher. + + D. Preserve all the copyright notices of the Document. + + E. Add an appropriate copyright notice for your modifications + adjacent to the other copyright notices. + + F. Include, immediately after the copyright notices, a license + notice giving the public permission to use the Modified + Version under the terms of this License, in the form shown in + the Addendum below. + + G. Preserve in that license notice the full lists of Invariant + Sections and required Cover Texts given in the Document’s + license notice. + + H. Include an unaltered copy of this License. + + I. Preserve the section Entitled “History”, Preserve its Title, + and add to it an item stating at least the title, year, new + authors, and publisher of the Modified Version as given on the + Title Page. If there is no section Entitled “History” in the + Document, create one stating the title, year, authors, and + publisher of the Document as given on its Title Page, then add + an item describing the Modified Version as stated in the + previous sentence. + + J. Preserve the network location, if any, given in the Document + for public access to a Transparent copy of the Document, and + likewise the network locations given in the Document for + previous versions it was based on. These may be placed in the + “History” section. You may omit a network location for a work + that was published at least four years before the Document + itself, or if the original publisher of the version it refers + to gives permission. + + K. For any section Entitled “Acknowledgements” or “Dedications”, + Preserve the Title of the section, and preserve in the section + all the substance and tone of each of the contributor + acknowledgements and/or dedications given therein. + + L. Preserve all the Invariant Sections of the Document, unaltered + in their text and in their titles. Section numbers or the + equivalent are not considered part of the section titles. + + M. Delete any section Entitled “Endorsements”. Such a section + may not be included in the Modified Version. + + N. Do not retitle any existing section to be Entitled + “Endorsements” or to conflict in title with any Invariant + Section. + + O. Preserve any Warranty Disclaimers. + + If the Modified Version includes new front-matter sections or + appendices that qualify as Secondary Sections and contain no + material copied from the Document, you may at your option designate + some or all of these sections as invariant. To do this, add their + titles to the list of Invariant Sections in the Modified Version’s + license notice. These titles must be distinct from any other + section titles. + + You may add a section Entitled “Endorsements”, provided it contains + nothing but endorsements of your Modified Version by various + parties—for example, statements of peer review or that the text has + been approved by an organization as the authoritative definition of + a standard. + + You may add a passage of up to five words as a Front-Cover Text, + and a passage of up to 25 words as a Back-Cover Text, to the end of + the list of Cover Texts in the Modified Version. Only one passage + of Front-Cover Text and one of Back-Cover Text may be added by (or + through arrangements made by) any one entity. If the Document + already includes a cover text for the same cover, previously added + by you or by arrangement made by the same entity you are acting on + behalf of, you may not add another; but you may replace the old + one, on explicit permission from the previous publisher that added + the old one. + + The author(s) and publisher(s) of the Document do not by this + License give permission to use their names for publicity for or to + assert or imply endorsement of any Modified Version. + + 5. COMBINING DOCUMENTS + + You may combine the Document with other documents released under + this License, under the terms defined in section 4 above for + modified versions, provided that you include in the combination all + of the Invariant Sections of all of the original documents, + unmodified, and list them all as Invariant Sections of your + combined work in its license notice, and that you preserve all + their Warranty Disclaimers. + + The combined work need only contain one copy of this License, and + multiple identical Invariant Sections may be replaced with a single + copy. If there are multiple Invariant Sections with the same name + but different contents, make the title of each such section unique + by adding at the end of it, in parentheses, the name of the + original author or publisher of that section if known, or else a + unique number. Make the same adjustment to the section titles in + the list of Invariant Sections in the license notice of the + combined work. + + In the combination, you must combine any sections Entitled + “History” in the various original documents, forming one section + Entitled “History”; likewise combine any sections Entitled + “Acknowledgements”, and any sections Entitled “Dedications”. You + must delete all sections Entitled “Endorsements.” + + 6. COLLECTIONS OF DOCUMENTS + + You may make a collection consisting of the Document and other + documents released under this License, and replace the individual + copies of this License in the various documents with a single copy + that is included in the collection, provided that you follow the + rules of this License for verbatim copying of each of the documents + in all other respects. + + You may extract a single document from such a collection, and + distribute it individually under this License, provided you insert + a copy of this License into the extracted document, and follow this + License in all other respects regarding verbatim copying of that + document. + + 7. AGGREGATION WITH INDEPENDENT WORKS + + A compilation of the Document or its derivatives with other + separate and independent documents or works, in or on a volume of a + storage or distribution medium, is called an “aggregate” if the + copyright resulting from the compilation is not used to limit the + legal rights of the compilation’s users beyond what the individual + works permit. When the Document is included in an aggregate, this + License does not apply to the other works in the aggregate which + are not themselves derivative works of the Document. + + If the Cover Text requirement of section 3 is applicable to these + copies of the Document, then if the Document is less than one half + of the entire aggregate, the Document’s Cover Texts may be placed + on covers that bracket the Document within the aggregate, or the + electronic equivalent of covers if the Document is in electronic + form. Otherwise they must appear on printed covers that bracket + the whole aggregate. + + 8. TRANSLATION + + Translation is considered a kind of modification, so you may + distribute translations of the Document under the terms of section + 4. Replacing Invariant Sections with translations requires special + permission from their copyright holders, but you may include + translations of some or all Invariant Sections in addition to the + original versions of these Invariant Sections. You may include a + translation of this License, and all the license notices in the + Document, and any Warranty Disclaimers, provided that you also + include the original English version of this License and the + original versions of those notices and disclaimers. In case of a + disagreement between the translation and the original version of + this License or a notice or disclaimer, the original version will + prevail. + + If a section in the Document is Entitled “Acknowledgements”, + “Dedications”, or “History”, the requirement (section 4) to + Preserve its Title (section 1) will typically require changing the + actual title. + + 9. TERMINATION + + You may not copy, modify, sublicense, or distribute the Document + except as expressly provided under this License. Any attempt + otherwise to copy, modify, sublicense, or distribute it is void, + and will automatically terminate your rights under this License. + + However, if you cease all violation of this License, then your + license from a particular copyright holder is reinstated (a) + provisionally, unless and until the copyright holder explicitly and + finally terminates your license, and (b) permanently, if the + copyright holder fails to notify you of the violation by some + reasonable means prior to 60 days after the cessation. + + Moreover, your license from a particular copyright holder is + reinstated permanently if the copyright holder notifies you of the + violation by some reasonable means, this is the first time you have + received notice of violation of this License (for any work) from + that copyright holder, and you cure the violation prior to 30 days + after your receipt of the notice. + + Termination of your rights under this section does not terminate + the licenses of parties who have received copies or rights from you + under this License. If your rights have been terminated and not + permanently reinstated, receipt of a copy of some or all of the + same material does not give you any rights to use it. + + 10. FUTURE REVISIONS OF THIS LICENSE + + The Free Software Foundation may publish new, revised versions of + the GNU Free Documentation License from time to time. Such new + versions will be similar in spirit to the present version, but may + differ in detail to address new problems or concerns. See + <https://www.gnu.org/licenses/>. + + Each version of the License is given a distinguishing version + number. If the Document specifies that a particular numbered + version of this License “or any later version” applies to it, you + have the option of following the terms and conditions either of + that specified version or of any later version that has been + published (not as a draft) by the Free Software Foundation. If the + Document does not specify a version number of this License, you may + choose any version ever published (not as a draft) by the Free + Software Foundation. If the Document specifies that a proxy can + decide which future versions of this License can be used, that + proxy’s public statement of acceptance of a version permanently + authorizes you to choose that version for the Document. + + 11. RELICENSING + + “Massive Multiauthor Collaboration Site” (or “MMC Site”) means any + World Wide Web server that publishes copyrightable works and also + provides prominent facilities for anybody to edit those works. A + public wiki that anybody can edit is an example of such a server. + A “Massive Multiauthor Collaboration” (or “MMC”) contained in the + site means any set of copyrightable works thus published on the MMC + site. + + “CC-BY-SA” means the Creative Commons Attribution-Share Alike 3.0 + license published by Creative Commons Corporation, a not-for-profit + corporation with a principal place of business in San Francisco, + California, as well as future copyleft versions of that license + published by that same organization. + + “Incorporate” means to publish or republish a Document, in whole or + in part, as part of another Document. + + An MMC is “eligible for relicensing” if it is licensed under this + License, and if all works that were first published under this + License somewhere other than this MMC, and subsequently + incorporated in whole or in part into the MMC, (1) had no cover + texts or invariant sections, and (2) were thus incorporated prior + to November 1, 2008. + + The operator of an MMC Site may republish an MMC contained in the + site under CC-BY-SA on the same site at any time before August 1, + 2009, provided the MMC is eligible for relicensing. + +ADDENDUM: How to use this License for your documents +==================================================== + +To use this License in a document you have written, include a copy of +the License in the document and put the following copyright and license +notices just after the title page: + + Copyright (C) YEAR YOUR NAME. + Permission is granted to copy, distribute and/or modify this document + under the terms of the GNU Free Documentation License, Version 1.3 + or any later version published by the Free Software Foundation; + with no Invariant Sections, no Front-Cover Texts, and no Back-Cover + Texts. A copy of the license is included in the section entitled ``GNU + Free Documentation License''. + + If you have Invariant Sections, Front-Cover Texts and Back-Cover +Texts, replace the “with...Texts.” line with this: + + with the Invariant Sections being LIST THEIR TITLES, with + the Front-Cover Texts being LIST, and with the Back-Cover Texts + being LIST. + + If you have Invariant Sections without Cover Texts, or some other +combination of the three, merge those two alternatives to suit the +situation. + + If your document contains nontrivial examples of program code, we +recommend releasing these examples in parallel under your choice of free +software license, such as the GNU General Public License, to permit +their use in free software. + + +File: coreutils.info, Node: Concept index, Prev: GNU Free Documentation License, Up: Top + +Index +***** + + +* Menu: + +* !: Connectives for test. + (line 23) +* !=: String tests. (line 29) +* %: Numeric expressions. (line 16) +* %b: printf invocation. (line 37) +* %q: printf invocation. (line 44) +* &: Relations for expr. (line 17) +* *: Numeric expressions. (line 16) +* +: String expressions. (line 51) +* + <1>: Numeric expressions. (line 12) +* +PAGE_RANGE: pr invocation. (line 39) +* -: Numeric expressions. (line 12) +* - <1>: env invocation. (line 102) +* - and Unix rm: rm invocation. (line 114) +* -, removing files beginning with: rm invocation. (line 102) +* --: Common options. (line 43) +* --across: pr invocation. (line 62) +* --additional-suffix: split invocation. (line 139) +* --address-radix: od invocation. (line 36) +* --adjustment: nice invocation. (line 51) +* --algorithm: cksum general options. + (line 5) +* --all: unexpand invocation. (line 51) +* --all <1>: Which files are listed. + (line 13) +* --all <2>: df invocation. (line 42) +* --all <3>: du invocation. (line 31) +* --all <4>: stty invocation. (line 26) +* --all <5>: who invocation. (line 35) +* --all <6>: nproc invocation. (line 20) +* --all <7>: uname invocation. (line 30) +* --all-repeated: uniq invocation. (line 70) +* --almost-all: Which files are listed. + (line 17) +* --apparent-size: du invocation. (line 34) +* --append: tee invocation. (line 26) +* --archive: cp invocation. (line 63) +* --attributes-only: cp invocation. (line 72) +* --author: What information is listed. + (line 10) +* --auto-reference: Output formatting in ptx. + (line 45) +* --backup: Backup options. (line 13) +* --backup <1>: cp invocation. (line 79) +* --backup <2>: install invocation. (line 41) +* --backup <3>: mv invocation. (line 56) +* --backup <4>: ln invocation. (line 82) +* --base16: basenc invocation. (line 49) +* --base2lsbf: basenc invocation. (line 55) +* --base2msbf: basenc invocation. (line 59) +* --base32: basenc invocation. (line 35) +* --base32hex: basenc invocation. (line 42) +* --base64: basenc invocation. (line 23) +* --base64 <1>: cksum general options. + (line 23) +* --base64url: basenc invocation. (line 29) +* --batch-size: sort invocation. (line 268) +* --before: tac invocation. (line 21) +* --binary: cksum common options. + (line 5) +* --block-size: Block size. (line 131) +* --block-size <1>: df invocation. (line 54) +* --block-size <2>: du invocation. (line 54) +* --block-size=SIZE: Block size. (line 12) +* --body-numbering: nl invocation. (line 45) +* --boot: who invocation. (line 39) +* --bourne-shell: dircolors invocation. + (line 34) +* --break-file: Input processing in ptx. + (line 8) +* --buffer-size: sort invocation. (line 322) +* --bytes: fold invocation. (line 23) +* --bytes <1>: head invocation. (line 24) +* --bytes <2>: tail invocation. (line 39) +* --bytes <3>: split invocation. (line 41) +* --bytes <4>: wc invocation. (line 46) +* --bytes <5>: cut invocation. (line 26) +* --bytes <6>: du invocation. (line 59) +* --c-shell: dircolors invocation. + (line 40) +* --cached=MODE: stat invocation. (line 33) +* --canonicalize: readlink invocation. (line 31) +* --canonicalize-existing: readlink invocation. (line 38) +* --canonicalize-existing <1>: realpath invocation. (line 22) +* --canonicalize-missing: readlink invocation. (line 45) +* --canonicalize-missing <1>: realpath invocation. (line 30) +* --changes: chown invocation. (line 74) +* --changes <1>: chgrp invocation. (line 24) +* --changes <2>: chmod invocation. (line 43) +* --characters: cut invocation. (line 34) +* --chars: wc invocation. (line 50) +* --chdir: env invocation. (line 107) +* --check: sort invocation. (line 39) +* --check <1>: sort invocation. (line 47) +* --check-chars: uniq invocation. (line 134) +* --classify: General output formatting. + (line 52) +* --color: General output formatting. + (line 28) +* --columns: pr invocation. (line 49) +* --compare: install invocation. (line 46) +* --complement: cut invocation. (line 86) +* --complement <1>: tr invocation. (line 31) +* --compute: runcon invocation. (line 32) +* --context: What information is listed. + (line 259) +* --context <1>: cp invocation. (line 417) +* --context <2>: install invocation. (line 143) +* --context <3>: mv invocation. (line 144) +* --context <4>: mkdir invocation. (line 59) +* --context <5>: mkfifo invocation. (line 28) +* --context <6>: mknod invocation. (line 53) +* --context <7>: id invocation. (line 51) +* --count: uniq invocation. (line 56) +* --count <1>: who invocation. (line 69) +* --count-links: du invocation. (line 125) +* --crown-margin: fmt invocation. (line 34) +* --csh: dircolors invocation. + (line 40) +* --data: sync invocation. (line 32) +* --date: touch invocation. (line 56) +* --date <1>: Options for date. (line 15) +* --dead: who invocation. (line 43) +* --debug: cksum general options. + (line 34) +* --debug <1>: cp invocation. (line 114) +* --debug <2>: install invocation. (line 72) +* --debug <3>: mv invocation. (line 60) +* --debug <4>: Options for date. (line 29) +* --debug <5>: env invocation. (line 177) +* --debug <6>: numfmt invocation. (line 29) +* --decode: base64 invocation. (line 33) +* --delete: tr invocation. (line 38) +* --delimiter: cut invocation. (line 66) +* --delimiter <1>: numfmt invocation. (line 34) +* --delimiters: paste invocation. (line 61) +* --dereference: Which files are listed. + (line 84) +* --dereference <1>: cp invocation. (line 153) +* --dereference <2>: chown invocation. (line 107) +* --dereference <3>: chgrp invocation. (line 34) +* --dereference <4>: du invocation. (line 119) +* --dereference <5>: stat invocation. (line 22) +* --dereference <6>: chcon invocation. (line 21) +* --dereference-args: du invocation. (line 69) +* --dereference-command-line: Which files are listed. + (line 36) +* --dereference-command-line-symlink-to-dir: Which files are listed. + (line 41) +* --dictionary-order: sort invocation. (line 87) +* --digits: csplit invocation. (line 82) +* --dir: rm invocation. (line 35) +* --directory: Which files are listed. + (line 28) +* --directory <1>: install invocation. (line 67) +* --directory <2>: ln invocation. (line 88) +* --directory <3>: mktemp invocation. (line 85) +* --dired: What information is listed. + (line 16) +* --double-space: pr invocation. (line 74) +* --dry-run: mktemp invocation. (line 97) +* --echo: shuf invocation. (line 19) +* --elide-empty-files: split invocation. (line 144) +* --elide-empty-files <1>: csplit invocation. (line 96) +* --endian: od invocation. (line 51) +* --equal-width: seq invocation. (line 50) +* --error: stdbuf invocation. (line 34) +* --escape: Formatting the file names. + (line 11) +* --exact: shred invocation. (line 164) +* --exclude-from=FILE: du invocation. (line 250) +* --exclude-type: df invocation. (line 224) +* --exclude=PATTERN: du invocation. (line 255) +* --expand-tabs: pr invocation. (line 98) +* --exponents: factor invocation. (line 18) +* --field: numfmt invocation. (line 38) +* --field-separator: sort invocation. (line 338) +* --fields: cut invocation. (line 43) +* --file: stty invocation. (line 31) +* --file <1>: Options for date. (line 34) +* --file-system: stat invocation. (line 28) +* --file-system <1>: sync invocation. (line 37) +* --file-type: General output formatting. + (line 68) +* --files0-from=FILE: wc invocation. (line 84) +* --files0-from=FILE <1>: sort invocation. (line 224) +* --files0-from=FILE <2>: du invocation. (line 81) +* --filter: split invocation. (line 63) +* --first-line-number: pr invocation. (line 174) +* --flag-truncation: Output formatting in ptx. + (line 71) +* --follow: tail invocation. (line 57) +* --footer-numbering: nl invocation. (line 72) +* --force: cp invocation. (line 119) +* --force <1>: mv invocation. (line 65) +* --force <2>: rm invocation. (line 39) +* --force <3>: shred invocation. (line 123) +* --force <4>: ln invocation. (line 94) +* --foreground: timeout invocation. (line 24) +* --form-feed: pr invocation. (line 106) +* --format: od invocation. (line 90) +* --format <1>: What information is listed. + (line 133) +* --format <2>: General output formatting. + (line 9) +* --format <3>: General output formatting. + (line 21) +* --format <4>: General output formatting. + (line 114) +* --format <5>: General output formatting. + (line 125) +* --format <6>: numfmt invocation. (line 48) +* --format <7>: seq invocation. (line 29) +* --format=FORMAT: stat invocation. (line 50) +* --format=roff: Output formatting in ptx. + (line 100) +* --format=tex: Output formatting in ptx. + (line 118) +* --from: chown invocation. (line 84) +* --from <1>: numfmt invocation. (line 59) +* --from-unit: numfmt invocation. (line 64) +* --full-time: What information is listed. + (line 103) +* --gap-size: Output formatting in ptx. + (line 26) +* --general-numeric-sort: sort invocation. (line 105) +* --goal: fmt invocation. (line 64) +* --group: uniq invocation. (line 101) +* --group <1>: install invocation. (line 77) +* --group <2>: id invocation. (line 29) +* --group-directories-first: Which files are listed. + (line 50) +* --grouping: numfmt invocation. (line 70) +* --groups: id invocation. (line 33) +* --groups <1>: chroot invocation. (line 24) +* --hardware-platform: uname invocation. (line 35) +* --head-count: shuf invocation. (line 31) +* --header: pr invocation. (line 111) +* --header <1>: General options in join. + (line 25) +* --header <2>: numfmt invocation. (line 76) +* --header-numbering: nl invocation. (line 76) +* --header=N: numfmt invocation. (line 76) +* --heading: who invocation. (line 47) +* --help: Common options. (line 36) +* --hex-suffixes: split invocation. (line 135) +* --hide-control-chars: Formatting the file names. + (line 23) +* --hide=PATTERN: Which files are listed. + (line 58) +* --human-numeric-sort: sort invocation. (line 132) +* --human-readable: Block size. (line 131) +* --human-readable <1>: What information is listed. + (line 118) +* --human-readable <2>: df invocation. (line 59) +* --human-readable <3>: du invocation. (line 98) +* --hyperlink: General output formatting. + (line 73) +* --ignore: nproc invocation. (line 26) +* --ignore-backups: Which files are listed. + (line 23) +* --ignore-case: sort invocation. (line 94) +* --ignore-case <1>: uniq invocation. (line 60) +* --ignore-case <2>: Charset selection in ptx. + (line 20) +* --ignore-case <3>: General options in join. + (line 35) +* --ignore-environment: env invocation. (line 102) +* --ignore-fail-on-non-empty: rmdir invocation. (line 17) +* --ignore-file: Input processing in ptx. + (line 26) +* --ignore-garbage: base64 invocation. (line 39) +* --ignore-interrupts: tee invocation. (line 31) +* --ignore-leading-blanks: sort invocation. (line 79) +* --ignore-missing: cksum common options. + (line 54) +* --ignore-nonprinting: sort invocation. (line 149) +* --ignore=PATTERN: Which files are listed. + (line 70) +* --indent: pr invocation. (line 180) +* --indicator-style: General output formatting. + (line 52) +* --indicator-style <1>: General output formatting. + (line 68) +* --indicator-style <2>: General output formatting. + (line 82) +* --indicator-style <3>: General output formatting. + (line 120) +* --initial: expand invocation. (line 46) +* --inode: What information is listed. + (line 125) +* --inodes: df invocation. (line 69) +* --inodes <1>: du invocation. (line 104) +* --input: stdbuf invocation. (line 26) +* --input-range: shuf invocation. (line 23) +* --interactive: cp invocation. (line 143) +* --interactive <1>: mv invocation. (line 71) +* --interactive <2>: rm invocation. (line 55) +* --interactive <3>: ln invocation. (line 98) +* --invalid: numfmt invocation. (line 79) +* --io-blocks: truncate invocation. (line 26) +* --iso-8601[=TIMESPEC]: Options for date. (line 42) +* --iterations=NUMBER: shred invocation. (line 127) +* --join-blank-lines: nl invocation. (line 85) +* --join-lines: pr invocation. (line 124) +* --keep-files: csplit invocation. (line 87) +* --kernel-name: uname invocation. (line 66) +* --kernel-release: uname invocation. (line 62) +* --kernel-version: uname invocation. (line 77) +* --key: sort invocation. (line 237) +* --kibibytes: General output formatting. + (line 101) +* --kill-after: timeout invocation. (line 41) +* --length: pr invocation. (line 133) +* --length <1>: cksum general options. + (line 39) +* --length <2>: b2sum invocation. (line 24) +* --line-bytes: split invocation. (line 56) +* --line-increment: nl invocation. (line 80) +* --lines: head invocation. (line 40) +* --lines <1>: tail invocation. (line 126) +* --lines <2>: split invocation. (line 33) +* --lines <3>: wc invocation. (line 60) +* --link: cp invocation. (line 149) +* --literal: Formatting the file names. + (line 17) +* --local: df invocation. (line 81) +* --logical: ln invocation. (line 103) +* --logical <1>: realpath invocation. (line 35) +* --logical <2>: pwd invocation. (line 15) +* --login: who invocation. (line 51) +* --lookup: who invocation. (line 56) +* --machine: uname invocation. (line 42) +* --macro-name: Output formatting in ptx. + (line 94) +* --max-depth=DEPTH: du invocation. (line 76) +* --max-line-length: wc invocation. (line 66) +* --max-unchanged-stats: tail invocation. (line 114) +* --merge: pr invocation. (line 140) +* --merge <1>: sort invocation. (line 53) +* --mesg: who invocation. (line 94) +* --message: who invocation. (line 94) +* --mode: install invocation. (line 83) +* --mode <1>: mkdir invocation. (line 19) +* --mode <2>: mkfifo invocation. (line 21) +* --mode <3>: mknod invocation. (line 47) +* --month-sort: sort invocation. (line 156) +* --multiple: basename invocation. (line 32) +* --name: id invocation. (line 37) +* --no-clobber: cp invocation. (line 160) +* --no-clobber <1>: mv invocation. (line 78) +* --no-copy: mv invocation. (line 85) +* --no-create: touch invocation. (line 52) +* --no-create <1>: truncate invocation. (line 22) +* --no-dereference: cp invocation. (line 166) +* --no-dereference <1>: ln invocation. (line 109) +* --no-dereference <2>: chown invocation. (line 119) +* --no-dereference <3>: chgrp invocation. (line 46) +* --no-dereference <4>: touch invocation. (line 70) +* --no-dereference <5>: du invocation. (line 135) +* --no-dereference <6>: chcon invocation. (line 26) +* --no-file-warnings: pr invocation. (line 187) +* --no-group: What information is listed. + (line 112) +* --no-newline: readlink invocation. (line 50) +* --no-preserve-root: rm invocation. (line 89) +* --no-preserve-root <1>: chown invocation. (line 132) +* --no-preserve-root <2>: chgrp invocation. (line 59) +* --no-preserve-root <3>: chmod invocation. (line 58) +* --no-preserve-root <4>: chcon invocation. (line 43) +* --no-renumber: nl invocation. (line 104) +* --no-symlinks: realpath invocation. (line 64) +* --no-sync: df invocation. (line 85) +* --no-target-directory: Target directory. (line 15) +* --no-target-directory <1>: cp invocation. (line 367) +* --no-target-directory <2>: install invocation. (line 134) +* --no-target-directory <3>: mv invocation. (line 139) +* --no-target-directory <4>: ln invocation. (line 177) +* --nodename: uname invocation. (line 47) +* --null: du invocation. (line 25) +* --null <1>: printenv invocation. (line 19) +* --null <2>: env invocation. (line 90) +* --number: cat invocation. (line 32) +* --number <1>: split invocation. (line 79) +* --number-format: nl invocation. (line 93) +* --number-lines: pr invocation. (line 153) +* --number-nonblank: cat invocation. (line 20) +* --number-separator: nl invocation. (line 108) +* --number-width: nl invocation. (line 118) +* --numeric-sort: sort invocation. (line 166) +* --numeric-suffixes: split invocation. (line 121) +* --numeric-uid-gid: What information is listed. + (line 227) +* --omit-header: pr invocation. (line 210) +* --omit-pagination: pr invocation. (line 220) +* --one-file-system: cp invocation. (line 411) +* --one-file-system <1>: rm invocation. (line 66) +* --one-file-system <2>: du invocation. (line 261) +* --only-delimited: cut invocation. (line 74) +* --only-file: Input processing in ptx. + (line 35) +* --operating-system: uname invocation. (line 58) +* --output: sort invocation. (line 294) +* --output <1>: shuf invocation. (line 36) +* --output <2>: df invocation. (line 92) +* --output <3>: stdbuf invocation. (line 30) +* --output-delimiter: cut invocation. (line 79) +* --output-duplicates: od invocation. (line 150) +* --output-error: tee invocation. (line 35) +* --output-tabs: pr invocation. (line 117) +* --owner: install invocation. (line 95) +* --padding: numfmt invocation. (line 87) +* --pages=PAGE_RANGE: pr invocation. (line 39) +* --page_width: pr invocation. (line 239) +* --parallel: sort invocation. (line 366) +* --parents: cp invocation. (line 249) +* --parents <1>: mkdir invocation. (line 36) +* --parents <2>: rmdir invocation. (line 21) +* --physical: ln invocation. (line 128) +* --physical <1>: realpath invocation. (line 40) +* --physical <2>: pwd invocation. (line 22) +* --pid: tail invocation. (line 133) +* --portability: df invocation. (line 149) +* --portability <1>: pathchk invocation. (line 44) +* --prefix: csplit invocation. (line 64) +* --preserve: cp invocation. (line 173) +* --preserve-context: install invocation. (line 100) +* --preserve-root: rm invocation. (line 82) +* --preserve-root <1>: chown invocation. (line 127) +* --preserve-root <2>: chgrp invocation. (line 54) +* --preserve-root <3>: chmod invocation. (line 53) +* --preserve-root <4>: chcon invocation. (line 38) +* --preserve-status: timeout invocation. (line 18) +* --preserve-timestamps: install invocation. (line 107) +* --print-database: dircolors invocation. + (line 45) +* --print-ls-colors: dircolors invocation. + (line 50) +* --print-type: df invocation. (line 201) +* --printf=FORMAT: stat invocation. (line 59) +* --process: who invocation. (line 65) +* --processor: uname invocation. (line 51) +* --quiet: head invocation. (line 47) +* --quiet <1>: tail invocation. (line 155) +* --quiet <2>: csplit invocation. (line 107) +* --quiet <3>: cksum common options. + (line 60) +* --quiet <4>: readlink invocation. (line 57) +* --quiet <5>: chown invocation. (line 80) +* --quiet <6>: chgrp invocation. (line 30) +* --quiet <7>: chmod invocation. (line 49) +* --quiet <8>: mktemp invocation. (line 92) +* --quiet <9>: realpath invocation. (line 46) +* --quiet <10>: tty invocation. (line 18) +* --quote-name: Formatting the file names. + (line 30) +* --quoting-style: Formatting the file names. + (line 11) +* --quoting-style <1>: Formatting the file names. + (line 17) +* --quoting-style <2>: Formatting the file names. + (line 30) +* --quoting-style <3>: Formatting the file names. + (line 34) +* --random-sort: sort invocation. (line 195) +* --random-source: sort invocation. (line 310) +* --random-source <1>: shuf invocation. (line 42) +* --random-source <2>: shred invocation. (line 133) +* --range: chcon invocation. (line 77) +* --range <1>: runcon invocation. (line 48) +* --raw: cksum general options. + (line 45) +* --read-bytes: od invocation. (line 76) +* --real: id invocation. (line 42) +* --recursive: Which files are listed. + (line 91) +* --recursive <1>: cp invocation. (line 262) +* --recursive <2>: rm invocation. (line 96) +* --recursive <3>: chown invocation. (line 151) +* --recursive <4>: chgrp invocation. (line 77) +* --recursive <5>: chmod invocation. (line 73) +* --recursive <6>: chcon invocation. (line 35) +* --reference: chown invocation. (line 136) +* --reference <1>: chgrp invocation. (line 63) +* --reference <2>: chmod invocation. (line 66) +* --reference <3>: touch invocation. (line 89) +* --reference <4>: truncate invocation. (line 30) +* --reference <5>: Options for date. (line 71) +* --reference <6>: chcon invocation. (line 30) +* --references: Input processing in ptx. + (line 48) +* --reflink[=WHEN]: cp invocation. (line 275) +* --regex: tac invocation. (line 26) +* --relative: ln invocation. (line 137) +* --relative-base: realpath invocation. (line 54) +* --relative-base <1>: Realpath usage examples. + (line 6) +* --relative-to: realpath invocation. (line 49) +* --relative-to <1>: Realpath usage examples. + (line 6) +* --remove: shred invocation. (line 144) +* --remove-destination: cp invocation. (line 302) +* --remove=unlink: shred invocation. (line 144) +* --remove=wipe: shred invocation. (line 144) +* --remove=wipesync: shred invocation. (line 144) +* --repeat: shuf invocation. (line 47) +* --repeated: uniq invocation. (line 64) +* --resolution: Options for date. (line 75) +* --retry: tail invocation. (line 158) +* --reverse: sort invocation. (line 189) +* --reverse <1>: Sorting the output. (line 25) +* --rfc-2822: Options for date. (line 91) +* --rfc-3339=TIMESPEC: Options for date. (line 100) +* --rfc-822: Options for date. (line 91) +* --rfc-email: Options for date. (line 85) +* --right-side-refs: Output formatting in ptx. + (line 56) +* --role: chcon invocation. (line 69) +* --role <1>: runcon invocation. (line 40) +* --round: numfmt invocation. (line 94) +* --round=down: numfmt invocation. (line 94) +* --round=from-zero: numfmt invocation. (line 94) +* --round=nearest: numfmt invocation. (line 94) +* --round=towards-zero: numfmt invocation. (line 94) +* --round=up: numfmt invocation. (line 94) +* --runlevel: who invocation. (line 74) +* --save: stty invocation. (line 41) +* --section-delimiter: nl invocation. (line 63) +* --sentence-regexp: Input processing in ptx. + (line 65) +* --sep-string: pr invocation. (line 201) +* --separate-dirs: du invocation. (line 140) +* --separator: tac invocation. (line 30) +* --separator <1>: pr invocation. (line 192) +* --separator <2>: split invocation. (line 152) +* --separator <3>: seq invocation. (line 45) +* --serial: paste invocation. (line 52) +* --set: Options for date. (line 129) +* --sh: dircolors invocation. + (line 34) +* --show-all: cat invocation. (line 16) +* --show-control-chars: pr invocation. (line 68) +* --show-control-chars <1>: Formatting the file names. + (line 78) +* --show-ends: cat invocation. (line 27) +* --show-nonprinting: cat invocation. (line 52) +* --show-nonprinting <1>: pr invocation. (line 225) +* --show-tabs: cat invocation. (line 45) +* --si: Block size. (line 131) +* --si <1>: What information is listed. + (line 251) +* --si <2>: df invocation. (line 168) +* --si <3>: du invocation. (line 147) +* --signal: timeout invocation. (line 58) +* --silent: head invocation. (line 47) +* --silent <1>: tail invocation. (line 155) +* --silent <2>: csplit invocation. (line 107) +* --silent <3>: readlink invocation. (line 57) +* --silent <4>: chown invocation. (line 80) +* --silent <5>: chgrp invocation. (line 30) +* --silent <6>: chmod invocation. (line 49) +* --silent <7>: tty invocation. (line 18) +* --size: What information is listed. + (line 236) +* --size <1>: truncate invocation. (line 34) +* --size=BYTES: shred invocation. (line 138) +* --skip-bytes: od invocation. (line 59) +* --skip-chars: uniq invocation. (line 42) +* --skip-chdir: chroot invocation. (line 37) +* --skip-fields: uniq invocation. (line 31) +* --sleep-interval: tail invocation. (line 175) +* --sort: sort invocation. (line 105) +* --sort <1>: sort invocation. (line 132) +* --sort <2>: sort invocation. (line 156) +* --sort <3>: sort invocation. (line 166) +* --sort <4>: sort invocation. (line 195) +* --sort <5>: Sorting the output. (line 32) +* --sort <6>: Sorting the output. (line 36) +* --sort <7>: Sorting the output. (line 64) +* --sort <8>: Sorting the output. (line 71) +* --sort <9>: Sorting the output. (line 77) +* --sort <10>: Sorting the output. (line 83) +* --spaces: fold invocation. (line 29) +* --sparse=WHEN: cp invocation. (line 306) +* --split-only: fmt invocation. (line 47) +* --split-string: env invocation. (line 192) +* --squeeze-blank: cat invocation. (line 37) +* --squeeze-repeats: tr invocation. (line 42) +* --stable: sort invocation. (line 315) +* --starting-line-number: nl invocation. (line 113) +* --status: cksum common options. + (line 68) +* --strict: cksum common options. + (line 104) +* --strings: od invocation. (line 81) +* --strip: install invocation. (line 117) +* --strip <1>: realpath invocation. (line 64) +* --strip-program: install invocation. (line 120) +* --strip-trailing-slashes: cp invocation. (line 345) +* --strip-trailing-slashes <1>: mv invocation. (line 125) +* --suffix: Backup options. (line 49) +* --suffix <1>: cp invocation. (line 358) +* --suffix <2>: install invocation. (line 124) +* --suffix <3>: mv invocation. (line 130) +* --suffix <4>: ln invocation. (line 168) +* --suffix <5>: basename invocation. (line 38) +* --suffix <6>: mktemp invocation. (line 113) +* --suffix <7>: numfmt invocation. (line 99) +* --suffix-format: csplit invocation. (line 68) +* --suffix-length: split invocation. (line 113) +* --summarize: du invocation. (line 155) +* --suppress-matched: csplit invocation. (line 90) +* --symbolic: ln invocation. (line 162) +* --symbolic-link: cp invocation. (line 350) +* --sync: df invocation. (line 175) +* --sysv: sum invocation. (line 29) +* --tabs: expand invocation. (line 22) +* --tabs <1>: unexpand invocation. (line 24) +* --tabsize: General output formatting. + (line 129) +* --tag: cksum common options. + (line 77) +* --tagged-paragraph: fmt invocation. (line 40) +* --target-directory: Target directory. (line 31) +* --target-directory <1>: cp invocation. (line 363) +* --target-directory <2>: install invocation. (line 129) +* --target-directory <3>: mv invocation. (line 135) +* --target-directory <4>: ln invocation. (line 173) +* --temporary-directory: sort invocation. (line 358) +* --terse: stat invocation. (line 70) +* --text: cksum common options. + (line 89) +* --threshold: du invocation. (line 159) +* --time: Sorting the output. (line 13) +* --time <1>: Sorting the output. (line 44) +* --time <2>: Sorting the output. (line 50) +* --time <3>: Sorting the output. (line 57) +* --time <4>: touch invocation. (line 48) +* --time <5>: touch invocation. (line 85) +* --time <6>: du invocation. (line 195) +* --time <7>: du invocation. (line 202) +* --time <8>: du invocation. (line 208) +* --time <9>: who invocation. (line 82) +* --time-style: Formatting file timestamps. + (line 24) +* --time-style <1>: du invocation. (line 212) +* --tmpdir: mktemp invocation. (line 105) +* --to: numfmt invocation. (line 103) +* --to-unit: numfmt invocation. (line 108) +* --total: df invocation. (line 181) +* --total <1>: du invocation. (line 63) +* --total=WHEN: wc invocation. (line 71) +* --traditional: od invocation. (line 200) +* --truncate-set1: tr invocation. (line 47) +* --type: df invocation. (line 195) +* --type <1>: chcon invocation. (line 73) +* --type <2>: runcon invocation. (line 44) +* --unbuffered: split invocation. (line 159) +* --uniform-spacing: fmt invocation. (line 53) +* --unique: sort invocation. (line 374) +* --unique <1>: uniq invocation. (line 128) +* --universal: Options for date. (line 135) +* --unset: env invocation. (line 96) +* --untagged: cksum general options. + (line 52) +* --update: mv invocation. (line 91) +* --update[=WHICH]: cp invocation. (line 372) +* --user: id invocation. (line 47) +* --user <1>: chcon invocation. (line 65) +* --user <2>: runcon invocation. (line 36) +* --userspec: chroot invocation. (line 30) +* --utc: Options for date. (line 135) +* --verbose: head invocation. (line 51) +* --verbose <1>: tail invocation. (line 186) +* --verbose <2>: split invocation. (line 163) +* --verbose <3>: cp invocation. (line 407) +* --verbose <4>: install invocation. (line 139) +* --verbose <5>: mv invocation. (line 122) +* --verbose <6>: rm invocation. (line 100) +* --verbose <7>: shred invocation. (line 159) +* --verbose <8>: ln invocation. (line 182) +* --verbose <9>: mkdir invocation. (line 54) +* --verbose <10>: readlink invocation. (line 61) +* --verbose <11>: rmdir invocation. (line 30) +* --verbose <12>: chown invocation. (line 143) +* --verbose <13>: chgrp invocation. (line 69) +* --verbose <14>: chmod invocation. (line 63) +* --verbose <15>: chcon invocation. (line 61) +* --verbose <16>: timeout invocation. (line 64) +* --version: Common options. (line 40) +* --version-sort: sort invocation. (line 183) +* --warn: cksum common options. + (line 99) +* --width: od invocation. (line 157) +* --width <1>: fmt invocation. (line 59) +* --width <2>: pr invocation. (line 229) +* --width <3>: fold invocation. (line 35) +* --width <4>: Output formatting in ptx. + (line 32) +* --width <5>: General output formatting. + (line 149) +* --word-regexp: Input processing in ptx. + (line 105) +* --words: wc invocation. (line 55) +* --wrap: base64 invocation. (line 25) +* --writable: who invocation. (line 94) +* --z85: basenc invocation. (line 63) +* --zero: cksum common options. + (line 109) +* --zero <1>: General output formatting. + (line 157) +* --zero <2>: shred invocation. (line 175) +* --zero <3>: readlink invocation. (line 65) +* --zero <4>: basename invocation. (line 42) +* --zero <5>: dirname invocation. (line 31) +* --zero <6>: realpath invocation. (line 71) +* --zero <7>: id invocation. (line 58) +* --zero-terminated: head invocation. (line 55) +* --zero-terminated <1>: tail invocation. (line 190) +* --zero-terminated <2>: sort invocation. (line 389) +* --zero-terminated <3>: shuf invocation. (line 55) +* --zero-terminated <4>: uniq invocation. (line 140) +* --zero-terminated <5>: comm invocation. (line 89) +* --zero-terminated <6>: cut invocation. (line 94) +* --zero-terminated <7>: paste invocation. (line 72) +* --zero-terminated <8>: General options in join. + (line 93) +* --zero-terminated <9>: numfmt invocation. (line 115) +* -0: du invocation. (line 25) +* -0 <1>: printenv invocation. (line 19) +* -0 <2>: env invocation. (line 90) +* -1: comm invocation. (line 23) +* -1 <1>: General options in join. + (line 40) +* -1 <2>: General output formatting. + (line 16) +* -2: comm invocation. (line 23) +* -2 <1>: General options in join. + (line 43) +* -3: comm invocation. (line 23) +* -A: cat invocation. (line 16) +* -A <1>: od invocation. (line 36) +* -a: od invocation. (line 169) +* -a <1>: pr invocation. (line 62) +* -a <2>: split invocation. (line 113) +* -a <3>: cksum general options. + (line 5) +* -A <2>: Output formatting in ptx. + (line 45) +* -a <4>: General options in join. + (line 10) +* -a <5>: unexpand invocation. (line 51) +* -a <6>: Which files are listed. + (line 13) +* -A <3>: Which files are listed. + (line 17) +* -a <7>: cp invocation. (line 63) +* -a <8>: touch invocation. (line 48) +* -a <9>: df invocation. (line 42) +* -a <10>: du invocation. (line 31) +* -a <11>: Connectives for test. + (line 29) +* -a <12>: tee invocation. (line 26) +* -a <13>: basename invocation. (line 32) +* -a <14>: stty invocation. (line 26) +* -a <15>: who invocation. (line 35) +* -a <16>: uname invocation. (line 30) +* -b: Backup options. (line 13) +* -b <1>: cat invocation. (line 20) +* -b <2>: tac invocation. (line 21) +* -b <3>: nl invocation. (line 45) +* -b <4>: od invocation. (line 172) +* -b <5>: fold invocation. (line 23) +* -b <6>: split invocation. (line 41) +* -b <7>: csplit invocation. (line 68) +* -b <8>: cksum common options. + (line 5) +* -b <9>: sort invocation. (line 79) +* -b <10>: Input processing in ptx. + (line 8) +* -b <11>: cut invocation. (line 26) +* -B: Which files are listed. + (line 23) +* -b <12>: Formatting the file names. + (line 11) +* -b <13>: dircolors invocation. + (line 34) +* -b <14>: cp invocation. (line 79) +* -b <15>: install invocation. (line 41) +* -b <16>: mv invocation. (line 56) +* -b <17>: ln invocation. (line 82) +* -B <1>: df invocation. (line 54) +* -B <2>: du invocation. (line 54) +* -b <18>: du invocation. (line 59) +* -b <19>: File type tests. (line 10) +* -b <20>: who invocation. (line 39) +* -c: od invocation. (line 175) +* -c <1>: fmt invocation. (line 34) +* -c <2>: pr invocation. (line 68) +* -c <3>: head invocation. (line 24) +* -c <4>: tail invocation. (line 39) +* -C: split invocation. (line 56) +* -c <5>: wc invocation. (line 46) +* -c <6>: sort invocation. (line 39) +* -c <7>: sort invocation. (line 47) +* -c <8>: shuf invocation. (line 19) +* -c <9>: uniq invocation. (line 56) +* -c <10>: cut invocation. (line 34) +* -c <11>: tr invocation. (line 31) +* -C <1>: tr invocation. (line 31) +* -c <12>: Sorting the output. (line 13) +* -C <2>: General output formatting. + (line 21) +* -c <13>: dircolors invocation. + (line 40) +* -C <3>: install invocation. (line 46) +* -c <14>: install invocation. (line 57) +* -c <15>: chown invocation. (line 74) +* -c <16>: chgrp invocation. (line 24) +* -c <17>: chmod invocation. (line 43) +* -c <18>: touch invocation. (line 52) +* -c <19>: du invocation. (line 63) +* -c <20>: stat invocation. (line 50) +* -c <21>: truncate invocation. (line 22) +* -c <22>: File type tests. (line 13) +* -c <23>: runcon invocation. (line 32) +* -C <4>: env invocation. (line 107) +* -COLUMN: pr invocation. (line 49) +* -d: nl invocation. (line 63) +* -d <1>: od invocation. (line 179) +* -d <2>: base64 invocation. (line 33) +* -d <3>: pr invocation. (line 74) +* -d <4>: split invocation. (line 121) +* -d <5>: sort invocation. (line 87) +* -d <6>: uniq invocation. (line 64) +* -D: uniq invocation. (line 70) +* -d <7>: cut invocation. (line 66) +* -d <8>: paste invocation. (line 61) +* -d <9>: tr invocation. (line 38) +* -d <10>: Which files are listed. + (line 28) +* -D <1>: What information is listed. + (line 16) +* -d <11>: cp invocation. (line 109) +* -D <2>: install invocation. (line 60) +* -d <12>: install invocation. (line 67) +* -d <13>: rm invocation. (line 35) +* -d <14>: ln invocation. (line 88) +* -d <15>: touch invocation. (line 56) +* -D <3>: du invocation. (line 69) +* -d <16>: File type tests. (line 16) +* -d <17>: mktemp invocation. (line 85) +* -d <18>: who invocation. (line 43) +* -d <19>: Options for date. (line 15) +* -d <20>: numfmt invocation. (line 34) +* -d DEPTH: du invocation. (line 76) +* -e: cat invocation. (line 23) +* -E: cat invocation. (line 27) +* -e <1>: pr invocation. (line 98) +* -e <2>: split invocation. (line 144) +* -e <3>: General options in join. + (line 21) +* -e <4>: readlink invocation. (line 38) +* -e <5>: echo invocation. (line 32) +* -E <1>: echo invocation. (line 68) +* -e <6>: File characteristic tests. + (line 9) +* -e <7>: realpath invocation. (line 22) +* -e <8>: stdbuf invocation. (line 34) +* -ef: File characteristic tests. + (line 23) +* -eq: Numeric tests. (line 16) +* -f: nl invocation. (line 72) +* -f <1>: od invocation. (line 182) +* -F: pr invocation. (line 106) +* -f <2>: pr invocation. (line 106) +* -f <3>: tail invocation. (line 57) +* -F <1>: tail invocation. (line 109) +* -f <4>: csplit invocation. (line 64) +* -f <5>: sort invocation. (line 94) +* -f <6>: uniq invocation. (line 31) +* -f <7>: Charset selection in ptx. + (line 20) +* -F <2>: Output formatting in ptx. + (line 71) +* -f <8>: cut invocation. (line 43) +* -f <9>: Sorting the output. (line 18) +* -F <3>: General output formatting. + (line 52) +* -f <10>: cp invocation. (line 119) +* -f <11>: mv invocation. (line 65) +* -f <12>: rm invocation. (line 39) +* -f <13>: shred invocation. (line 123) +* -F <4>: ln invocation. (line 88) +* -f <14>: ln invocation. (line 94) +* -f <15>: readlink invocation. (line 31) +* -f <16>: chown invocation. (line 80) +* -f <17>: chgrp invocation. (line 30) +* -f <18>: chmod invocation. (line 49) +* -f <19>: touch invocation. (line 66) +* -f <20>: stat invocation. (line 28) +* -f <21>: File type tests. (line 19) +* -F <5>: stty invocation. (line 31) +* -f <22>: Options for date. (line 34) +* -f <23>: seq invocation. (line 29) +* -g: fmt invocation. (line 64) +* -g <1>: sort invocation. (line 105) +* -g <2>: Output formatting in ptx. + (line 26) +* -g <3>: What information is listed. + (line 108) +* -G: What information is listed. + (line 112) +* -g <4>: install invocation. (line 77) +* -g <5>: Access permission tests. + (line 9) +* -G <1>: Access permission tests. + (line 31) +* -g <6>: stty invocation. (line 41) +* -g <7>: id invocation. (line 29) +* -G <2>: id invocation. (line 33) +* -ge: Numeric tests. (line 16) +* -gt: Numeric tests. (line 16) +* -h: Block size. (line 131) +* -H: Traversing symlinks. (line 18) +* -h <1>: nl invocation. (line 76) +* -h <2>: pr invocation. (line 111) +* -h <3>: sort invocation. (line 132) +* -H <1>: Which files are listed. + (line 36) +* -h <4>: What information is listed. + (line 118) +* -H <2>: cp invocation. (line 136) +* -h <5>: chown invocation. (line 119) +* -H <3>: chown invocation. (line 154) +* -h <6>: chgrp invocation. (line 46) +* -H <4>: chgrp invocation. (line 81) +* -h <7>: touch invocation. (line 70) +* -h <8>: df invocation. (line 59) +* -H <5>: df invocation. (line 65) +* -H <6>: du invocation. (line 94) +* -h <9>: du invocation. (line 98) +* -h <10>: File type tests. (line 23) +* -H <7>: who invocation. (line 47) +* -h <11>: chcon invocation. (line 26) +* -H <8>: chcon invocation. (line 47) +* -h <12>: factor invocation. (line 18) +* -i: nl invocation. (line 80) +* -i <1>: od invocation. (line 185) +* -i <2>: base64 invocation. (line 39) +* -i <3>: pr invocation. (line 117) +* -i <4>: sort invocation. (line 149) +* -i <5>: shuf invocation. (line 23) +* -i <6>: uniq invocation. (line 60) +* -i <7>: Input processing in ptx. + (line 26) +* -i <8>: General options in join. + (line 35) +* -i <9>: expand invocation. (line 46) +* -I: Which files are listed. + (line 70) +* -i <10>: What information is listed. + (line 125) +* -i <11>: cp invocation. (line 143) +* -i <12>: mv invocation. (line 71) +* -i <13>: rm invocation. (line 43) +* -I <1>: rm invocation. (line 49) +* -i <14>: ln invocation. (line 98) +* -i <15>: df invocation. (line 69) +* -i <16>: tee invocation. (line 31) +* -i <17>: uname invocation. (line 35) +* -i <18>: env invocation. (line 102) +* -i <19>: stdbuf invocation. (line 26) +* -I[TIMESPEC]: Options for date. (line 42) +* -j: od invocation. (line 59) +* -J: pr invocation. (line 124) +* -k: Block size. (line 131) +* -k <1>: csplit invocation. (line 87) +* -k <2>: sort invocation. (line 237) +* -k <3>: General output formatting. + (line 101) +* -k <4>: df invocation. (line 75) +* -k <5>: du invocation. (line 113) +* -k <6>: Access permission tests. + (line 12) +* -k <7>: timeout invocation. (line 41) +* -L: Traversing symlinks. (line 22) +* -l: nl invocation. (line 85) +* -l <1>: od invocation. (line 188) +* -l <2>: pr invocation. (line 133) +* -l <3>: split invocation. (line 33) +* -l <4>: wc invocation. (line 60) +* -L <1>: wc invocation. (line 66) +* -l <5>: cksum general options. + (line 39) +* -l <6>: b2sum invocation. (line 24) +* -L <2>: Which files are listed. + (line 84) +* -l <7>: What information is listed. + (line 133) +* -l <8>: cp invocation. (line 149) +* -L <3>: cp invocation. (line 153) +* -L <4>: ln invocation. (line 103) +* -L <5>: chown invocation. (line 159) +* -L <6>: chgrp invocation. (line 86) +* -l <9>: df invocation. (line 81) +* -L <7>: du invocation. (line 119) +* -l <10>: du invocation. (line 125) +* -L <8>: stat invocation. (line 22) +* -L <9>: File type tests. (line 23) +* -L <10>: realpath invocation. (line 35) +* -L <11>: pwd invocation. (line 15) +* -l <11>: who invocation. (line 51) +* -L <12>: chcon invocation. (line 52) +* -l <12>: chcon invocation. (line 77) +* -l <13>: runcon invocation. (line 48) +* -le: Numeric tests. (line 16) +* -lt: Numeric tests. (line 16) +* -m: pr invocation. (line 140) +* -m <1>: wc invocation. (line 50) +* -m <2>: sort invocation. (line 53) +* -M: sort invocation. (line 156) +* -M <1>: Output formatting in ptx. + (line 94) +* -m <3>: General output formatting. + (line 114) +* -m <4>: install invocation. (line 83) +* -m <5>: mkdir invocation. (line 19) +* -m <6>: mkfifo invocation. (line 21) +* -m <7>: mknod invocation. (line 47) +* -m <8>: readlink invocation. (line 45) +* -m <9>: touch invocation. (line 85) +* -m <10>: du invocation. (line 129) +* -m <11>: realpath invocation. (line 30) +* -m <12>: who invocation. (line 61) +* -m <13>: uname invocation. (line 42) +* -n: cat invocation. (line 32) +* -n <1>: nl invocation. (line 93) +* -N: od invocation. (line 76) +* -n <2>: pr invocation. (line 153) +* -N <1>: pr invocation. (line 174) +* -n <3>: head invocation. (line 40) +* -n <4>: tail invocation. (line 126) +* -n <5>: split invocation. (line 79) +* -n <6>: csplit invocation. (line 82) +* -n <7>: sort invocation. (line 166) +* -n <8>: shuf invocation. (line 31) +* -n <9>: cut invocation. (line 70) +* -n <10>: What information is listed. + (line 227) +* -N <2>: Formatting the file names. + (line 17) +* -n <11>: cp invocation. (line 160) +* -n <12>: mv invocation. (line 78) +* -n <13>: ln invocation. (line 109) +* -n <14>: readlink invocation. (line 50) +* -n <15>: echo invocation. (line 29) +* -N <3>: File characteristic tests. + (line 27) +* -n <16>: String tests. (line 19) +* -n <17>: id invocation. (line 37) +* -n <18>: uname invocation. (line 47) +* -n <19>: nice invocation. (line 51) +* -n NUMBER: shred invocation. (line 127) +* -ne: Numeric tests. (line 16) +* -nt: File characteristic tests. + (line 15) +* -o: od invocation. (line 191) +* -o <1>: pr invocation. (line 180) +* -o <2>: sort invocation. (line 294) +* -o <3>: shuf invocation. (line 36) +* -o <4>: Input processing in ptx. + (line 35) +* -O: Output formatting in ptx. + (line 100) +* -o <5>: What information is listed. + (line 231) +* -o <6>: install invocation. (line 95) +* -o <7>: truncate invocation. (line 26) +* -O <1>: Access permission tests. + (line 28) +* -o <8>: Connectives for test. + (line 33) +* -o <9>: uname invocation. (line 58) +* -o <10>: stdbuf invocation. (line 30) +* -ot: File characteristic tests. + (line 19) +* -P: Traversing symlinks. (line 26) +* -p: nl invocation. (line 104) +* -p <1>: General output formatting. + (line 120) +* -p <2>: dircolors invocation. + (line 45) +* -P <1>: cp invocation. (line 166) +* -p <3>: cp invocation. (line 173) +* -p <4>: install invocation. (line 107) +* -P <2>: ln invocation. (line 128) +* -p <5>: mkdir invocation. (line 36) +* -p <6>: rmdir invocation. (line 21) +* -P <3>: chown invocation. (line 172) +* -P <4>: chgrp invocation. (line 99) +* -P <5>: df invocation. (line 149) +* -P <6>: du invocation. (line 135) +* -p <7>: File type tests. (line 28) +* -p <8>: tee invocation. (line 35) +* -p <9>: pathchk invocation. (line 27) +* -P <7>: pathchk invocation. (line 40) +* -p <10>: mktemp invocation. (line 105) +* -P <8>: realpath invocation. (line 40) +* -P <9>: pwd invocation. (line 22) +* -p <11>: who invocation. (line 65) +* -p <12>: uname invocation. (line 51) +* -P <10>: chcon invocation. (line 56) +* -q: head invocation. (line 47) +* -q <1>: tail invocation. (line 155) +* -q <2>: csplit invocation. (line 107) +* -q <3>: Formatting the file names. + (line 23) +* -Q: Formatting the file names. + (line 30) +* -q <4>: readlink invocation. (line 57) +* -q <5>: mktemp invocation. (line 92) +* -q <6>: realpath invocation. (line 46) +* -q <7>: who invocation. (line 69) +* -r: tac invocation. (line 26) +* -r <1>: pr invocation. (line 187) +* -r <2>: sum invocation. (line 23) +* -r <3>: sort invocation. (line 189) +* -R: sort invocation. (line 195) +* -r <4>: shuf invocation. (line 47) +* -r <5>: Input processing in ptx. + (line 48) +* -R <1>: Output formatting in ptx. + (line 56) +* -R <2>: Which files are listed. + (line 91) +* -r <6>: Sorting the output. (line 25) +* -R <3>: cp invocation. (line 262) +* -r <7>: cp invocation. (line 262) +* -r <8>: rm invocation. (line 96) +* -R <4>: rm invocation. (line 96) +* -r <9>: ln invocation. (line 137) +* -R <5>: chown invocation. (line 151) +* -R <6>: chgrp invocation. (line 77) +* -R <7>: chmod invocation. (line 73) +* -r <10>: touch invocation. (line 89) +* -r <11>: truncate invocation. (line 30) +* -r <12>: Access permission tests. + (line 15) +* -r <13>: id invocation. (line 42) +* -r <14>: who invocation. (line 74) +* -r <15>: Options for date. (line 71) +* -R <8>: Options for date. (line 85) +* -r <16>: uname invocation. (line 62) +* -R <9>: chcon invocation. (line 35) +* -r <17>: chcon invocation. (line 69) +* -r <18>: runcon invocation. (line 40) +* -S: Backup options. (line 49) +* -s: cat invocation. (line 37) +* -s <1>: tac invocation. (line 30) +* -s <2>: nl invocation. (line 108) +* -S <1>: od invocation. (line 81) +* -s <3>: od invocation. (line 194) +* -s <4>: fmt invocation. (line 47) +* -s <5>: pr invocation. (line 192) +* -S <2>: pr invocation. (line 201) +* -s <6>: fold invocation. (line 29) +* -s <7>: tail invocation. (line 175) +* -s <8>: csplit invocation. (line 107) +* -s <9>: sum invocation. (line 29) +* -s <10>: sort invocation. (line 315) +* -S <3>: sort invocation. (line 322) +* -s <11>: uniq invocation. (line 42) +* -S <4>: Input processing in ptx. + (line 65) +* -s <12>: cut invocation. (line 74) +* -s <13>: paste invocation. (line 52) +* -s <14>: tr invocation. (line 42) +* -s <15>: What information is listed. + (line 236) +* -S <5>: Sorting the output. (line 32) +* -s <16>: cp invocation. (line 350) +* -S <6>: cp invocation. (line 358) +* -s <17>: install invocation. (line 117) +* -S <7>: install invocation. (line 124) +* -S <8>: mv invocation. (line 130) +* -s <18>: ln invocation. (line 162) +* -S <9>: ln invocation. (line 168) +* -s <19>: readlink invocation. (line 57) +* -S <10>: du invocation. (line 140) +* -s <20>: du invocation. (line 155) +* -s <21>: truncate invocation. (line 34) +* -S <11>: File type tests. (line 31) +* -s <22>: File characteristic tests. + (line 12) +* -s <23>: basename invocation. (line 38) +* -s <24>: realpath invocation. (line 64) +* -s <25>: tty invocation. (line 18) +* -s <26>: who invocation. (line 78) +* -s <27>: Options for date. (line 129) +* -s <28>: uname invocation. (line 66) +* -S <12>: env invocation. (line 192) +* -s <29>: timeout invocation. (line 58) +* -s <30>: seq invocation. (line 45) +* -s BYTES: shred invocation. (line 138) +* -S, env and single quotes: env invocation. (line 268) +* -t: cat invocation. (line 41) +* -T: cat invocation. (line 45) +* -t <1>: od invocation. (line 90) +* -t <2>: fmt invocation. (line 40) +* -t <3>: pr invocation. (line 210) +* -T <1>: pr invocation. (line 220) +* -t <4>: split invocation. (line 152) +* -t <5>: cksum common options. + (line 89) +* -t <6>: sort invocation. (line 338) +* -T <2>: sort invocation. (line 358) +* -T <3>: Output formatting in ptx. + (line 118) +* -t <7>: tr invocation. (line 47) +* -t <8>: expand invocation. (line 22) +* -t <9>: unexpand invocation. (line 24) +* -t <10>: Sorting the output. (line 36) +* -T <4>: General output formatting. + (line 129) +* -t <11>: cp invocation. (line 363) +* -T <5>: cp invocation. (line 367) +* -t <12>: install invocation. (line 129) +* -T <6>: install invocation. (line 134) +* -t <13>: mv invocation. (line 135) +* -T <7>: mv invocation. (line 139) +* -t <14>: ln invocation. (line 173) +* -T <8>: ln invocation. (line 177) +* -t <15>: df invocation. (line 195) +* -T <9>: df invocation. (line 201) +* -t <16>: du invocation. (line 159) +* -t <17>: stat invocation. (line 70) +* -t <18>: File type tests. (line 34) +* -t <19>: mktemp invocation. (line 121) +* -t <20>: who invocation. (line 82) +* -T <10>: who invocation. (line 94) +* -t <21>: chcon invocation. (line 73) +* -t <22>: runcon invocation. (line 44) +* -u: cat invocation. (line 48) +* -u <1>: fmt invocation. (line 53) +* -u <2>: split invocation. (line 159) +* -u <3>: sort invocation. (line 374) +* -u <4>: uniq invocation. (line 128) +* -u <5>: Sorting the output. (line 44) +* -U: Sorting the output. (line 64) +* -u <6>: cp invocation. (line 372) +* -u <7>: mv invocation. (line 91) +* -u <8>: shred invocation. (line 144) +* -u <9>: Access permission tests. + (line 18) +* -u <10>: mktemp invocation. (line 97) +* -u <11>: id invocation. (line 47) +* -u <12>: who invocation. (line 85) +* -u <13>: Options for date. (line 135) +* -u <14>: chcon invocation. (line 65) +* -u <15>: runcon invocation. (line 36) +* -u <16>: env invocation. (line 96) +* -v: cat invocation. (line 52) +* -v <1>: nl invocation. (line 113) +* -v <2>: od invocation. (line 150) +* -v <3>: pr invocation. (line 225) +* -v <4>: head invocation. (line 51) +* -v <5>: tail invocation. (line 186) +* -V: sort invocation. (line 183) +* -v <6>: Sorting the output. (line 71) +* -v <7>: cp invocation. (line 407) +* -v <8>: install invocation. (line 139) +* -v <9>: mv invocation. (line 122) +* -v <10>: rm invocation. (line 100) +* -v <11>: shred invocation. (line 159) +* -v <12>: ln invocation. (line 182) +* -v <13>: mkdir invocation. (line 54) +* -v <14>: readlink invocation. (line 61) +* -v <15>: rmdir invocation. (line 30) +* -v <16>: chown invocation. (line 143) +* -v <17>: chgrp invocation. (line 69) +* -v <18>: chmod invocation. (line 63) +* -v <19>: uname invocation. (line 77) +* -v <20>: chcon invocation. (line 61) +* -v <21>: env invocation. (line 177) +* -v <22>: timeout invocation. (line 64) +* -w: nl invocation. (line 118) +* -w <1>: od invocation. (line 157) +* -w <2>: base64 invocation. (line 25) +* -w <3>: fmt invocation. (line 59) +* -w <4>: pr invocation. (line 229) +* -W: pr invocation. (line 239) +* -w <5>: fold invocation. (line 35) +* -w <6>: wc invocation. (line 55) +* -w <7>: cksum common options. + (line 99) +* -w <8>: uniq invocation. (line 134) +* -W <1>: Input processing in ptx. + (line 105) +* -w <9>: Output formatting in ptx. + (line 32) +* -w <10>: General output formatting. + (line 149) +* -w <11>: Access permission tests. + (line 21) +* -w <12>: who invocation. (line 94) +* -w <13>: seq invocation. (line 50) +* -WIDTH: fmt invocation. (line 59) +* -x: od invocation. (line 197) +* -x <1>: split invocation. (line 135) +* -X: Sorting the output. (line 83) +* -x <2>: General output formatting. + (line 125) +* -x <3>: cp invocation. (line 411) +* -x <4>: shred invocation. (line 164) +* -x <5>: df invocation. (line 224) +* -x <6>: du invocation. (line 261) +* -x <7>: Access permission tests. + (line 24) +* -X FILE: du invocation. (line 250) +* -z: head invocation. (line 55) +* -z <1>: tail invocation. (line 190) +* -z <2>: csplit invocation. (line 96) +* -z <3>: cksum common options. + (line 109) +* -z <4>: sort invocation. (line 389) +* -z <5>: shuf invocation. (line 55) +* -z <6>: uniq invocation. (line 140) +* -z <7>: comm invocation. (line 89) +* -z <8>: cut invocation. (line 94) +* -z <9>: paste invocation. (line 72) +* -z <10>: General options in join. + (line 93) +* -Z: What information is listed. + (line 259) +* -Z <1>: cp invocation. (line 417) +* -Z <2>: install invocation. (line 143) +* -Z <3>: mv invocation. (line 144) +* -z <11>: shred invocation. (line 175) +* -Z <4>: mkdir invocation. (line 59) +* -Z <5>: mkfifo invocation. (line 28) +* -Z <6>: mknod invocation. (line 53) +* -z <12>: readlink invocation. (line 65) +* -z <13>: String tests. (line 15) +* -z <14>: basename invocation. (line 42) +* -z <15>: dirname invocation. (line 31) +* -z <16>: realpath invocation. (line 71) +* -Z <7>: id invocation. (line 51) +* -z <17>: id invocation. (line 58) +* -z <18>: numfmt invocation. (line 115) +* /: Numeric expressions. (line 16) +* 128-bit checksum: md5sum invocation. (line 6) +* 16-bit checksum: sum invocation. (line 6) +* 160-bit checksum: sha1sum invocation. (line 6) +* 224-bit checksum: sha2 utilities. (line 6) +* 256-bit checksum: sha2 utilities. (line 6) +* 32-bit checksum: cksum invocation. (line 6) +* 384-bit checksum: sha2 utilities. (line 6) +* 512-bit checksum: b2sum invocation. (line 6) +* 512-bit checksum <1>: sha2 utilities. (line 6) +* <: Relations for expr. (line 22) +* <=: Relations for expr. (line 22) +* =: Relations for expr. (line 22) +* = <1>: String tests. (line 22) +* ==: Relations for expr. (line 22) +* == <1>: String tests. (line 25) +* >: Relations for expr. (line 22) +* >=: Relations for expr. (line 22) +* \( regexp operator: String expressions. (line 23) +* \+ regexp operator: String expressions. (line 27) +* \? regexp operator: String expressions. (line 27) +* \c: printf invocation. (line 28) +* \OOO: printf invocation. (line 67) +* \uhhhh: printf invocation. (line 74) +* \Uhhhhhhhh: printf invocation. (line 74) +* \xHH: printf invocation. (line 67) +* \| regexp operator: String expressions. (line 27) +* _POSIX2_VERSION: Standards conformance. + (line 20) +* _POSIX2_VERSION <1>: tail invocation. (line 205) +* _POSIX2_VERSION <2>: sort invocation. (line 421) +* _POSIX2_VERSION <3>: uniq invocation. (line 47) +* _POSIX2_VERSION <4>: touch invocation. (line 107) +* |: Relations for expr. (line 11) +* abbreviations for months: Calendar date items. (line 36) +* access control lists (ACLs): cp invocation. (line 178) +* access control lists (ACLs) <1>: cp invocation. (line 220) +* access permission tests: Access permission tests. + (line 6) +* access permissions, changing: chmod invocation. (line 6) +* access time, changing: touch invocation. (line 48) +* access timestamp: dd invocation. (line 324) +* access timestamp, printing or sorting files by: Sorting the output. + (line 44) +* access timestamp, show the most recent: du invocation. (line 208) +* across columns: pr invocation. (line 62) +* across, listing files: General output formatting. + (line 125) +* adding permissions: Setting Permissions. (line 35) +* addition: Numeric expressions. (line 12) +* ago in date strings: Relative items in date strings. + (line 23) +* all lines, grouping: uniq invocation. (line 101) +* all repeated lines, outputting: uniq invocation. (line 70) +* alnum: Character arrays. (line 108) +* alpha: Character arrays. (line 110) +* alternate ebcdic, converting to: dd invocation. (line 149) +* always classify option: General output formatting. + (line 59) +* always color option: General output formatting. + (line 32) +* always hyperlink option: General output formatting. + (line 77) +* always interactive option: rm invocation. (line 60) +* always total option: wc invocation. (line 76) +* am i: who invocation. (line 21) +* am in date strings: Time of day items. (line 21) +* and operator: Connectives for test. + (line 29) +* and operator <1>: Relations for expr. (line 17) +* append: dd invocation. (line 253) +* appending to the output file: dd invocation. (line 253) +* appropriate privileges: install invocation. (line 95) +* appropriate privileges <1>: Setting the time. (line 6) +* appropriate privileges <2>: hostname invocation. (line 6) +* appropriate privileges <3>: nice invocation. (line 6) +* arbitrary date strings, debugging: Options for date. (line 29) +* arbitrary date strings, parsing: Options for date. (line 15) +* arbitrary text, displaying: echo invocation. (line 6) +* arch: arch invocation. (line 6) +* arithmetic tests: Numeric tests. (line 6) +* arrays of characters in tr: Character arrays. (line 6) +* ASCII dump of files: od invocation. (line 6) +* ascii, converting to: dd invocation. (line 138) +* atime: File timestamps. (line 6) +* atime, changing: touch invocation. (line 48) +* atime, printing or sorting files by: Sorting the output. (line 44) +* atime, show the most recent: du invocation. (line 208) +* attribute caching: stat invocation. (line 33) +* attributes, file: Changing file attributes. + (line 6) +* authors of parse_datetime: Authors of parse_datetime. + (line 6) +* auto classify option: General output formatting. + (line 58) +* auto color option: General output formatting. + (line 31) +* auto hyperlink option: General output formatting. + (line 76) +* auto total option: wc invocation. (line 73) +* b for block special file: mknod invocation. (line 31) +* b2sum: b2sum invocation. (line 6) +* background jobs, stopping at terminal write: Local. (line 41) +* backslash escapes: Character arrays. (line 30) +* backslash escapes <1>: echo invocation. (line 32) +* backslash escapes <2>: echo invocation. (line 68) +* backslash sequences for file names: Formatting the file names. + (line 11) +* backup files, ignoring: Which files are listed. + (line 23) +* backup options: Backup options. (line 6) +* backup suffix: Backup options. (line 49) +* backups, making: Backup options. (line 13) +* backups, making <1>: cp invocation. (line 79) +* backups, making <2>: install invocation. (line 41) +* backups, making <3>: mv invocation. (line 56) +* backups, making <4>: ln invocation. (line 82) +* backups, making only: cp invocation. (line 51) +* base32: base32 invocation. (line 6) +* base32 encoding: base32 invocation. (line 6) +* base32 encoding <1>: basenc invocation. (line 6) +* base64: base64 invocation. (line 6) +* base64 checksum encoding: cksum general options. + (line 23) +* Base64 decoding: base64 invocation. (line 33) +* base64 encoding: base64 invocation. (line 6) +* basename: basename invocation. (line 6) +* basenc: basenc invocation. (line 6) +* baud rate, setting: Special. (line 54) +* beeping at input buffer full: Input. (line 59) +* beginning of time: Time conversion specifiers. + (line 32) +* beginning of time, for POSIX: Seconds since the Epoch. + (line 13) +* Bellovin, Steven M.: Authors of parse_datetime. + (line 6) +* Berets, Jim: Authors of parse_datetime. + (line 6) +* Berry, K.: Introduction. (line 29) +* Berry, K. <1>: Authors of parse_datetime. + (line 19) +* binary: dd invocation. (line 341) +* binary I/O: dd invocation. (line 341) +* binary input files: cksum common options. + (line 5) +* bind mount: rm invocation. (line 68) +* bind mount <1>: stat invocation. (line 199) +* birth time, printing or sorting files by: Sorting the output. + (line 57) +* birthtime: File timestamps. (line 6) +* BLAKE2: b2sum invocation. (line 6) +* BLAKE2 hash length: cksum general options. + (line 39) +* BLAKE2 hash length <1>: b2sum invocation. (line 24) +* blank: Character arrays. (line 112) +* blank lines, numbering: nl invocation. (line 85) +* blanks, ignoring leading: sort invocation. (line 79) +* block (space-padding): dd invocation. (line 159) +* block size: Block size. (line 6) +* block size <1>: dd invocation. (line 60) +* block size of conversion: dd invocation. (line 67) +* block size of input: dd invocation. (line 52) +* block size of output: dd invocation. (line 56) +* block special check: File type tests. (line 10) +* block special files: mknod invocation. (line 11) +* block special files, creating: mknod invocation. (line 6) +* BLOCKSIZE: Block size. (line 12) +* BLOCK_SIZE: Block size. (line 12) +* body, numbering: nl invocation. (line 17) +* Bourne shell syntax for color setup: dircolors invocation. + (line 34) +* breaks, cause interrupts: Input. (line 12) +* breaks, ignoring: Input. (line 9) +* brkint: Input. (line 12) +* bs: dd invocation. (line 60) +* BSD output: cksum common options. + (line 77) +* BSD sum: sum invocation. (line 23) +* BSD tail: tail invocation. (line 26) +* BSD touch compatibility: touch invocation. (line 66) +* bsN: Output. (line 55) +* btrfs file system type: df invocation. (line 212) +* bugs, reporting: Introduction. (line 12) +* built-in shell commands, conflicts with: mknod invocation. (line 20) +* built-in shell commands, conflicts with <1>: stat invocation. + (line 15) +* built-in shell commands, conflicts with <2>: echo invocation. + (line 11) +* built-in shell commands, conflicts with <3>: printf invocation. + (line 16) +* built-in shell commands, conflicts with <4>: test invocation. + (line 28) +* built-in shell commands, conflicts with <5>: pwd invocation. + (line 30) +* built-in shell commands, conflicts with <6>: nice invocation. + (line 38) +* built-in shell commands, conflicts with <7>: kill invocation. + (line 13) +* built-in shell commands, conflicts with <8>: sleep invocation. + (line 40) +* byte count: wc invocation. (line 6) +* byte-swapping: od invocation. (line 51) +* byte-swapping <1>: dd invocation. (line 195) +* c for character special file: mknod invocation. (line 34) +* C shell syntax for color setup: dircolors invocation. + (line 40) +* C-s/C-q flow control: Input. (line 40) +* calendar date item: Calendar date items. (line 6) +* calling combined multi-call program: Multi-call invocation. + (line 6) +* canonical file name: readlink invocation. (line 6) +* canonical file name <1>: realpath invocation. (line 6) +* canonicalize a file name: readlink invocation. (line 6) +* canonicalize a file name <1>: realpath invocation. (line 6) +* case folding: sort invocation. (line 94) +* case translation: Local. (line 36) +* case, ignored in dates: General date syntax. (line 60) +* cat: cat invocation. (line 6) +* cbreak: Combination. (line 52) +* cbs: dd invocation. (line 67) +* CD-ROM file system type: df invocation. (line 216) +* cdfs file system type: df invocation. (line 216) +* cdtrdsr: Control. (line 44) +* change or print terminal settings: stty invocation. (line 6) +* change SELinux context: chcon invocation. (line 6) +* changed files, verbosely describing: chgrp invocation. (line 24) +* changed owners, verbosely describing: chown invocation. (line 74) +* changing access permissions: chmod invocation. (line 6) +* changing file attributes: Changing file attributes. + (line 6) +* changing file ownership: chown invocation. (line 6) +* changing file timestamps: touch invocation. (line 6) +* changing group ownership: chown invocation. (line 6) +* changing group ownership <1>: chgrp invocation. (line 6) +* changing security context: chcon invocation. (line 6) +* changing special mode bits: Changing Special Mode Bits. + (line 6) +* character classes: Character arrays. (line 94) +* character count: wc invocation. (line 6) +* character size: Control. (line 24) +* character special check: File type tests. (line 13) +* character special files: mknod invocation. (line 11) +* character special files, creating: mknod invocation. (line 6) +* characters, special: Characters. (line 6) +* chcon: chcon invocation. (line 6) +* check file types: test invocation. (line 6) +* checking whether a file is sorted: sort invocation. (line 39) +* checking whether a file is sorted <1>: sort invocation. (line 47) +* checksum, 128-bit: md5sum invocation. (line 6) +* checksum, 16-bit: sum invocation. (line 6) +* checksum, 160-bit: sha1sum invocation. (line 6) +* checksum, 224-bit: sha2 utilities. (line 6) +* checksum, 256-bit: sha2 utilities. (line 6) +* checksum, 32-bit: cksum invocation. (line 6) +* checksum, 384-bit: sha2 utilities. (line 6) +* checksum, 512-bit: b2sum invocation. (line 6) +* checksum, 512-bit <1>: sha2 utilities. (line 6) +* chgrp: chgrp invocation. (line 6) +* chmod: chmod invocation. (line 6) +* chown: chown invocation. (line 6) +* chroot: chroot invocation. (line 6) +* cio: dd invocation. (line 261) +* cksum: cksum invocation. (line 6) +* clocal: Control. (line 38) +* clock skew: Formatting file timestamps. + (line 11) +* clock skew <1>: File timestamps. (line 39) +* clone: cp invocation. (line 275) +* cmspar: Control. (line 16) +* cntrl: Character arrays. (line 114) +* color database, printing: dircolors invocation. + (line 45) +* color setup: dircolors invocation. + (line 6) +* color, distinguishing file types with: General output formatting. + (line 28) +* cols: Special. (line 27) +* column to wrap data after: base64 invocation. (line 25) +* COLUMNS: General output formatting. + (line 149) +* COLUMNS <1>: Special. (line 41) +* columns: Special. (line 27) +* combination settings: Combination. (line 6) +* combined: Multi-call invocation. + (line 6) +* combined date and time of day item: Combined date and time of day items. + (line 6) +* comm: comm invocation. (line 6) +* command-line operands to shuffle: shuf invocation. (line 19) +* commands for controlling processes: Process control. (line 6) +* commands for delaying: Delaying. (line 6) +* commands for exit status: Conditions. (line 6) +* commands for file name manipulation: File name manipulation. + (line 6) +* commands for invoking other commands: Modified command invocation. + (line 6) +* commands for printing text: Printing text. (line 6) +* commands for printing the working context: Working context. (line 6) +* commands for printing user information: User information. (line 6) +* commands for redirection: Redirection. (line 6) +* commands for SELinux context: SELinux context. (line 6) +* commands for system context: System context. (line 6) +* commas, outputting between files: General output formatting. + (line 114) +* comments, in dates: General date syntax. (line 60) +* common field, joining on: join invocation. (line 6) +* common lines: comm invocation. (line 18) +* common options: Common options. (line 6) +* compare values: test invocation. (line 6) +* comparing sorted files: comm invocation. (line 6) +* comparison operators: Relations for expr. (line 22) +* compression and du: du invocation. (line 277) +* concatenate and write files: cat invocation. (line 6) +* concurrent I/O: dd invocation. (line 261) +* conditional executability: Conditional Executability. + (line 6) +* conditions: Conditions. (line 6) +* conflicts with shell built-ins: mknod invocation. (line 20) +* conflicts with shell built-ins <1>: stat invocation. (line 15) +* conflicts with shell built-ins <2>: echo invocation. (line 11) +* conflicts with shell built-ins <3>: printf invocation. (line 16) +* conflicts with shell built-ins <4>: test invocation. (line 28) +* conflicts with shell built-ins <5>: pwd invocation. (line 30) +* conflicts with shell built-ins <6>: nice invocation. (line 38) +* conflicts with shell built-ins <7>: kill invocation. (line 13) +* conflicts with shell built-ins <8>: sleep invocation. (line 40) +* connectives, logical: Connectives for test. + (line 6) +* connectives, logical <1>: Relations for expr. (line 6) +* constant parity: Control. (line 16) +* context splitting: csplit invocation. (line 6) +* context, system: System context. (line 6) +* control characters, using ^C: Local. (line 51) +* control settings: Control. (line 6) +* controlling terminal: dd invocation. (line 330) +* conv: dd invocation. (line 132) +* conversion block size: dd invocation. (line 67) +* conversion specifiers, date: Date conversion specifiers. + (line 6) +* conversion specifiers, literal: Literal conversion specifiers. + (line 6) +* conversion specifiers, time: Time conversion specifiers. + (line 6) +* converting tabs to spaces: expand invocation. (line 6) +* converting while copying a file: dd invocation. (line 6) +* cooked: Combination. (line 37) +* Coordinated Universal Time: Options for date. (line 135) +* copy on write: cp invocation. (line 275) +* copy-on-write and du: du invocation. (line 272) +* copying directories recursively: cp invocation. (line 96) +* copying directories recursively <1>: cp invocation. (line 262) +* copying existing permissions: Copying Permissions. (line 6) +* copying files: cat invocation. (line 6) +* copying files and directories: cp invocation. (line 6) +* copying files and setting attributes: install invocation. (line 6) +* core utilities: Top. (line 18) +* count: dd invocation. (line 86) +* COW: cp invocation. (line 275) +* cp: cp invocation. (line 6) +* crashes and corruption: sync invocation. (line 17) +* CRC checksum: cksum invocation. (line 6) +* cread: Control. (line 35) +* creating directories: mkdir invocation. (line 6) +* creating FIFOs (named pipes): mkfifo invocation. (line 6) +* creating links (hard only): link invocation. (line 6) +* creating links (hard or soft): ln invocation. (line 6) +* creating output file, avoiding: dd invocation. (line 210) +* creating output file, requiring: dd invocation. (line 206) +* creation timestamp, printing or sorting files by: Sorting the output. + (line 57) +* crN: Output. (line 45) +* crown margin: fmt invocation. (line 34) +* crt: Combination. (line 75) +* crterase: Local. (line 22) +* crtkill: Local. (line 56) +* crtscts: Control. (line 41) +* csh syntax for color setup: dircolors invocation. + (line 40) +* csN: Control. (line 24) +* csplit: csplit invocation. (line 6) +* cstopb: Control. (line 32) +* ctime: File timestamps. (line 6) +* ctime, printing or sorting by: Sorting the output. (line 13) +* ctime, show the most recent: du invocation. (line 202) +* ctlecho: Local. (line 51) +* current working directory, printing: pwd invocation. (line 6) +* cut: cut invocation. (line 6) +* cyclic redundancy check: cksum invocation. (line 6) +* data modification time, printing or sorting files by: Sorting the output. + (line 50) +* data, erasing: shred invocation. (line 6) +* database for color setup, printing: dircolors invocation. + (line 45) +* date: date invocation. (line 6) +* date and time of day format, ISO 8601: Combined date and time of day items. + (line 6) +* date conversion specifiers: Date conversion specifiers. + (line 6) +* date format, ISO 8601: Calendar date items. (line 28) +* date input formats: Date input formats. (line 6) +* date options: Options for date. (line 6) +* date strings, debugging: Options for date. (line 29) +* date strings, parsing: Options for date. (line 15) +* day in date strings: Relative items in date strings. + (line 15) +* day in date strings <1>: Relative items in date strings. + (line 29) +* day of week item: Day of week items. (line 6) +* dd: dd invocation. (line 6) +* ddrescue: dd invocation. (line 397) +* debugging date strings: Options for date. (line 29) +* debugging, copying: cp invocation. (line 114) +* debugging, copying <1>: install invocation. (line 72) +* debugging, copying <2>: mv invocation. (line 60) +* debugging, env -S: env invocation. (line 277) +* dec: Combination. (line 78) +* decctlq: Combination. (line 63) +* Decode base64 data: base64 invocation. (line 33) +* delay for a specified time: sleep invocation. (line 6) +* delaying commands: Delaying. (line 6) +* deleting characters: Squeezing and deleting. + (line 6) +* dereferencing symbolic links: ln invocation. (line 42) +* descriptor follow option: tail invocation. (line 57) +* destination directory: Target directory. (line 15) +* destination directory <1>: Target directory. (line 31) +* destination directory <2>: cp invocation. (line 363) +* destination directory <3>: cp invocation. (line 367) +* destination directory <4>: install invocation. (line 129) +* destination directory <5>: install invocation. (line 134) +* destination directory <6>: mv invocation. (line 135) +* destination directory <7>: mv invocation. (line 139) +* destination directory <8>: ln invocation. (line 173) +* destination directory <9>: ln invocation. (line 177) +* destinations, multiple output: tee invocation. (line 6) +* device file: df invocation. (line 30) +* df: df invocation. (line 6) +* DF_BLOCK_SIZE: Block size. (line 12) +* diagnostic: chcon invocation. (line 61) +* dictionary order: sort invocation. (line 87) +* differing lines: comm invocation. (line 18) +* digest: cksum invocation. (line 6) +* digest algorithm: cksum general options. + (line 5) +* digit: Character arrays. (line 116) +* dir: dir invocation. (line 6) +* dircolors: dircolors invocation. + (line 6) +* direct: dd invocation. (line 267) +* direct I/O: dd invocation. (line 267) +* directories, copying: cp invocation. (line 6) +* directories, copying recursively: cp invocation. (line 96) +* directories, copying recursively <1>: cp invocation. (line 262) +* directories, creating: mkdir invocation. (line 6) +* directories, creating with given attributes: install invocation. + (line 67) +* directories, removing: rm invocation. (line 35) +* directories, removing (recursively): rm invocation. (line 96) +* directories, removing empty: rmdir invocation. (line 6) +* directory: dd invocation. (line 275) +* directory check: File type tests. (line 16) +* directory components, printing: dirname invocation. (line 6) +* directory deletion, ignoring failures: rmdir invocation. (line 17) +* directory deletion, reporting: rmdir invocation. (line 30) +* directory I/O: dd invocation. (line 275) +* directory listing: ls invocation. (line 6) +* directory listing, brief: dir invocation. (line 6) +* directory listing, recursive: Which files are listed. + (line 91) +* directory listing, verbose: vdir invocation. (line 6) +* directory order, listing by: Sorting the output. (line 18) +* directory, creating temporary: mktemp invocation. (line 6) +* directory, stripping from file names: basename invocation. (line 6) +* dired Emacs mode support: What information is listed. + (line 16) +* dirname: dirname invocation. (line 6) +* disabling special characters: Characters. (line 12) +* disambiguating group names and IDs: Disambiguating names and IDs. + (line 6) +* discard: Characters. (line 39) +* discarding file cache: dd invocation. (line 292) +* disk device file: df invocation. (line 30) +* disk usage: File space usage. (line 6) +* disk usage by file system: df invocation. (line 6) +* disk usage for files: du invocation. (line 6) +* displacement of dates: Relative items in date strings. + (line 6) +* displaying text: echo invocation. (line 6) +* displaying value of a symbolic link: readlink invocation. (line 6) +* division: Numeric expressions. (line 16) +* do nothing, successfully: true invocation. (line 6) +* do nothing, unsuccessfully: false invocation. (line 6) +* DOS file system: df invocation. (line 220) +* double spacing: pr invocation. (line 74) +* down columns: pr invocation. (line 49) +* drain: Special. (line 30) +* dsusp: Characters. (line 58) +* dsync: dd invocation. (line 281) +* DTR/DSR flow control: Control. (line 44) +* du: du invocation. (line 6) +* DU_BLOCK_SIZE: Block size. (line 12) +* DVD file system type: df invocation. (line 216) +* ebcdic, converting to: dd invocation. (line 144) +* echo: echo invocation. (line 6) +* echo <1>: Local. (line 18) +* echoctl: Local. (line 51) +* echoe: Local. (line 22) +* echok: Local. (line 26) +* echoke: Local. (line 56) +* echonl: Local. (line 29) +* echoprt: Local. (line 46) +* effective user and group IDs, printing: id invocation. (line 6) +* effective user name, printing: whoami invocation. (line 6) +* Eggert, Paul: Authors of parse_datetime. + (line 6) +* eight-bit characters: Control. (line 24) +* eight-bit characters <1>: Combination. (line 55) +* eight-bit input: Input. (line 25) +* ek: Combination. (line 22) +* empty files, creating: touch invocation. (line 11) +* empty lines, numbering: nl invocation. (line 85) +* endianness: od invocation. (line 51) +* entire files, output of: Output of entire files. + (line 6) +* env: env invocation. (line 6) +* env -S, and single quotes: env invocation. (line 268) +* env -S, debugging: env invocation. (line 277) +* env in scripts: env invocation. (line 192) +* environment variables, printing: printenv invocation. (line 6) +* environment, printing: env invocation. (line 50) +* environment, running a program in a modified: env invocation. + (line 6) +* eof: Characters. (line 30) +* eol: Characters. (line 33) +* eol2: Characters. (line 36) +* Epoch, for POSIX: Seconds since the Epoch. + (line 13) +* Epoch, seconds since: Time conversion specifiers. + (line 32) +* equal string check: String tests. (line 22) +* equal string check <1>: String tests. (line 25) +* equivalence classes: Character arrays. (line 133) +* erase: Characters. (line 24) +* erasing data: shred invocation. (line 6) +* error messages, omitting: chown invocation. (line 80) +* error messages, omitting <1>: chgrp invocation. (line 30) +* error messages, omitting <2>: chmod invocation. (line 49) +* evaluation of expressions: expr invocation. (line 6) +* even parity: Control. (line 13) +* evenp: Combination. (line 9) +* exabyte, definition of: Block size. (line 106) +* examples of date: Examples of date. (line 6) +* examples of expr: Examples of expr. (line 6) +* exbibyte, definition of: Block size. (line 109) +* excl: dd invocation. (line 206) +* excluding files from du: du invocation. (line 250) +* excluding files from du <1>: du invocation. (line 255) +* executable file check: Access permission tests. + (line 24) +* executables and file type, marking: General output formatting. + (line 52) +* execute/search permission: Mode Structure. (line 16) +* execute/search permission, symbolic: Setting Permissions. (line 56) +* existence-of-file check: File characteristic tests. + (line 9) +* existing backup method: Backup options. (line 39) +* exit status commands: Conditions. (line 6) +* exit status of chroot: chroot invocation. (line 78) +* exit status of env: env invocation. (line 197) +* exit status of expr: expr invocation. (line 42) +* exit status of false: false invocation. (line 6) +* exit status of ls: ls invocation. (line 29) +* exit status of mktemp: mktemp invocation. (line 128) +* exit status of nice: nice invocation. (line 63) +* exit status of nohup: nohup invocation. (line 48) +* exit status of pathchk: pathchk invocation. (line 47) +* exit status of printenv: printenv invocation. (line 23) +* exit status of realpath: realpath invocation. (line 75) +* exit status of runcon: runcon invocation. (line 50) +* exit status of sort: sort invocation. (line 58) +* exit status of stdbuf: stdbuf invocation. (line 70) +* exit status of test: test invocation. (line 41) +* exit status of timeout: timeout invocation. (line 76) +* exit status of true: true invocation. (line 6) +* exit status of tty: tty invocation. (line 20) +* expand: expand invocation. (line 6) +* expr: expr invocation. (line 6) +* expression evaluation: test invocation. (line 6) +* expression evaluation <1>: expr invocation. (line 6) +* expressions, numeric: Numeric expressions. (line 6) +* expressions, string: String expressions. (line 6) +* ext2 file system type: df invocation. (line 212) +* ext3 file system type: df invocation. (line 212) +* ext4 file system type: df invocation. (line 212) +* extended attributes, xattr: install invocation. (line 34) +* extended attributes, xattr <1>: mv invocation. (line 30) +* extension, sorting files by: Sorting the output. (line 83) +* extproc: Local. (line 61) +* factor: factor invocation. (line 6) +* failure exit status: false invocation. (line 6) +* false: false invocation. (line 6) +* fat file system file: df invocation. (line 220) +* fdatasync: dd invocation. (line 223) +* ffN: Output. (line 63) +* field separator character: sort invocation. (line 338) +* fields, padding numeric: Padding and other flags. + (line 6) +* FIFOs, creating: mkfifo invocation. (line 6) +* file attributes, changing: Changing file attributes. + (line 6) +* file characteristic tests: File characteristic tests. + (line 6) +* file contents, dumping unambiguously: od invocation. (line 6) +* file information, preserving: cp invocation. (line 245) +* file information, preserving, extended attributes, xattr: cp invocation. + (line 173) +* file mode bits, numeric: Numeric Modes. (line 6) +* file name manipulation: File name manipulation. + (line 6) +* file names, canonicalization: realpath invocation. (line 6) +* file names, checking validity and portability: pathchk invocation. + (line 6) +* file names, creating temporary: mktemp invocation. (line 6) +* file names, stripping directory and suffix: basename invocation. + (line 6) +* file offset radix: od invocation. (line 36) +* file ownership, changing: chown invocation. (line 6) +* file sizes: du invocation. (line 54) +* File space usage: File space usage. (line 6) +* file space usage: du invocation. (line 6) +* file status: stat invocation. (line 6) +* file system allocation: What information is listed. + (line 236) +* file system sizes: df invocation. (line 54) +* file system space, retrieving current data more slowly: df invocation. + (line 175) +* file system space, retrieving old data more quickly: df invocation. + (line 85) +* file system status: stat invocation. (line 6) +* file system types, limiting output to certain: df invocation. + (line 81) +* file system types, limiting output to certain <1>: df invocation. + (line 195) +* file system types, printing: df invocation. (line 201) +* file system usage: df invocation. (line 6) +* file systems: stat invocation. (line 28) +* file systems and hard links: ln invocation. (line 6) +* file systems, omitting copying to different: cp invocation. (line 411) +* file timestamp resolution: File timestamps. (line 45) +* file timestamps, changing: touch invocation. (line 6) +* file type and executables, marking: General output formatting. + (line 52) +* file type tests: File type tests. (line 6) +* file type, marking: General output formatting. + (line 68) +* file type, marking <1>: General output formatting. + (line 120) +* file types: Special file types. (line 9) +* file types, special: Special file types. (line 6) +* file utilities: Top. (line 18) +* files beginning with -, removing: rm invocation. (line 102) +* files, copying: cp invocation. (line 6) +* files, creating: truncate invocation. (line 11) +* fingerprint, 128-bit: md5sum invocation. (line 6) +* fingerprint, 160-bit: sha1sum invocation. (line 6) +* fingerprint, 224-bit: sha2 utilities. (line 6) +* fingerprint, 256-bit: sha2 utilities. (line 6) +* fingerprint, 384-bit: sha2 utilities. (line 6) +* fingerprint, 512-bit: b2sum invocation. (line 6) +* fingerprint, 512-bit <1>: sha2 utilities. (line 6) +* first in date strings: General date syntax. (line 22) +* first part of files, outputting: head invocation. (line 6) +* fixed-length records, converting to variable-length: dd invocation. + (line 67) +* floating point: Floating point. (line 6) +* flow control, hardware: Control. (line 41) +* flow control, hardware <1>: Control. (line 44) +* flow control, software: Input. (line 45) +* flush: Characters. (line 39) +* flushing, disabling: Local. (line 32) +* flusho: Local. (line 67) +* fmt: fmt invocation. (line 6) +* fold: fold invocation. (line 6) +* folding long input lines: fold invocation. (line 6) +* footers, numbering: nl invocation. (line 17) +* force deletion: shred invocation. (line 123) +* formatting file contents: Formatting file contents. + (line 6) +* formatting of numbers in seq: seq invocation. (line 29) +* formatting times: pr invocation. (line 78) +* formatting times <1>: Date format specifiers. + (line 6) +* fortnight in date strings: Relative items in date strings. + (line 15) +* fsync: dd invocation. (line 234) +* fullblock: dd invocation. (line 349) +* general date syntax: General date syntax. (line 6) +* general numeric sort: sort invocation. (line 105) +* gibibyte, definition of: Block size. (line 94) +* gigabyte, definition of: Block size. (line 91) +* giving away permissions: Umask and Protection. + (line 12) +* GMT: Options for date. (line 135) +* grand total of file system size, usage and available space: df invocation. + (line 181) +* grand total of file system space: du invocation. (line 63) +* graph: Character arrays. (line 118) +* Greenwich Mean Time: Options for date. (line 135) +* group IDs, disambiguating: Disambiguating names and IDs. + (line 6) +* group names, disambiguating: Disambiguating names and IDs. + (line 6) +* group owner, default: Mode Structure. (line 27) +* group ownership of installed files, setting: install invocation. + (line 77) +* group ownership, changing: chown invocation. (line 6) +* group ownership, changing <1>: chgrp invocation. (line 6) +* group, permissions for: Setting Permissions. (line 25) +* groups: groups invocation. (line 6) +* growing files: tail invocation. (line 57) +* hangups, immunity to: nohup invocation. (line 6) +* hard link check: File characteristic tests. + (line 23) +* hard link, defined: ln invocation. (line 32) +* hard links: dd invocation. (line 338) +* hard links to directories: ln invocation. (line 88) +* hard links to symbolic links: ln invocation. (line 184) +* hard links, counting in du: du invocation. (line 125) +* hard links, creating: link invocation. (line 6) +* hard links, creating <1>: ln invocation. (line 6) +* hard links, preserving: cp invocation. (line 109) +* hardware class: uname invocation. (line 42) +* hardware flow control: Control. (line 41) +* hardware flow control <1>: Control. (line 44) +* hardware platform: uname invocation. (line 35) +* hardware type: uname invocation. (line 42) +* hat notation for control characters: Local. (line 51) +* head: head invocation. (line 6) +* head of output: shuf invocation. (line 31) +* headers, numbering: nl invocation. (line 17) +* help, online: Common options. (line 36) +* hex dump of files: od invocation. (line 6) +* holes, copying files with: cp invocation. (line 306) +* holes, creating files with: truncate invocation. (line 13) +* horizontal, listing files: General output formatting. + (line 125) +* host processor type: uname invocation. (line 51) +* hostid: hostid invocation. (line 6) +* hostname: hostname invocation. (line 6) +* hostname <1>: uname invocation. (line 47) +* hour in date strings: Relative items in date strings. + (line 15) +* human numeric sort: sort invocation. (line 132) +* human-readable output: Block size. (line 42) +* human-readable output <1>: What information is listed. + (line 118) +* human-readable output <2>: df invocation. (line 59) +* human-readable output <3>: du invocation. (line 98) +* hup[cl]: Control. (line 28) +* hurd, author, printing: What information is listed. + (line 10) +* hyperlink, linking to files: General output formatting. + (line 73) +* ibs: dd invocation. (line 52) +* icanon: Local. (line 11) +* icrnl: Input. (line 34) +* id: id invocation. (line 6) +* idle time: who invocation. (line 85) +* IEEE floating point: Floating point. (line 6) +* iexten: Local. (line 15) +* if: dd invocation. (line 45) +* iflag: dd invocation. (line 243) +* ignbrk: Input. (line 9) +* igncr: Input. (line 31) +* ignore file systems: df invocation. (line 42) +* Ignore garbage in base64 stream: base64 invocation. (line 39) +* ignoring case: sort invocation. (line 94) +* ignpar: Input. (line 15) +* imaxbel: Input. (line 59) +* immunity to hangups: nohup invocation. (line 6) +* implementation, hardware: uname invocation. (line 35) +* indenting lines: pr invocation. (line 180) +* index: String expressions. (line 43) +* information, about current users: who invocation. (line 6) +* initial part of files, outputting: head invocation. (line 6) +* initial tabs, converting: expand invocation. (line 46) +* inlcr: Input. (line 28) +* inode number, printing: What information is listed. + (line 125) +* inode usage: df invocation. (line 69) +* inode usage, dereferencing in du: du invocation. (line 104) +* inode, and hard links: ln invocation. (line 32) +* inodes, written buffered: sync invocation. (line 11) +* inpck: Input. (line 22) +* input block size: dd invocation. (line 52) +* input encoding, UTF-8: Input. (line 37) +* input range to shuffle: shuf invocation. (line 23) +* input settings: Input. (line 6) +* input tabs: pr invocation. (line 98) +* install: install invocation. (line 6) +* intr: Characters. (line 18) +* invocation of commands, modified: Modified command invocation. + (line 6) +* iseek: dd invocation. (line 73) +* isig: Local. (line 7) +* ISO 8601 date and time of day format: Combined date and time of day items. + (line 6) +* ISO 8601 date format: Calendar date items. (line 28) +* ISO/IEC 10646: printf invocation. (line 74) +* ISO9660 file system type: df invocation. (line 216) +* iso9660 file system type: df invocation. (line 216) +* ispeed: Special. (line 16) +* istrip: Input. (line 25) +* items in date strings: General date syntax. (line 6) +* iterations, selecting the number of: shred invocation. (line 127) +* iuclc: Input. (line 50) +* iutf8: Input. (line 37) +* ixany: Input. (line 55) +* ixoff: Input. (line 45) +* ixon: Input. (line 40) +* join: join invocation. (line 6) +* kernel name: uname invocation. (line 66) +* kernel release: uname invocation. (line 62) +* kernel version: uname invocation. (line 77) +* kibibyte, definition of: Block size. (line 82) +* kibibytes for file sizes: du invocation. (line 113) +* kibibytes for file system sizes: df invocation. (line 75) +* kill: kill invocation. (line 6) +* kill <1>: Characters. (line 27) +* kilobyte, definition of: Block size. (line 78) +* Knuth, Donald E.: fmt invocation. (line 19) +* language, in dates: General date syntax. (line 36) +* language, in dates <1>: General date syntax. (line 40) +* last DAY: Day of week items. (line 15) +* last DAY <1>: Options for date. (line 15) +* last in date strings: General date syntax. (line 22) +* last modified dates, displaying in du: du invocation. (line 195) +* last part of files, outputting: tail invocation. (line 6) +* lcase: Combination. (line 71) +* LCASE: Combination. (line 71) +* lcase, converting to: dd invocation. (line 172) +* lchown: chown invocation. (line 107) +* lchown <1>: chown invocation. (line 119) +* lchown <2>: chgrp invocation. (line 34) +* lchown <3>: chgrp invocation. (line 46) +* LC_ALL: sort invocation. (line 23) +* LC_ALL <1>: ls invocation. (line 17) +* LC_COLLATE: sort invocation. (line 23) +* LC_COLLATE <1>: uniq invocation. (line 21) +* LC_COLLATE <2>: comm invocation. (line 12) +* LC_COLLATE <3>: Sorting files for join. + (line 16) +* LC_COLLATE <4>: Relations for expr. (line 22) +* LC_CTYPE: sort invocation. (line 79) +* LC_CTYPE <1>: sort invocation. (line 87) +* LC_CTYPE <2>: sort invocation. (line 94) +* LC_CTYPE <3>: sort invocation. (line 149) +* LC_CTYPE <4>: printf invocation. (line 74) +* LC_MESSAGES: pr invocation. (line 13) +* LC_NUMERIC: Block size. (line 57) +* LC_NUMERIC <1>: Floating point. (line 29) +* LC_NUMERIC <2>: sort invocation. (line 105) +* LC_NUMERIC <3>: sort invocation. (line 132) +* LC_NUMERIC <4>: sort invocation. (line 166) +* LC_NUMERIC <5>: printf invocation. (line 61) +* LC_TIME: pr invocation. (line 85) +* LC_TIME <1>: sort invocation. (line 156) +* LC_TIME <2>: Formatting file timestamps. + (line 28) +* LC_TIME <3>: Formatting file timestamps. + (line 73) +* LC_TIME <4>: Formatting file timestamps. + (line 97) +* LC_TIME <5>: du invocation. (line 217) +* LC_TIME <6>: date invocation. (line 15) +* leading directories, creating missing: install invocation. (line 67) +* leading directory components, stripping: basename invocation. + (line 6) +* leap seconds: touch invocation. (line 99) +* leap seconds <1>: Time conversion specifiers. + (line 32) +* leap seconds <2>: Time conversion specifiers. + (line 36) +* leap seconds <3>: Options for date. (line 135) +* leap seconds <4>: Examples of date. (line 104) +* leap seconds <5>: General date syntax. (line 65) +* leap seconds <6>: Time of day items. (line 14) +* leap seconds <7>: Seconds since the Epoch. + (line 27) +* left margin: pr invocation. (line 180) +* length: String expressions. (line 48) +* limiting output of du: du invocation. (line 76) +* line: Special. (line 48) +* line buffered: stdbuf invocation. (line 6) +* line count: wc invocation. (line 6) +* line numbering: nl invocation. (line 6) +* line separator character: split invocation. (line 152) +* line settings of terminal: stty invocation. (line 6) +* line-breaking: fmt invocation. (line 19) +* line-by-line comparison: comm invocation. (line 6) +* LINES: Special. (line 41) +* link: link invocation. (line 6) +* links, creating: link invocation. (line 6) +* links, creating <1>: ln invocation. (line 6) +* Linux file system types: df invocation. (line 212) +* literal conversion specifiers: Literal conversion specifiers. + (line 6) +* litout: Combination. (line 59) +* ln: ln invocation. (line 6) +* ln format for nl: nl invocation. (line 96) +* lnext: Characters. (line 67) +* local file system types: df invocation. (line 212) +* local settings: Local. (line 6) +* logging out and continuing to run: nohup invocation. (line 6) +* logical and operator: Connectives for test. + (line 29) +* logical and operator <1>: Relations for expr. (line 17) +* logical connectives: Connectives for test. + (line 6) +* logical connectives <1>: Relations for expr. (line 6) +* logical or operator: Connectives for test. + (line 33) +* logical or operator <1>: Relations for expr. (line 11) +* logical pages, numbering on: nl invocation. (line 12) +* login name, printing: logname invocation. (line 6) +* login sessions, printing users with: users invocation. (line 6) +* login time: who invocation. (line 11) +* logname: logname invocation. (line 6) +* long ls format: What information is listed. + (line 133) +* lower: Character arrays. (line 120) +* lowercase, translating to output: Output. (line 12) +* ls: ls invocation. (line 6) +* LS_BLOCK_SIZE: Block size. (line 12) +* LS_COLORS: General output formatting. + (line 37) +* LS_COLORS <1>: dircolors invocation. + (line 23) +* lutimes: touch invocation. (line 70) +* machine type: uname invocation. (line 42) +* machine-readable stty output: stty invocation. (line 41) +* MacKenzie, D.: Introduction. (line 29) +* MacKenzie, David: Authors of parse_datetime. + (line 6) +* Makefiles, installing programs in: install invocation. (line 29) +* manipulating files: Basic operations. (line 6) +* manipulation of file names: File name manipulation. + (line 6) +* mark parity: Control. (line 16) +* match: String expressions. (line 34) +* matching patterns: String expressions. (line 11) +* MD5: md5sum invocation. (line 6) +* md5sum: md5sum invocation. (line 6) +* mebibyte, definition of: Block size. (line 89) +* mebibytes for file sizes: du invocation. (line 129) +* megabyte, definition of: Block size. (line 86) +* merging files: paste invocation. (line 6) +* merging files in parallel: pr invocation. (line 6) +* merging sorted files: sort invocation. (line 53) +* message status: who invocation. (line 94) +* message-digest, 128-bit: md5sum invocation. (line 6) +* message-digest, 160-bit: sha1sum invocation. (line 6) +* message-digest, 224-bit: sha2 utilities. (line 6) +* message-digest, 256-bit: sha2 utilities. (line 6) +* message-digest, 384-bit: sha2 utilities. (line 6) +* message-digest, 512-bit: b2sum invocation. (line 6) +* message-digest, 512-bit <1>: sha2 utilities. (line 6) +* Meyering, J.: Introduction. (line 29) +* Meyering, Jim: Authors of parse_datetime. + (line 6) +* midnight in date strings: Time of day items. (line 21) +* min: Special. (line 7) +* minute in date strings: Relative items in date strings. + (line 15) +* minutes, time zone correction by: Time of day items. (line 29) +* mkdir: mkdir invocation. (line 6) +* mkfifo: mkfifo invocation. (line 6) +* mknod: mknod invocation. (line 6) +* mktemp: mktemp invocation. (line 6) +* modem control: Control. (line 38) +* modes and umask: Umask and Protection. + (line 6) +* modes of created directories, setting: mkdir invocation. (line 19) +* modes of created FIFOs, setting: mkfifo invocation. (line 21) +* modification timestamp, sorting files by: Sorting the output. + (line 36) +* modified command invocation: Modified command invocation. + (line 6) +* modified environment, running a program in a: env invocation. + (line 6) +* modify time, changing: touch invocation. (line 85) +* month in date strings: Relative items in date strings. + (line 15) +* month names in date strings: Calendar date items. (line 36) +* months, sorting by: sort invocation. (line 156) +* months, written-out: General date syntax. (line 32) +* MS-DOS file system: df invocation. (line 220) +* MS-Windows file system: df invocation. (line 220) +* mtime: File timestamps. (line 6) +* mtime, changing: touch invocation. (line 85) +* mtime, printing or sorting files by: Sorting the output. (line 50) +* mtime-greater-atime file check: File characteristic tests. + (line 27) +* multicall: Multi-call invocation. + (line 6) +* multicolumn output, generating: pr invocation. (line 6) +* multiple changes to permissions: Multiple Changes. (line 6) +* multiplication: Numeric expressions. (line 16) +* multipliers after numbers: dd invocation. (line 369) +* multithreaded sort: sort invocation. (line 366) +* mv: mv invocation. (line 6) +* name follow option: tail invocation. (line 57) +* name of kernel: uname invocation. (line 66) +* named pipe check: File type tests. (line 28) +* named pipes, creating: mkfifo invocation. (line 6) +* network node name: uname invocation. (line 47) +* networked file systems and du: du invocation. (line 282) +* never interactive option: rm invocation. (line 57) +* newer files, copying only: cp invocation. (line 372) +* newer files, moving only: mv invocation. (line 91) +* newer-than file check: File characteristic tests. + (line 15) +* newline echoing after kill: Local. (line 26) +* newline, echoing: Local. (line 29) +* newline, translating to crlf: Output. (line 19) +* newline, translating to return: Input. (line 28) +* next DAY: Day of week items. (line 15) +* next DAY <1>: Options for date. (line 15) +* next in date strings: General date syntax. (line 22) +* NFS file system type: df invocation. (line 207) +* NFS mounts from BSD to HP-UX: What information is listed. + (line 244) +* nice: nice invocation. (line 6) +* niceness: nice invocation. (line 6) +* nl: nl invocation. (line 6) +* nl <1>: Combination. (line 18) +* nlN: Output. (line 39) +* no dereference: chcon invocation. (line 26) +* no-op: true invocation. (line 6) +* noatime: dd invocation. (line 324) +* nocache: dd invocation. (line 292) +* nocreat: dd invocation. (line 210) +* noctty: dd invocation. (line 330) +* node name: uname invocation. (line 47) +* noerror: dd invocation. (line 220) +* noflsh: Local. (line 32) +* nofollow: dd invocation. (line 335) +* nohup: nohup invocation. (line 6) +* nohup.out: nohup invocation. (line 6) +* nohup.out <1>: nohup invocation. (line 20) +* nolinks: dd invocation. (line 338) +* non-directories, copying as special files: cp invocation. (line 96) +* non-directories, copying as special files <1>: cp invocation. + (line 262) +* non-directory suffix, stripping: dirname invocation. (line 6) +* nonblock: dd invocation. (line 321) +* nonblocking I/O: dd invocation. (line 321) +* nonblocking stty setting: Special. (line 30) +* none backup method: Backup options. (line 31) +* none classify option: General output formatting. + (line 57) +* none color option: General output formatting. + (line 30) +* none dd status=: dd invocation. (line 101) +* none hyperlink option: General output formatting. + (line 75) +* none total option: wc invocation. (line 81) +* none, sorting option for ls: Sorting the output. (line 64) +* nonempty file check: File characteristic tests. + (line 12) +* nonprinting characters, ignoring: sort invocation. (line 149) +* nonzero-length string check: String tests. (line 19) +* noon in date strings: Time of day items. (line 21) +* not-equal string check: String tests. (line 29) +* notrunc: dd invocation. (line 217) +* now in date strings: Relative items in date strings. + (line 33) +* noxfer dd status=: dd invocation. (line 105) +* NO_NEW_PRIVS: runcon invocation. (line 22) +* nproc: nproc invocation. (line 6) +* NTFS file system: df invocation. (line 220) +* ntfs file system file: df invocation. (line 220) +* number of inputs to merge, nmerge: sort invocation. (line 268) +* numbered backup method: Backup options. (line 35) +* numbering lines: nl invocation. (line 6) +* numbers, written-out: General date syntax. (line 22) +* numeric expressions: Numeric expressions. (line 6) +* numeric field padding: Padding and other flags. + (line 6) +* numeric modes: Numeric Modes. (line 6) +* numeric operations: Numeric operations. (line 6) +* numeric sequences: seq invocation. (line 6) +* numeric sort: sort invocation. (line 166) +* numeric tests: Numeric tests. (line 6) +* numeric uid and gid: What information is listed. + (line 227) +* numeric user and group IDs: What information is listed. + (line 227) +* numfmt: numfmt invocation. (line 6) +* obs: dd invocation. (line 56) +* ocrnl: Output. (line 16) +* octal dump of files: od invocation. (line 6) +* octal numbers for file modes: Numeric Modes. (line 6) +* od: od invocation. (line 6) +* odd parity: Control. (line 13) +* oddp: Combination. (line 14) +* of: dd invocation. (line 48) +* ofdel: Output. (line 34) +* ofill: Output. (line 30) +* oflag: dd invocation. (line 247) +* olcuc: Output. (line 12) +* older-than file check: File characteristic tests. + (line 19) +* once interactive option: rm invocation. (line 58) +* one file system, restricting du to: du invocation. (line 261) +* one file system, restricting rm to: rm invocation. (line 66) +* one-line output format: df invocation. (line 149) +* onlcr: Output. (line 19) +* onlret: Output. (line 27) +* only total option: wc invocation. (line 78) +* onocr: Output. (line 23) +* operating on characters: Operating on characters. + (line 6) +* operating on sorted files: Operating on sorted files. + (line 6) +* operating system name: uname invocation. (line 58) +* opost: Output. (line 9) +* option delimiter: Common options. (line 43) +* options for date: Options for date. (line 6) +* or operator: Connectives for test. + (line 33) +* or operator <1>: Relations for expr. (line 11) +* ordinal numbers: General date syntax. (line 22) +* oseek: dd invocation. (line 80) +* ospeed: Special. (line 19) +* other permissions: Setting Permissions. (line 27) +* output block size: dd invocation. (line 56) +* output file name prefix: split invocation. (line 15) +* output file name prefix <1>: csplit invocation. (line 64) +* output file name suffix: csplit invocation. (line 68) +* output format: stat invocation. (line 50) +* output format <1>: stat invocation. (line 59) +* output format, portable: df invocation. (line 149) +* output NUL-byte-terminated lines: cksum common options. + (line 109) +* output NUL-byte-terminated lines <1>: General output formatting. + (line 157) +* output NUL-byte-terminated lines <2>: readlink invocation. (line 65) +* output NUL-byte-terminated lines <3>: du invocation. (line 25) +* output NUL-byte-terminated lines <4>: basename invocation. (line 42) +* output NUL-byte-terminated lines <5>: dirname invocation. (line 31) +* output NUL-byte-terminated lines <6>: realpath invocation. (line 71) +* output NUL-byte-terminated lines <7>: printenv invocation. (line 19) +* output NUL-byte-terminated lines <8>: env invocation. (line 90) +* output of entire files: Output of entire files. + (line 6) +* output of parts of files: Output of parts of files. + (line 6) +* output settings: Output. (line 6) +* output tabs: pr invocation. (line 117) +* overwriting of input, allowed: sort invocation. (line 294) +* overwriting of input, allowed <1>: shuf invocation. (line 36) +* owned by effective group ID check: Access permission tests. + (line 31) +* owned by effective user ID check: Access permission tests. + (line 28) +* owner of file, permissions for: Setting Permissions. (line 23) +* owner, default: Mode Structure. (line 27) +* ownership of installed files, setting: install invocation. (line 95) +* p for FIFO file: mknod invocation. (line 28) +* pad character: Output. (line 34) +* pad instead of timing for delaying: Output. (line 30) +* padding of numeric fields: Padding and other flags. + (line 6) +* paragraphs, reformatting: fmt invocation. (line 6) +* parenb: Control. (line 9) +* parent directories and cp: cp invocation. (line 249) +* parent directories, creating: mkdir invocation. (line 36) +* parent directories, creating missing: install invocation. (line 67) +* parent directories, removing: rmdir invocation. (line 21) +* parentheses for grouping: expr invocation. (line 31) +* parity: Combination. (line 10) +* parity errors, marking: Input. (line 18) +* parity, ignoring: Input. (line 15) +* parmrk: Input. (line 18) +* parodd: Control. (line 13) +* parse_datetime: Date input formats. (line 6) +* parsing date strings: Options for date. (line 15) +* parts of files, output of: Output of parts of files. + (line 6) +* pass8: Combination. (line 55) +* paste: paste invocation. (line 6) +* Paterson, R.: Introduction. (line 29) +* PATH: env invocation. (line 28) +* pathchk: pathchk invocation. (line 6) +* pattern matching: String expressions. (line 11) +* pebibyte, definition of: Block size. (line 104) +* permission tests: Access permission tests. + (line 6) +* permissions of installed files, setting: install invocation. + (line 83) +* permissions, changing access: chmod invocation. (line 6) +* permissions, copying existing: Copying Permissions. (line 6) +* permissions, for changing file timestamps: touch invocation. + (line 21) +* permissions, output by ls: What information is listed. + (line 184) +* petabyte, definition of: Block size. (line 101) +* phone directory order: sort invocation. (line 87) +* pieces, splitting a file into: split invocation. (line 6) +* Pinard, F.: Introduction. (line 29) +* Pinard, F. <1>: Authors of parse_datetime. + (line 19) +* pipe fitting: tee invocation. (line 6) +* Plass, Michael F.: fmt invocation. (line 19) +* platform, hardware: uname invocation. (line 35) +* pm in date strings: Time of day items. (line 21) +* portable file names, checking for: pathchk invocation. (line 6) +* portable output format: df invocation. (line 149) +* POSIX: Introduction. (line 11) +* POSIX output format: df invocation. (line 149) +* POSIXLY_CORRECT: Common options. (line 11) +* POSIXLY_CORRECT <1>: Standards conformance. + (line 6) +* POSIXLY_CORRECT <2>: pr invocation. (line 85) +* POSIXLY_CORRECT <3>: sort invocation. (line 305) +* POSIXLY_CORRECT <4>: sort invocation. (line 421) +* POSIXLY_CORRECT <5>: dd invocation. (line 441) +* POSIXLY_CORRECT <6>: echo invocation. (line 72) +* POSIXLY_CORRECT <7>: printf invocation. (line 53) +* POSIXLY_CORRECT <8>: id invocation. (line 15) +* POSIXLY_CORRECT, and block size: Block size. (line 12) +* pr: pr invocation. (line 6) +* prime factors: factor invocation. (line 6) +* print: Character arrays. (line 122) +* print machine hardware name: arch invocation. (line 6) +* print name of current directory: pwd invocation. (line 6) +* print system information: uname invocation. (line 6) +* print terminal file name: tty invocation. (line 6) +* Print the number of processors: nproc invocation. (line 6) +* printenv: printenv invocation. (line 6) +* printf: printf invocation. (line 6) +* printing all or some environment variables: printenv invocation. + (line 6) +* printing color database: dircolors invocation. + (line 45) +* printing current user information: who invocation. (line 6) +* printing current usernames: users invocation. (line 6) +* printing groups a user is in: groups invocation. (line 6) +* printing ls colors: dircolors invocation. + (line 50) +* printing real and effective user and group IDs: id invocation. + (line 6) +* printing text: echo invocation. (line 6) +* printing text, commands for: Printing text. (line 6) +* printing the current time: date invocation. (line 6) +* printing the effective user ID: whoami invocation. (line 6) +* printing the host identifier: hostid invocation. (line 6) +* printing the hostname: hostname invocation. (line 6) +* printing the system uptime and load: uptime invocation. (line 6) +* printing user’s login name: logname invocation. (line 6) +* printing, preparing files for: pr invocation. (line 6) +* process zero-terminated items: head invocation. (line 55) +* process zero-terminated items <1>: tail invocation. (line 190) +* process zero-terminated items <2>: sort invocation. (line 389) +* process zero-terminated items <3>: shuf invocation. (line 55) +* process zero-terminated items <4>: uniq invocation. (line 140) +* process zero-terminated items <5>: comm invocation. (line 89) +* process zero-terminated items <6>: cut invocation. (line 94) +* process zero-terminated items <7>: paste invocation. (line 72) +* process zero-terminated items <8>: General options in join. + (line 93) +* process zero-terminated items <9>: numfmt invocation. (line 115) +* processes, commands for controlling: Process control. (line 6) +* progress dd status=: dd invocation. (line 109) +* prompting, and ln: ln invocation. (line 98) +* prompting, and mv: mv invocation. (line 34) +* prompting, and rm: rm invocation. (line 11) +* prompts, forcing: mv invocation. (line 71) +* prompts, omitting: mv invocation. (line 65) +* prompts, omitting <1>: mv invocation. (line 78) +* prterase: Local. (line 46) +* ptx: ptx invocation. (line 6) +* punct: Character arrays. (line 124) +* pure numbers in date strings: Pure numbers in date strings. + (line 6) +* pwd: pwd invocation. (line 6) +* quettabyte, definition of: Block size. (line 126) +* quit: Characters. (line 21) +* quoting style: Formatting the file names. + (line 34) +* radix for file offsets: od invocation. (line 36) +* random seed: Random sources. (line 31) +* random sort: sort invocation. (line 195) +* random source for shredding: shred invocation. (line 133) +* random source for shuffling: shuf invocation. (line 42) +* random source for sorting: sort invocation. (line 310) +* random sources: Random sources. (line 6) +* ranges: Character arrays. (line 65) +* raw: Combination. (line 43) +* raw binary checksum: cksum general options. + (line 45) +* read errors, ignoring: dd invocation. (line 220) +* read from standard input and write to standard output and files: tee invocation. + (line 6) +* read permission: Mode Structure. (line 12) +* read permission, symbolic: Setting Permissions. (line 52) +* read system call, and holes: cp invocation. (line 306) +* readable file check: Access permission tests. + (line 15) +* readlink: readlink invocation. (line 6) +* real user and group IDs, printing: id invocation. (line 6) +* realpath: realpath invocation. (line 6) +* realpath <1>: realpath invocation. (line 6) +* realpath <2>: realpath invocation. (line 6) +* realpath <3>: readlink invocation. (line 6) +* record separator character: split invocation. (line 152) +* recursive directory listing: Which files are listed. + (line 91) +* recursively changing access permissions: chmod invocation. (line 73) +* recursively changing file ownership: chown invocation. (line 151) +* recursively changing group ownership: chgrp invocation. (line 77) +* recursively copying directories: cp invocation. (line 96) +* recursively copying directories <1>: cp invocation. (line 262) +* redirection: Redirection. (line 6) +* reference file: chcon invocation. (line 30) +* reformatting paragraph text: fmt invocation. (line 6) +* regular expression matching: String expressions. (line 11) +* regular file check: File type tests. (line 19) +* relations, numeric or string: Relations for expr. (line 6) +* relative items in date strings: Relative items in date strings. + (line 6) +* release of kernel: uname invocation. (line 62) +* relpath: realpath invocation. (line 49) +* remainder: Numeric expressions. (line 16) +* remote hostname: who invocation. (line 11) +* removing characters: Squeezing and deleting. + (line 6) +* removing empty directories: rmdir invocation. (line 6) +* removing files after shredding: shred invocation. (line 144) +* removing files or directories: rm invocation. (line 6) +* removing files or directories (via the unlink syscall): unlink invocation. + (line 6) +* removing permissions: Setting Permissions. (line 38) +* renaming files without copying them: mv invocation. (line 85) +* repeat output values: shuf invocation. (line 47) +* repeated characters: Character arrays. (line 85) +* repeated lines, outputting: uniq invocation. (line 64) +* repeated output of a string: yes invocation. (line 6) +* restricted deletion flag: Mode Structure. (line 52) +* restricted security context: runcon invocation. (line 22) +* return, ignoring: Input. (line 31) +* return, translating to newline: Input. (line 34) +* return, translating to newline <1>: Output. (line 16) +* reverse sorting: sort invocation. (line 189) +* reverse sorting <1>: Sorting the output. (line 25) +* reversing files: tac invocation. (line 6) +* rm: rm invocation. (line 6) +* rmdir: rmdir invocation. (line 6) +* rn format for nl: nl invocation. (line 98) +* ronnabyte, definition of: Block size. (line 121) +* root as default owner: install invocation. (line 95) +* root directory, allow recursive destruction: rm invocation. (line 89) +* root directory, allow recursive modification: chown invocation. + (line 132) +* root directory, allow recursive modification <1>: chgrp invocation. + (line 59) +* root directory, allow recursive modification <2>: chmod invocation. + (line 58) +* root directory, disallow recursive destruction: rm invocation. + (line 82) +* root directory, disallow recursive modification: chown invocation. + (line 127) +* root directory, disallow recursive modification <1>: chgrp invocation. + (line 54) +* root directory, disallow recursive modification <2>: chmod invocation. + (line 53) +* root directory, running a program in a specified: chroot invocation. + (line 6) +* rows: Special. (line 22) +* rprnt: Characters. (line 61) +* RTS/CTS flow control: Control. (line 41) +* run commands with bounded time: timeout invocation. (line 6) +* run with security context: runcon invocation. (line 6) +* runcon: runcon invocation. (line 6) +* running a program in a modified environment: env invocation. + (line 6) +* running a program in a specified root directory: chroot invocation. + (line 6) +* rz format for nl: nl invocation. (line 100) +* Salz, Rich: Authors of parse_datetime. + (line 6) +* same file check: File characteristic tests. + (line 23) +* sane: Combination. (line 26) +* scheduling, affecting: nice invocation. (line 6) +* screen columns: fold invocation. (line 14) +* scripts arguments: env invocation. (line 192) +* seconds since the Epoch: Time conversion specifiers. + (line 32) +* section delimiters of pages: nl invocation. (line 63) +* security context: What information is listed. + (line 259) +* security context <1>: cp invocation. (line 417) +* security context <2>: install invocation. (line 100) +* security context <3>: install invocation. (line 143) +* security context <4>: mv invocation. (line 144) +* security context <5>: mkdir invocation. (line 59) +* security context <6>: mkfifo invocation. (line 28) +* security context <7>: mknod invocation. (line 53) +* security context <8>: id invocation. (line 51) +* seek: dd invocation. (line 80) +* self-backups: cp invocation. (line 51) +* SELinux: What information is listed. + (line 259) +* SELinux <1>: install invocation. (line 100) +* SELinux <2>: id invocation. (line 51) +* SELinux context: SELinux context. (line 6) +* SELinux, context: SELinux context. (line 6) +* SELinux, restoring security context: mv invocation. (line 144) +* SELinux, setting/restoring security context: cp invocation. (line 417) +* SELinux, setting/restoring security context <1>: install invocation. + (line 143) +* SELinux, setting/restoring security context <2>: mkdir invocation. + (line 59) +* SELinux, setting/restoring security context <3>: mkfifo invocation. + (line 28) +* SELinux, setting/restoring security context <4>: mknod invocation. + (line 53) +* send a signal to processes: kill invocation. (line 6) +* sentences and line-breaking: fmt invocation. (line 19) +* separator for numbers in seq: seq invocation. (line 45) +* seq: seq invocation. (line 6) +* sequence of numbers: seq invocation. (line 6) +* set-group-ID: Mode Structure. (line 45) +* set-group-ID check: Access permission tests. + (line 9) +* set-user-ID: Mode Structure. (line 39) +* set-user-ID check: Access permission tests. + (line 18) +* setgid: Mode Structure. (line 45) +* setting permissions: Setting Permissions. (line 41) +* setting the hostname: hostname invocation. (line 6) +* setting the time: Setting the time. (line 6) +* setuid: Mode Structure. (line 39) +* setup for color: dircolors invocation. + (line 6) +* sh syntax for color setup: dircolors invocation. + (line 34) +* SHA-1: sha1sum invocation. (line 6) +* SHA-2: sha2 utilities. (line 6) +* sha1sum: sha1sum invocation. (line 6) +* sha224sum: sha2 utilities. (line 6) +* sha256sum: sha2 utilities. (line 6) +* sha384sum: sha2 utilities. (line 6) +* sha512sum: sha2 utilities. (line 6) +* shebang arguments: env invocation. (line 192) +* SHELL environment variable, and color: General output formatting. + (line 37) +* SHELL environment variable, and color <1>: dircolors invocation. + (line 23) +* shell utilities: Top. (line 18) +* shred: shred invocation. (line 6) +* shuf: shuf invocation. (line 6) +* shuffling files: shuf invocation. (line 6) +* SI output: Block size. (line 42) +* SI output <1>: What information is listed. + (line 251) +* SI output <2>: df invocation. (line 168) +* SI output <3>: du invocation. (line 147) +* signals, specifying: Signal specifications. + (line 6) +* simple backup method: Backup options. (line 44) +* SIMPLE_BACKUP_SUFFIX: Backup options. (line 49) +* single quotes, and env -S: env invocation. (line 268) +* single-column output of files: General output formatting. + (line 9) +* size: Special. (line 41) +* size for main memory sorting: sort invocation. (line 322) +* size of file to shred: shred invocation. (line 138) +* size of files, reporting: What information is listed. + (line 236) +* size of files, sorting files by: Sorting the output. (line 32) +* skip: dd invocation. (line 73) +* sleep: sleep invocation. (line 6) +* socket check: File type tests. (line 31) +* software flow control: Input. (line 45) +* sort: sort invocation. (line 6) +* sort field: sort invocation. (line 237) +* sort stability: sort invocation. (line 12) +* sort stability <1>: sort invocation. (line 315) +* sort’s last-resort comparison: sort invocation. (line 12) +* sort’s last-resort comparison <1>: sort invocation. (line 315) +* sorted files, operations on: Operating on sorted files. + (line 6) +* sorting files: sort invocation. (line 6) +* sorting ls output: Sorting the output. (line 6) +* space: Character arrays. (line 126) +* space parity: Control. (line 16) +* sparse: dd invocation. (line 180) +* sparse files, copying: cp invocation. (line 306) +* sparse files, creating: truncate invocation. (line 13) +* special characters: Characters. (line 6) +* special file types: Special file types. (line 6) +* special file types <1>: Special file types. (line 9) +* special files: mknod invocation. (line 11) +* special settings: Special. (line 6) +* speed: Special. (line 51) +* split: split invocation. (line 6) +* splitting a file into pieces: split invocation. (line 6) +* splitting a file into pieces by context: csplit invocation. (line 6) +* squeezing blank lines: cat invocation. (line 37) +* squeezing empty lines: cat invocation. (line 37) +* squeezing repeat characters: Squeezing and deleting. + (line 6) +* Stallman, R.: Introduction. (line 29) +* standard input: Common options. (line 47) +* standard output: Common options. (line 47) +* standard streams, buffering: stdbuf invocation. (line 6) +* start: Characters. (line 49) +* stat: stat invocation. (line 6) +* status: dd invocation. (line 96) +* status <1>: Characters. (line 45) +* status time, printing or sorting by: Sorting the output. (line 13) +* status time, show the most recent: du invocation. (line 202) +* stdbuf: stdbuf invocation. (line 6) +* stick parity: Control. (line 16) +* sticky: Mode Structure. (line 52) +* sticky bit check: Access permission tests. + (line 12) +* stop: Characters. (line 52) +* stop bits: Control. (line 32) +* storage devices, failing: dd invocation. (line 397) +* strftime and date: Date format specifiers. + (line 6) +* string constants, outputting: od invocation. (line 81) +* string expressions: String expressions. (line 6) +* string tests: String tests. (line 6) +* strip directory and suffix from file names: basename invocation. + (line 6) +* stripping non-directory suffix: dirname invocation. (line 6) +* stripping symbol table information: install invocation. (line 117) +* stripping trailing slashes: cp invocation. (line 345) +* stripping trailing slashes <1>: mv invocation. (line 125) +* stty: stty invocation. (line 6) +* substr: String expressions. (line 38) +* subtracting permissions: Setting Permissions. (line 38) +* subtraction: Numeric expressions. (line 12) +* successful exit: true invocation. (line 6) +* suffix, stripping from file names: basename invocation. (line 6) +* sum: sum invocation. (line 6) +* summarizing files: Summarizing files. (line 6) +* superblock, writing: sync invocation. (line 11) +* supplementary groups, printing: groups invocation. (line 6) +* susp: Characters. (line 55) +* swab (byte-swapping): dd invocation. (line 195) +* swap space, saving text image in: Mode Structure. (line 52) +* swtch: Characters. (line 42) +* symbol table information, stripping: install invocation. (line 117) +* symbol table information, stripping, program: install invocation. + (line 120) +* symbolic (soft) links, creating: ln invocation. (line 6) +* symbolic link check: File type tests. (line 23) +* symbolic link to directory, controlling traversal of: Traversing symlinks. + (line 6) +* symbolic link to directory, never traverse: Traversing symlinks. + (line 26) +* symbolic link to directory, never traverse <1>: chown invocation. + (line 172) +* symbolic link to directory, never traverse <2>: chgrp invocation. + (line 99) +* symbolic link to directory, never traverse <3>: chcon invocation. + (line 56) +* symbolic link to directory, traverse each that is encountered: Traversing symlinks. + (line 22) +* symbolic link to directory, traverse each that is encountered <1>: chown invocation. + (line 159) +* symbolic link to directory, traverse each that is encountered <2>: chgrp invocation. + (line 86) +* symbolic link to directory, traverse each that is encountered <3>: chcon invocation. + (line 52) +* symbolic link to directory, traverse if on the command line: Traversing symlinks. + (line 18) +* symbolic link to directory, traverse if on the command line <1>: chown invocation. + (line 154) +* symbolic link to directory, traverse if on the command line <2>: chgrp invocation. + (line 81) +* symbolic link to directory, traverse if on the command line <3>: chcon invocation. + (line 47) +* symbolic link, defined: ln invocation. (line 42) +* symbolic links and ln: ln invocation. (line 184) +* symbolic links and pwd: pwd invocation. (line 26) +* symbolic links, changing group: chgrp invocation. (line 46) +* symbolic links, changing owner: chown invocation. (line 84) +* symbolic links, changing owner <1>: chown invocation. (line 107) +* symbolic links, changing owner <2>: chown invocation. (line 119) +* symbolic links, changing owner <3>: chgrp invocation. (line 34) +* symbolic links, changing time: touch invocation. (line 70) +* symbolic links, copying: cp invocation. (line 109) +* symbolic links, copying <1>: cp invocation. (line 166) +* symbolic links, copying with: cp invocation. (line 350) +* symbolic links, dereferencing: Which files are listed. + (line 36) +* symbolic links, dereferencing <1>: Which files are listed. + (line 41) +* symbolic links, dereferencing <2>: Which files are listed. + (line 84) +* symbolic links, dereferencing in du: du invocation. (line 119) +* symbolic links, dereferencing in du <1>: du invocation. (line 135) +* symbolic links, dereferencing in stat: stat invocation. (line 22) +* symbolic links, following: dd invocation. (line 335) +* symbolic links, permissions of: chmod invocation. (line 10) +* symbolic modes: Symbolic Modes. (line 6) +* symlinks, resolution: realpath invocation. (line 6) +* sync: sync invocation. (line 6) +* sync <1>: dd invocation. (line 289) +* sync (padding with ASCII NULs): dd invocation. (line 198) +* Synchronize cached writes to persistent storage: sync invocation. + (line 6) +* synchronize file system and memory: sync invocation. (line 6) +* synchronized data and metadata I/O: dd invocation. (line 289) +* synchronized data and metadata writes, before finishing: dd invocation. + (line 234) +* synchronized data reads: dd invocation. (line 281) +* synchronized data writes, before finishing: dd invocation. (line 223) +* system context: System context. (line 6) +* system information, printing: arch invocation. (line 6) +* system information, printing <1>: nproc invocation. (line 6) +* system information, printing <2>: uname invocation. (line 6) +* system name, printing: hostname invocation. (line 6) +* System V sum: sum invocation. (line 29) +* tab stops, setting: expand invocation. (line 22) +* tabN: Output. (line 51) +* tabs: Combination. (line 66) +* tabs to spaces, converting: expand invocation. (line 6) +* tac: tac invocation. (line 6) +* tagged paragraphs: fmt invocation. (line 40) +* tail: tail invocation. (line 6) +* tandem: Input. (line 45) +* target directory: Target directory. (line 6) +* target directory <1>: Target directory. (line 15) +* target directory <2>: Target directory. (line 31) +* target directory <3>: cp invocation. (line 363) +* target directory <4>: cp invocation. (line 367) +* target directory <5>: install invocation. (line 129) +* target directory <6>: install invocation. (line 134) +* target directory <7>: mv invocation. (line 135) +* target directory <8>: mv invocation. (line 139) +* target directory <9>: ln invocation. (line 173) +* target directory <10>: ln invocation. (line 177) +* tebibyte, definition of: Block size. (line 99) +* tee: tee invocation. (line 6) +* telephone directory order: sort invocation. (line 87) +* temporary directory: sort invocation. (line 358) +* temporary files and directories: mktemp invocation. (line 6) +* terabyte, definition of: Block size. (line 96) +* terminal check: File type tests. (line 34) +* terminal file name, printing: tty invocation. (line 6) +* terminal lines, currently used: who invocation. (line 11) +* terminal settings: stty invocation. (line 6) +* terminal, using classify iff: General output formatting. + (line 58) +* terminal, using color iff: General output formatting. + (line 31) +* terminal, using hyperlink iff: General output formatting. + (line 76) +* terse output: stat invocation. (line 70) +* test: test invocation. (line 6) +* text: dd invocation. (line 345) +* text I/O: dd invocation. (line 345) +* text image, saving in swap space: Mode Structure. (line 52) +* text input files: cksum common options. + (line 89) +* text utilities: Top. (line 18) +* text, displaying: echo invocation. (line 6) +* text, reformatting: fmt invocation. (line 6) +* this in date strings: Relative items in date strings. + (line 33) +* time: touch invocation. (line 56) +* time <1>: Special. (line 11) +* time conversion specifiers: Time conversion specifiers. + (line 6) +* time formats: pr invocation. (line 78) +* time formats <1>: Date format specifiers. + (line 6) +* time limit: timeout invocation. (line 6) +* time of day item: Time of day items. (line 6) +* time setting: Setting the time. (line 6) +* time style: Formatting file timestamps. + (line 24) +* time style <1>: du invocation. (line 212) +* time units: timeout invocation. (line 66) +* time units <1>: sleep invocation. (line 11) +* time zone correction: Time of day items. (line 29) +* time zone item: General date syntax. (line 40) +* time zone item <1>: Time zone items. (line 6) +* time, printing or setting: date invocation. (line 6) +* timeout: timeout invocation. (line 6) +* timestamps of installed files, preserving: install invocation. + (line 107) +* timestamps, changing file: touch invocation. (line 6) +* TIME_STYLE: Formatting file timestamps. + (line 103) +* TIME_STYLE <1>: du invocation. (line 240) +* TMPDIR: sort invocation. (line 64) +* TMPDIR <1>: sort invocation. (line 358) +* today in date strings: Relative items in date strings. + (line 33) +* tomorrow: Options for date. (line 15) +* tomorrow in date strings: Relative items in date strings. + (line 29) +* topological sort: tsort invocation. (line 6) +* tostop: Local. (line 41) +* total counts: wc invocation. (line 13) +* touch: touch invocation. (line 6) +* tr: tr invocation. (line 6) +* trailing slashes: Trailing slashes. (line 6) +* translating characters: Translating. (line 6) +* true: true invocation. (line 6) +* truncate: truncate invocation. (line 6) +* truncating output file, avoiding: dd invocation. (line 217) +* truncating, file sizes: truncate invocation. (line 6) +* tsort: tsort invocation. (line 6) +* tty: tty invocation. (line 6) +* two-way parity: Control. (line 9) +* type size: od invocation. (line 122) +* TZ: pr invocation. (line 91) +* TZ <1>: Formatting file timestamps. + (line 17) +* TZ <2>: touch invocation. (line 35) +* TZ <3>: stat invocation. (line 220) +* TZ <4>: who invocation. (line 26) +* TZ <5>: date invocation. (line 20) +* TZ <6>: Options for date. (line 135) +* TZ <7>: Specifying time zone rules. + (line 6) +* u, and disabling special characters: Characters. (line 12) +* ucase, converting to: dd invocation. (line 175) +* umask and modes: Umask and Protection. + (line 6) +* uname: uname invocation. (line 6) +* unblock: dd invocation. (line 164) +* unexpand: unexpand invocation. (line 6) +* Unicode: printf invocation. (line 74) +* uniq: uniq invocation. (line 6) +* unique lines, outputting: uniq invocation. (line 128) +* uniquify files: uniq invocation. (line 6) +* uniquifying output: sort invocation. (line 374) +* Universal Time: Options for date. (line 135) +* unlink: unlink invocation. (line 6) +* unprintable characters, ignoring: sort invocation. (line 149) +* unsorted directory listing: Sorting the output. (line 18) +* upper: Character arrays. (line 128) +* uppercase, translating to lowercase: Input. (line 50) +* uptime: uptime invocation. (line 6) +* use time, changing: touch invocation. (line 48) +* use time, printing or sorting files by: Sorting the output. (line 13) +* use time, printing or sorting files by <1>: Sorting the output. + (line 44) +* use time, show the most recent: du invocation. (line 202) +* user IDs, disambiguating: Disambiguating names and IDs. + (line 6) +* user information, commands for: User information. (line 6) +* user name, printing: logname invocation. (line 6) +* user names, disambiguating: Disambiguating names and IDs. + (line 6) +* usernames, printing current: users invocation. (line 6) +* users: users invocation. (line 6) +* UTC: Options for date. (line 135) +* utmp: logname invocation. (line 6) +* utmp <1>: users invocation. (line 14) +* utmp <2>: who invocation. (line 15) +* valid file names, checking for: pathchk invocation. (line 6) +* variable-length records, converting to fixed-length: dd invocation. + (line 67) +* vdir: vdir invocation. (line 6) +* verbose ls format: What information is listed. + (line 133) +* verifying checksums: cksum common options. + (line 54) +* verifying checksums <1>: cksum common options. + (line 60) +* verifying checksums <2>: cksum common options. + (line 68) +* verifying checksums <3>: cksum common options. + (line 99) +* verifying checksums <4>: cksum common options. + (line 104) +* version number sort: sort invocation. (line 183) +* version number, finding: Common options. (line 40) +* version of kernel: uname invocation. (line 77) +* version, sorting option for ls: Sorting the output. (line 71) +* version-control Emacs variable: Backup options. (line 24) +* VERSION_CONTROL: Backup options. (line 13) +* VERSION_CONTROL <1>: cp invocation. (line 79) +* VERSION_CONTROL <2>: install invocation. (line 41) +* VERSION_CONTROL <3>: mv invocation. (line 56) +* VERSION_CONTROL <4>: ln invocation. (line 82) +* vertical sorted files in columns: General output formatting. + (line 21) +* vtN: Output. (line 59) +* wc: wc invocation. (line 6) +* week in date strings: Relative items in date strings. + (line 15) +* werase: Characters. (line 64) +* who: who invocation. (line 6) +* who am i: who invocation. (line 21) +* whoami: whoami invocation. (line 6) +* width, sorting option for ls: Sorting the output. (line 77) +* word count: wc invocation. (line 6) +* working context: Working context. (line 6) +* working directory, printing: pwd invocation. (line 6) +* wrap data: base64 invocation. (line 25) +* wrapping long input lines: fold invocation. (line 6) +* writable file check: Access permission tests. + (line 21) +* write permission: Mode Structure. (line 14) +* write permission, symbolic: Setting Permissions. (line 54) +* write, allowed: who invocation. (line 94) +* wtmp: users invocation. (line 14) +* wtmp <1>: who invocation. (line 15) +* xcase: Local. (line 36) +* xdigit: Character arrays. (line 130) +* xfs file system type: df invocation. (line 212) +* XON/XOFF flow control: Input. (line 40) +* year in date strings: Relative items in date strings. + (line 15) +* yes: yes invocation. (line 6) +* yesterday: Options for date. (line 15) +* yesterday in date strings: Relative items in date strings. + (line 29) +* yottabyte, definition of: Block size. (line 116) +* Youmans, B.: Introduction. (line 29) +* zero-length string check: String tests. (line 15) +* zettabyte, definition of: Block size. (line 111) + + + +Tag Table: +Node: Top8616 +Node: Introduction23304 +Node: Common options25185 +Node: Backup options28636 +Node: Block size30662 +Node: Signal specifications36347 +Node: Disambiguating names and IDs38513 +Node: Random sources40157 +Node: Target directory42166 +Node: Trailing slashes45816 +Node: Traversing symlinks46855 +Node: Treating / specially47985 +Node: Special built-in utilities49617 +Node: Exit status50806 +Node: Floating point51681 +Node: Standards conformance53543 +Node: Multi-call invocation55277 +Node: Output of entire files55839 +Node: cat invocation56576 +Node: tac invocation58574 +Node: nl invocation60007 +Node: od invocation64287 +Node: base32 invocation72123 +Node: base64 invocation72722 +Node: basenc invocation74296 +Node: Formatting file contents77979 +Node: fmt invocation78430 +Node: pr invocation81423 +Node: fold invocation93699 +Node: Output of parts of files95214 +Node: head invocation95711 +Node: tail invocation98657 +Node: split invocation109890 +Node: csplit invocation118398 +Node: Summarizing files123884 +Node: wc invocation124595 +Node: sum invocation129058 +Node: cksum invocation130398 +Node: cksum output modes131551 +Node: cksum general options133473 +Node: cksum common options136178 +Node: md5sum invocation141927 +Node: b2sum invocation143455 +Node: sha1sum invocation144515 +Node: sha2 utilities145929 +Node: Operating on sorted files146799 +Node: sort invocation147386 +Ref: sort invocation-Footnote-1173774 +Node: shuf invocation174384 +Node: uniq invocation177585 +Node: comm invocation183726 +Node: ptx invocation187828 +Node: General options in ptx190662 +Node: Charset selection in ptx191262 +Node: Input processing in ptx192170 +Node: Output formatting in ptx197715 +Node: Compatibility in ptx204551 +Node: tsort invocation207934 +Node: tsort background211138 +Node: Operating on fields212846 +Node: cut invocation213208 +Node: paste invocation217988 +Node: join invocation220160 +Node: General options in join221624 +Node: Sorting files for join226832 +Node: Working with fields228542 +Ref: Working with fields-Footnote-1230124 +Node: Paired and unpaired lines230222 +Node: Header lines233160 +Node: Set operations234071 +Node: Operating on characters235591 +Node: tr invocation236014 +Node: Character arrays237872 +Node: Translating244093 +Node: Squeezing and deleting246250 +Node: expand invocation249240 +Node: unexpand invocation251408 +Node: Directory listing253929 +Node: ls invocation254427 +Ref: ls invocation-Footnote-1256594 +Node: Which files are listed256838 +Node: What information is listed260866 +Node: Sorting the output270742 +Node: General output formatting273930 +Node: Formatting file timestamps281563 +Node: Formatting the file names287166 +Node: dir invocation290522 +Node: vdir invocation290949 +Node: dircolors invocation291374 +Node: Basic operations293308 +Node: cp invocation293928 +Node: dd invocation313748 +Node: install invocation333088 +Node: mv invocation339574 +Node: rm invocation345819 +Node: shred invocation350736 +Node: Special file types361099 +Node: link invocation362630 +Node: ln invocation363887 +Node: mkdir invocation373043 +Node: mkfifo invocation376098 +Node: mknod invocation377573 +Node: readlink invocation380122 +Node: rmdir invocation382681 +Node: unlink invocation384301 +Node: Changing file attributes385295 +Node: chown invocation386121 +Node: chgrp invocation393591 +Node: chmod invocation397833 +Node: touch invocation401350 +Node: File space usage407061 +Node: df invocation407765 +Node: du invocation417602 +Node: stat invocation429725 +Node: sync invocation439469 +Node: truncate invocation441661 +Node: Printing text443719 +Node: echo invocation444099 +Node: printf invocation447352 +Node: yes invocation453398 +Node: Conditions454050 +Node: false invocation454645 +Node: true invocation455734 +Node: test invocation457067 +Node: File type tests459240 +Node: Access permission tests460159 +Node: File characteristic tests461073 +Node: String tests461964 +Node: Numeric tests462803 +Node: Connectives for test463638 +Node: expr invocation464892 +Node: String expressions467359 +Node: Numeric expressions470026 +Node: Relations for expr470734 +Node: Examples of expr471963 +Node: Redirection472712 +Node: tee invocation473179 +Node: File name manipulation480274 +Node: basename invocation480849 +Node: dirname invocation483068 +Node: pathchk invocation484885 +Node: mktemp invocation486699 +Node: realpath invocation492517 +Node: Realpath usage examples495580 +Node: Working context497395 +Node: pwd invocation498039 +Node: stty invocation499460 +Node: Control502445 +Node: Input503521 +Node: Output505275 +Node: Local506693 +Node: Combination508780 +Node: Characters511192 +Node: Special513027 +Node: printenv invocation515425 +Node: tty invocation516436 +Node: User information517170 +Node: id invocation517805 +Node: logname invocation520518 +Node: whoami invocation521175 +Node: groups invocation521686 +Node: users invocation522921 +Node: who invocation524101 +Node: System context527436 +Node: date invocation528101 +Node: Date format specifiers529444 +Node: Time conversion specifiers530302 +Node: Date conversion specifiers533049 +Node: Literal conversion specifiers536525 +Node: Padding and other flags536908 +Node: Setting the time540538 +Node: Options for date541701 +Node: Examples of date547351 +Ref: %s-examples548853 +Node: arch invocation552125 +Node: nproc invocation552684 +Node: uname invocation553904 +Node: hostname invocation556632 +Node: hostid invocation557462 +Node: uptime invocation558335 +Node: SELinux context559817 +Node: chcon invocation560192 +Node: runcon invocation562597 +Node: Modified command invocation564378 +Node: chroot invocation565070 +Ref: chroot invocation-Footnote-1568964 +Node: env invocation569481 +Node: nice invocation586342 +Node: nohup invocation590475 +Node: stdbuf invocation592977 +Node: timeout invocation595929 +Node: Process control600721 +Node: kill invocation600944 +Node: Delaying604138 +Node: sleep invocation604335 +Node: Numeric operations605751 +Node: factor invocation606136 +Node: numfmt invocation608104 +Node: seq invocation620199 +Node: File permissions624597 +Node: Mode Structure625290 +Node: Symbolic Modes628969 +Node: Setting Permissions630087 +Node: Copying Permissions632753 +Node: Changing Special Mode Bits633623 +Node: Conditional Executability635505 +Node: Multiple Changes636057 +Node: Umask and Protection637730 +Node: Numeric Modes638875 +Node: Operator Numeric Modes641221 +Node: Directory Setuid and Setgid642281 +Node: File timestamps645136 +Node: Date input formats648459 +Node: General date syntax650948 +Node: Calendar date items654080 +Node: Time of day items656075 +Node: Time zone items658379 +Node: Combined date and time of day items659780 +Node: Day of week items660651 +Node: Relative items in date strings661735 +Node: Pure numbers in date strings664653 +Node: Seconds since the Epoch665642 +Node: Specifying time zone rules667373 +Node: Authors of parse_datetime670988 +Ref: Authors of get_date671179 +Node: Version sort ordering672178 +Node: Version sort overview672499 +Node: Using version sort in GNU Coreutils673511 +Node: Version sort and natural sort675027 +Node: Variations in version sort order675901 +Node: Version sort implementation676681 +Node: Version-sort ordering rules677492 +Node: Version sort is not the same as numeric sort680289 +Node: Version sort punctuation682327 +Node: Punctuation vs letters683958 +Node: The tilde ~684797 +Node: Version sort ignores locale686156 +Node: Differences from Debian version sort687252 +Node: Hyphen-minus and colon687833 +Node: Special priority in GNU Coreutils version sort689464 +Node: Special handling of file extensions690640 +Node: Comparing two strings using Debian's algorithm695713 +Node: Advanced version sort topics697631 +Node: Reporting version sort bugs697921 +Node: Other version/natural sort implementations699126 +Node: Related source code701275 +Node: Opening the software toolbox702041 +Node: Toolbox introduction702839 +Node: I/O redirection705591 +Node: The who command708479 +Node: The cut command709404 +Node: The sort command710506 +Node: The uniq command711224 +Node: Putting the tools together711939 +Node: GNU Free Documentation License724276 +Node: Concept index749655 + +End Tag Table + + +Local Variables: +coding: utf-8 +End: diff --git a/doc/coreutils.texi b/doc/coreutils.texi new file mode 100644 index 0000000..373a407 --- /dev/null +++ b/doc/coreutils.texi @@ -0,0 +1,20122 @@ +\input texinfo +@c %**start of header +@setfilename coreutils.info +@include version.texi +@settitle GNU Coreutils @value{VERSION} +@documentencoding UTF-8 +@set txicodequoteundirected +@set txicodequotebacktick +@allowcodebreaks false + +@c %**end of header + +@include constants.texi + +@c Define new indices. +@defcodeindex op +@defcodeindex fl + +@c Put everything in one index (arbitrarily chosen to be the concept index). +@syncodeindex fl cp +@syncodeindex fn cp +@syncodeindex ky cp +@syncodeindex op cp +@syncodeindex pg cp +@syncodeindex vr cp + +@dircategory Basics +@direntry +* Coreutils: (coreutils). Core GNU (file, text, shell) utilities. +* Common options: (coreutils)Common options. +* File permissions: (coreutils)File permissions. Access modes. +* Date input formats: (coreutils)Date input formats. +@end direntry + +@c FIXME: the following need documentation +@c * [: (coreutils)[ invocation. File/string tests. +@c * pinky: (coreutils)pinky invocation. FIXME. + +@dircategory Individual utilities +@direntry +* arch: (coreutils)arch invocation. Print machine hardware name. +* b2sum: (coreutils)b2sum invocation. Print or check BLAKE2 digests. +* base32: (coreutils)base32 invocation. Base32 encode/decode data. +* base64: (coreutils)base64 invocation. Base64 encode/decode data. +* basename: (coreutils)basename invocation. Strip directory and suffix. +* basenc: (coreutils)basenc invocation. Encoding/decoding of data. +* cat: (coreutils)cat invocation. Concatenate and write files. +* chcon: (coreutils)chcon invocation. Change SELinux CTX of files. +* chgrp: (coreutils)chgrp invocation. Change file groups. +* chmod: (coreutils)chmod invocation. Change access permissions. +* chown: (coreutils)chown invocation. Change file owners and groups. +* chroot: (coreutils)chroot invocation. Specify the root directory. +* cksum: (coreutils)cksum invocation. Print POSIX CRC checksum. +* comm: (coreutils)comm invocation. Compare sorted files by line. +* cp: (coreutils)cp invocation. Copy files. +* csplit: (coreutils)csplit invocation. Split by context. +* cut: (coreutils)cut invocation. Print selected parts of lines. +* date: (coreutils)date invocation. Print/set system date and time. +* dd: (coreutils)dd invocation. Copy and convert a file. +* df: (coreutils)df invocation. Report file system usage. +* dir: (coreutils)dir invocation. List directories briefly. +* dircolors: (coreutils)dircolors invocation. Color setup for ls. +* dirname: (coreutils)dirname invocation. Strip last file name component. +* du: (coreutils)du invocation. Report file usage. +* echo: (coreutils)echo invocation. Print a line of text. +* env: (coreutils)env invocation. Modify the environment. +* expand: (coreutils)expand invocation. Convert tabs to spaces. +* expr: (coreutils)expr invocation. Evaluate expressions. +* factor: (coreutils)factor invocation. Print prime factors +* false: (coreutils)false invocation. Do nothing, unsuccessfully. +* fmt: (coreutils)fmt invocation. Reformat paragraph text. +* fold: (coreutils)fold invocation. Wrap long input lines. +* groups: (coreutils)groups invocation. Print group names a user is in. +* head: (coreutils)head invocation. Output the first part of files. +* hostid: (coreutils)hostid invocation. Print numeric host identifier. +* hostname: (coreutils)hostname invocation. Print or set system name. +* id: (coreutils)id invocation. Print user identity. +* install: (coreutils)install invocation. Copy files and set attributes. +* join: (coreutils)join invocation. Join lines on a common field. +* kill: (coreutils)kill invocation. Send a signal to processes. +* link: (coreutils)link invocation. Make hard links between files. +* ln: (coreutils)ln invocation. Make links between files. +* logname: (coreutils)logname invocation. Print current login name. +* ls: (coreutils)ls invocation. List directory contents. +* md5sum: (coreutils)md5sum invocation. Print or check MD5 digests. +* mkdir: (coreutils)mkdir invocation. Create directories. +* mkfifo: (coreutils)mkfifo invocation. Create FIFOs (named pipes). +* mknod: (coreutils)mknod invocation. Create special files. +* mktemp: (coreutils)mktemp invocation. Create temporary files. +* mv: (coreutils)mv invocation. Rename files. +* nice: (coreutils)nice invocation. Modify niceness. +* nl: (coreutils)nl invocation. Number lines and write files. +* nohup: (coreutils)nohup invocation. Immunize to hangups. +* nproc: (coreutils)nproc invocation. Print the number of processors. +* numfmt: (coreutils)numfmt invocation. Reformat numbers. +* od: (coreutils)od invocation. Dump files in octal, etc. +* paste: (coreutils)paste invocation. Merge lines of files. +* pathchk: (coreutils)pathchk invocation. Check file name portability. +* pr: (coreutils)pr invocation. Paginate or columnate files. +* printenv: (coreutils)printenv invocation. Print environment variables. +* printf: (coreutils)printf invocation. Format and print data. +* ptx: (coreutils)ptx invocation. Produce permuted indexes. +* pwd: (coreutils)pwd invocation. Print working directory. +* readlink: (coreutils)readlink invocation. Print referent of a symlink. +* realpath: (coreutils)realpath invocation. Print resolved file names. +* rm: (coreutils)rm invocation. Remove files. +* rmdir: (coreutils)rmdir invocation. Remove empty directories. +* runcon: (coreutils)runcon invocation. Run in specified SELinux CTX. +* seq: (coreutils)seq invocation. Print numeric sequences +* sha1sum: (coreutils)sha1sum invocation. Print or check SHA-1 digests. +* sha2: (coreutils)sha2 utilities. Print or check SHA-2 digests. +* shred: (coreutils)shred invocation. Remove files more securely. +* shuf: (coreutils)shuf invocation. Shuffling text files. +* sleep: (coreutils)sleep invocation. Delay for a specified time. +* sort: (coreutils)sort invocation. Sort text files. +* split: (coreutils)split invocation. Split into pieces. +* stat: (coreutils)stat invocation. Report file(system) status. +* stdbuf: (coreutils)stdbuf invocation. Modify stdio buffering. +* stty: (coreutils)stty invocation. Print/change terminal settings. +* sum: (coreutils)sum invocation. Print traditional checksum. +* sync: (coreutils)sync invocation. Sync files to stable storage. +* tac: (coreutils)tac invocation. Reverse files. +* tail: (coreutils)tail invocation. Output the last part of files. +* tee: (coreutils)tee invocation. Redirect to multiple files. +* test: (coreutils)test invocation. File/string tests. +* timeout: (coreutils)timeout invocation. Run with time limit. +* touch: (coreutils)touch invocation. Change file timestamps. +* tr: (coreutils)tr invocation. Translate characters. +* true: (coreutils)true invocation. Do nothing, successfully. +* truncate: (coreutils)truncate invocation. Shrink/extend size of a file. +* tsort: (coreutils)tsort invocation. Topological sort. +* tty: (coreutils)tty invocation. Print terminal name. +* uname: (coreutils)uname invocation. Print system information. +* unexpand: (coreutils)unexpand invocation. Convert spaces to tabs. +* uniq: (coreutils)uniq invocation. Uniquify files. +* unlink: (coreutils)unlink invocation. Removal via unlink(2). +* uptime: (coreutils)uptime invocation. Print uptime and load. +* users: (coreutils)users invocation. Print current user names. +* vdir: (coreutils)vdir invocation. List directories verbosely. +* wc: (coreutils)wc invocation. Line, word, and byte counts. +* who: (coreutils)who invocation. Print who is logged in. +* whoami: (coreutils)whoami invocation. Print effective user ID. +* yes: (coreutils)yes invocation. Print a string indefinitely. +@end direntry + +@copying +This manual documents version @value{VERSION} of the GNU core +utilities, including the standard programs for text and file manipulation. + +Copyright @copyright{} 1994--2023 Free Software Foundation, Inc. + +@quotation +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with no +Invariant Sections, with no Front-Cover Texts, and with no Back-Cover +Texts. A copy of the license is included in the section entitled ``GNU +Free Documentation License''. +@end quotation +@end copying + +@titlepage +@title GNU @code{Coreutils} +@subtitle Core GNU utilities +@subtitle for version @value{VERSION}, @value{UPDATED} +@author David MacKenzie et al. + +@page +@vskip 0pt plus 1filll +@insertcopying +@end titlepage +@shortcontents +@contents + +@ifnottex +@node Top +@top GNU Coreutils + +@insertcopying +@end ifnottex + +@cindex core utilities +@cindex text utilities +@cindex shell utilities +@cindex file utilities + +@menu +* Introduction:: Caveats, overview, and authors +* Common options:: Common options +* Output of entire files:: cat tac nl od base32 base64 basenc +* Formatting file contents:: fmt pr fold +* Output of parts of files:: head tail split csplit +* Summarizing files:: wc sum cksum b2sum md5sum sha1sum sha2 +* Operating on sorted files:: sort shuf uniq comm ptx tsort +* Operating on fields:: cut paste join +* Operating on characters:: tr expand unexpand +* Directory listing:: ls dir vdir dircolors +* Basic operations:: cp dd install mv rm shred +* Special file types:: mkdir rmdir unlink mkfifo mknod ln link readlink +* Changing file attributes:: chgrp chmod chown touch +* File space usage:: df du stat sync truncate +* Printing text:: echo printf yes +* Conditions:: false true test expr +* Redirection:: tee +* File name manipulation:: dirname basename pathchk mktemp realpath +* Working context:: pwd stty printenv tty +* User information:: id logname whoami groups users who +* System context:: date arch nproc uname hostname hostid uptime +* SELinux context:: chcon runcon +* Modified command invocation:: chroot env nice nohup stdbuf timeout +* Process control:: kill +* Delaying:: sleep +* Numeric operations:: factor numfmt seq +* File permissions:: Access modes +* File timestamps:: File timestamp issues +* Date input formats:: Specifying date strings +* Version sort ordering:: Details on version-sort algorithm +* Opening the software toolbox:: The software tools philosophy +* GNU Free Documentation License:: Copying and sharing this manual +* Concept index:: General index + +@detailmenu + --- The Detailed Node Listing --- + +Common Options + +* Exit status:: Indicating program success or failure +* Backup options:: Backup options +* Block size:: Block size +* Floating point:: Floating point number representation +* Signal specifications:: Specifying signals +* Disambiguating names and IDs:: chgrp, chown, chroot, id: user and group syntax +* Random sources:: Sources of random data +* Target directory:: Target directory +* Trailing slashes:: Trailing slashes +* Traversing symlinks:: Traversing symlinks to directories +* Treating / specially:: Treating / specially +* Standards conformance:: Standards conformance +* Multi-call invocation:: Multi-call program invocation + +Output of entire files + +* cat invocation:: Concatenate and write files +* tac invocation:: Concatenate and write files in reverse +* nl invocation:: Number lines and write files +* od invocation:: Write files in octal or other formats +* base32 invocation:: Transform data into printable data +* base64 invocation:: Transform data into printable data +* basenc invocation:: Transform data into printable data + +Formatting file contents + +* fmt invocation:: Reformat paragraph text +* pr invocation:: Paginate or columnate files for printing +* fold invocation:: Wrap input lines to fit in specified width + +Output of parts of files + +* head invocation:: Output the first part of files +* tail invocation:: Output the last part of files +* split invocation:: Split a file into fixed-size pieces +* csplit invocation:: Split a file into context-determined pieces + +Summarizing files + +* wc invocation:: Print newline, word, and byte counts +* sum invocation:: Print checksum and block counts +* cksum invocation:: Print CRC checksum and byte counts +* md5sum invocation:: Print or check MD5 digests +* b2sum invocation:: Print or check BLAKE2 digests +* sha1sum invocation:: Print or check SHA-1 digests +* sha2 utilities:: Print or check SHA-2 digests + +Operating on sorted files + +* sort invocation:: Sort text files +* shuf invocation:: Shuffle text files +* uniq invocation:: Uniquify files +* comm invocation:: Compare two sorted files line by line +* ptx invocation:: Produce a permuted index of file contents +* tsort invocation:: Topological sort + +@command{ptx}: Produce permuted indexes + +* General options in ptx:: Options which affect general program behavior +* Charset selection in ptx:: Underlying character set considerations +* Input processing in ptx:: Input fields, contexts, and keyword selection +* Output formatting in ptx:: Types of output format, and sizing the fields +* Compatibility in ptx:: The GNU extensions to @command{ptx} + +Operating on fields + +* cut invocation:: Print selected parts of lines +* paste invocation:: Merge lines of files +* join invocation:: Join lines on a common field + +Operating on characters + +* tr invocation:: Translate, squeeze, and/or delete characters +* expand invocation:: Convert tabs to spaces +* unexpand invocation:: Convert spaces to tabs + +@command{tr}: Translate, squeeze, and/or delete characters + +* Character arrays:: Specifying arrays of characters +* Translating:: Changing one set of characters to another +* Squeezing and deleting:: Removing characters + +Directory listing + +* ls invocation:: List directory contents +* dir invocation:: Briefly list directory contents +* vdir invocation:: Verbosely list directory contents +* dircolors invocation:: Color setup for @command{ls} + +@command{ls}: List directory contents + +* Which files are listed:: Which files are listed +* What information is listed:: What information is listed +* Sorting the output:: Sorting the output +* General output formatting:: General output formatting +* Formatting the file names:: Formatting the file names + +Basic operations + +* cp invocation:: Copy files and directories +* dd invocation:: Convert and copy a file +* install invocation:: Copy files and set attributes +* mv invocation:: Move (rename) files +* rm invocation:: Remove files or directories +* shred invocation:: Remove files more securely + +Special file types + +* link invocation:: Make a hard link via the link syscall +* ln invocation:: Make links between files +* mkdir invocation:: Make directories +* mkfifo invocation:: Make FIFOs (named pipes) +* mknod invocation:: Make block or character special files +* readlink invocation:: Print value of a symlink or canonical file name +* rmdir invocation:: Remove empty directories +* unlink invocation:: Remove files via unlink syscall + +Changing file attributes + +* chown invocation:: Change file owner and group +* chgrp invocation:: Change group ownership +* chmod invocation:: Change access permissions +* touch invocation:: Change file timestamps + +File space usage + +* df invocation:: Report file system space usage +* du invocation:: Estimate file space usage +* stat invocation:: Report file or file system status +* sync invocation:: Synchronize cached writes to persistent storage +* truncate invocation:: Shrink or extend the size of a file + +Printing text + +* echo invocation:: Print a line of text +* printf invocation:: Format and print data +* yes invocation:: Print a string until interrupted + +Conditions + +* false invocation:: Do nothing, unsuccessfully +* true invocation:: Do nothing, successfully +* test invocation:: Check file types and compare values +* expr invocation:: Evaluate expressions + +@command{test}: Check file types and compare values + +* File type tests:: File type tests +* Access permission tests:: Access permission tests +* File characteristic tests:: File characteristic tests +* String tests:: String tests +* Numeric tests:: Numeric tests + +@command{expr}: Evaluate expression + +* String expressions:: @code{+ : match substr index length} +* Numeric expressions:: @code{+ - * / %} +* Relations for expr:: @code{| & < <= = == != >= >} +* Examples of expr:: Examples of using @command{expr} + +Redirection + +* tee invocation:: Redirect output to multiple files or processes + +File name manipulation + +* basename invocation:: Strip directory and suffix from a file name +* dirname invocation:: Strip last file name component +* pathchk invocation:: Check file name validity and portability +* mktemp invocation:: Create temporary file or directory +* realpath invocation:: Print resolved file names + +Working context + +* pwd invocation:: Print working directory +* stty invocation:: Print or change terminal characteristics +* printenv invocation:: Print all or some environment variables +* tty invocation:: Print file name of terminal on standard input + +@command{stty}: Print or change terminal characteristics + +* Control:: Control settings +* Input:: Input settings +* Output:: Output settings +* Local:: Local settings +* Combination:: Combination settings +* Characters:: Special characters +* Special:: Special settings + +User information + +* id invocation:: Print user identity +* logname invocation:: Print current login name +* whoami invocation:: Print effective user ID +* groups invocation:: Print group names a user is in +* users invocation:: Print login names of users currently logged in +* who invocation:: Print who is currently logged in + +System context + +* arch invocation:: Print machine hardware name +* date invocation:: Print or set system date and time +* nproc invocation:: Print the number of processors +* uname invocation:: Print system information +* hostname invocation:: Print or set system name +* hostid invocation:: Print numeric host identifier +* uptime invocation:: Print system uptime and load + +@command{date}: Print or set system date and time + +* Time conversion specifiers:: %[HIklMNpPrRsSTXzZ] +* Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY] +* Literal conversion specifiers:: %[%nt] +* Padding and other flags:: Pad with zeros, spaces, etc. +* Setting the time:: Changing the system clock +* Options for date:: Instead of the current time +* Date input formats:: Specifying date strings +* Examples of date:: Examples + +SELinux context + +* chcon invocation:: Change SELinux context of file +* runcon invocation:: Run a command in specified SELinux context + +Modified command invocation + +* chroot invocation:: Run a command with a different root directory +* env invocation:: Run a command in a modified environment +* nice invocation:: Run a command with modified niceness +* nohup invocation:: Run a command immune to hangups +* stdbuf invocation:: Run a command with modified I/O buffering +* timeout invocation:: Run a command with a time limit + +Process control + +* kill invocation:: Sending a signal to processes. + +Delaying + +* sleep invocation:: Delay for a specified time + +Numeric operations + +* factor invocation:: Print prime factors +* numfmt invocation:: Reformat numbers +* seq invocation:: Print numeric sequences + + +File timestamps + +* File timestamps:: File timestamp issues + +File permissions + +* Mode Structure:: Structure of file mode bits +* Symbolic Modes:: Mnemonic representation of file mode bits +* Numeric Modes:: File mode bits as octal numbers +* Directory Setuid and Setgid:: Set-user-ID and set-group-ID on directories + +Date input formats + +* General date syntax:: Common rules +* Calendar date items:: @samp{14 Nov 2022} +* Time of day items:: @samp{9:02pm} +* Time zone items:: @samp{UTC}, @samp{-0700}, @samp{+0900}, @dots{} +* Combined date and time of day items:: @samp{2022-11-14T21:02:42,000000-0500} +* Day of week items:: @samp{Monday} and others +* Relative items in date strings:: @samp{next tuesday, 2 years ago} +* Pure numbers in date strings:: @samp{20221114}, @samp{2102} +* Seconds since the Epoch:: @samp{@@1668477762} +* Specifying time zone rules:: @samp{TZ="America/New_York"}, @samp{TZ="UTC0"} +* Authors of parse_datetime:: Bellovin, Eggert, Salz, Berets, et al. + +Version sorting order + +* Version sort overview:: +* Version sort implementation:: +* Differences from Debian version sort:: +* Advanced version sort topics:: + +Opening the software toolbox + +* Toolbox introduction:: Toolbox introduction +* I/O redirection:: I/O redirection +* The who command:: The @command{who} command +* The cut command:: The @command{cut} command +* The sort command:: The @command{sort} command +* The uniq command:: The @command{uniq} command +* Putting the tools together:: Putting the tools together + +Copying This Manual + +* GNU Free Documentation License:: Copying and sharing this manual + +@end detailmenu +@end menu + + +@node Introduction +@chapter Introduction + +This manual is a work in progress: many sections make no attempt to explain +basic concepts in a way suitable for novices. Thus, if you are interested, +please get involved in improving this manual. The entire GNU community +will benefit. + +@cindex POSIX +The GNU utilities documented here are mostly compatible with the +POSIX standard. +@cindex bugs, reporting + +Please report bugs to @email{bug-coreutils@@gnu.org}. +Include the version number, machine architecture, input files, and +any other information needed to reproduce the bug: your input, what you +expected, what you got, and why it is wrong. + +If you have a problem with @command{sort} or @command{date}, try using the +@option{--debug} option, as it can often help find and fix problems without +having to wait for an answer to a bug report. If the debug output +does not suffice to fix the problem on your own, please compress and +attach it to the rest of your bug report. + +Although diffs are welcome, +please include a description of the problem as well, since this is +sometimes difficult to infer. @xref{Bugs, , , gcc, Using and Porting GNU CC}. + +@cindex Berry, K. +@cindex Paterson, R. +@cindex Stallman, R. +@cindex Pinard, F. +@cindex MacKenzie, D. +@cindex Meyering, J. +@cindex Youmans, B. +This manual was originally derived from the Unix man pages in the +distributions, which were written by David MacKenzie and updated by Jim +Meyering. What you are reading now is the authoritative documentation +for these utilities; the man pages are no longer being maintained. The +original @command{fmt} man page was written by Ross Paterson. Fran@,{c}ois +Pinard did the initial conversion to Texinfo format. Karl Berry did the +indexing, some reorganization, and editing of the results. Brian +Youmans of the Free Software Foundation office staff combined the +manuals for textutils, fileutils, and sh-utils to produce the present +omnibus manual. Richard Stallman contributed his usual invaluable +insights to the overall process. + +@node Common options +@chapter Common options + +@macro optBackup +@item -b +@itemx --backup[=@var{method}] +@opindex -b +@opindex --backup +@vindex VERSION_CONTROL +@cindex backups, making +@xref{Backup options}. +Make a backup of each file that would otherwise be overwritten or removed. +@end macro + +@macro optBackupSuffix +@item -S @var{suffix} +@itemx --suffix=@var{suffix} +@opindex -S +@opindex --suffix +Append @var{suffix} to each backup file made with @option{-b}. +@xref{Backup options}. +@end macro + +@macro optTargetDirectory +@item -t @var{directory} +@itemx --target-directory=@var{directory} +@opindex -t +@opindex --target-directory +@cindex target directory +@cindex destination directory +Specify the destination @var{directory}. +@xref{Target directory}. +@end macro + +@macro optNoTargetDirectory +@item -T +@itemx --no-target-directory +@opindex -T +@opindex --no-target-directory +@cindex target directory +@cindex destination directory +Do not treat the last operand specially when it is a directory or a +symbolic link to a directory. @xref{Target directory}. +@end macro + +@macro outputNUL +@cindex output NUL-byte-terminated lines +Output a zero byte (ASCII NUL) at the end of each line, +rather than a newline. This option enables other programs to parse the +output even when that output would contain data with embedded newlines. +@end macro + +@macro optNull +@item -0 +@itemx --null +@opindex -0 +@opindex --null +@outputNUL +@end macro + +@macro optZero +@item -z +@itemx --zero +@opindex -z +@opindex --zero +@outputNUL +@end macro + +@macro optZeroTerminated +@item -z +@itemx --zero-terminated +@opindex -z +@opindex --zero-terminated +@cindex process zero-terminated items +Delimit items with a zero byte rather than a newline (ASCII LF). +I.e., treat input as items separated by ASCII NUL +and terminate output items with ASCII NUL. +This option can be useful in conjunction with @samp{perl -0} or +@samp{find -print0} and @samp{xargs -0} which do the same in order to +reliably handle arbitrary file names (even those containing blanks +or other special characters). +@end macro + +@macro optSi +@item --si +@opindex --si +@cindex SI output +Append an SI-style abbreviation to each size, such as @samp{M} for +megabytes. Powers of 1000 are used, not 1024; @samp{M} stands for +1,000,000 bytes. This option is equivalent to +@option{--block-size=si}. Use the @option{-h} or +@option{--human-readable} option if +you prefer powers of 1024. +@end macro + +@macro optHumanReadable +@item -h +@itemx --human-readable +@opindex -h +@opindex --human-readable +@cindex human-readable output +Append a size letter to each size, such as @samp{M} for mebibytes. +Powers of 1024 are used, not 1000; @samp{M} stands for 1,048,576 bytes. +This option is equivalent to @option{--block-size=human-readable}. +Use the @option{--si} option if you prefer powers of 1000. +@end macro + +@macro optStripTrailingSlashes +@item --strip-trailing-slashes +@opindex --strip-trailing-slashes +@cindex stripping trailing slashes +Remove any trailing slashes from each @var{source} argument. +@xref{Trailing slashes}. +@end macro + +@macro mayConflictWithShellBuiltIn{cmd} +@cindex conflicts with shell built-ins +@cindex built-in shell commands, conflicts with +Due to shell aliases and built-in @command{\cmd\} functions, using an +unadorned @command{\cmd\} interactively or in a script may get you +different functionality than that described here. Invoke it via +@command{env} (i.e., @code{env \cmd\ @dots{}}) to avoid interference +from the shell. + +@end macro + +@macro multiplierSuffixes{varName} +@var{\varName\} may be, or may be an integer optionally followed by, +one of the following multiplicative suffixes: +@example +@samp{b} => 512 ("blocks") +@samp{KB} => 1000 (KiloBytes) +@samp{K} => 1024 (KibiBytes) +@samp{MB} => 1000*1000 (MegaBytes) +@samp{M} => 1024*1024 (MebiBytes) +@samp{GB} => 1000*1000*1000 (GigaBytes) +@samp{G} => 1024*1024*1024 (GibiBytes) +@end example +and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, @samp{Y}, +@samp{R}, and @samp{Q}. +Binary prefixes can be used, too: @samp{KiB}=@samp{K}, @samp{MiB}=@samp{M}, +and so on. +@end macro + +@c FIXME: same as above, but no ``blocks'' line. +@macro multiplierSuffixesNoBlocks{varName} +@var{\varName\} may be, or may be an integer optionally followed by, +one of the following multiplicative suffixes: +@example +@samp{KB} => 1000 (KiloBytes) +@samp{K} => 1024 (KibiBytes) +@samp{MB} => 1000*1000 (MegaBytes) +@samp{M} => 1024*1024 (MebiBytes) +@samp{GB} => 1000*1000*1000 (GigaBytes) +@samp{G} => 1024*1024*1024 (GibiBytes) +@end example +and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, @samp{Y}, +@samp{R}, and @samp{Q}. +Binary prefixes can be used, too: @samp{KiB}=@samp{K}, @samp{MiB}=@samp{M}, +and so on. +@end macro + +@cindex common options + +Certain options are available in all of these programs. Rather than +writing identical descriptions for each of the programs, they are +described here. (In fact, every GNU program accepts (or should accept) +these options.) + +@vindex POSIXLY_CORRECT +Normally options and operands can appear in any order, and programs act +as if all the options appear before any operands. For example, +@samp{sort -r passwd -t :} acts like @samp{sort -r -t : passwd}, since +@samp{:} is an option-argument of @option{-t}. However, if the +@env{POSIXLY_CORRECT} environment variable is set, options must appear +before operands, unless otherwise specified for a particular command. + +A few programs can usefully have trailing operands with leading +@samp{-}. With such a program, options must precede operands even if +@env{POSIXLY_CORRECT} is not set, and this fact is noted in the +program description. For example, the @command{env} command's options +must appear before its operands, since in some cases the operands +specify a command that itself contains options. + +Most programs that accept long options recognize unambiguous +abbreviations of those options. For example, @samp{rmdir +--ignore-fail-on-non-empty} can be invoked as @samp{rmdir +--ignore-fail} or even @samp{rmdir --i}. Ambiguous options, such as +@samp{ls --h}, are identified as such. + +Some of these programs recognize the @option{--help} and @option{--version} +options only when one of them is the sole command line argument. For +these programs, abbreviations of the long options are not always recognized. + +@table @samp + +@item --help +@opindex --help +@cindex help, online +Print a usage message listing all available options, then exit successfully. + +@item --version +@opindex --version +@cindex version number, finding +Print the version number, then exit successfully. + +@item -- +@opindex -- +@cindex option delimiter +Delimit the option list. Later arguments, if any, are treated as +operands even if they begin with @samp{-}. For example, @samp{sort -- +-r} reads from the file named @file{-r}. + +@end table + +@cindex standard input +@cindex standard output +A single @samp{-} operand is not really an option, though it looks like one. It +stands for a file operand, and some tools treat it as standard input, or as +standard output if that is clear from the context. For example, @samp{sort -} +reads from standard input, and is equivalent to plain @samp{sort}. Unless +otherwise specified, a @samp{-} can appear as any operand that requires a file +name. + +@menu +Items shared between some programs: + +* Backup options:: @option{-b} @option{-S}. +* Block size:: BLOCK_SIZE and @option{--block-size}. +* Signal specifications:: Specifying signals with @option{--signal}. +* Disambiguating names and IDs:: chgrp, chown, chroot, id: user and group syntax +* Random sources:: @option{--random-source}. +* Target directory:: Specifying a target directory. +* Trailing slashes:: @option{--strip-trailing-slashes}. +* Traversing symlinks:: @option{-H}, @option{-L}, or @option{-P}. +* Treating / specially:: @option{--preserve-root} and the converse. +* Special built-in utilities:: @command{break}, @command{:}, @dots{} + +Items applicable to all programs: + +* Exit status:: Indicating program success or failure. +* Floating point:: Floating point number representation. +* Standards conformance:: Conformance to the POSIX standard. +* Multi-call invocation:: Multi-call program invocation. +@end menu + + +@node Backup options +@section Backup options + +@cindex backup options + +Some GNU programs (at least @command{cp}, @command{install}, +@command{ln}, and @command{mv}) optionally make backups of files +before writing new versions. +These options control the details of these backups. The options are also +briefly mentioned in the descriptions of the particular programs. + +@table @samp + +@item -b +@itemx --backup[=@var{method}] +@opindex -b +@opindex --backup +@vindex VERSION_CONTROL +@cindex backups, making +Make a backup of each file that would otherwise be overwritten or removed. +Without this option, the original versions are destroyed. +Use @var{method} to determine the type of backups to make. +When this option is used but @var{method} is not specified, +then the value of the @env{VERSION_CONTROL} +environment variable is used. And if @env{VERSION_CONTROL} is not set, +the default backup type is @samp{existing}. + +Note that the short form of this option, @option{-b} does not accept any +argument. Using @option{-b} is equivalent to using @option{--backup=existing}. + +@vindex version-control @r{Emacs variable} +This option corresponds to the Emacs variable @samp{version-control}; +the values for @var{method} are the same as those used in Emacs. +This option also accepts more descriptive names. +The valid @var{method}s are (unique abbreviations are accepted): + +@table @samp +@item none +@itemx off +@opindex none @r{backup method} +Never make backups. + +@item numbered +@itemx t +@opindex numbered @r{backup method} +Always make numbered backups. + +@item existing +@itemx nil +@opindex existing @r{backup method} +Make numbered backups of files that already have them, simple backups +of the others. + +@item simple +@itemx never +@opindex simple @r{backup method} +Always make simple backups. Please note @samp{never} is not to be +confused with @samp{none}. + +@end table + +@item -S @var{suffix} +@itemx --suffix=@var{suffix} +@opindex -S +@opindex --suffix +@cindex backup suffix +@vindex SIMPLE_BACKUP_SUFFIX +Append @var{suffix} to each backup file made with @option{-b}. If this +option is not specified, the value of the @env{SIMPLE_BACKUP_SUFFIX} +environment variable is used. And if @env{SIMPLE_BACKUP_SUFFIX} is not +set, the default is @samp{~}, just as in Emacs. + +@end table + +@node Block size +@section Block size + +@cindex block size + +Some GNU programs (at least @command{df}, @command{du}, and +@command{ls}) display sizes in ``blocks''. You can adjust the block size +and method of display to make sizes easier to read. The block size +used for display is independent of any file system block size. +Fractional block counts are rounded up to the nearest integer. + +@opindex --block-size=@var{size} +@vindex BLOCKSIZE +@vindex BLOCK_SIZE +@vindex DF_BLOCK_SIZE +@vindex DU_BLOCK_SIZE +@vindex LS_BLOCK_SIZE +@vindex POSIXLY_CORRECT@r{, and block size} + +The default block size is chosen by examining the following environment +variables in turn; the first one that is set determines the block size. + +@table @code + +@item DF_BLOCK_SIZE +This specifies the default block size for the @command{df} command. +Similarly, @env{DU_BLOCK_SIZE} specifies the default for @command{du} and +@env{LS_BLOCK_SIZE} for @command{ls}. + +@item BLOCK_SIZE +This specifies the default block size for all three commands, if the +above command-specific environment variables are not set. + +@item BLOCKSIZE +This specifies the default block size for all values that are normally +printed as blocks, if neither @env{BLOCK_SIZE} nor the above +command-specific environment variables are set. Unlike the other +environment variables, @env{BLOCKSIZE} does not affect values that are +normally printed as byte counts, e.g., the file sizes contained in +@code{ls -l} output. + +@item POSIXLY_CORRECT +If neither @env{@var{command}_BLOCK_SIZE}, nor @env{BLOCK_SIZE}, nor +@env{BLOCKSIZE} is set, but this variable is set, the block size +defaults to 512. + +@end table + +If none of the above environment variables are set, the block size +currently defaults to 1024 bytes in most contexts, but this number may +change in the future. For @command{ls} file sizes, the block size +defaults to 1 byte. + +@cindex human-readable output +@cindex SI output + +A block size specification can be a positive integer specifying the number +of bytes per block, or it can be @code{human-readable} or @code{si} to +select a human-readable format. Integers may be followed by suffixes +that are upward compatible with the +@uref{http://www.bipm.org/en/publications/si-brochure/chapter3.html, +SI prefixes} +for decimal multiples and with the +@uref{https://physics.nist.gov/cuu/Units/binary.html, ISO/IEC 80000-13 +(formerly IEC 60027-2) prefixes} for binary multiples. + +With human-readable formats, output sizes are followed by a size letter +such as @samp{M} for megabytes. @code{BLOCK_SIZE=human-readable} uses +powers of 1024; @samp{M} stands for 1,048,576 bytes. +@code{BLOCK_SIZE=si} is similar, but uses powers of 1000 and appends +@samp{B}; @samp{MB} stands for 1,000,000 bytes. + +@vindex LC_NUMERIC +A block size specification preceded by @samp{'} causes output sizes to +be displayed with thousands separators. The @env{LC_NUMERIC} locale +specifies the thousands separator and grouping. For example, in an +American English locale, @samp{--block-size="'1kB"} would cause a size +of 1234000 bytes to be displayed as @samp{1,234}. In the default C +locale, there is no thousands separator so a leading @samp{'} has no +effect. + +An integer block size can be followed by a suffix to specify a +multiple of that size. A bare size letter, +or one followed by @samp{iB}, specifies +a multiple using powers of 1024. A size letter followed by @samp{B} +specifies powers of 1000 instead. For example, @samp{1M} and +@samp{1MiB} are equivalent to @samp{1048576}, whereas @samp{1MB} is +equivalent to @samp{1000000}. + +A plain suffix without a preceding integer acts as if @samp{1} were +prepended, except that it causes a size indication to be appended to +the output. For example, @samp{--block-size="kB"} displays 3000 as +@samp{3kB}. + +The following suffixes are defined. Large sizes like @code{1Q} +may be rejected by your computer due to limitations of its arithmetic. + +@table @samp +@item kB +@cindex kilobyte, definition of +kilobyte: @math{10^3 = 1000}. +@item k +@itemx K +@itemx KiB +@cindex kibibyte, definition of +kibibyte: @math{2^{10} = 1024}. @samp{K} is special: the SI prefix is +@samp{k} and the ISO/IEC 80000-13 prefix is @samp{Ki}, but tradition and +POSIX use @samp{k} to mean @samp{KiB}. +@item MB +@cindex megabyte, definition of +megabyte: @math{10^6 = 1,000,000}. +@item M +@itemx MiB +@cindex mebibyte, definition of +mebibyte: @math{2^{20} = 1,048,576}. +@item GB +@cindex gigabyte, definition of +gigabyte: @math{10^9 = 1,000,000,000}. +@item G +@itemx GiB +@cindex gibibyte, definition of +gibibyte: @math{2^{30} = 1,073,741,824}. +@item TB +@cindex terabyte, definition of +terabyte: @math{10^{12} = 1,000,000,000,000}. +@item T +@itemx TiB +@cindex tebibyte, definition of +tebibyte: @math{2^{40} = 1,099,511,627,776}. +@item PB +@cindex petabyte, definition of +petabyte: @math{10^{15} = 1,000,000,000,000,000}. +@item P +@itemx PiB +@cindex pebibyte, definition of +pebibyte: @math{2^{50} = 1,125,899,906,842,624}. +@item EB +@cindex exabyte, definition of +exabyte: @math{10^{18} = 1,000,000,000,000,000,000}. +@item E +@itemx EiB +@cindex exbibyte, definition of +exbibyte: @math{2^{60} = 1,152,921,504,606,846,976}. +@item ZB +@cindex zettabyte, definition of +zettabyte: @math{10^{21} = 1,000,000,000,000,000,000,000} +@item Z +@itemx ZiB +zebibyte: @math{2^{70} = 1,180,591,620,717,411,303,424}. +@item YB +@cindex yottabyte, definition of +yottabyte: @math{10^{24} = 1,000,000,000,000,000,000,000,000}. +@item Y +@itemx YiB +yobibyte: @math{2^{80} = 1,208,925,819,614,629,174,706,176}. +@item RB +@cindex ronnabyte, definition of +ronnabyte: @math{10^{27} = 1,000,000,000,000,000,000,000,000,000}. +@item R +@itemx RiB +robibyte: @math{2^{90} = 1,237,940,039,285,380,274,899,124,224}. +@item QB +@cindex quettabyte, definition of +quettabyte: @math{10^{30} = 1,000,000,000,000,000,000,000,000,000,000}. +@item Q +@itemx QiB +quebibyte: @math{2^{100} = 1,267,650,600,228,229,401,496,703,205,376}. +@end table + +@opindex -k +@opindex -h +@opindex --block-size +@opindex --human-readable +@opindex --si + +Block size defaults can be overridden by an explicit +@option{--block-size=@var{size}} option. The @option{-k} +option is equivalent to @option{--block-size=1K}, which +is the default unless the @env{POSIXLY_CORRECT} environment variable is +set. The @option{-h} or @option{--human-readable} option is equivalent to +@option{--block-size=human-readable}. The @option{--si} option is +equivalent to @option{--block-size=si}. Note for @command{ls} +the @option{-k} option does not control the display of the +apparent file sizes, whereas the @option{--block-size} option does. + +@node Signal specifications +@section Signal specifications +@cindex signals, specifying + +A @var{signal} may be a signal name like @samp{HUP}, or a signal +number like @samp{1}, or an exit status of a process terminated by the +signal. A signal name can be given in canonical form or prefixed by +@samp{SIG}@. The case of the letters is ignored. The following signal names +and numbers are supported on all POSIX compliant systems: + +@table @samp +@item HUP +1. Hangup. +@item INT +2. Terminal interrupt. +@item QUIT +3. Terminal quit. +@item ABRT +6. Process abort. +@item KILL +9. Kill (cannot be caught or ignored). +@item ALRM +14. Alarm Clock. +@item TERM +15. Termination. +@end table + +@noindent +Other supported signal names have system-dependent corresponding +numbers. All systems conforming to POSIX 1003.1-2001 also +support the following signals: + +@table @samp +@item BUS +Access to an undefined portion of a memory object. +@item CHLD +Child process terminated, stopped, or continued. +@item CONT +Continue executing, if stopped. +@item FPE +Erroneous arithmetic operation. +@item ILL +Illegal Instruction. +@item PIPE +Write on a pipe with no one to read it. +@item SEGV +Invalid memory reference. +@item STOP +Stop executing (cannot be caught or ignored). +@item TSTP +Terminal stop. +@item TTIN +Background process attempting read. +@item TTOU +Background process attempting write. +@item URG +High bandwidth data is available at a socket. +@item USR1 +User-defined signal 1. +@item USR2 +User-defined signal 2. +@end table + +@noindent +POSIX 1003.1-2001 systems that support the XSI extension +also support the following signals: + +@table @samp +@item POLL +Pollable event. +@item PROF +Profiling timer expired. +@item SYS +Bad system call. +@item TRAP +Trace/breakpoint trap. +@item VTALRM +Virtual timer expired. +@item XCPU +CPU time limit exceeded. +@item XFSZ +File size limit exceeded. +@end table + +@noindent +POSIX 1003.1-2001 systems that support the XRT extension +also support at least eight real-time signals called @samp{RTMIN}, +@samp{RTMIN+1}, @dots{}, @samp{RTMAX-1}, @samp{RTMAX}. + +@node Disambiguating names and IDs +@section chown, chgrp, chroot, id: Disambiguating user names and IDs +@cindex user names, disambiguating +@cindex user IDs, disambiguating +@cindex group names, disambiguating +@cindex group IDs, disambiguating +@cindex disambiguating group names and IDs + +Since the @var{user} and @var{group} arguments to these commands +may be specified as names or numeric IDs, there is an +apparent ambiguity. +What if a user or group @emph{name} is a string of digits? +Should the command interpret it as a user name or as an ID@? +(Using a number as a user name is common in some environments.) +POSIX requires that these commands +first attempt to resolve the specified string as a name, and +only once that fails, then try to interpret it as an ID@. +This is troublesome when you want to specify a numeric ID, say 42, +and it must work even in a pathological situation where +@samp{42} is a user name that maps to some other user ID, say 1000. +Simply invoking @code{chown 42 F}, will set @file{F}s owner ID to +1000 -- not what you intended. + +GNU @command{chown}, @command{chgrp}, @command{chroot}, and @command{id} +provide a way to work around this, that at the same time may result in a +significant performance improvement by eliminating a database look-up. +Simply precede each numeric user ID and/or group ID with a @samp{+}, +in order to force its interpretation as an integer: + +@example +chown +42 F +chgrp +$numeric_group_id another-file +chown +0:+0 / +@end example + +The name look-up process is skipped for each @samp{+}-prefixed string, +because a string containing @samp{+} is never a valid user or group name. +This syntax is accepted on most common Unix systems, but not on Solaris 10. + +@node Random sources +@section Sources of random data + +@cindex random sources + +The @command{shuf}, @command{shred}, and @command{sort} commands +sometimes need random data to do their work. For example, @samp{sort +-R} must choose a hash function at random, and it needs random data to +make this selection. + +By default these commands use an internal pseudo-random generator +initialized by a small amount of entropy, but can be directed to use +an external source with the @option{--random-source=@var{file}} option. +An error is reported if @var{file} does not contain enough bytes. + +For example, the device file @file{/dev/urandom} could be used as the +source of random data. Typically, this device gathers environmental +noise from device drivers and other sources into an entropy pool, and +uses the pool to generate random bits. If the pool is short of data, +the device reuses the internal pool to produce more bits, using a +cryptographically secure pseudo-random number generator. But be aware +that this device is not designed for bulk random data generation +and is relatively slow. + +@file{/dev/urandom} suffices for most practical uses, but applications +requiring high-value or long-term protection of private data may +require an alternate data source like @file{/dev/random} or +@file{/dev/arandom}. The set of available sources depends on your +operating system. + +To reproduce the results of an earlier invocation of a command, you +can save some random data into a file and then use that file as the +random source in earlier and later invocations of the command. +@cindex random seed +Rather than depending on a file, one can generate a reproducible +arbitrary amount of pseudo-random data given a seed value, using +for example: + +@example +get_seeded_random() +@{ + seed="$1" + openssl enc -aes-256-ctr -pass pass:"$seed" -nosalt \ + </dev/zero 2>/dev/null +@} + +shuf -i1-100 --random-source=<(get_seeded_random 42) +@end example + +@node Target directory +@section Target directory + +@cindex target directory + +The @command{cp}, @command{install}, @command{ln}, and @command{mv} +commands normally treat the last operand specially when it is a +directory or a symbolic link to a directory. For example, @samp{cp +source dest} is equivalent to @samp{cp source dest/source} if +@file{dest} is a directory. Sometimes this behavior is not exactly +what is wanted, so these commands support the following options to +allow more fine-grained control: + +@table @samp + +@item -T +@itemx --no-target-directory +@opindex --no-target-directory +@cindex target directory +@cindex destination directory +Do not treat the last operand specially when it is a directory or a +symbolic link to a directory. This can help avoid race conditions in +programs that operate in a shared area. For example, when the command +@samp{mv /tmp/source /tmp/dest} succeeds, there is no guarantee that +@file{/tmp/source} was renamed to @file{/tmp/dest}: it could have been +renamed to @file{/tmp/dest/source} instead, if some other process +created @file{/tmp/dest} as a directory. However, if @file{mv +-T /tmp/source /tmp/dest} succeeds, there is no +question that @file{/tmp/source} was renamed to @file{/tmp/dest}. + +In the opposite situation, where you want the last operand to be +treated as a directory and want a diagnostic otherwise, you can use +the @option{--target-directory} (@option{-t}) option. + +@item -t @var{directory} +@itemx --target-directory=@var{directory} +@opindex --target-directory +@cindex target directory +@cindex destination directory +Use @var{directory} as the directory component of each destination +file name. + +The interface for most programs is that after processing options and a +finite (possibly zero) number of fixed-position arguments, the remaining +argument list is either expected to be empty, or is a list of items +(usually files) that will all be handled identically. The @command{xargs} +program is designed to work well with this convention. + +The commands in the @command{mv}-family are unusual in that they take +a variable number of arguments with a special case at the @emph{end} +(namely, the target directory). This makes it nontrivial to perform some +operations, e.g., ``move all files from here to ../d/'', because +@code{mv * ../d/} might exhaust the argument space, and @code{ls | xargs ...} +doesn't have a clean way to specify an extra final argument for each +invocation of the subject command. (It can be done by going through a +shell command, but that requires more human labor and brain power than +it should.) + +The @option{--target-directory} (@option{-t}) option allows the @command{cp}, +@command{install}, @command{ln}, and @command{mv} programs to be used +conveniently with @command{xargs}. For example, you can move the files +from the current directory to a sibling directory, @code{d} like this: + +@example +ls | xargs mv -t ../d -- +@end example + +However, this doesn't move files whose names begin with @samp{.}. +If you use the GNU @command{find} program, you can move those +files too, with this command: + +@example +find . -mindepth 1 -maxdepth 1 \ + | xargs mv -t ../d +@end example + +But both of the above approaches fail if there are no files in the +current directory, or if any file has a name containing a blank or +some other special characters. +The following example removes those limitations and requires both +GNU @command{find} and GNU @command{xargs}: + +@example +find . -mindepth 1 -maxdepth 1 -print0 \ + | xargs --null --no-run-if-empty \ + mv -t ../d +@end example + +@end table + +@noindent +The @option{--target-directory} (@option{-t}) and +@option{--no-target-directory} (@option{-T}) +options cannot be combined. + +@node Trailing slashes +@section Trailing slashes + +@cindex trailing slashes + +Some GNU programs (at least @command{cp} and @command{mv}) allow you to +remove any trailing slashes from each @var{source} argument before +operating on it. The @option{--strip-trailing-slashes} option enables +this behavior. + +This is useful when a @var{source} argument may have a trailing slash and +@c FIXME: mv's behavior in this case is system-dependent +specify a symbolic link to a directory. This scenario is in fact rather +common because some shells can automatically append a trailing slash when +performing file name completion on such symbolic links. Without this +option, @command{mv}, for example, (via the system's rename function) must +interpret a trailing slash as a request to dereference the symbolic link +and so must rename the indirectly referenced @emph{directory} and not +the symbolic link. Although it may seem surprising that such behavior +be the default, it is required by POSIX and is consistent with +other parts of that standard. + +@node Traversing symlinks +@section Traversing symlinks + +@cindex symbolic link to directory, controlling traversal of + +The following options modify how @command{chown} and @command{chgrp} +@c FIXME: note that 'du' has these options, too, but they have slightly +@c different meaning. +traverse a hierarchy when the @option{--recursive} (@option{-R}) +option is also specified. +If more than one of the following options is specified, only the final +one takes effect. +These options specify whether processing a symbolic link to a directory +entails operating on just the symbolic link or on all files in the +hierarchy rooted at that directory. + +These options are independent of @option{--dereference} and +@option{--no-dereference} (@option{-h}), which control whether to modify +a symlink or its referent. + +@table @samp + +@macro choptH +@item -H +@opindex -H +@cindex symbolic link to directory, traverse if on the command line +If @option{--recursive} (@option{-R}) is specified and +a command line argument is a symbolic link to a directory, traverse it. +@end macro +@choptH + +@macro choptL +@item -L +@opindex -L +@cindex symbolic link to directory, traverse each that is encountered +In a recursive traversal, traverse every symbolic link to a directory +that is encountered. +@end macro + +@c Append the following warning to -L where appropriate (e.g. chown). +@macro warnOptDerefWithRec + +Combining this dereferencing option with the @option{--recursive} option +may create a security risk: +During the traversal of the directory tree, an attacker may be able to +introduce a symlink to an arbitrary target; when the tool reaches that, +the operation will be performed on the target of that symlink, +possibly allowing the attacker to escalate privileges. + +@end macro + +@choptL + +@macro choptP +@item -P +@opindex -P +@cindex symbolic link to directory, never traverse +Do not traverse any symbolic links. +This is the default if none of @option{-H}, @option{-L}, +or @option{-P} is specified. +@end macro +@choptP + +@end table + + +@node Treating / specially +@section Treating @file{/} specially + +Certain commands can operate destructively on entire hierarchies. +For example, if a user with appropriate privileges mistakenly runs +@samp{rm -rf / tmp/junk}, that may remove +all files on the entire system. Since there are so few +legitimate uses for such a command, +GNU @command{rm} normally declines to operate on any directory +that resolves to @file{/}. If you really want to try to remove all +the files on your system, you can use the @option{--no-preserve-root} +option, but the default behavior, specified by the +@option{--preserve-root} option, is safer for most purposes. + +The commands @command{chgrp}, @command{chmod} and @command{chown} +can also operate destructively on entire hierarchies, so they too +support these options. Although, unlike @command{rm}, they don't +actually unlink files, these commands are arguably more dangerous +when operating recursively on @file{/}, since they often work much +more quickly, and hence damage more files before an alert user can +interrupt them. Tradition and POSIX require these commands +to operate recursively on @file{/}, so they default to +@option{--no-preserve-root}, but using the @option{--preserve-root} +option makes them safer for most purposes. For convenience you can +specify @option{--preserve-root} in an alias or in a shell function. + +Note that the @option{--preserve-root} option also ensures +that @command{chgrp} and @command{chown} do not modify @file{/} +even when dereferencing a symlink pointing to @file{/}. + +@node Special built-in utilities +@section Special built-in utilities + +Some programs like @command{nice} can invoke other programs; for +example, the command @samp{nice cat file} invokes the program +@command{cat} by executing the command @samp{cat file}. However, +@dfn{special built-in utilities} like @command{exit} cannot be invoked +this way. For example, the command @samp{nice exit} does not have a +well-defined behavior: it may generate an error message instead of +exiting. + +Here is a list of the special built-in utilities that are standardized +by POSIX 1003.1-2004. + +@quotation +@t{.@: : break continue eval exec exit export readonly +return set shift times trap unset} +@end quotation + +For example, because @samp{.}, @samp{:}, and @samp{exec} are special, +the commands @samp{nice . foo.sh}, @samp{nice :}, and @samp{nice exec +pwd} do not work as you might expect. + +Many shells extend this list. For example, Bash has several extra +special built-in utilities like @command{history}, and +@command{suspend}, and with Bash the command @samp{nice suspend} +generates an error message instead of suspending. + + +@node Exit status +@section Exit status + +@macro exitstatus +An exit status of zero indicates success, +and a nonzero value indicates failure. +@end macro + +Nearly every command invocation yields an integral @dfn{exit status} +that can be used to change how other commands work. +For the vast majority of commands, an exit status of zero indicates +success. Failure is indicated by a nonzero value -- typically +@samp{1}, though it may differ on unusual platforms as POSIX +requires only that it be nonzero. + +However, some of the programs documented here do produce +other exit status values and a few associate different +meanings with the values @samp{0} and @samp{1}. +Here are the exceptions: +@c You can generate the following list with: +@c grep initialize_exit_failure src/*.c | cut -f1 -d: | +@c sed -n 's|src/\(.*\)\.c|@command{\1},|p' | sort | fmt +@command{chroot}, @command{env}, @command{expr}, @command{ls}, +@command{nice}, @command{nohup}, @command{numfmt}, @command{printenv}, +@command{runcon}, @command{sort}, @command{stdbuf}, @command{test}, +@command{timeout}, @command{tty}. + +@node Floating point +@section Floating point numbers +@cindex floating point +@cindex IEEE floating point + +Commands that accept or produce floating point numbers employ the +floating point representation of the underlying system, and suffer +from rounding error, overflow, and similar floating-point issues. +Almost all modern systems use IEEE-754 floating point, and it is +typically portable to assume IEEE-754 behavior these days. IEEE-754 +has positive and negative infinity, distinguishes positive from +negative zero, and uses special values called NaNs to represent +invalid computations such as dividing zero by itself. For more +information, please see David Goldberg's paper +@uref{https://@/docs.oracle.com/@/cd/@/E19957-01/@/806-3568/@/ncg_goldberg.html, +What Every Computer Scientist Should Know About Floating-Point Arithmetic}. + +Commands that accept floating point numbers as options, operands or +input use the standard C functions @code{strtod} and @code{strtold} to +convert from text to floating point numbers. These floating point +numbers therefore can use scientific notation like @code{1.0e-34} and +@code{-10e100}. Commands that parse floating point also understand +case-insensitive @code{inf}, @code{infinity}, and @code{NaN}, although +whether such values are useful depends on the command in question. +Modern C implementations also accept hexadecimal floating point +numbers such as @code{-0x.ep-3}, which stands for @minus{}14/16 times +@math{2^-3}, which equals @minus{}0.109375. @xref{Parsing of +Floats,,, libc, The GNU C Library Reference Manual}. + +@vindex LC_NUMERIC +Normally the @env{LC_NUMERIC} locale determines the decimal-point +character. However, some commands' descriptions specify that they +accept numbers in either the current or the C locale; for example, +they treat @samp{3.14} like @samp{3,14} if the current locale uses +comma as a decimal point. + + +@node Standards conformance +@section Standards conformance + +@vindex POSIXLY_CORRECT +In a few cases, the GNU utilities' default behavior is +incompatible with the POSIX standard. To suppress these +incompatibilities, define the @env{POSIXLY_CORRECT} environment +variable. Unless you are checking for POSIX conformance, you +probably do not need to define @env{POSIXLY_CORRECT}. + +Newer versions of POSIX are occasionally incompatible with older +versions. For example, older versions of POSIX required the +command @samp{sort +1} to sort based on the second and succeeding +fields in each input line, but in POSIX 1003.1-2001 +the same command is required to sort the file named @file{+1}, and you +must instead use the command @samp{sort -k 2} to get the field-based +sort. To complicate things further, POSIX 1003.1-2008 allows an +implementation to have either the old or the new behavior. + +@vindex _POSIX2_VERSION +The GNU utilities normally conform to the version of POSIX +that is standard for your system. To cause them to conform to a +different version of POSIX, define the @env{_POSIX2_VERSION} +environment variable to a value of the form @var{yyyymm} specifying +the year and month the standard was adopted. Three values are currently +supported for @env{_POSIX2_VERSION}: @samp{199209} stands for +POSIX 1003.2-1992, @samp{200112} stands for POSIX +1003.1-2001, and @samp{200809} stands for POSIX 1003.1-2008. +For example, if you have a POSIX 1003.1-2001 system but are running software +containing traditional usage like @samp{sort +1} or @samp{tail +10}, +you can work around the compatibility problems by setting +@samp{_POSIX2_VERSION=200809} in your environment. + +@c This node is named "Multi-call invocation", not the usual +@c "coreutils invocation", so that shell commands like +@c 'info coreutils "touch invocation"' work as expected. +@node Multi-call invocation +@section @command{coreutils}: Multi-call program + +@pindex multicall +@cindex combined +@cindex calling combined multi-call program + +The @command{coreutils} command invokes an individual utility, either +implicitly selected by the last component of the name used to invoke +@command{coreutils}, or explicitly with the +@option{--coreutils-prog} option. Synopsis: + +@example +coreutils @option{--coreutils-prog=PROGRAM} @dots{} +@end example + +The @command{coreutils} command is not installed by default, so +portable scripts should not rely on its existence. + +@node Output of entire files +@chapter Output of entire files + +@cindex output of entire files +@cindex entire files, output of + +These commands read and write entire files, possibly transforming them +in some way. + +@menu +* cat invocation:: Concatenate and write files. +* tac invocation:: Concatenate and write files in reverse. +* nl invocation:: Number lines and write files. +* od invocation:: Write files in octal or other formats. +* base32 invocation:: Transform data into printable data. +* base64 invocation:: Transform data into printable data. +* basenc invocation:: Transform data into printable data. +@end menu + +@node cat invocation +@section @command{cat}: Concatenate and write files + +@pindex cat +@cindex concatenate and write files +@cindex copying files + +@command{cat} copies each @var{file} (@samp{-} means standard input), or +standard input if none are given, to standard output. Synopsis: + +@example +cat [@var{option}] [@var{file}]@dots{} +@end example + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -A +@itemx --show-all +@opindex -A +@opindex --show-all +Equivalent to @option{-vET}. + +@item -b +@itemx --number-nonblank +@opindex -b +@opindex --number-nonblank +Number all nonempty output lines, starting with 1. + +@item -e +@opindex -e +Equivalent to @option{-vE}. + +@item -E +@itemx --show-ends +@opindex -E +@opindex --show-ends +Display a @samp{$} after the end of each line. +The @code{\r\n} combination is shown as @samp{^M$}. + +@item -n +@itemx --number +@opindex -n +@opindex --number +Number all output lines, starting with 1. This option is ignored +if @option{-b} is in effect. + +@item -s +@itemx --squeeze-blank +@opindex -s +@opindex --squeeze-blank +@cindex squeezing empty lines +@cindex squeezing blank lines +Suppress repeated adjacent blank lines; output just one empty line +instead of several. + +@item -t +@opindex -t +Equivalent to @option{-vT}. + +@item -T +@itemx --show-tabs +@opindex -T +@opindex --show-tabs +Display TAB characters as @samp{^I}. + +@item -u +@opindex -u +Ignored; for POSIX compatibility. + +@item -v +@itemx --show-nonprinting +@opindex -v +@opindex --show-nonprinting +Display control characters except for LFD and TAB using +@samp{^} notation and precede characters that have the high bit set with +@samp{M-}. + +@end table + +On systems like MS-DOS that distinguish between text and binary files, +@command{cat} normally reads and writes in binary mode. However, +@command{cat} reads in text mode if one of the options +@option{-bensAE} is used or if @command{cat} is reading from standard +input and standard input is a terminal. Similarly, @command{cat} +writes in text mode if one of the options @option{-bensAE} is used or +if standard output is a terminal. + +@exitstatus + +Examples: + +@example +# Output f's contents, then standard input, then g's contents. +cat f - g + +# Copy standard input to standard output. +cat +@end example + + +@node tac invocation +@section @command{tac}: Concatenate and write files in reverse + +@pindex tac +@cindex reversing files + +@command{tac} copies each @var{file} (@samp{-} means standard input), or +standard input if none are given, to standard output, reversing the +records (lines by default) in each separately. Synopsis: + +@example +tac [@var{option}]@dots{} [@var{file}]@dots{} +@end example + +@dfn{Records} are separated by instances of a string (newline by +default). By default, this separator string is attached to the end of +the record that it follows in the file. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -b +@itemx --before +@opindex -b +@opindex --before +The separator is attached to the beginning of the record that it +precedes in the file. + +@item -r +@itemx --regex +@opindex -r +@opindex --regex +Treat the separator string as a regular expression. + +@item -s @var{separator} +@itemx --separator=@var{separator} +@opindex -s +@opindex --separator +Use @var{separator} as the record separator, instead of newline. +Note an empty @var{separator} is treated as a zero byte. +I.e., input and output items are delimited with ASCII NUL. + +@end table + +On systems like MS-DOS that distinguish between text and binary files, +@command{tac} reads and writes in binary mode. + +@exitstatus + +Example: + +@example +# Reverse a file character by character. +tac -r -s 'x\|[^x]' +@end example + + +@node nl invocation +@section @command{nl}: Number lines and write files + +@pindex nl +@cindex numbering lines +@cindex line numbering + +@command{nl} writes each @var{file} (@samp{-} means standard input), or +standard input if none are given, to standard output, with line numbers +added to some or all of the lines. Synopsis: + +@example +nl [@var{option}]@dots{} [@var{file}]@dots{} +@end example + +@cindex logical pages, numbering on +@command{nl} decomposes its input into (logical) page sections; +by default, the line number is reset to 1 at each logical page section. +@command{nl} treats all of the input files as a single document; +it does not reset line numbers or logical pages between files. + +@cindex headers, numbering +@cindex body, numbering +@cindex footers, numbering +A logical page consists of three sections: header, body, and footer. +Any of the sections can be empty. Each can be numbered in a different +style from the others. + +The beginnings of the sections of logical pages are indicated in the +input file by a line containing exactly one of these delimiter strings: + +@table @samp +@item \:\:\: +start of header; +@item \:\: +start of body; +@item \: +start of footer. +@end table + +The characters from which these strings are made can be changed from +@samp{\} and @samp{:} via options (see below), but the pattern +of each string cannot be changed. + +A section delimiter is replaced by an empty line on output. Any text +that comes before the first section delimiter string in the input file +is considered to be part of a body section, so @command{nl} treats a +file that contains no section delimiters as a single body section. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -b @var{style} +@itemx --body-numbering=@var{style} +@opindex -b +@opindex --body-numbering +Select the numbering style for lines in the body section of each +logical page. When a line is not numbered, the current line number +is not incremented, but the line number separator character is still +prepended to the line. The styles are: + +@table @samp +@item a +number all lines, +@item t +number only nonempty lines (default for body), +@item n +do not number lines (default for header and footer), +@item p@var{bre} +number only lines that contain a match for the basic regular +expression @var{bre}. +@xref{Regular Expressions, , Regular Expressions, grep, The GNU Grep Manual}. +@end table + +@item -d @var{cd} +@itemx --section-delimiter=@var{cd} +@opindex -d +@opindex --section-delimiter +@cindex section delimiters of pages +Set the section delimiter characters to @var{cd}; default is +@samp{\:}. If only @var{c} is given, the second remains @samp{:}. +As a GNU extension more than two characters can be specified, +and also if @var{cd} is empty (@option{-d ''}), then section +matching is disabled. +(Remember to protect @samp{\} or other metacharacters from shell +expansion with quotes or extra backslashes.) + +@item -f @var{style} +@itemx --footer-numbering=@var{style} +@opindex -f +@opindex --footer-numbering +Analogous to @option{--body-numbering}. + +@item -h @var{style} +@itemx --header-numbering=@var{style} +@opindex -h +@opindex --header-numbering +Analogous to @option{--body-numbering}. + +@item -i @var{number} +@itemx --line-increment=@var{number} +@opindex -i +@opindex --line-increment +Increment line numbers by @var{number} (default 1). +@var{number} can be negative to decrement. + +@item -l @var{number} +@itemx --join-blank-lines=@var{number} +@opindex -l +@opindex --join-blank-lines +@cindex empty lines, numbering +@cindex blank lines, numbering +Consider @var{number} (default 1) consecutive empty lines to be one +logical line for numbering, and only number the last one. Where fewer +than @var{number} consecutive empty lines occur, do not number them. +An empty line is one that contains no characters, not even spaces +or tabs. + +@item -n @var{format} +@itemx --number-format=@var{format} +@opindex -n +@opindex --number-format +Select the line numbering format (default is @code{rn}): + +@table @samp +@item ln +@opindex ln @r{format for @command{nl}} +left justified, no leading zeros; +@item rn +@opindex rn @r{format for @command{nl}} +right justified, no leading zeros; +@item rz +@opindex rz @r{format for @command{nl}} +right justified, leading zeros. +@end table + +@item -p +@itemx --no-renumber +@opindex -p +@opindex --no-renumber +Do not reset the line number at the start of a logical page. + +@item -s @var{string} +@itemx --number-separator=@var{string} +@opindex -s +@opindex --number-separator +Separate the line number from the text line in the output with +@var{string} (default is the TAB character). + +@item -v @var{number} +@itemx --starting-line-number=@var{number} +@opindex -v +@opindex --starting-line-number +Set the initial line number on each logical page to @var{number} (default 1). +The starting @var{number} can be negative. + +@item -w @var{number} +@itemx --number-width=@var{number} +@opindex -w +@opindex --number-width +Use @var{number} characters for line numbers (default 6). + +@end table + +@exitstatus + + +@node od invocation +@section @command{od}: Write files in octal or other formats + +@pindex od +@cindex octal dump of files +@cindex hex dump of files +@cindex ASCII dump of files +@cindex file contents, dumping unambiguously + +@command{od} writes an unambiguous representation of each @var{file} +(@samp{-} means standard input), or standard input if none are given. +Synopses: + +@example +od [@var{option}]@dots{} [@var{file}]@dots{} +od [-abcdfilosx]@dots{} [@var{file}] [[+]@var{offset}[.][b]] +od [@var{option}]@dots{} --traditional [@var{file}]@c + [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]] +@end example + +Each line of output consists of the offset in the input, followed by +groups of data from the file. By default, @command{od} prints the offset in +octal, and each group of file data is a C @code{short int}'s worth of input +printed as a single octal number. + +If @var{offset} is given, it specifies how many input bytes to skip +before formatting and writing. By default, it is interpreted as an +octal number, but the optional trailing decimal point causes it to be +interpreted as decimal. If no decimal is specified and the offset +begins with @samp{0x} or @samp{0X} it is interpreted as a hexadecimal +number. If there is a trailing @samp{b}, the number of bytes skipped +will be @var{offset} multiplied by 512. + +If a command is of both the first and second forms, the second form is +assumed if the last operand begins with @samp{+} or (if there are two +operands) a digit. For example, in @samp{od foo 10} and @samp{od +10} +the @samp{10} is an offset, whereas in @samp{od 10} the @samp{10} is a +file name. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -A @var{radix} +@itemx --address-radix=@var{radix} +@opindex -A +@opindex --address-radix +@cindex radix for file offsets +@cindex file offset radix +Select the base in which file offsets are printed. @var{radix} can +be one of the following: + +@table @samp +@item d +decimal; +@item o +octal; +@item x +hexadecimal; +@item n +none (do not print offsets). +@end table + +The default is octal. + +@item --endian=@var{order} +@opindex --endian +@cindex byte-swapping +@cindex endianness +Reorder input bytes, to handle inputs with differing byte orders, +or to provide consistent output independent of the endian convention +of the current system. Swapping is performed according to the +specified @option{--type} size and endian @var{order}, which can be +@samp{little} or @samp{big}. + +@item -j @var{bytes} +@itemx --skip-bytes=@var{bytes} +@opindex -j +@opindex --skip-bytes +Skip @var{bytes} input bytes before formatting and writing. If +@var{bytes} begins with @samp{0x} or @samp{0X}, it is interpreted in +hexadecimal; otherwise, if it begins with @samp{0}, in octal; otherwise, +in decimal. +@multiplierSuffixes{bytes} + +@item -N @var{bytes} +@itemx --read-bytes=@var{bytes} +@opindex -N +@opindex --read-bytes +Output at most @var{bytes} bytes of the input. Prefixes and suffixes on +@code{bytes} are interpreted as for the @option{-j} option. + +@item -S @var{bytes} +@itemx --strings[=@var{bytes}] +@opindex -S +@opindex --strings +@cindex string constants, outputting +Instead of the normal output, output only @dfn{string constants}: at +least @var{bytes} consecutive printable characters, +followed by a zero byte (ASCII NUL). +Prefixes and suffixes on @var{bytes} are interpreted as for the +@option{-j} option. + +If @var{bytes} is omitted with @option{--strings}, the default is 3. + +@item -t @var{type} +@itemx --format=@var{type} +@opindex -t +@opindex --format +Select the format in which to output the file data. @var{type} is a +string of one or more of the below type indicator characters. If you +include more than one type indicator character in a single @var{type} +string, or use this option more than once, @command{od} writes one copy +of each output line using each of the data types that you specified, +in the order that you specified. + +Adding a trailing ``z'' to any type specification appends a display +of the single byte character representation of the printable characters +to the output line generated by the type specification. + +@table @samp +@item a +named character, ignoring high-order bit +@item c +printable single byte character, C backslash escape +or a 3 digit octal sequence +@item d +signed decimal +@item f +floating point (@pxref{Floating point}) +@item o +octal +@item u +unsigned decimal +@item x +hexadecimal +@end table + +The type @code{a} outputs things like @samp{sp} for space, @samp{nl} for +newline, and @samp{nul} for a zero byte. Only the least significant +seven bits of each byte is used; the high-order bit is ignored. +Type @code{c} outputs +@samp{ }, @samp{\n}, and @code{\0}, respectively. + +@cindex type size +Except for types @samp{a} and @samp{c}, you can specify the number +of bytes to use in interpreting each number in the given data type +by following the type indicator character with a decimal integer. +Alternately, you can specify the size of one of the C compiler's +built-in data types by following the type indicator character with +one of the following characters. For integers (@samp{d}, @samp{o}, +@samp{u}, @samp{x}): + +@table @samp +@item C +char +@item S +short +@item I +int +@item L +long +@end table + +For floating point (@code{f}): + +@table @asis +@item F +float +@item D +double +@item L +long double +@end table + +@item -v +@itemx --output-duplicates +@opindex -v +@opindex --output-duplicates +Output consecutive lines that are identical. By default, when two or +more consecutive output lines would be identical, @command{od} outputs only +the first line, and puts just an asterisk on the following line to +indicate the elision. + +@item -w[@var{n}] +@itemx --width[=@var{n}] +@opindex -w +@opindex --width +Dump @code{n} input bytes per output line. This must be a multiple of +the least common multiple of the sizes associated with the specified +output types. + +If this option is not given at all, the default is 16. If @var{n} is +omitted, the default is 32. + +@end table + +The next several options are shorthands for format specifications. +GNU @command{od} accepts any combination of shorthands and format +specification options. These options accumulate. + +@table @samp + +@item -a +@opindex -a +Output as named characters. Equivalent to @samp{-t a}. + +@item -b +@opindex -b +Output as octal bytes. Equivalent to @samp{-t o1}. + +@item -c +@opindex -c +Output as printable single byte characters, C backslash escapes +or 3 digit octal sequences. Equivalent to @samp{-t c}. + +@item -d +@opindex -d +Output as unsigned decimal two-byte units. Equivalent to @samp{-t u2}. + +@item -f +@opindex -f +Output as floats. Equivalent to @samp{-t fF}. + +@item -i +@opindex -i +Output as decimal ints. Equivalent to @samp{-t dI}. + +@item -l +@opindex -l +Output as decimal long ints. Equivalent to @samp{-t dL}. + +@item -o +@opindex -o +Output as octal two-byte units. Equivalent to @option{-t o2}. + +@item -s +@opindex -s +Output as decimal two-byte units. Equivalent to @option{-t d2}. + +@item -x +@opindex -x +Output as hexadecimal two-byte units. Equivalent to @samp{-t x2}. + +@item --traditional +@opindex --traditional +Recognize the non-option label argument that traditional @command{od} +accepted. The following syntax: + +@example +od --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]] +@end example + +@noindent +can be used to specify at most one file and optional arguments +specifying an offset and a pseudo-start address, @var{label}. +The @var{label} argument is interpreted +just like @var{offset}, but it specifies an initial pseudo-address. The +pseudo-addresses are displayed in parentheses following any normal +address. + +@end table + +@exitstatus + + +@node base32 invocation +@section @command{base32}: Transform data into printable data + +@pindex base32 +@cindex base32 encoding + +@command{base32} transforms data read from a file, or standard input, +into (or from) base32 encoded form. The base32 encoded form uses +printable ASCII characters to represent binary data. +The usage and options of this command are precisely the +same as for @command{base64}. @xref{base64 invocation}. +For more general encoding functionality see @ref{basenc invocation}. + + +@node base64 invocation +@section @command{base64}: Transform data into printable data + +@pindex base64 +@cindex base64 encoding + +@command{base64} transforms data read from a file, or standard input, +into (or from) base64 encoded form. The base64 encoded form uses +printable ASCII characters to represent binary data. +Synopses: + +@example +base64 [@var{option}]@dots{} [@var{file}] +base64 --decode [@var{option}]@dots{} [@var{file}] +@end example + +The base64 encoding expands data to roughly 133% of the original. +The base32 encoding expands data to roughly 160% of the original. +The format conforms to +@uref{https://tools.ietf.org/search/rfc4648, RFC 4648}. + +For more general encoding functionality see @ref{basenc invocation}. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -w @var{cols} +@itemx --wrap=@var{cols} +@opindex -w +@opindex --wrap +@cindex wrap data +@cindex column to wrap data after +During encoding, wrap lines after @var{cols} characters. This must be +a positive number. + +The default is to wrap after 76 characters. Use the value 0 to +disable line wrapping altogether. + +@item -d +@itemx --decode +@opindex -d +@opindex --decode +@cindex Decode base64 data +@cindex Base64 decoding +Change the mode of operation, from the default of encoding data, to +decoding data. Input is expected to be base64 encoded data, and the +output will be the original data. + +@item -i +@itemx --ignore-garbage +@opindex -i +@opindex --ignore-garbage +@cindex Ignore garbage in base64 stream +When decoding, newlines are always accepted. +During decoding, ignore unrecognized bytes, +to permit distorted data to be decoded. + +@end table + +@exitstatus + +@node basenc invocation +@section @command{basenc}: Transform data into printable data + +@pindex basenc +@cindex base32 encoding + +@command{basenc} transforms data read from a file, or standard input, +into (or from) various common encoding forms. The encoded form uses +printable ASCII characters to represent binary data. + +Synopses: + +@example +basenc @var{encoding} [@var{option}]@dots{} [@var{file}] +basenc @var{encoding} --decode [@var{option}]@dots{} [@var{file}] +@end example + +The @var{encoding} argument is required. If @var{file} is omitted, +@command{basenc} reads from standard input. +The @option{-w/--wrap},@option{-i/--ignore-garbage}, +@option{-d/--decode} options of this command are precisely the same as +for @command{base64}. @xref{base64 invocation}. + + +Supported @var{encoding}s are: + +@table @samp + +@item --base64 +@opindex --base64 +Encode into (or decode from with @option{-d/--decode}) base64 form. +The format conforms to +@uref{https://tools.ietf.org/search/rfc4648#section-4, RFC 4648#4}. +Equivalent to the @command{base64} command. + +@item --base64url +@opindex --base64url +Encode into (or decode from with @option{-d/--decode}) file-and-url-safe +base64 form (using @samp{_} and @samp{-} instead of @samp{+} and @samp{/}). +The format conforms to +@uref{https://tools.ietf.org/search/rfc4648#section-5, RFC 4648#5}. + +@item --base32 +@opindex --base32 +Encode into (or decode from with @option{-d/--decode}) base32 form. +The encoded data uses the @samp{ABCDEFGHIJKLMNOPQRSTUVWXYZ234567=} characters. +The format conforms to +@uref{https://tools.ietf.org/search/rfc4648#section-6, RFC 4648#6}. +Equivalent to the @command{base32} command. + +@item --base32hex +@opindex --base32hex +Encode into (or decode from with @option{-d/--decode}) Extended Hex Alphabet +base32 form. The encoded data uses the +@samp{0123456789ABCDEFGHIJKLMNOPQRSTUV=} characters. The format conforms to +@uref{https://tools.ietf.org/search/rfc4648#section-7, RFC 4648#7}. + +@item --base16 +@opindex --base16 +Encode into (or decode from with @option{-d/--decode}) base16 (hexadecimal) +form. The encoded data uses the @samp{0123456789ABCDEF} characters. The format +conforms to +@uref{https://tools.ietf.org/search/rfc4648#section-8, RFC 4648#8}. + +@item --base2lsbf +@opindex --base2lsbf +Encode into (or decode from with @option{-d/--decode}) binary string form +(@samp{0} and @samp{1}) with the @emph{least} significant bit of every byte +first. + +@item --base2msbf +@opindex --base2msbf +Encode into (or decode from with @option{-d/--decode}) binary string form +(@samp{0} and @samp{1}) with the @emph{most} significant bit of every byte +first. + +@item --z85 +@opindex --z85 +Encode into (or decode from with @option{-d/--decode}) Z85 form +(a modified Ascii85 form). The encoded data uses the +@samp{0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTU@ +VWXYZ.-:+=^!/*?&<>()[]@{@}@@%$#}. +characters. The format conforms to +@uref{https://rfc.zeromq.org/spec:32/Z85/, ZeroMQ spec:32/Z85}. + +When encoding with @option{--z85}, input length must be a multiple of 4; +when decoding with @option{--z85}, input length must be a multiple of 5. + +@end table + + + +Encoding/decoding examples: + +@example +$ printf '\376\117\202' | basenc --base64 +/k+C + +$ printf '\376\117\202' | basenc --base64url +_k-C + +$ printf '\376\117\202' | basenc --base32 +7ZHYE=== + +$ printf '\376\117\202' | basenc --base32hex +VP7O4=== + +$ printf '\376\117\202' | basenc --base16 +FE4F82 + +$ printf '\376\117\202' | basenc --base2lsbf +011111111111001001000001 + +$ printf '\376\117\202' | basenc --base2msbf +111111100100111110000010 + +$ printf '\376\117\202\000' | basenc --z85 +@@.FaC + +$ printf 01010100 | basenc --base2msbf --decode +T + +$ printf 01010100 | basenc --base2lsbf --decode +* +@end example + + + +@node Formatting file contents +@chapter Formatting file contents + +@cindex formatting file contents + +These commands reformat the contents of files. + +@menu +* fmt invocation:: Reformat paragraph text. +* pr invocation:: Paginate or columnate files for printing. +* fold invocation:: Wrap input lines to fit in specified width. +@end menu + + +@node fmt invocation +@section @command{fmt}: Reformat paragraph text + +@pindex fmt +@cindex reformatting paragraph text +@cindex paragraphs, reformatting +@cindex text, reformatting + +@command{fmt} fills and joins lines to produce output lines of (at most) +a given number of characters (75 by default). Synopsis: + +@example +fmt [@var{option}]@dots{} [@var{file}]@dots{} +@end example + +@command{fmt} reads from the specified @var{file} arguments (or standard +input if none are given), and writes to standard output. + +By default, blank lines, spaces between words, and indentation are +preserved in the output; successive input lines with different +indentation are not joined; tabs are expanded on input and introduced on +output. + +@cindex line-breaking +@cindex sentences and line-breaking +@cindex Knuth, Donald E. +@cindex Plass, Michael F. +@command{fmt} prefers breaking lines at the end of a sentence, and tries to +avoid line breaks after the first word of a sentence or before the last +word of a sentence. A @dfn{sentence break} is defined as either the end +of a paragraph or a word ending in any of @samp{.?!}, followed by two +spaces or end of line, ignoring any intervening parentheses or quotes. +Like @TeX{}, @command{fmt} reads entire ``paragraphs'' before choosing line +breaks; the algorithm is a variant of that given by Donald E. Knuth +and Michael F. Plass in ``Breaking Paragraphs Into Lines'', +@cite{Software: Practice & Experience} @b{11}, 11 (November 1981), +1119--1184. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -c +@itemx --crown-margin +@opindex -c +@opindex --crown-margin +@cindex crown margin +@dfn{Crown margin} mode: preserve the indentation of the first two +lines within a paragraph, and align the left margin of each subsequent +line with that of the second line. + +@item -t +@itemx --tagged-paragraph +@opindex -t +@opindex --tagged-paragraph +@cindex tagged paragraphs +@dfn{Tagged paragraph} mode: like crown margin mode, except that if +indentation of the first line of a paragraph is the same as the +indentation of the second, the first line is treated as a one-line +paragraph. + +@item -s +@itemx --split-only +@opindex -s +@opindex --split-only +Split lines only. Do not join short lines to form longer ones. This +prevents sample lines of code, and other such ``formatted'' text from +being unduly combined. + +@item -u +@itemx --uniform-spacing +@opindex -u +@opindex --uniform-spacing +Uniform spacing. Reduce spacing between words to one space, and spacing +between sentences to two spaces. + +@item -@var{width} +@itemx -w @var{width} +@itemx --width=@var{width} +@opindex -@var{width} +@opindex -w +@opindex --width +Fill output lines up to @var{width} characters (default 75 or @var{goal} +plus 10, if @var{goal} is provided). + +@item -g @var{goal} +@itemx --goal=@var{goal} +@opindex -g +@opindex --goal +@command{fmt} initially tries to make lines @var{goal} characters wide. +By default, this is 7% shorter than @var{width}. + +@item -p @var{prefix} +@itemx --prefix=@var{prefix} +Only lines beginning with @var{prefix} (possibly preceded by whitespace) +are subject to formatting. The prefix and any preceding whitespace are +stripped for the formatting and then re-attached to each formatted output +line. One use is to format certain kinds of program comments, while +leaving the code unchanged. + +@end table + +@exitstatus + +@node pr invocation +@section @command{pr}: Paginate or columnate files for printing + +@pindex pr +@cindex printing, preparing files for +@cindex multicolumn output, generating +@cindex merging files in parallel + +@command{pr} writes each @var{file} (@samp{-} means standard input), or +standard input if none are given, to standard output, paginating and +optionally outputting in multicolumn format; optionally merges all +@var{file}s, printing all in parallel, one per column. Synopsis: + +@example +pr [@var{option}]@dots{} [@var{file}]@dots{} +@end example + +@vindex LC_MESSAGES +By default, a 5-line header is printed at each page: two blank lines; +a line with the date, the file name, and the page count; and two more +blank lines. A footer of five blank lines is also printed. +The default @var{page_length} is 66 +lines. The default number of text lines is therefore 56. +The text line of the header takes the form +@samp{@var{date} @var{string} @var{page}}, with spaces inserted around +@var{string} so that the line takes up the full @var{page_width}. Here, +@var{date} is the date (see the @option{-D} or @option{--date-format} +option for details), @var{string} is the centered header string, and +@var{page} identifies the page number. The @env{LC_MESSAGES} locale +category affects the spelling of @var{page}; in the default C locale, it +is @samp{Page @var{number}} where @var{number} is the decimal page +number. + +Form feeds in the input cause page breaks in the output. Multiple form +feeds produce empty pages. + +Columns are of equal width, separated by an optional string (default +is @samp{space}). For multicolumn output, lines will always be truncated to +@var{page_width} (default 72), unless you use the @option{-J} option. +For single +column output no line truncation occurs by default. Use @option{-W} option to +truncate lines in that case. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item +@var{first_page}[:@var{last_page}] +@itemx --pages=@var{first_page}[:@var{last_page}] +@c The two following @opindex lines evoke warnings because they contain ':' +@c The 'info' spec does not permit that. If we use those lines, we end +@c up with truncated index entries that don't work. +@c @opindex +@var{first_page}[:@var{last_page}] +@c @opindex --pages=@var{first_page}[:@var{last_page}] +@opindex +@var{page_range} +@opindex --pages=@var{page_range} +Begin printing with page @var{first_page} and stop with @var{last_page}. +Missing @samp{:@var{last_page}} implies end of file. While estimating +the number of skipped pages each form feed in the input file results +in a new page. Page counting with and without @samp{+@var{first_page}} +is identical. By default, counting starts with the first page of input +file (not first page printed). Line numbering may be altered by @option{-N} +option. + +@item -@var{column} +@itemx --columns=@var{column} +@opindex -@var{column} +@opindex --columns +@cindex down columns +With each single @var{file}, produce @var{column} columns of output +(default is 1) and print columns down, unless @option{-a} is used. The +column width is automatically decreased as @var{column} increases; unless +you use the @option{-W/-w} option to increase @var{page_width} as well. +This option might well cause some lines to be truncated. The number of +lines in the columns on each page are balanced. The options @option{-e} +and @option{-i} are on for multiple text-column output. Together with +@option{-J} option column alignment and line truncation is turned off. +Lines of full length are joined in a free field format and @option{-S} +option may set field separators. @option{-@var{column}} may not be used +with @option{-m} option. + +@item -a +@itemx --across +@opindex -a +@opindex --across +@cindex across columns +With each single @var{file}, print columns across rather than down. The +@option{-@var{column}} option must be given with @var{column} greater than one. +If a line is too long to fit in a column, it is truncated. + +@item -c +@itemx --show-control-chars +@opindex -c +@opindex --show-control-chars +Print control characters using hat notation (e.g., @samp{^G}); print +other nonprinting characters in octal backslash notation. By default, +nonprinting characters are not changed. + +@item -d +@itemx --double-space +@opindex -d +@opindex --double-space +@cindex double spacing +Double space the output. + +@item -D @var{format} +@itemx --date-format=@var{format} +@cindex time formats +@cindex formatting times +Format header dates using @var{format}, using the same conventions as +for the command @samp{date +@var{format}}. @xref{date invocation}. +Except for directives, which start with +@samp{%}, characters in @var{format} are printed unchanged. You can use +this option to specify an arbitrary string in place of the header date, +e.g., @option{--date-format="Monday morning"}. + +@vindex POSIXLY_CORRECT +@vindex LC_TIME +The default date format is @samp{%Y-%m-%d %H:%M} (for example, +@samp{2020-07-09 23:59}); +but if the @env{POSIXLY_CORRECT} environment variable is set +and the @env{LC_TIME} locale category specifies the POSIX +locale, the default is @samp{%b %e %H:%M %Y} (for example, +@samp{Jul@ @ 9 23:59 2020}. + +@vindex TZ +Timestamps are listed according to the time zone rules specified by +the @env{TZ} environment variable, or by the system default rules if +@env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone +with @env{TZ}, libc, The GNU C Library Reference Manual}. + +@item -e[@var{in-tabchar}[@var{in-tabwidth}]] +@itemx --expand-tabs[=@var{in-tabchar}[@var{in-tabwidth}]] +@opindex -e +@opindex --expand-tabs +@cindex input tabs +Expand @var{tab}s to spaces on input. Optional argument @var{in-tabchar} is +the input tab character (default is the TAB character). Second optional +argument @var{in-tabwidth} is the input tab character's width (default +is 8). + +@item -f +@itemx -F +@itemx --form-feed +@opindex -F +@opindex -f +@opindex --form-feed +Use a form feed instead of newlines to separate output pages. This does +not alter the default page length of 66 lines. + +@item -h @var{header} +@itemx --header=@var{header} +@opindex -h +@opindex --header +Replace the file name in the header with the centered string @var{header}. +When using the shell, @var{header} should be quoted and should be +separated from @option{-h} by a space. + +@item -i[@var{out-tabchar}[@var{out-tabwidth}]] +@itemx --output-tabs[=@var{out-tabchar}[@var{out-tabwidth}]] +@opindex -i +@opindex --output-tabs +@cindex output tabs +Replace spaces with @var{tab}s on output. Optional argument @var{out-tabchar} +is the output tab character (default is the TAB character). Second optional +argument @var{out-tabwidth} is the output tab character's width (default +is 8). + +@item -J +@itemx --join-lines +@opindex -J +@opindex --join-lines +Merge lines of full length. Used together with the column options +@option{-@var{column}}, @option{-a -@var{column}} or @option{-m}. Turns off +@option{-W/-w} line truncation; +no column alignment used; may be used with +@option{--sep-string[=@var{string}]}. @option{-J} has been introduced +(together with @option{-W} and @option{--sep-string}) +to disentangle the old (POSIX-compliant) options @option{-w} and +@option{-s} along with the three column options. + + +@item -l @var{page_length} +@itemx --length=@var{page_length} +@opindex -l +@opindex --length +Set the page length to @var{page_length} (default 66) lines, including +the lines of the header [and the footer]. If @var{page_length} is less +than or equal to 10, the header and footer are omitted, as if the +@option{-t} option had been given. + +@item -m +@itemx --merge +@opindex -m +@opindex --merge +Merge and print all @var{file}s in parallel, one in each column. If a +line is too long to fit in a column, it is truncated, unless the @option{-J} +option is used. @option{--sep-string[=@var{string}]} may be used. +Empty pages in +some @var{file}s (form feeds set) produce empty columns, still marked +by @var{string}. The result is a continuous line numbering and column +marking throughout the whole merged file. Completely empty merged pages +show no separators or line numbers. The default header becomes +@samp{@var{date} @var{page}} with spaces inserted in the middle; this +may be used with the @option{-h} or @option{--header} option to fill up +the middle blank part. + +@item -n[@var{number-separator}[@var{digits}]] +@itemx --number-lines[=@var{number-separator}[@var{digits}]] +@opindex -n +@opindex --number-lines +Provide @var{digits} digit line numbering (default for @var{digits} is +5). With multicolumn output the number occupies the first @var{digits} +column positions of each text column or only each line of @option{-m} +output. With single column output the number precedes each line just as +@option{-m} does. Default counting of the line numbers starts with the +first line of the input file (not the first line printed, compare the +@option{--page} option and @option{-N} option). +Optional argument @var{number-separator} is the character appended to +the line number to separate it from the text followed. The default +separator is the TAB character. In a strict sense a TAB is always +printed with single column output only. The TAB width varies +with the TAB position, e.g., with the left @var{margin} specified +by @option{-o} option. With multicolumn output priority is given to +@samp{equal width of output columns} (a POSIX specification). +The TAB width is fixed to the value of the first column and does +not change with different values of left @var{margin}. That means a +fixed number of spaces is always printed in the place of the +@var{number-separator} TAB@. The tabification depends upon the output +position. + +@item -N @var{line_number} +@itemx --first-line-number=@var{line_number} +@opindex -N +@opindex --first-line-number +Start line counting with the number @var{line_number} at first line of +first page printed (in most cases not the first line of the input file). + +@item -o @var{margin} +@itemx --indent=@var{margin} +@opindex -o +@opindex --indent +@cindex indenting lines +@cindex left margin +Indent each line with a margin @var{margin} spaces wide (default is zero). +The total page width is the size of the margin plus the @var{page_width} +set with the @option{-W/-w} option. A limited overflow may occur with +numbered single column output (compare @option{-n} option). + +@item -r +@itemx --no-file-warnings +@opindex -r +@opindex --no-file-warnings +Do not print a warning message when an argument @var{file} cannot be +opened. (The exit status will still be nonzero, however.) + +@item -s[@var{char}] +@itemx --separator[=@var{char}] +@opindex -s +@opindex --separator +Separate columns by a single character @var{char}. The default for +@var{char} is the TAB character without @option{-w} and @samp{no +character} with @option{-w}. Without @option{-s} the default separator +@samp{space} is set. @option{-s[char]} turns off line truncation of all +three column options (@option{-COLUMN}|@option{-a -COLUMN}|@option{-m}) unless +@option{-w} is set. This is a POSIX-compliant formulation. + + +@item -S[@var{string}] +@itemx --sep-string[=@var{string}] +@opindex -S +@opindex --sep-string +Use @var{string} to separate output columns. The @option{-S} option doesn't +affect the @option{-W/-w} option, unlike the @option{-s} option which does. It +does not affect line truncation or column alignment. +Without @option{-S}, and with @option{-J}, @command{pr} uses the default output +separator, TAB@. +Without @option{-S} or @option{-J}, @command{pr} uses a @samp{space} +(same as @option{-S"@w{ }"}). +If no @samp{@var{string}} argument is specified, @samp{""} is assumed. + +@item -t +@itemx --omit-header +@opindex -t +@opindex --omit-header +Do not print the usual header [and footer] on each page, and do not fill +out the bottom of pages (with blank lines or a form feed). No page +structure is produced, but form feeds set in the input files are retained. +The predefined pagination is not changed. @option{-t} or @option{-T} may be +useful together with other options; e.g.: @option{-t -e4}, expand TAB characters +in the input file to 4 spaces but don't make any other changes. Use of +@option{-t} overrides @option{-h}. + +@item -T +@itemx --omit-pagination +@opindex -T +@opindex --omit-pagination +Do not print header [and footer]. In addition eliminate all form feeds +set in the input files. + +@item -v +@itemx --show-nonprinting +@opindex -v +@opindex --show-nonprinting +Print nonprinting characters in octal backslash notation. + +@item -w @var{page_width} +@itemx --width=@var{page_width} +@opindex -w +@opindex --width +Set page width to @var{page_width} characters for multiple text-column +output only (default for @var{page_width} is 72). The specified +@var{page_width} is rounded down so that columns have equal width. +@option{-s[CHAR]} turns off the default page width and any line truncation +and column alignment. +Lines of full length are merged, regardless of the column options +set. No @var{page_width} setting is possible with single column output. +A POSIX-compliant formulation. + +@item -W @var{page_width} +@itemx --page_width=@var{page_width} +@opindex -W +@opindex --page_width +Set the page width to @var{page_width} characters, honored with and +without a column option. With a column option, the specified @var{page_width} +is rounded down so that columns have equal width. Text lines are truncated, +unless @option{-J} is used. Together with one of the three column options +(@option{-@var{column}}, @option{-a -@var{column}} or @option{-m}) column +alignment is always used. The separator options @option{-S} or @option{-s} +don't disable the @option{-W} option. Default is 72 characters. Without +@option{-W @var{page_width}} and without any of the column options NO line +truncation is used (defined to keep downward compatibility and to meet +most frequent tasks). That's equivalent to @option{-W 72 -J}@. The header +line is never truncated. + +@end table + +@exitstatus + + +@node fold invocation +@section @command{fold}: Wrap input lines to fit in specified width + +@pindex fold +@cindex wrapping long input lines +@cindex folding long input lines + +@command{fold} writes each @var{file} (@option{-} means standard input), or +standard input if none are given, to standard output, breaking long +lines. Synopsis: + +@example +fold [@var{option}]@dots{} [@var{file}]@dots{} +@end example + +By default, @command{fold} breaks lines wider than 80 columns. The output +is split into as many lines as necessary. + +@cindex screen columns +@command{fold} counts screen columns by default; thus, a tab may count more +than one column, backspace decreases the column count, and carriage +return sets the column to zero. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -b +@itemx --bytes +@opindex -b +@opindex --bytes +Count bytes rather than columns, so that tabs, backspaces, and carriage +returns are each counted as taking up one column, just like other +characters. + +@item -s +@itemx --spaces +@opindex -s +@opindex --spaces +Break at word boundaries: the line is broken after the last blank before +the maximum line length. If the line contains no such blanks, the line +is broken at the maximum line length as usual. + +@item -w @var{width} +@itemx --width=@var{width} +@opindex -w +@opindex --width +Use a maximum line length of @var{width} columns instead of 80. + +For compatibility @command{fold} supports an obsolete option syntax +@option{-@var{width}}. New scripts should use @option{-w @var{width}} +instead. + +@end table + +@exitstatus + + +@node Output of parts of files +@chapter Output of parts of files + +@cindex output of parts of files +@cindex parts of files, output of + +These commands output pieces of the input. + +@menu +* head invocation:: Output the first part of files. +* tail invocation:: Output the last part of files. +* split invocation:: Split a file into pieces. +* csplit invocation:: Split a file into context-determined pieces. +@end menu + +@node head invocation +@section @command{head}: Output the first part of files + +@pindex head +@cindex initial part of files, outputting +@cindex first part of files, outputting + +@command{head} prints the first part (10 lines by default) of each +@var{file}; it reads from standard input if no files are given or +when given a @var{file} of @option{-}. Synopsis: + +@example +head [@var{option}]@dots{} [@var{file}]@dots{} +@end example + +If more than one @var{file} is specified, @command{head} prints a +one-line header consisting of: + +@example +==> @var{file name} <== +@end example + +@noindent +before the output for each @var{file}. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -c [-]@var{num} +@itemx --bytes=[-]@var{num} +@opindex -c +@opindex --bytes +Print the first @var{num} bytes, instead of initial lines. +However, if @var{num} is prefixed with a @samp{-}, +print all but the last @var{num} bytes of each file. +@multiplierSuffixes{num} + +@item -n [-]@var{num} +@itemx --lines=[-]@var{num} +@opindex -n +@opindex --lines +Output the first @var{num} lines. +However, if @var{num} is prefixed with a @samp{-}, +print all but the last @var{num} lines of each file. +Size multiplier suffixes are the same as with the @option{-c} option. + +@item -q +@itemx --quiet +@itemx --silent +@opindex -q +@opindex --quiet +@opindex --silent +Never print file name headers. + +@item -v +@itemx --verbose +@opindex -v +@opindex --verbose +Always print file name headers. + +@optZeroTerminated + +@end table + +For compatibility @command{head} also supports an obsolete option syntax +@option{-[@var{num}][bkm][cqv]}, which is recognized only if it is +specified first. @var{num} is a decimal number optionally followed +by a size letter (@samp{b}, @samp{k}, @samp{m}) as in @option{-c}, or +@samp{l} to mean count by lines, or other option letters (@samp{cqv}). +Scripts intended for standard hosts should use @option{-c @var{num}} +or @option{-n @var{num}} instead. If your script must also run on +hosts that support only the obsolete syntax, it is usually simpler to +avoid @command{head}, e.g., by using @samp{sed 5q} instead of +@samp{head -5}. + +@exitstatus + + +@node tail invocation +@section @command{tail}: Output the last part of files + +@pindex tail +@cindex last part of files, outputting + +@command{tail} prints the last part (10 lines by default) of each +@var{file}; it reads from standard input if no files are given or +when given a @var{file} of @samp{-}. Synopsis: + +@example +tail [@var{option}]@dots{} [@var{file}]@dots{} +@end example + +If more than one @var{file} is specified, @command{tail} prints a +one-line header before the output for each @var{file}, consisting of: + +@example +==> @var{file name} <== +@end example + +For further processing of tail output, it can be useful to convert the +file headers to line prefixes, which can be done like: + +@example +tail @dots{} | +awk ' + /^==> .* <==$/ @{prefix=substr($0,5,length-8)":"; next@} + @{print prefix$0@} +' | @dots{} +@end example + +@cindex BSD @command{tail} +GNU @command{tail} can output any amount of data (some other versions of +@command{tail} cannot). It also has no @option{-r} option (print in +reverse), since reversing a file is really a different job from printing +the end of a file; BSD @command{tail} (which is the one with @option{-r}) can +only reverse files that are at most as large as its buffer, which is +typically 32 KiB@. A more reliable and versatile way to reverse files is +the GNU @command{tac} command. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -c [+]@var{num} +@itemx --bytes=[+]@var{num} +@opindex -c +@opindex --bytes +Output the last @var{num} bytes, instead of final lines. +If @var{num} is prefixed with a @samp{+}, start printing with +byte @var{num} from the start of each file. For example to skip the first byte +use @code{tail -c +2}, while to skip all but the last byte use @code{tail -c 1}. +@multiplierSuffixes{num} + +@item -f +@itemx --follow[=@var{how}] +@opindex -f +@opindex --follow +@cindex growing files +@vindex name @r{follow option} +@vindex descriptor @r{follow option} +Loop forever trying to read more characters at the end of the file, +presumably because the file is growing. +If more than one file is given, @command{tail} prints a header whenever it +gets output from a different file, to indicate which file that output is +from. + +There are two ways to specify how you'd like to track files with this option, +but that difference is noticeable only when a followed file is removed or +renamed. +If you'd like to continue to track the end of a growing file even after +it has been unlinked, use @option{--follow=descriptor}. This is the default +behavior, but it is not useful if you're tracking a log file that may be +rotated (removed or renamed, then reopened). In that case, use +@option{--follow=name} to track the named file, perhaps by reopening it +periodically to see if it has been removed and recreated by some other program. +Note that the inotify-based implementation handles this case without +the need for any periodic reopening. + +No matter which method you use, if the tracked file is determined to have +shrunk, @command{tail} prints a message saying the file has been truncated +and resumes tracking from the start of the file, assuming it has been +truncated to 0, which is the usual truncation operation for log files. + +When a file is removed, @command{tail}'s behavior depends on whether it is +following the name or the descriptor. When following by name, tail can +detect that a file has been removed and gives a message to that effect, +and if @option{--retry} has been specified it will continue checking +periodically to see if the file reappears. +When following a descriptor, tail does not detect that the file has +been unlinked or renamed and issues no message; even though the file +may no longer be accessible via its original name, it may still be +growing. + +The option values @samp{descriptor} and @samp{name} may be specified only +with the long form of the option, not with @option{-f}. + +The @option{-f} option is ignored if +no @var{file} operand is specified and standard input is a FIFO or a pipe. +Likewise, the @option{-f} option has no effect for any +operand specified as @samp{-}, when standard input is a FIFO or a pipe. + +With kernel inotify support, output is triggered by file changes +and is generally very prompt. +Otherwise, @command{tail} sleeps for one second between checks -- +use @option{--sleep-interval=@var{n}} to change that default -- which can +make the output appear slightly less responsive or bursty. +When using tail without inotify support, you can make it more responsive +by using a sub-second sleep interval, e.g., via an alias like this: + +@example +alias tail='tail -s.1' +@end example + +@item -F +@opindex -F +This option is the same as @option{--follow=name --retry}. That is, tail +will attempt to reopen a file when it is removed. Should this fail, tail +will keep trying until it becomes accessible again. + +@item --max-unchanged-stats=@var{n} +@opindex --max-unchanged-stats +When tailing a file by name, if there have been @var{n} (default +n=@value{DEFAULT_MAX_N_UNCHANGED_STATS_BETWEEN_OPENS}) consecutive +iterations for which the file has not changed, then +@code{open}/@code{fstat} the file to determine if that file name is +still associated with the same device/inode-number pair as before. +When following a log file that is rotated, this is approximately the +number of seconds between when tail prints the last pre-rotation lines +and when it prints the lines that have accumulated in the new log file. +This option is meaningful only when polling (i.e., without inotify) +and when following by name. + +@item -n [+]@var{num} +@itemx --lines=[+]@var{} +@opindex -n +@opindex --lines +Output the last @var{num} lines. +If @var{num} is prefixed with a @samp{+}, start printing with +line @var{num} from the start of each file. For example to skip the first line +use @code{tail -n +2}, while to skip all but the last line use @code{tail -n 1}. +Size multiplier suffixes are the same as with the @option{-c} option. + +@item --pid=@var{pid} +@opindex --pid +When following by name or by descriptor, you may specify the process ID, +@var{pid}, of the sole writer of all @var{file} arguments. Then, shortly +after that process terminates, tail will also terminate. This will +work properly only if the writer and the tailing process are running on +the same machine. For example, to save the output of a build in a file +and to watch the file grow, if you invoke @command{make} and @command{tail} +like this then the tail process will stop when your build completes. +Without this option, you would have had to kill the @code{tail -f} +process yourself. + +@example +$ make >& makerr & tail --pid=$! -f makerr +@end example + +If you specify a @var{pid} that is not in use or that does not correspond +to the process that is writing to the tailed files, then @command{tail} +may terminate long before any @var{file}s stop growing or it may not +terminate until long after the real writer has terminated. +Note that @option{--pid} cannot be supported on some systems; @command{tail} +will print a warning if this is the case. + +@item -q +@itemx --quiet +@itemx --silent +@opindex -q +@opindex --quiet +@opindex --silent +Never print file name headers. + +@item --retry +@opindex --retry +Indefinitely try to open the specified file. +This option is useful mainly when following (and otherwise issues a warning). + +When following by file descriptor (i.e., with @option{--follow=descriptor}), +this option only affects the initial open of the file, as after a successful +open, @command{tail} will start following the file descriptor. + +When following by name (i.e., with @option{--follow=name}), @command{tail} +infinitely retries to re-open the given files until killed. + +Without this option, when @command{tail} encounters a file that doesn't +exist or is otherwise inaccessible, it reports that fact and +never checks it again. + +@item -s @var{number} +@itemx --sleep-interval=@var{number} +@opindex -s +@opindex --sleep-interval +Change the number of seconds to wait between iterations (the default is 1.0). +During one iteration, every specified file is checked to see if it has +changed size. +When @command{tail} uses inotify, this polling-related option +is usually ignored. However, if you also specify @option{--pid=@var{p}}, +@command{tail} checks whether process @var{p} is alive at least +every @var{number} seconds. +The @var{number} must be non-negative and can be a floating-point number +in either the current or the C locale. @xref{Floating point}. + +@item -v +@itemx --verbose +@opindex -v +@opindex --verbose +Always print file name headers. + +@optZeroTerminated + +@end table + +For compatibility @command{tail} also supports an obsolete usage +@samp{tail -[@var{num}][bcl][f] [@var{file}]}, which is recognized +only if it does not conflict with the usage described +above. This obsolete form uses exactly one option and at most one +file. In the option, @var{num} is an optional decimal number optionally +followed by a size letter (@samp{b}, @samp{c}, @samp{l}) to mean count +by 512-byte blocks, bytes, or lines, optionally followed by @samp{f} +which has the same meaning as @option{-f}. + +@vindex _POSIX2_VERSION +On systems not conforming to POSIX 1003.1-2001, the leading @samp{-} +can be replaced by @samp{+} in the traditional option syntax with the +same meaning as in counts, and on obsolete systems predating POSIX +1003.1-2001 traditional usage overrides normal usage when the two +conflict. This behavior can be controlled with the +@env{_POSIX2_VERSION} environment variable (@pxref{Standards +conformance}). + +Scripts intended for use on standard hosts should avoid traditional +syntax and should use @option{-c @var{num}[b]}, @option{-n +@var{num}}, and/or @option{-f} instead. If your script must also +run on hosts that support only the traditional syntax, you can often +rewrite it to avoid problematic usages, e.g., by using @samp{sed -n +'$p'} rather than @samp{tail -1}. If that's not possible, the script +can use a test like @samp{if tail -c +1 </dev/null >/dev/null 2>&1; +then @dots{}} to decide which syntax to use. + +Even if your script assumes the standard behavior, you should still +beware usages whose behaviors differ depending on the POSIX +version. For example, avoid @samp{tail - main.c}, since it might be +interpreted as either @samp{tail main.c} or as @samp{tail -- - +main.c}; avoid @samp{tail -c 4}, since it might mean either @samp{tail +-c4} or @samp{tail -c 10 4}; and avoid @samp{tail +4}, since it might +mean either @samp{tail ./+4} or @samp{tail -n +4}. + +@exitstatus + + +@node split invocation +@section @command{split}: Split a file into pieces. + +@pindex split +@cindex splitting a file into pieces +@cindex pieces, splitting a file into + +@command{split} creates output files containing consecutive or interleaved +sections of @var{input} (standard input if none is given or @var{input} +is @samp{-}). Synopsis: + +@example +split [@var{option}] [@var{input} [@var{prefix}]] +@end example + +By default, @command{split} puts 1000 lines of @var{input} (or whatever is +left over for the last section), into each output file. + +@cindex output file name prefix +The output files' names consist of @var{prefix} (@samp{x} by default) +followed by a group of characters (@samp{aa}, @samp{ab}, @dots{} by +default), such that concatenating the output files in traditional +sorted order by file name produces the original input file (except +@option{-nr/@var{n}}). By default split will initially create files +with two generated suffix characters, and will increase this width by two +when the next most significant position reaches the last character. +(@samp{yz}, @samp{zaaa}, @samp{zaab}, @dots{}). In this way an arbitrary +number of output files are supported, which sort as described above, +even in the presence of an @option{--additional-suffix} option. +If the @option{-a} option is specified and the output file names are +exhausted, @command{split} reports an error without deleting the +output files that it did create. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -l @var{lines} +@itemx --lines=@var{lines} +@opindex -l +@opindex --lines +Put @var{lines} lines of @var{input} into each output file. +If @option{--separator} is specified, then @var{lines} determines +the number of records. + +For compatibility @command{split} also supports an obsolete +option syntax @option{-@var{lines}}. New scripts should use +@option{-l @var{lines}} instead. + +@item -b @var{size} +@itemx --bytes=@var{size} +@opindex -b +@opindex --bytes +Put @var{size} bytes of @var{input} into each output file. +@multiplierSuffixes{size} + +@item -C @var{size} +@itemx --line-bytes=@var{size} +@opindex -C +@opindex --line-bytes +Put into each output file as many complete lines of @var{input} as +possible without exceeding @var{size} bytes. Individual lines or records +longer than @var{size} bytes are broken into multiple files. +@var{size} has the same format as for the @option{--bytes} option. +If @option{--separator} is specified, then @var{lines} determines +the number of records. + +@item --filter=@var{command} +@opindex --filter +With this option, rather than simply writing to each output file, +write through a pipe to the specified shell @var{command} for each output file. +@var{command} should use the $FILE environment variable, which is set +to a different output file name for each invocation of the command. +For example, imagine that you have a 1TiB compressed file +that, if uncompressed, would be too large to reside on secondary storage, +yet you must split it into individually-compressed pieces +of a more manageable size. +To do that, you might run this command: + +@example +xz -dc BIG.xz | split -b200G --filter='xz > $FILE.xz' - big- +@end example + +Assuming a 10:1 compression ratio, that would create about fifty 20GiB files +with names @file{big-aa.xz}, @file{big-ab.xz}, @file{big-ac.xz}, etc. + +@item -n @var{chunks} +@itemx --number=@var{chunks} +@opindex -n +@opindex --number + +Split @var{input} to @var{chunks} output files where @var{chunks} may be: + +@example +@var{n} generate @var{n} files based on current size of @var{input} +@var{k}/@var{n} output only @var{k}th of @var{n} to standard output +l/@var{n} generate @var{n} files without splitting lines or records +l/@var{k}/@var{n} likewise but output only @var{k}th of @var{n} to stdout +r/@var{n} like @samp{l} but use round robin distribution +r/@var{k}/@var{n} likewise but output only @var{k}th of @var{n} to stdout +@end example + +If the input size is not a multiple of @var{n}, early output files are +one byte longer than later output files, to make up the difference. +Any excess bytes appearing after the initial calculation are discarded +(except when using @samp{r} mode). + +All @var{n} files are created even if there are fewer than @var{n} lines, +or the @var{input} is truncated. + +For @samp{l} mode, chunks are approximately @var{input} size / @var{n}. +Although the @var{input} is still partitioned as before into @var{n} regions +of approximately equal size, if a line @emph{starts} within a partition +it is written completely to the corresponding file. Since lines or records +are not split even if they overlap a partition, the files written +can be larger or smaller than the partition size, and even empty +if a line/record is so long as to completely overlap the partition. + +When the input is a pipe or some other special file where the size +cannot easily be determined, there is no trouble for @samp{r} mode +because the size of the input is irrelevant. For other modes, such an +input is first copied to a temporary to determine its size. + +@item -a @var{length} +@itemx --suffix-length=@var{length} +@opindex -a +@opindex --suffix-length +Use suffixes of length @var{length}. If a @var{length} of 0 is specified, +this is the same as if (any previous) @option{-a} was not specified, and +thus enables the default behavior, which starts the suffix length at 2, +and unless @option{-n} or @option{--numeric-suffixes=@var{from}} is +specified, will auto increase the length by 2 as required. + +@item -d +@itemx --numeric-suffixes[=@var{from}] +@opindex -d +@opindex --numeric-suffixes +Use digits in suffixes rather than lower-case letters. The numerical +suffix counts from @var{from} if specified, 0 otherwise. + +@var{from} is supported with the long form option, and is used to either set the +initial suffix for a single run, or to set the suffix offset for independently +split inputs, and consequently the auto suffix length expansion described above +is disabled. Therefore you may also want to use option @option{-a} to allow +suffixes beyond @samp{99}. Note if option @option{--number} is specified and +the number of files is less than @var{from}, a single run is assumed and the +minimum suffix length required is automatically determined. + +@item -x +@itemx --hex-suffixes[=@var{from}] +@opindex -x +@opindex --hex-suffixes +Like @option{--numeric-suffixes}, but use hexadecimal numbers (in lower case). + +@item --additional-suffix=@var{suffix} +@opindex --additional-suffix +Append an additional @var{suffix} to output file names. @var{suffix} +must not contain slash. + +@item -e +@itemx --elide-empty-files +@opindex -e +@opindex --elide-empty-files +Suppress the generation of zero-length output files. This can happen +with the @option{--number} option if a file is (truncated to be) shorter +than the number requested, or if a line is so long as to completely +span a chunk. The output file sequence numbers, always run consecutively +even when this option is specified. + +@item -t @var{separator} +@itemx --separator=@var{separator} +@opindex -t +@opindex --separator +@cindex line separator character +@cindex record separator character +Use character @var{separator} as the record separator instead of the default +newline character (ASCII LF). +To specify ASCII NUL as the separator, use the two-character string @samp{\0}, +e.g., @samp{split -t '\0'}. + +@item -u +@itemx --unbuffered +@opindex -u +@opindex --unbuffered +Immediately copy input to output in @option{--number r/@dots{}} mode, +which is a much slower mode of operation. + +@item --verbose +@opindex --verbose +Write a diagnostic just before each output file is opened. + +@end table + +@exitstatus + +Here are a few examples to illustrate how the +@option{--number} (@option{-n}) option works: + +Notice how, by default, one line may be split onto two or more: + +@example +$ seq -w 6 10 > k; split -n3 k; head xa? +==> xaa <== +06 +07 +==> xab <== + +08 +0 +==> xac <== +9 +10 +@end example + +Use the "l/" modifier to suppress that: + +@example +$ seq -w 6 10 > k; split -nl/3 k; head xa? +==> xaa <== +06 +07 + +==> xab <== +08 +09 + +==> xac <== +10 +@end example + +Use the "r/" modifier to distribute lines in a round-robin fashion: + +@example +$ seq -w 6 10 > k; split -nr/3 k; head xa? +==> xaa <== +06 +09 + +==> xab <== +07 +10 + +==> xac <== +08 +@end example + +You can also extract just the Kth chunk. +This extracts and prints just the 7th "chunk" of 33: + +@example +$ seq 100 > k; split -nl/7/33 k +20 +21 +22 +@end example + + +@node csplit invocation +@section @command{csplit}: Split a file into context-determined pieces + +@pindex csplit +@cindex context splitting +@cindex splitting a file into pieces by context + +@command{csplit} creates zero or more output files containing sections of +@var{input} (standard input if @var{input} is @samp{-}). Synopsis: + +@example +csplit [@var{option}]@dots{} @var{input} @var{pattern}@dots{} +@end example + +The contents of the output files are determined by the @var{pattern} +arguments, as detailed below. An error occurs if a @var{pattern} +argument refers to a nonexistent line of the input file (e.g., if no +remaining line matches a given regular expression). After every +@var{pattern} has been matched, any remaining input is copied into one +last output file. + +By default, @command{csplit} prints the number of bytes written to each +output file after it has been created. + +The types of pattern arguments are: + +@table @samp + +@item @var{n} +Create an output file containing the input up to but not including line +@var{n} (a positive integer). If followed by a repeat count, also +create an output file containing the next @var{n} lines of the input +file once for each repeat. + +@item /@var{regexp}/[@var{offset}] +Create an output file containing the current line up to (but not +including) the next line of the input file that contains a match for +@var{regexp}. The optional @var{offset} is an integer, that can +be preceded by @samp{+} or @samp{-}. +If it is given, the input up to (but not including) the +matching line plus or minus @var{offset} is put into the output file, +and the line after that begins the next section of input. +Note lines within a negative offset of a regexp pattern +are not matched in subsequent regexp patterns. + +@item %@var{regexp}%[@var{offset}] +Like the previous type, except that it does not create an output +file, so that section of the input file is effectively ignored. + +@item @{@var{repeat-count}@} +Repeat the previous pattern @var{repeat-count} additional +times. The @var{repeat-count} can either be a positive integer or an +asterisk, meaning repeat as many times as necessary until the input is +exhausted. + +@end table + +The output files' names consist of a prefix (@samp{xx} by default) +followed by a suffix. By default, the suffix is an ascending sequence +of two-digit decimal numbers from @samp{00} to @samp{99}. In any case, +concatenating the output files in sorted order by file name produces the +original input file, excluding portions skipped with a %@var{regexp}% +pattern or the @option{--suppress-matched} option. + +By default, if @command{csplit} encounters an error or receives a hangup, +interrupt, quit, or terminate signal, it removes any output files +that it has created so far before it exits. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -f @var{prefix} +@itemx --prefix=@var{prefix} +@opindex -f +@opindex --prefix +@cindex output file name prefix +Use @var{prefix} as the output file name prefix. + +@item -b @var{format} +@itemx --suffix-format=@var{format} +@opindex -b +@opindex --suffix-format +@cindex output file name suffix +Use @var{format} as the output file name suffix. When this option is +specified, the suffix string must include exactly one +@code{printf(3)}-style conversion specification, possibly including +format specification flags, a field width, a precision specification, +or all of these kinds of modifiers. The format letter must convert a +binary unsigned integer argument to readable form. The format letters +@samp{d} and @samp{i} are aliases for @samp{u}, and the +@samp{u}, @samp{o}, @samp{x}, and @samp{X} conversions are allowed. The +entire @var{format} is given (with the current output file number) to +@code{sprintf(3)} to form the file name suffixes for each of the +individual output files in turn. If this option is used, the +@option{--digits} option is ignored. + +@item -n @var{digits} +@itemx --digits=@var{digits} +@opindex -n +@opindex --digits +Use output file names containing numbers that are @var{digits} digits +long instead of the default 2. + +@item -k +@itemx --keep-files +@opindex -k +@opindex --keep-files +Do not remove output files when errors are encountered. + +@item --suppress-matched +@opindex --suppress-matched +Do not output lines matching the specified @var{pattern}. +I.e., suppress the boundary line from the start of the second +and subsequent splits. + +@item -z +@itemx --elide-empty-files +@opindex -z +@opindex --elide-empty-files +Suppress the generation of zero-length output files. (In cases where +the section delimiters of the input file are supposed to mark the first +lines of each of the sections, the first output file will generally be a +zero-length file unless you use this option.) The output file sequence +numbers always run consecutively starting from 0, even when this option +is specified. + +@item -s +@itemx -q +@itemx --silent +@itemx --quiet +@opindex -s +@opindex -q +@opindex --silent +@opindex --quiet +Do not print counts of output file sizes. + +@end table + +@exitstatus + +Here is an example of its usage. +First, create an empty directory for the exercise, +and cd into it: + +@example +$ mkdir d && cd d +@end example + +Now, split the sequence of 1..14 on lines that end with 0 or 5: + +@example +$ seq 14 | csplit - '/[05]$/' '@{*@}' +8 +10 +15 +@end example + +Each number printed above is the size of an output +file that csplit has just created. +List the names of those output files: + +@example +$ ls +xx00 xx01 xx02 +@end example + +Use @command{head} to show their contents: + +@example +$ head xx* +==> xx00 <== +1 +2 +3 +4 + +==> xx01 <== +5 +6 +7 +8 +9 + +==> xx02 <== +10 +11 +12 +13 +14 +@end example + +Example of splitting input by empty lines: + +@example +$ csplit --suppress-matched @var{input.txt} '/^$/' '@{*@}' +@end example + +@c +@c TODO: "uniq" already supports "--group". +@c when it gets the "--key" option, uncomment this example. +@c +@c Example of splitting input file, based on the value of column 2: +@c +@c @example +@c $ cat @var{input.txt} | +@c sort -k2,2 | +@c uniq --group -k2,2 | +@c csplit -m '/^$/' '@{*@}' +@c @end example + +@node Summarizing files +@chapter Summarizing files + +@cindex summarizing files + +These commands generate just a few numbers representing entire +contents of files. + +@menu +* wc invocation:: Print newline, word, and byte counts. +* sum invocation:: Print checksum and block counts. +* cksum invocation:: Print CRC checksum and byte counts. +* md5sum invocation:: Print or check MD5 digests. +* b2sum invocation:: Print or check BLAKE2 digests. +* sha1sum invocation:: Print or check SHA-1 digests. +* sha2 utilities:: Print or check SHA-2 digests. +@end menu + + +@node wc invocation +@section @command{wc}: Print newline, word, and byte counts + +@pindex wc +@cindex byte count +@cindex character count +@cindex word count +@cindex line count + +@command{wc} counts the number of bytes, characters, words, and newlines +in each given @var{file}, or standard input if none are given +or for a @var{file} of @samp{-}. A word is a nonzero length +sequence of printable characters delimited by white space. Synopsis: + +@example +wc [@var{option}]@dots{} [@var{file}]@dots{} +@end example + +@cindex total counts +@command{wc} prints one line of counts for each file, and if the file was +given as an argument, it prints the file name following the counts. By default +if more than one @var{file} is given, @command{wc} prints a final line +containing the cumulative counts, with the file name @file{total}. +This @samp{total} line can be controlled with the @option{--total} option, +which is a GNU extension. +The counts are printed in this order: newlines, words, characters, bytes, +maximum line length. +Each count is printed right-justified in a field with at least one +space between fields so that the numbers and file names normally line +up nicely in columns. The width of the count fields varies depending +on the inputs, so you should not depend on a particular field width. +However, as a GNU extension, if only one count is printed, +it is guaranteed to be printed without leading spaces. + +By default, @command{wc} prints three counts: the newline, words, and byte +counts. Options can specify that only certain counts be printed. +Options do not undo others previously given, so + +@example +wc --bytes --words +@end example + +@noindent +prints both the byte counts and the word counts. + +With the @option{--max-line-length} option, @command{wc} prints the length +of the longest line per file, and if there is more than one file it +prints the maximum (not the sum) of those lengths. The line lengths here +are measured in screen columns, according to the current locale and +assuming tab positions in every 8th column. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -c +@itemx --bytes +@opindex -c +@opindex --bytes +Print only the byte counts. + +@item -m +@itemx --chars +@opindex -m +@opindex --chars +Print only the character counts, as per the current locale. +Invalid characters are not counted. + +@item -w +@itemx --words +@opindex -w +@opindex --words +Print only the word counts. A word is a nonzero length +sequence of printable characters separated by white space. + +@item -l +@itemx --lines +@opindex -l +@opindex --lines +Print only the newline character counts. +Note a file without a trailing newline character, +will not have that last portion included in the line count. + +@item -L +@itemx --max-line-length +@opindex -L +@opindex --max-line-length +Print only the maximum display widths. +Tabs are set at every 8th column. +Display widths of wide characters are considered. +Non-printable characters are given 0 width. + +@item --total=@var{when} +@opindex --total=@var{when} +Control when and how the final line with cumulative counts is printed. +@var{when} is one of: +@itemize @bullet +@item auto +@vindex auto @r{total option} +- This is the default mode of @command{wc} when no @option{--total} +option is specified. Output a total line if more than one @var{file} +is specified. +@item always +@vindex always @r{total option} +- Always output a total line, irrespective of the number of files processed. +@item only +@vindex only @r{total option} +- Only output total counts. I.e., don't print individual file counts, +suppress any leading spaces, and don't print the @samp{total} word itself, +to simplify subsequent processing. +@item never +@vindex none @r{total option} +- Never output a total line. +@end itemize + +@macro filesZeroFromOption{cmd,withTotalOption,subListOutput} +@item --files0-from=@var{file} +@opindex --files0-from=@var{file} +@c This is commented out to avoid a texi2dvi failure. +@c texi2dvi (GNU Texinfo 4.11) 1.104 +@c @cindex including files from @command{\cmd\} +Disallow processing files named on the command line, and instead process +those named in file @var{file}; each name being terminated by a zero byte +(ASCII NUL). +This is useful \withTotalOption\ +when the list of file names is so long that it may exceed a command line +length limitation. +In such cases, running @command{\cmd\} via @command{xargs} is undesirable +because it splits the list into pieces and makes @command{\cmd\} print +\subListOutput\ for each sublist rather than for the entire list. +One way to produce a list of ASCII NUL terminated file +names is with GNU +@command{find}, using its @option{-print0} predicate. +If @var{file} is @samp{-} then the ASCII NUL terminated +file names are read from standard input. +@end macro +@filesZeroFromOption{wc,,a total} + +For example, to find the length of the longest line in any @file{.c} or +@file{.h} file in the current hierarchy, do this: + +@example +find . -name '*.[ch]' -print0 | + wc -L --files0-from=- | tail -n1 +@end example + +@end table + +@exitstatus + + +@node sum invocation +@section @command{sum}: Print checksum and block counts + +@pindex sum +@cindex 16-bit checksum +@cindex checksum, 16-bit + +@command{sum} computes a 16-bit checksum for each given @var{file}, or +standard input if none are given or for a @var{file} of @samp{-}. Synopsis: + +@example +sum [@var{option}]@dots{} [@var{file}]@dots{} +@end example + +@command{sum} prints the checksum for each @var{file} followed by the +number of blocks in the file (rounded up). If at least one @var{file} +is given, file names are also printed. + +By default, GNU @command{sum} computes checksums using an algorithm +compatible with BSD @command{sum} and prints file sizes in units of +1024-byte blocks. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -r +@opindex -r +@cindex BSD @command{sum} +Use the default (BSD compatible) algorithm. This option is included for +compatibility with the System V @command{sum}. Unless @option{-s} was also +given, it has no effect. + +@item -s +@itemx --sysv +@opindex -s +@opindex --sysv +@cindex System V @command{sum} +Compute checksums using an algorithm compatible with System V +@command{sum}'s default, and print file sizes in units of 512-byte blocks. + +@end table + +@command{sum} is provided for compatibility; the @command{cksum} program (see +next section) is preferable in new applications. + +@exitstatus + + +@node cksum invocation +@section @command{cksum}: Print and verify file checksums + +@pindex cksum +@cindex cyclic redundancy check +@cindex CRC checksum +@cindex 32-bit checksum +@cindex checksum, 32-bit +@cindex digest + +@command{cksum} by default computes a 32-bit cyclic redundancy check (CRC) +checksum for each given @var{file}, or standard input if none are given or for +a @var{file} of @samp{-}. + +cksum also supports the @option{-a/--algorithm} option to select the +digest algorithm to use. @command{cksum} is the preferred interface +to these digests, subsuming the other standalone checksumming utilities, +which can be emulated using @code{cksum -a md5 --untagged "$@@"} etc. +Synopsis: + +@example +cksum [@var{option}]@dots{} [@var{file}]@dots{} +@end example + +@command{cksum} is typically used to ensure that files have not been corrupted, +by comparing the @command{cksum} output for the received files with the +@command{cksum} output for the original files (typically given in the +distribution). + +@menu +* cksum output modes:: Legacy and non Legacy output formats +* cksum general options:: Options supported only by cksum +* cksum common options:: Options supported also by standalone utilities +@end menu + +@node cksum output modes + +@table @asis + +@item Legacy output format +@command{cksum} by default prints the POSIX standard CRC checksum +for each file along with the number of bytes in the file, +and the file name unless no arguments were given. +The 32-bit CRC used is based on the polynomial used +for CRC error checking in the ISO/IEC 8802-3:1996 standard (Ethernet). +Similar output formats are used for the other legacy checksums +selectable with @option{--algorithm=sysv} or @option{--algorithm=bsd}, +detailed at @ref{sum invocation}. + +@item Tagged output format +With the @option{--algorithm} option selecting non legacy checksums, +the @command{cksum} command defaults to output of the form: +@example +@var{digest_name} (@var{file name}) = @var{digest} +@end example +Note the standalone checksum utilities can select this output +mode by using the @option{--tag} option. + +@item Untagged output format +With the @option{--untagged} option and the @option{--algorithm} option +selecting non legacy checksums, the following output format is used. +Note this is the default output format of the standalone checksum utilities. +For each @var{file}, we print the checksum, a space, a flag indicating +binary or text input mode, and the file name. +Binary mode is indicated with @samp{*}, text mode with @samp{ } (space). +Binary mode is the default on systems where it's significant, +otherwise text mode is the default. + +@end table + +Note without @option{--zero}, and with non legacy output formats, +if @var{file} contains a backslash, newline, or carriage return, +the line is started with a backslash, and each problematic character +in the file name is escaped with a backslash, making the output unambiguous +even in the presence of arbitrary file names. +Since the backslash character itself is escaped, any other backslash +escape sequences are reserved for future use. + +@node cksum general options +@table @samp + +@item -a +@itemx --algorithm +@opindex -a +@opindex --algorithm +@cindex digest algorithm +Compute checksums using the specified digest algorithm. + +Supported legacy checksums (which are not supported by @option{--check}): +@example +@samp{sysv} equivalent to @command{sum -s} +@samp{bsd} equivalent to @command{sum -r} +@samp{crc} equivalent to @command{cksum} (the default) +@end example + +Supported more modern digest algorithms are: +@example +@samp{md5} equivalent to @command{md5sum} +@samp{sha1} equivalent to @command{sha1sum} +@samp{sha224} equivalent to @command{sha224sum} +@samp{sha256} equivalent to @command{sha256sum} +@samp{sha384} equivalent to @command{sha384sum} +@samp{sha512} equivalent to @command{sha512sum} +@samp{blake2b} equivalent to @command{b2sum} +@samp{sm3} only available through @command{cksum} +@end example + +@item --base64 +@opindex --base64 +@cindex base64 checksum encoding +Print base64-encoded digests not hexadecimal. +This option is ignored with @option{--check}. +The format conforms to +@uref{https://tools.ietf.org/search/rfc4648#section-4, RFC 4648#4}. + +Note that each base64-encoded digest has zero, one or two trailing padding +(@samp{=}) bytes. The length of that padding is the checksum-bit-length +modulo 3, and the @option{--check} parser requires precisely the same +input digest string as what is output. I.e., removing or adding any +@samp{=} padding renders a digest non-matching. + +@item --debug +@opindex --debug +Output extra information to stderr, like the checksum implementation being used. + +@macro cksumLengthOption +@item -l +@itemx --length +@opindex -l +@opindex --length +@cindex BLAKE2 hash length +Change (shorten) the default digest length. +This is specified in bits and thus must be a multiple of 8. +This option is ignored when @option{--check} is specified, +as the length is automatically determined when checking. +@end macro +@cksumLengthOption + +@item --raw +@opindex --raw +@cindex raw binary checksum +Print only the unencoded raw binary digest for a single input. +Do not output the file name or anything else. +Use network byte order (big endian) where applicable: +for @samp{bsd}, @samp{crc}, and @samp{sysv}. +This option works only with a single input. +Unlike other output formats, @command{cksum} provides no way to +@option{--check} a @option{--raw} checksum. + +@item --untagged +@opindex --untagged +Output using the original Coreutils format used by the other +standalone checksum utilities like @command{md5sum} for example. +This format has the checksum at the start of the line, and may be +more amenable to further processing by other utilities, +especially in combination with the @option{--zero} option. +Note this does not identify the digest algorithm used for the checksum. +@xref{cksum output modes} for details of this format. +@end table + +@node cksum common options +@table @samp + +@item -b +@itemx --binary +@opindex -b +@opindex --binary +@cindex binary input files +Note this option is not supported by the @command{cksum} command, +as it operates in binary mode exclusively. +Treat each input file as binary, by reading it in binary mode and +outputting a @samp{*} flag. This is the inverse of @option{--text}. +On systems like GNU that do not distinguish between binary +and text files, this option merely flags each input mode as binary: +the checksum is unaffected. This option is the default on systems +like MS-DOS that distinguish between binary and text files, except +for reading standard input when standard input is a terminal. + +@item -c +@itemx --check +Read file names and checksum information (not data) from each +@var{file} (or from standard input if no @var{file} was specified) and report +whether the checksums match the contents of the named files. +The input to this mode is usually the output of +a prior, checksum-generating run of the command. + +Three input formats are supported. Either the default output +format described above, the @option{--tag} output format, +or the BSD reversed mode format which is similar to the default mode, +but doesn't use a character to distinguish binary and text modes. + +For the @command{cksum} command, the @option{--check} option +supports auto-detecting the digest algorithm to use, +when presented with checksum information in the @option{--tag} output format. + +Also for the @command{cksum} command, the @option{--check} option +auto-detects the digest encoding, accepting both standard hexadecimal +checksums and those generated via @command{cksum} with its +@option{--base64} option. + +Output with @option{--zero} enabled is not supported by @option{--check}. +@sp 1 +For each such line, @command{cksum} reads the named file and computes its +checksum. Then, if the computed message digest does not match the +one on the line with the file name, the file is noted as having +failed the test. Otherwise, the file passes the test. +By default, for each valid line, one line is written to standard +output indicating whether the named file passed the test. +After all checks have been performed, if there were any failures, +a warning is issued to standard error. +Use the @option{--status} option to inhibit that output. +If any listed file cannot be opened or read, if any valid line has +a checksum inconsistent with the associated file, or if no valid +line is found, @command{cksum} exits with nonzero status. Otherwise, +it exits successfully. +Note the @command{cksum} command doesn't support @option{--check} +with the older @samp{sysv}, @samp{bsd}, or @samp{crc} algorithms. + +@item --ignore-missing +@opindex --ignore-missing +@cindex verifying checksums +This option is useful only when verifying checksums. +When verifying checksums, don't fail or report any status +for missing files. This is useful when verifying a subset +of downloaded files given a larger list of checksums. + +@item --quiet +@opindex --quiet +@cindex verifying checksums +This option is useful only when verifying checksums. +When verifying checksums, don't generate an 'OK' message per successfully +checked file. Files that fail the verification are reported in the +default one-line-per-file format. If there is any checksum mismatch, +print a warning summarizing the failures to standard error. + +@item --status +@opindex --status +@cindex verifying checksums +This option is useful only when verifying checksums. +When verifying checksums, don't generate the default one-line-per-file +diagnostic and don't output the warning summarizing any failures. +Failures to open or read a file still evoke individual diagnostics to +standard error. +If all listed files are readable and are consistent with the associated +checksums, exit successfully. Otherwise exit with a status code +indicating there was a failure. + +@item --tag +@opindex --tag +@cindex BSD output +Output BSD style checksums, which indicate the checksum algorithm used. +As a GNU extension, if @option{--zero} is not used, file names with problematic +characters are escaped as described above, using the same escaping indicator of +@samp{\} at the start of the line, as used with the other output format. +The @option{--tag} option implies binary mode, and is disallowed with +@option{--text} mode as supporting that would unnecessarily complicate +the output format, while providing little benefit. +@xref{cksum output modes} for details of this format. +The @command{cksum} command, uses @option{--tag} as its default output format. + +@item -t +@itemx --text +@opindex -t +@opindex --text +@cindex text input files +Note this option is not supported by the @command{cksum} command. +Treat each input file as text, by reading it in text mode and +outputting a @samp{ } flag. This is the inverse of @option{--binary}. +This option is the default on systems like GNU that do not +distinguish between binary and text files. On other systems, it is +the default for reading standard input when standard input is a +terminal. This mode is never defaulted to if @option{--tag} is used. + +@item -w +@itemx --warn +@opindex -w +@opindex --warn +@cindex verifying checksums +When verifying checksums, warn about improperly formatted checksum lines. +This option is useful only if all but a few lines in the checked input +are valid. + +@item --strict +@opindex --strict +@cindex verifying checksums +When verifying checksums, +if one or more input line is invalid, +exit nonzero after all warnings have been issued. + +@optZero +Also file name escaping is not used. +@end table + +@node md5sum invocation +@section @command{md5sum}: Print or check MD5 digests + +@pindex md5sum +@cindex MD5 +@cindex 128-bit checksum +@cindex checksum, 128-bit +@cindex fingerprint, 128-bit +@cindex message-digest, 128-bit + +@command{md5sum} computes a 128-bit checksum (or @dfn{fingerprint} or +@dfn{message-digest}) for each specified @var{file}. + +@macro weakHash{hash} +Note: The \hash\ digest is more reliable than a simple CRC (provided by +the @command{cksum} command) for detecting accidental file corruption, +as the chances of accidentally having two files with identical \hash\ +are vanishingly small. However, it should not be considered secure +against malicious tampering: although finding a file with a given \hash\ +fingerprint is considered infeasible at the moment, it is known how +to modify certain files, including digital certificates, so that they +appear valid when signed with an \hash\ digest. For more secure hashes, +consider using SHA-2, or the newer @command{b2sum} command. +@xref{sha2 utilities}. @xref{b2sum invocation}. +@end macro +@weakHash{MD5} + +@macro checksumUsage{command} +If a @var{file} is specified as @samp{-} or if no files are given +@command{\command\} computes the checksum for the standard input. +@command{\command\} can also determine whether a file and checksum are +consistent. Synopsis: + +@example +\command\ [@var{option}]@dots{} [@var{file}]@dots{} +@end example + +@command{\command\} uses the @samp{Untagged output format} +for each specified file, as described at @ref{cksum output modes}. + +The program accepts @ref{cksum common options}. Also see @ref{Common options}. +@end macro +@checksumUsage{md5sum} + +@exitstatus + + +@node b2sum invocation +@section @command{b2sum}: Print or check BLAKE2 digests + +@pindex b2sum +@cindex BLAKE2 +@cindex 512-bit checksum +@cindex checksum, 512-bit +@cindex fingerprint, 512-bit +@cindex message-digest, 512-bit + +@command{b2sum} computes a 512-bit checksum for each specified +@var{file}. + +@checksumUsage{b2sum} + +In addition @command{b2sum} supports the following options. + +@table @samp +@cksumLengthOption +@end table + + +@node sha1sum invocation +@section @command{sha1sum}: Print or check SHA-1 digests + +@pindex sha1sum +@cindex SHA-1 +@cindex 160-bit checksum +@cindex checksum, 160-bit +@cindex fingerprint, 160-bit +@cindex message-digest, 160-bit + +@command{sha1sum} computes a 160-bit checksum for each specified @var{file}. + +@weakHash{SHA-1} + +@checksumUsage{sha1sum} + +@node sha2 utilities +@section sha2 utilities: Print or check SHA-2 digests + +@pindex sha224sum +@pindex sha256sum +@pindex sha384sum +@pindex sha512sum +@cindex SHA-2 +@cindex 224-bit checksum +@cindex 256-bit checksum +@cindex 384-bit checksum +@cindex 512-bit checksum +@cindex checksum, 224-bit +@cindex checksum, 256-bit +@cindex checksum, 384-bit +@cindex checksum, 512-bit +@cindex fingerprint, 224-bit +@cindex fingerprint, 256-bit +@cindex fingerprint, 384-bit +@cindex fingerprint, 512-bit +@cindex message-digest, 224-bit +@cindex message-digest, 256-bit +@cindex message-digest, 384-bit +@cindex message-digest, 512-bit + +The commands @command{sha224sum}, @command{sha256sum}, +@command{sha384sum} and @command{sha512sum} compute checksums of +various lengths (respectively 224, 256, 384 and 512 bits), +collectively known as the SHA-2 hashes. + +@checksumUsage{sha???sum} + + +@node Operating on sorted files +@chapter Operating on sorted files + +@cindex operating on sorted files +@cindex sorted files, operations on + +These commands work with (or produce) sorted files. + +@menu +* sort invocation:: Sort text files. +* shuf invocation:: Shuffle text files. +* uniq invocation:: Uniquify files. +* comm invocation:: Compare two sorted files line by line. +* ptx invocation:: Produce a permuted index of file contents. +* tsort invocation:: Topological sort. +@end menu + + +@node sort invocation +@section @command{sort}: Sort text files + +@pindex sort +@cindex sorting files + +@command{sort} sorts, merges, or compares all the lines from the given +files, or standard input if none are given or for a @var{file} of +@samp{-}. By default, @command{sort} writes the results to standard +output. Synopsis: + +@example +sort [@var{option}]@dots{} [@var{file}]@dots{} +@end example + +@cindex sort stability +@cindex sort's last-resort comparison +Many options affect how @command{sort} compares lines; if the results +are unexpected, try the @option{--debug} option to see what happened. +A pair of lines is compared as follows: +@command{sort} compares each pair of fields (see @option{--key}), in the +order specified on the command line, according to the associated +ordering options, until a difference is found or no fields are left. +If no key fields are specified, @command{sort} uses a default key of +the entire line. Finally, as a last resort when all keys compare +equal, @command{sort} compares entire lines as if no ordering options +other than @option{--reverse} (@option{-r}) were specified. The +@option{--stable} (@option{-s}) option disables this @dfn{last-resort +comparison} so that lines in which all fields compare equal are left +in their original relative order. The @option{--unique} +(@option{-u}) option also disables the last-resort comparison. +@vindex LC_ALL +@vindex LC_COLLATE + +Unless otherwise specified, all comparisons use the character collating +sequence specified by the @env{LC_COLLATE} locale.@footnote{If you +use a non-POSIX locale (e.g., by setting @env{LC_ALL} +to @samp{en_US}), then @command{sort} may produce output that is sorted +differently than you're accustomed to. In that case, set the @env{LC_ALL} +environment variable to @samp{C}@. Note that setting only @env{LC_COLLATE} +has two problems. First, it is ineffective if @env{LC_ALL} is also set. +Second, it has undefined behavior if @env{LC_CTYPE} (or @env{LANG}, if +@env{LC_CTYPE} is unset) is set to an incompatible value. For example, +you get undefined behavior if @env{LC_CTYPE} is @code{ja_JP.PCK} but +@env{LC_COLLATE} is @code{en_US.UTF-8}.} +A line's trailing newline is not part of the line for comparison +purposes. If the final byte of an input file is not a newline, GNU +@command{sort} silently supplies one. GNU @command{sort} (as +specified for all GNU utilities) has no limit on input line length or +restrictions on bytes allowed within lines. + +@command{sort} has three modes of operation: sort (the default), merge, +and check for order. The following options change the operation +mode: + +@table @samp + +@item -c +@itemx --check +@itemx --check=diagnose-first +@opindex -c +@opindex --check +@cindex checking whether a file is sorted +Check whether the given file is already sorted: if it is not all +sorted, print a diagnostic containing the first out-of-order line and +exit with a status of 1. +Otherwise, exit successfully. +At most one input file can be given. + +@item -C +@itemx --check=quiet +@itemx --check=silent +@opindex -c +@opindex --check +@cindex checking whether a file is sorted +Exit successfully if the given file is already sorted, and +exit with status 1 otherwise. +At most one input file can be given. +This is like @option{-c}, except it does not print a diagnostic. + +@item -m +@itemx --merge +@opindex -m +@opindex --merge +@cindex merging sorted files +Merge the given files by sorting them as a group. Each input file must +always be individually sorted. It always works to sort instead of +merge; merging is provided because it is faster, in the case where it +works. + +@end table + +@cindex exit status of @command{sort} +Exit status: + +@display +0 if no error occurred +1 if invoked with @option{-c} or @option{-C} and the input is not sorted +2 if an error occurred +@end display + +@vindex TMPDIR +If the environment variable @env{TMPDIR} is set, @command{sort} uses its +value as the directory for temporary files instead of @file{/tmp}. The +@option{--temporary-directory} (@option{-T}) option in turn overrides +the environment variable. + +The following options affect the ordering of output lines. They may be +specified globally or as part of a specific key field. If no key +fields are specified, global options apply to comparison of entire +lines; otherwise the global options are inherited by key fields that do +not specify any special options of their own. In pre-POSIX +versions of @command{sort}, global options affect only later key fields, +so portable shell scripts should specify global options first. + +@table @samp + +@item -b +@itemx --ignore-leading-blanks +@opindex -b +@opindex --ignore-leading-blanks +@cindex blanks, ignoring leading +@vindex LC_CTYPE +Ignore leading blanks when finding sort keys in each line. +By default a blank is a space or a tab, but the @env{LC_CTYPE} locale +can change this. Note blanks may be ignored by your locale's collating +rules, but without this option they will be significant for character +positions specified in keys with the @option{-k} option. + +@item -d +@itemx --dictionary-order +@opindex -d +@opindex --dictionary-order +@cindex dictionary order +@cindex phone directory order +@cindex telephone directory order +@vindex LC_CTYPE +Sort in @dfn{phone directory} order: ignore all characters except +letters, digits and blanks when sorting. +By default letters and digits are those of ASCII and a blank +is a space or a tab, but the @env{LC_CTYPE} locale can change this. + +@item -f +@itemx --ignore-case +@opindex -f +@opindex --ignore-case +@cindex ignoring case +@cindex case folding +@vindex LC_CTYPE +Fold lowercase characters into the equivalent uppercase characters when +comparing so that, for example, @samp{b} and @samp{B} sort as equal. +The @env{LC_CTYPE} locale determines character types. +When used with @option{--unique} those lower case equivalent lines are +thrown away. (There is currently no way to throw away the upper case +equivalent instead. (Any @option{--reverse} given would only affect +the final result, after the throwing away.)) + +@item -g +@itemx --general-numeric-sort +@itemx --sort=general-numeric +@opindex -g +@opindex --general-numeric-sort +@opindex --sort +@cindex general numeric sort +@vindex LC_NUMERIC +Sort numerically, converting a prefix of each line to a long +double-precision floating point number. @xref{Floating point}. +Do not report overflow, underflow, or conversion errors. +Use the following collating sequence: + +@itemize @bullet +@item +Lines that do not start with numbers (all considered to be equal). +@item +NaNs (``Not a Number'' values, in IEEE floating point arithmetic) +in a consistent but machine-dependent order. +@item +Minus infinity. +@item +Finite numbers in ascending numeric order (with @math{-0} and @math{+0} equal). +@item +Plus infinity. +@end itemize + +Use this option only if there is no alternative; it is much slower than +@option{--numeric-sort} (@option{-n}) and it can lose information when +converting to floating point. + +You can use this option to sort hexadecimal numbers prefixed with +@samp{0x} or @samp{0X}, where those numbers are not fixed width, +or of varying case. However for hex numbers of consistent case, +and left padded with @samp{0} to a consistent width, a standard +lexicographic sort will be faster. + +@item -h +@itemx --human-numeric-sort +@itemx --sort=human-numeric +@opindex -h +@opindex --human-numeric-sort +@opindex --sort +@cindex human numeric sort +@vindex LC_NUMERIC +Sort numerically, first by numeric sign (negative, zero, or positive); +then by SI suffix (either empty, or @samp{k} or @samp{K}, or +one of @samp{MGTPEZYRQ}, in that order; @pxref{Block size}); and finally +by numeric value. For example, @samp{1023M} sorts before @samp{1G} +because @samp{M} (mega) precedes @samp{G} (giga) as an SI +suffix. This option sorts values that are consistently scaled to the +nearest suffix, regardless of whether suffixes denote powers of 1000 +or 1024, and it therefore sorts the output of any single invocation of +the @command{df}, @command{du}, or @command{ls} commands that are +invoked with their @option{--human-readable} or @option{--si} options. +The syntax for numbers is the same as for the @option{--numeric-sort} +option; the SI suffix must immediately follow the number. +Note also the @command{numfmt} command, which can be used to reformat +numbers to human format @emph{after} the sort, thus often allowing +sort to operate on more accurate numbers. + +@item -i +@itemx --ignore-nonprinting +@opindex -i +@opindex --ignore-nonprinting +@cindex nonprinting characters, ignoring +@cindex unprintable characters, ignoring +@vindex LC_CTYPE +Ignore nonprinting characters. +The @env{LC_CTYPE} locale determines character types. +This option has no effect if the stronger @option{--dictionary-order} +(@option{-d}) option is also given. + +@item -M +@itemx --month-sort +@itemx --sort=month +@opindex -M +@opindex --month-sort +@opindex --sort +@cindex months, sorting by +@vindex LC_TIME +An initial string, consisting of any amount of blanks, followed +by a month name abbreviation, is folded to UPPER case and +compared in the order @samp{JAN} < @samp{FEB} < @dots{} < @samp{DEC}@. +Invalid names compare low to valid names. The @env{LC_TIME} locale +category determines the month spellings. +By default a blank is a space or a tab, but the @env{LC_CTYPE} locale +can change this. + +@item -n +@itemx --numeric-sort +@itemx --sort=numeric +@opindex -n +@opindex --numeric-sort +@opindex --sort +@cindex numeric sort +@vindex LC_NUMERIC +Sort numerically. The number begins each line and consists +of optional blanks, an optional @samp{-} sign, and zero or more +digits possibly separated by thousands separators, optionally followed +by a decimal-point character and zero or more digits. An empty +number is treated as @samp{0}. The @env{LC_NUMERIC} +locale specifies the decimal-point character and thousands separator. +By default a blank is a space or a tab, but the @env{LC_CTYPE} locale +can change this. + +Comparison is exact; there is no rounding error. + +Neither a leading @samp{+} nor exponential notation is recognized. +To compare such strings numerically, use the +@option{--general-numeric-sort} (@option{-g}) option. + +@item -V +@itemx --version-sort +@opindex -V +@opindex --version-sort +@cindex version number sort +Sort by version name and number. It behaves like a standard sort, +except that each sequence of decimal digits is treated numerically +as an index/version number. (@xref{Version sort ordering}.) + +@item -r +@itemx --reverse +@opindex -r +@opindex --reverse +@cindex reverse sorting +Reverse the result of comparison, so that lines with greater key values +appear earlier in the output instead of later. + +@item -R +@itemx --random-sort +@itemx --sort=random +@opindex -R +@opindex --random-sort +@opindex --sort +@cindex random sort +Sort by hashing the input keys and then sorting the hash values. +Choose the hash function at random, ensuring that it is free of +collisions so that differing keys have differing hash values. This is +like a random permutation of the inputs (@pxref{shuf invocation}), +except that keys with the same value sort together. + +If multiple random sort fields are specified, the same random hash +function is used for all fields. To use different random hash +functions for different fields, you can invoke @command{sort} more +than once. + +The choice of hash function is affected by the +@option{--random-source} option. + +@end table + +Other options are: + +@table @samp + +@item --compress-program=@var{prog} +Compress any temporary files with the program @var{prog}. + +With no arguments, @var{prog} must compress standard input to standard +output, and when given the @option{-d} option it must decompress +standard input to standard output. + +Terminate with an error if @var{prog} exits with nonzero status. + +White space and the backslash character should not appear in +@var{prog}; they are reserved for future use. + +@filesZeroFromOption{sort,,sorted output} + +@item -k @var{pos1}[,@var{pos2}] +@itemx --key=@var{pos1}[,@var{pos2}] +@opindex -k +@opindex --key +@cindex sort field +Specify a sort field that consists of the part of the line between +@var{pos1} and @var{pos2} (or the end of the line, if @var{pos2} is +omitted), @emph{inclusive}. + +In its simplest form @var{pos} specifies a field number (starting with 1), +with fields being separated by runs of blank characters, and by default +those blanks being included in the comparison at the start of each field. +To adjust the handling of blank characters see the @option{-b} and +@option{-t} options. + +More generally, +each @var{pos} has the form @samp{@var{f}[.@var{c}][@var{opts}]}, +where @var{f} is the number of the field to use, and @var{c} is the number +of the first character from the beginning of the field. Fields and character +positions are numbered starting with 1; a character position of zero in +@var{pos2} indicates the field's last character. If @samp{.@var{c}} is +omitted from @var{pos1}, it defaults to 1 (the beginning of the field); +if omitted from @var{pos2}, it defaults to 0 (the end of the field). +@var{opts} are ordering options, allowing individual keys to be sorted +according to different rules; see below for details. Keys can span +multiple fields. + +Example: To sort on the second field, use @option{--key=2,2} +(@option{-k 2,2}). See below for more notes on keys and more examples. +See also the @option{--debug} option to help determine the part +of the line being used in the sort. + +@item --debug +Highlight the portion of each line used for sorting. +Also issue warnings about questionable usage to standard error. + +@item --batch-size=@var{nmerge} +@opindex --batch-size +@cindex number of inputs to merge, nmerge +Merge at most @var{nmerge} inputs at once. + +When @command{sort} has to merge more than @var{nmerge} inputs, +it merges them in groups of @var{nmerge}, saving the result in +a temporary file, which is then used as an input in a subsequent merge. + +A large value of @var{nmerge} may improve merge performance and decrease +temporary storage utilization at the expense of increased memory usage +and I/O@. Conversely a small value of @var{nmerge} may reduce memory +requirements and I/O at the expense of temporary storage consumption and +merge performance. + +The value of @var{nmerge} must be at least 2. The default value is +currently 16, but this is implementation-dependent and may change in +the future. + +The value of @var{nmerge} may be bounded by a resource limit for open +file descriptors. The commands @samp{ulimit -n} or @samp{getconf +OPEN_MAX} may display limits for your systems; these limits may be +modified further if your program already has some files open, or if +the operating system has other limits on the number of open files. If +the value of @var{nmerge} exceeds the resource limit, @command{sort} +silently uses a smaller value. + +@item -o @var{output-file} +@itemx --output=@var{output-file} +@opindex -o +@opindex --output +@cindex overwriting of input, allowed +Write output to @var{output-file} instead of standard output. +Normally, @command{sort} reads all input before opening +@var{output-file}, so you can sort a file in place by using +commands like @code{sort -o F F} and @code{cat F | sort -o F}@. +However, it is often safer to output to an otherwise-unused file, as +data may be lost if the system crashes or @command{sort} encounters +an I/O or other serious error while a file is being sorted in place. +Also, @command{sort} with @option{--merge} (@option{-m}) can open +the output file before reading all input, so a command like @code{cat +F | sort -m -o F - G} is not safe as @command{sort} might start +writing @file{F} before @command{cat} is done reading it. + +@vindex POSIXLY_CORRECT +On newer systems, @option{-o} cannot appear after an input file if +@env{POSIXLY_CORRECT} is set, e.g., @samp{sort F -o F}@. Portable +scripts should specify @option{-o @var{output-file}} before any input +files. + +@item --random-source=@var{file} +@opindex --random-source +@cindex random source for sorting +Use @var{file} as a source of random data used to determine which +random hash function to use with the @option{-R} option. @xref{Random +sources}. + +@item -s +@itemx --stable +@opindex -s +@opindex --stable +@cindex sort stability +@cindex sort's last-resort comparison + +Make @command{sort} stable by disabling its last-resort comparison. +This option has no effect if no fields or global ordering options +other than @option{--reverse} (@option{-r}) are specified. + +@item -S @var{size} +@itemx --buffer-size=@var{size} +@opindex -S +@opindex --buffer-size +@cindex size for main memory sorting +Use a main-memory sort buffer of the given @var{size}. By default, +@var{size} is in units of 1024 bytes. Appending @samp{%} causes +@var{size} to be interpreted as a percentage of physical memory. +Appending @samp{K} multiplies @var{size} by 1024 (the default), +@samp{M} by 1,048,576, @samp{G} by 1,073,741,824, and so on for +@samp{T}, @samp{P}, @samp{E}, @samp{Z}, @samp{Y}, @samp{R}, and @samp{Q}@. +Appending +@samp{b} causes @var{size} to be interpreted as a byte count, with no +multiplication. + +This option can improve the performance of @command{sort} by causing it +to start with a larger or smaller sort buffer than the default. +However, this option affects only the initial buffer size. The buffer +grows beyond @var{size} if @command{sort} encounters input lines larger +than @var{size}. + +@item -t @var{separator} +@itemx --field-separator=@var{separator} +@opindex -t +@opindex --field-separator +@cindex field separator character +Use character @var{separator} as the field separator when finding the +sort keys in each line. By default, fields are separated by the empty +string between a non-blank character and a blank character. +By default a blank is a space or a tab, but the @env{LC_CTYPE} locale +can change this. + +That is, given the input line @w{@samp{ foo bar}}, @command{sort} breaks it +into fields @w{@samp{ foo}} and @w{@samp{ bar}}. The field separator is +not considered to be part of either the field preceding or the field +following, so with @samp{sort @w{-t " "}} the same input line has +three fields: an empty field, @samp{foo}, and @samp{bar}. +However, fields that extend to the end of the line, +as @option{-k 2}, or fields consisting of a range, as @option{-k 2,3}, +retain the field separators present between the endpoints of the range. + +To specify ASCII NUL as the field separator, +use the two-character string @samp{\0}, e.g., @samp{sort -t '\0'}. + +@item -T @var{tempdir} +@itemx --temporary-directory=@var{tempdir} +@opindex -T +@opindex --temporary-directory +@cindex temporary directory +@vindex TMPDIR +Use directory @var{tempdir} to store temporary files, overriding the +@env{TMPDIR} environment variable. If this option is given more than +once, temporary files are stored in all the directories given. If you +have a large sort or merge that is I/O-bound, you can often improve +performance by using this option to specify directories on different +file systems. + +@item --parallel=@var{n} +@opindex --parallel +@cindex multithreaded sort +Set the number of sorts run in parallel to @var{n}. By default, +@var{n} is set to the number of available processors, but limited +to 8, as there are diminishing performance gains after that. +Note also that using @var{n} threads increases the memory usage by +a factor of log @var{n}. Also see @ref{nproc invocation}. + +@item -u +@itemx --unique +@opindex -u +@opindex --unique +@cindex uniquifying output + +Normally, output only the first of a sequence of lines that compare +equal. For the @option{--check} (@option{-c} or @option{-C}) option, +check that no pair of consecutive lines compares equal. + +This option also disables the default last-resort comparison. + +The commands @code{sort -u} and @code{sort | uniq} are equivalent, but +this equivalence does not extend to arbitrary @command{sort} options. +For example, @code{sort -n -u} inspects only the value of the initial +numeric string when checking for uniqueness, whereas @code{sort -n | +uniq} inspects the entire line. @xref{uniq invocation}. + +@optZeroTerminated +@macro newlineFieldSeparator +Note with @option{-z} the newline character is treated as a field separator. +@end macro + +@end table + +Historical (BSD and System V) implementations of @command{sort} have +differed in their interpretation of some options, particularly +@option{-b}, @option{-f}, and @option{-n}. +GNU sort follows the POSIX +behavior, which is usually (but not always!) like the System V behavior. +According to POSIX, @option{-n} no longer implies @option{-b}. For +consistency, @option{-M} has been changed in the same way. This may +affect the meaning of character positions in field specifications in +obscure cases. The only fix is to add an explicit @option{-b}. + +A position in a sort field specified with @option{-k} may have any +of the option letters @samp{MbdfghinRrV} appended to it, in which case no +global ordering options are inherited by that particular field. The +@option{-b} option may be independently attached to either or both of +the start and end positions of a field specification, and if it is +inherited from the global options it will be attached to both. +If input lines can contain leading or adjacent blanks and @option{-t} +is not used, then @option{-k} is typically combined with @option{-b} or +an option that implicitly ignores leading blanks (@samp{Mghn}) as otherwise +the varying numbers of leading blanks in fields can cause confusing results. + +If the start position in a sort field specifier falls after the end of +the line or after the end field, the field is empty. If the @option{-b} +option was specified, the @samp{.@var{c}} part of a field specification +is counted from the first nonblank character of the field. + +@vindex _POSIX2_VERSION +@vindex POSIXLY_CORRECT +On systems not conforming to POSIX 1003.1-2001, +@command{sort} supports a traditional origin-zero +syntax @samp{+@var{pos1} [-@var{pos2}]} for specifying sort keys. +The traditional command @samp{sort +@var{a}.@var{x} -@var{b}.@var{y}} +is equivalent to @samp{sort -k @var{a+1}.@var{x+1},@var{b}} if @var{y} +is @samp{0} or absent, otherwise it is equivalent to @samp{sort -k +@var{a+1}.@var{x+1},@var{b+1}.@var{y}}. + +This traditional behavior can be controlled with the +@env{_POSIX2_VERSION} environment variable (@pxref{Standards +conformance}); it can also be enabled when @env{POSIXLY_CORRECT} is +not set by using the traditional syntax with @samp{-@var{pos2}} present. + +Scripts intended for use on standard hosts should avoid traditional +syntax and should use @option{-k} instead. For example, avoid +@samp{sort +2}, since it might be interpreted as either @samp{sort +./+2} or @samp{sort -k 3}. If your script must also run on hosts that +support only the traditional syntax, it can use a test like @samp{if sort +-k 1 </dev/null >/dev/null 2>&1; then @dots{}} to decide which syntax +to use. + +Here are some examples to illustrate various combinations of options. + +@itemize @bullet + +@item +Sort in descending (reverse) numeric order. + +@example +sort -n -r +@end example + +@item +Run no more than 4 sorts concurrently, using a buffer size of 10M. + +@example +sort --parallel=4 -S 10M +@end example + +@item +Sort alphabetically, omitting the first and second fields +and the blanks at the start of the third field. +This uses a single key composed of the characters beginning +at the start of the first nonblank character in field three +and extending to the end of each line. + +@example +sort -k 3b +@end example + +@item +Sort numerically on the second field and resolve ties by sorting +alphabetically on the third and fourth characters of field five. +Use @samp{:} as the field delimiter. + +@example +sort -t : -k 2,2n -k 5.3,5.4 +@end example + +Note that if you had written @option{-k 2n} instead of @option{-k 2,2n} +@command{sort} would have used all characters beginning in the second field +and extending to the end of the line as the primary @emph{numeric} +key. For the large majority of applications, treating keys spanning +more than one field as numeric will not do what you expect. + +Also note that the @samp{n} modifier was applied to the field-end +specifier for the first key. It would have been equivalent to +specify @option{-k 2n,2} or @option{-k 2n,2n}. All modifiers except +@samp{b} apply to the associated @emph{field}, regardless of whether +the modifier character is attached to the field-start and/or the +field-end part of the key specifier. + +@item +Sort the password file on the fifth field and ignore any +leading blanks. Sort lines with equal values in field five +on the numeric user ID in field three. Fields are separated +by @samp{:}. + +@example +sort -t : -k 5b,5 -k 3,3n /etc/passwd +sort -t : -n -k 5b,5 -k 3,3 /etc/passwd +sort -t : -b -k 5,5 -k 3,3n /etc/passwd +@end example + +These three commands have equivalent effect. The first specifies that +the first key's start position ignores leading blanks and the second +key is sorted numerically. The other two commands rely on global +options being inherited by sort keys that lack modifiers. The inheritance +works in this case because @option{-k 5b,5b} and @option{-k 5b,5} are +equivalent, as the location of a field-end lacking a @samp{.@var{c}} +character position is not affected by whether initial blanks are +skipped. + +@item +Sort a set of log files, primarily by IPv4 address and secondarily by +timestamp. If two lines' primary and secondary keys are identical, +output the lines in the same order that they were input. The log +files contain lines that look like this: + +@example +4.150.156.3 - - [01/Apr/2020:06:31:51 +0000] message 1 +211.24.3.231 - - [24/Apr/2020:20:17:39 +0000] message 2 +@end example + +Fields are separated by exactly one space. Sort IPv4 addresses +lexicographically, e.g., 212.61.52.2 sorts before 212.129.233.201 +because 61 is less than 129. + +@example +sort -s -t ' ' -k 4.9n -k 4.5M -k 4.2n -k 4.14,4.21 file*.log | +sort -s -t '.' -k 1,1n -k 2,2n -k 3,3n -k 4,4n +@end example + +This example cannot be done with a single POSIX @command{sort} invocation, +since IPv4 address components are separated by @samp{.} while dates +come just after a space. So it is broken down into two invocations of +@command{sort}: the first sorts by timestamp and the second by IPv4 +address. The timestamp is sorted by year, then month, then day, and +finally by hour-minute-second field, using @option{-k} to isolate each +field. Except for hour-minute-second there's no need to specify the +end of each key field, since the @samp{n} and @samp{M} modifiers sort +based on leading prefixes that cannot cross field boundaries. The +IPv4 addresses are sorted lexicographically. The second sort uses +@samp{-s} so that ties in the primary key are broken by the secondary +key; the first sort uses @samp{-s} so that the combination of the two +sorts is stable. Note as a GNU extension, the above example could +be achieved in a single @command{sort} invocation by sorting the +IPv4 address field using a @samp{V} version type, like @samp{-k1,1V}. + +@item +Generate a tags file in case-insensitive sorted order. + +@example +find src -type f -print0 | sort -z -f | xargs -0 etags --append +@end example + +The use of @option{-print0}, @option{-z}, and @option{-0} in this case means +that file names that contain blanks or other special characters are +not broken up +by the sort operation. + +@c This example is a bit contrived and needs more explanation. +@c @item +@c Sort records separated by an arbitrary string by using a pipe to convert +@c each record delimiter string to @samp{\0}, +@c then using sort's @option{-z} option, +@c and converting each @samp{\0} back to the original record delimiter. +@c +@c @example +@c printf 'c\n\nb\n\na\n' | +@c perl -0pe 's/\n\n/\n\0/g' | +@c sort -z | +@c perl -0pe 's/\0/\n/g' +@c @end example + +@item +Use the common DSU, Decorate Sort Undecorate idiom to +sort lines according to their length. + +@example +awk '@{print length, $0@}' /etc/passwd | sort -n | cut -f2- -d' ' +@end example + +In general this technique can be used to sort data that the @command{sort} +command does not support, or is inefficient at, sorting directly. + +@item +Shuffle a list of directories, but preserve the order of files within +each directory. For instance, one could use this to generate a music +playlist in which albums are shuffled but the songs of each album are +played in order. + +@example +ls */* | sort -t / -k 1,1R -k 2,2 +@end example + +@end itemize + + +@node shuf invocation +@section @command{shuf}: Shuffling text + +@pindex shuf +@cindex shuffling files + +@command{shuf} shuffles its input by outputting a random permutation +of its input lines. Each output permutation is equally likely. +Synopses: + +@example +shuf [@var{option}]@dots{} [@var{file}] +shuf -e [@var{option}]@dots{} [@var{arg}]@dots{} +shuf -i @var{lo}-@var{hi} [@var{option}]@dots{} +@end example + +@command{shuf} has three modes of operation that affect where it +obtains its input lines. By default, it reads lines from standard +input. The following options change the operation mode: + +@table @samp + +@item -e +@itemx --echo +@opindex -c +@opindex --echo +@cindex command-line operands to shuffle +Treat each command-line operand as an input line. + +@item -i @var{lo}-@var{hi} +@itemx --input-range=@var{lo}-@var{hi} +@opindex -i +@opindex --input-range +@cindex input range to shuffle +Act as if input came from a file containing the range of unsigned +decimal integers @var{lo}@dots{}@var{hi}, one per line. + +@end table + +@command{shuf}'s other options can affect its behavior in all +operation modes: + +@table @samp + +@item -n @var{count} +@itemx --head-count=@var{count} +@opindex -n +@opindex --head-count +@cindex head of output +Output at most @var{count} lines. By default, all input lines are +output. + +@item -o @var{output-file} +@itemx --output=@var{output-file} +@opindex -o +@opindex --output +@cindex overwriting of input, allowed +Write output to @var{output-file} instead of standard output. +@command{shuf} reads all input before opening +@var{output-file}, so you can safely shuffle a file in place by using +commands like @code{shuf -o F <F} and @code{cat F | shuf -o F}. + +@item --random-source=@var{file} +@opindex --random-source +@cindex random source for shuffling +Use @var{file} as a source of random data used to determine which +permutation to generate. @xref{Random sources}. + +@item -r +@itemx --repeat +@opindex -r +@opindex --repeat +@cindex repeat output values +Repeat output values, that is, select with replacement. With this +option the output is not a permutation of the input; instead, each +output line is randomly chosen from all the inputs. This option is +typically combined with @option{--head-count}; if +@option{--head-count} is not given, @command{shuf} repeats +indefinitely. + +@optZeroTerminated + +@end table + +For example: + +@example +shuf <<EOF +A man, +a plan, +a canal: +Panama! +EOF +@end example + +@noindent +might produce the output + +@example +Panama! +A man, +a canal: +a plan, +@end example + +@noindent +Similarly, the command: + +@example +shuf -e clubs hearts diamonds spades +@end example + +@noindent +might output: + +@example +clubs +diamonds +spades +hearts +@end example + +@noindent +and the command @samp{shuf -i 1-4} might output: + +@example +4 +2 +1 +3 +@end example + +@noindent +The above examples all have four input lines, so @command{shuf} might +produce any of the twenty-four possible permutations of the input. In +general, if there are @var{n} input lines, there are @var{n}! (i.e., +@var{n} factorial, or @var{n} * (@var{n} - 1) * @dots{} * 1) possible +output permutations. + +@noindent +To output 50 random numbers each in the range 0 through 9, use: + +@example +shuf -r -n 50 -i 0-9 +@end example + +@noindent +To simulate 100 coin flips, use: + +@example +shuf -r -n 100 -e Head Tail +@end example + +@exitstatus + + +@node uniq invocation +@section @command{uniq}: Uniquify files + +@pindex uniq +@cindex uniquify files + +@command{uniq} writes the unique lines in the given @file{input}, or +standard input if nothing is given or for an @var{input} name of +@samp{-}. Synopsis: + +@example +uniq [@var{option}]@dots{} [@var{input} [@var{output}]] +@end example + +By default, @command{uniq} prints its input lines, except that +it discards all but the first of adjacent repeated lines, so that +no output lines are repeated. Optionally, it can instead discard +lines that are not repeated, or all repeated lines. + +The input need not be sorted, but repeated input lines are detected +only if they are adjacent. If you want to discard non-adjacent +duplicate lines, perhaps you want to use @code{sort -u}. +@xref{sort invocation}. + +@vindex LC_COLLATE +Comparisons honor the rules specified by the @env{LC_COLLATE} +locale category. + +If no @var{output} file is specified, @command{uniq} writes to standard +output. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -f @var{n} +@itemx --skip-fields=@var{n} +@opindex -f +@opindex --skip-fields +Skip @var{n} fields on each line before checking for uniqueness. Use +a null string for comparison if a line has fewer than @var{n} fields. +Fields are a sequence of blank characters followed by non-blank characters. +Field numbers are one based, i.e., @option{-f 1} will skip the first +field (which may optionally have leading blanks). + +For compatibility @command{uniq} supports a traditional option syntax +@option{-@var{n}}. New scripts should use @option{-f @var{n}} instead. + +@item -s @var{n} +@itemx --skip-chars=@var{n} +@opindex -s +@opindex --skip-chars +Skip @var{n} characters before checking for uniqueness. Use a null string +for comparison if a line has fewer than @var{n} characters. If you use both +the field and character skipping options, fields are skipped over first. + +@vindex _POSIX2_VERSION +On systems not conforming to POSIX 1003.1-2001, +@command{uniq} supports a traditional option syntax +@option{+@var{n}}. +Although this traditional behavior can be controlled with the +@env{_POSIX2_VERSION} environment variable (@pxref{Standards +conformance}), portable scripts should avoid commands whose +behavior depends on this variable. +For example, use @samp{uniq ./+10} or @samp{uniq -s 10} rather than +the ambiguous @samp{uniq +10}. + +@item -c +@itemx --count +@opindex -c +@opindex --count +Print the number of times each line occurred along with the line. + +@item -i +@itemx --ignore-case +@opindex -i +@opindex --ignore-case +Ignore differences in case when comparing lines. + +@item -d +@itemx --repeated +@opindex -d +@opindex --repeated +@cindex repeated lines, outputting +Discard lines that are not repeated. When used by itself, this option +causes @command{uniq} to print the first copy of each repeated line, +and nothing else. + +@item -D +@itemx --all-repeated[=@var{delimit-method}] +@opindex -D +@opindex --all-repeated +@cindex all repeated lines, outputting +Do not discard the second and subsequent repeated input lines, +but discard lines that are not repeated. +This option is useful mainly in conjunction with other options e.g., +to ignore case or to compare only selected fields. +The optional @var{delimit-method}, supported with the long form option, +specifies how to delimit groups of repeated lines, and must be one of the +following: + +@table @samp + +@item none +Do not delimit groups of repeated lines. +This is equivalent to @option{--all-repeated} (@option{-D}). + +@item prepend +Output a newline before each group of repeated lines. +@macro nulOutputNote +With @option{--zero-terminated} (@option{-z}), use a zero +byte (ASCII NUL) instead of a newline as the delimiter. +@end macro +@nulOutputNote + +@item separate +Separate groups of repeated lines with a single newline. +This is the same as using @samp{prepend}, except that +no delimiter is inserted before the first group, and hence +may be better suited for output direct to users. +@nulOutputNote +@end table + +@macro ambiguousGroupNote +Note that when groups are delimited and the input stream contains +blank lines, then the output is ambiguous. +To avoid that, filter the input through @samp{tr -s '\\n'} to +remove blank lines. +@end macro +@ambiguousGroupNote + +This is a GNU extension. +@c FIXME: give an example showing *how* it's useful + +@item --group[=@var{delimit-method}] +@opindex --group +@cindex all lines, grouping +Output all lines, and delimit each unique group. +@nulOutputNote +The optional @var{delimit-method} specifies how to delimit +groups, and must be one of the following: + +@table @samp + +@item separate +Separate unique groups with a single delimiter. +This is the default delimiting method if none is specified, +and better suited for output direct to users. + +@item prepend +Output a delimiter before each group of unique items. + +@item append +Output a delimiter after each group of unique items. + +@item both +Output a delimiter around each group of unique items. +@end table + +@ambiguousGroupNote + +This is a GNU extension. + +@item -u +@itemx --unique +@opindex -u +@opindex --unique +@cindex unique lines, outputting +Discard the last line that would be output for a repeated input group. +When used by itself, this option causes @command{uniq} to print unique +lines, and nothing else. + +@item -w @var{n} +@itemx --check-chars=@var{n} +@opindex -w +@opindex --check-chars +Compare at most @var{n} characters on each line (after skipping any specified +fields and characters). By default the entire rest of the lines are +compared. + +@optZeroTerminated +@newlineFieldSeparator + +@end table + +@exitstatus + + +@node comm invocation +@section @command{comm}: Compare two sorted files line by line + +@pindex comm +@cindex line-by-line comparison +@cindex comparing sorted files + +@command{comm} writes to standard output lines that are common, and lines +that are unique, to two input files; a file name of @samp{-} means +standard input. Synopsis: + +@example +comm [@var{option}]@dots{} @var{file1} @var{file2} +@end example + +@vindex LC_COLLATE +Before @command{comm} can be used, the input files must be sorted using the +collating sequence specified by the @env{LC_COLLATE} locale. +If an input file ends in a non-newline +character, a newline is silently appended. The @command{sort} command with +no options always outputs a file that is suitable input to @command{comm}. + +@cindex differing lines +@cindex common lines +With no options, @command{comm} produces three-column output. Column one +contains lines unique to @var{file1}, column two contains lines unique +to @var{file2}, and column three contains lines common to both files. +Columns are separated by a single TAB character. +@c FIXME: when there's an option to supply an alternative separator +@c string, append "by default" to the above sentence. + +@opindex -1 +@opindex -2 +@opindex -3 +The options @option{-1}, @option{-2}, and @option{-3} suppress printing of +the corresponding columns (and separators). Also see @ref{Common options}. + +Unlike some other comparison utilities, @command{comm} has an exit +status that does not depend on the result of the comparison. +Upon normal completion @command{comm} produces an exit code of zero. +If there is an error it exits with nonzero status. + +@macro checkOrderOption{cmd} +If the @option{--check-order} option is given, unsorted inputs will +cause a fatal error message. If the option @option{--nocheck-order} +is given, unsorted inputs will never cause an error message. If neither +of these options is given, wrongly sorted inputs are diagnosed +only if an input file is found to contain unpairable +@ifset JOIN_COMMAND +lines, and when both input files are non empty. +@end ifset +@ifclear JOIN_COMMAND +lines. +@end ifclear +If an input file is diagnosed as being unsorted, the @command{\cmd\} +command will exit with a nonzero status (and the output should not be used). + +Forcing @command{\cmd\} to process wrongly sorted input files +containing unpairable lines by specifying @option{--nocheck-order} is +not guaranteed to produce any particular output. The output will +probably not correspond with whatever you hoped it would be. +@end macro +@checkOrderOption{comm} + +@table @samp + +@item --check-order +Fail with an error message if either input file is wrongly ordered. + +@item --nocheck-order +Do not check that both input files are in sorted order. + +Other options are: + +@item --output-delimiter=@var{str} +Print @var{str} between adjacent output columns, +rather than the default of a single TAB character. + +The delimiter @var{str} may be empty, in which case +the ASCII NUL character is used to delimit output columns. + +@item --total +Output a summary at the end. + +Similar to the regular output, +column one contains the total number of lines unique to @var{file1}, +column two contains the total number of lines unique to @var{file2}, and +column three contains the total number of lines common to both files, +followed by the word @samp{total} in the additional column four. + +In the following example, @command{comm} omits the regular output +(@option{-123}), thus just printing the summary: + +@example +$ printf '%s\n' a b c d e > file1 +$ printf '%s\n' b c d e f g > file2 +$ comm --total -123 file1 file2 +1 2 4 total +@end example + +This option is a GNU extension. Portable scripts should use @command{wc} to +get the totals, e.g. for the above example files: + +@example +$ comm -23 file1 file2 | wc -l # number of lines only in file1 +1 +$ comm -13 file1 file2 | wc -l # number of lines only in file2 +2 +$ comm -12 file1 file2 | wc -l # number of lines common to both files +4 +@end example + +@optZeroTerminated + +@end table + +@node ptx invocation +@section @command{ptx}: Produce permuted indexes + +@pindex ptx + +@command{ptx} reads a text file and essentially produces a permuted index, with +each keyword in its context. The calling sketch is either one of: + +@example +ptx [@var{option} @dots{}] [@var{file} @dots{}] +ptx -G [@var{option} @dots{}] [@var{input} [@var{output}]] +@end example + +The @option{-G} (or its equivalent: @option{--traditional}) option disables +all GNU extensions and reverts to traditional mode, thus introducing some +limitations and changing several of the program's default option values. +When @option{-G} is not specified, GNU extensions are always enabled. +GNU extensions to @command{ptx} are documented wherever appropriate in this +document. @xref{Compatibility in ptx}, for the full list. + +Individual options are explained in the following sections. + +When GNU extensions are enabled, there may be zero, one or several +@var{file}s after the options. If there is no @var{file}, the program +reads the standard input. If there is one or several @var{file}s, they +give the name of input files which are all read in turn, as if all the +input files were concatenated. However, there is a full contextual +break between each file and, when automatic referencing is requested, +file names and line numbers refer to individual text input files. In +all cases, the program outputs the permuted index to the standard +output. + +When GNU extensions are @emph{not} enabled, that is, when the program +operates in traditional mode, there may be zero, one or two parameters +besides the options. If there are no parameters, the program reads the +standard input and outputs the permuted index to the standard output. +If there is only one parameter, it names the text @var{input} to be read +instead of the standard input. If two parameters are given, they give +respectively the name of the @var{input} file to read and the name of +the @var{output} file to produce. @emph{Be very careful} to note that, +in this case, the contents of file given by the second parameter is +destroyed. This behavior is dictated by System V @command{ptx} +compatibility; GNU Standards normally discourage output parameters not +introduced by an option. + +Note that for @emph{any} file named as the value of an option or as an +input text file, a single dash @samp{-} may be used, in which case +standard input is assumed. However, it would not make sense to use this +convention more than once per program invocation. + +@menu +* General options in ptx:: Options which affect general program behavior. +* Charset selection in ptx:: Underlying character set considerations. +* Input processing in ptx:: Input fields, contexts, and keyword selection. +* Output formatting in ptx:: Types of output format, and sizing the fields. +* Compatibility in ptx:: +@end menu + + +@node General options in ptx +@subsection General options + +@table @samp + +@item -G +@itemx --traditional +As already explained, this option disables all GNU extensions to +@command{ptx} and switches to traditional mode. + +@item --help +Print a short help on standard output, then exit without further +processing. + +@item --version +Print the program version on standard output, then exit without further +processing. + +@end table + +@exitstatus + + +@node Charset selection in ptx +@subsection Charset selection + +As it is set up now, @command{ptx} assumes that the input file is coded +using 8-bit characters, and it may not work well in multibyte locales. +In a single-byte locale, the default regular expression +for a keyword allows foreign or diacriticized letters. Keyword sorting, +however, is still crude; it obeys the underlying character set ordering +quite blindly. + +The output of @command{ptx} assumes the locale's character encoding. +For example, with @command{ptx}'s @option{-T} option, if the locale +uses the Latin-1 encoding you may need a LaTeX directive like +@samp{\usepackage[latin1]@{inputenc@}} to render non-ASCII characters +correctly. + +@table @samp + +@item -f +@itemx --ignore-case +@opindex -f +@opindex --ignore-case +Fold lower case letters to upper case for sorting. + +@end table + + +@node Input processing in ptx +@subsection Word selection and input processing + +@table @samp + +@item -b @var{file} +@itemx --break-file=@var{file} +@opindex -b +@opindex --break-file + +This option provides an alternative (to @option{-W}) method of describing +which characters make up words. It introduces the name of a +file which contains a list of characters which can@emph{not} be part of +one word; this file is called the @dfn{Break file}. Any character which +is not part of the Break file is a word constituent. If both options +@option{-b} and @option{-W} are specified, then @option{-W} has precedence and +@option{-b} is ignored. + +When GNU extensions are enabled, the only way to avoid newline as a +break character is to write all the break characters in the file with no +newline at all, not even at the end of the file. When GNU extensions +are disabled, spaces, tabs and newlines are always considered as break +characters even if not included in the Break file. + +@item -i @var{file} +@itemx --ignore-file=@var{file} +@opindex -i +@opindex --ignore-file + +The file associated with this option contains a list of words which will +never be taken as keywords in concordance output. It is called the +@dfn{Ignore file}. The file contains exactly one word in each line; the +end of line separation of words is not subject to the value of the +@option{-S} option. + +@item -o @var{file} +@itemx --only-file=@var{file} +@opindex -o +@opindex --only-file + +The file associated with this option contains a list of words which will +be retained in concordance output; any word not mentioned in this file +is ignored. The file is called the @dfn{Only file}. The file contains +exactly one word in each line; the end of line separation of words is +not subject to the value of the @option{-S} option. + +There is no default for the Only file. When both an Only file and an +Ignore file are specified, a word is considered a keyword only +if it is listed in the Only file and not in the Ignore file. + +@item -r +@itemx --references +@opindex -r +@opindex --references + +On each input line, the leading sequence of non-white space characters will be +taken to be a reference that has the purpose of identifying this input +line in the resulting permuted index. +@xref{Output formatting in ptx}, +for more information about reference production. +Using this option changes the default value for option @option{-S}. + +Using this option, the program does not try very hard to remove +references from contexts in output, but it succeeds in doing so +@emph{when} the context ends exactly at the newline. If option +@option{-r} is used with @option{-S} default value, or when GNU extensions +are disabled, this condition is always met and references are completely +excluded from the output contexts. + +@item -S @var{regexp} +@itemx --sentence-regexp=@var{regexp} +@opindex -S +@opindex --sentence-regexp + +This option selects which regular expression will describe the end of a +line or the end of a sentence. In fact, this regular expression is not +the only distinction between end of lines or end of sentences, and input +line boundaries have no special significance outside this option. By +default, when GNU extensions are enabled and if @option{-r} option is not +used, end of sentences are used. In this case, this @var{regex} is +imported from GNU Emacs: + +@example +[.?!][]\"')@}]*\\($\\|\t\\| \\)[ \t\n]* +@end example + +Whenever GNU extensions are disabled or if @option{-r} option is used, end +of lines are used; in this case, the default @var{regexp} is just: + +@example +\n +@end example + +Using an empty @var{regexp} is equivalent to completely disabling end of +line or end of sentence recognition. In this case, the whole file is +considered to be a single big line or sentence. The user might want to +disallow all truncation flag generation as well, through option @option{-F +""}. @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs +Manual}. + +When the keywords happen to be near the beginning of the input line or +sentence, this often creates an unused area at the beginning of the +output context line; when the keywords happen to be near the end of the +input line or sentence, this often creates an unused area at the end of +the output context line. The program tries to fill those unused areas +by wrapping around context in them; the tail of the input line or +sentence is used to fill the unused area on the left of the output line; +the head of the input line or sentence is used to fill the unused area +on the right of the output line. + +As a matter of convenience to the user, many usual backslashed escape +sequences from the C language are recognized and converted to the +corresponding characters by @command{ptx} itself. + +@item -W @var{regexp} +@itemx --word-regexp=@var{regexp} +@opindex -W +@opindex --word-regexp + +This option selects which regular expression will describe each keyword. +By default, if GNU extensions are enabled, a word is a sequence of +letters; the @var{regexp} used is @samp{\w+}. When GNU extensions are +disabled, a word is by default anything which ends with a space, a tab +or a newline; the @var{regexp} used is @samp{[^ \t\n]+}. + +An empty @var{regexp} is equivalent to not using this option. +@xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs +Manual}. + +As a matter of convenience to the user, many usual backslashed escape +sequences, as found in the C language, are recognized and converted to +the corresponding characters by @command{ptx} itself. + +@end table + + +@node Output formatting in ptx +@subsection Output formatting + +Output format is mainly controlled by the @option{-O} and @option{-T} options +described in the table below. When neither @option{-O} nor @option{-T} are +selected, and if GNU extensions are enabled, the program chooses an +output format suitable for a dumb terminal. Each keyword occurrence is +output to the center of one line, surrounded by its left and right +contexts. Each field is properly justified, so the concordance output +can be readily observed. As a special feature, if automatic +references are selected by option @option{-A} and are output before the +left context, that is, if option @option{-R} is @emph{not} selected, then +a colon is added after the reference; this nicely interfaces with GNU +Emacs @code{next-error} processing. In this default output format, each +white space character, like newline and tab, is merely changed to +exactly one space, with no special attempt to compress consecutive +spaces. This might change in the future. Except for those white space +characters, every other character of the underlying set of 256 +characters is transmitted verbatim. + +Output format is further controlled by the following options. + +@table @samp + +@item -g @var{number} +@itemx --gap-size=@var{number} +@opindex -g +@opindex --gap-size + +Select the size of the minimum white space gap between the fields on the +output line. + +@item -w @var{number} +@itemx --width=@var{number} +@opindex -w +@opindex --width + +Select the maximum output width of each final line. If references are +used, they are included or excluded from the maximum output width +depending on the value of option @option{-R}@. If this option is not +selected, that is, when references are output before the left context, +the maximum output width takes into account the maximum length of all +references. If this option is selected, that is, when references are +output after the right context, the maximum output width does not take +into account the space taken by references, nor the gap that precedes +them. + +@item -A +@itemx --auto-reference +@opindex -A +@opindex --auto-reference + +Select automatic references. Each input line will have an automatic +reference made up of the file name and the line ordinal, with a single +colon between them. However, the file name will be empty when standard +input is being read. If both @option{-A} and @option{-r} are selected, then +the input reference is still read and skipped, but the automatic +reference is used at output time, overriding the input reference. + +@item -R +@itemx --right-side-refs +@opindex -R +@opindex --right-side-refs + +In the default output format, when option @option{-R} is not used, any +references produced by the effect of options @option{-r} or @option{-A} are +placed to the far right of output lines, after the right context. With +default output format, when the @option{-R} option is specified, references +are rather placed at the beginning of each output line, before the left +context. For any other output format, option @option{-R} is +ignored, with one exception: with @option{-R} the width of references +is @emph{not} taken into account in total output width given by @option{-w}. + +This option is automatically selected whenever GNU extensions are +disabled. + +@item -F @var{string} +@itemx --flag-truncation=@var{string} +@opindex -F +@opindex --flag-truncation + +This option will request that any truncation in the output be reported +using the string @var{string}. Most output fields theoretically extend +towards the beginning or the end of the current line, or current +sentence, as selected with option @option{-S}@. But there is a maximum +allowed output line width, changeable through option @option{-w}, which is +further divided into space for various output fields. When a field has +to be truncated because it cannot extend beyond the beginning or the end of +the current line to fit in, then a truncation occurs. By default, +the string used is a single slash, as in @option{-F /}. + +@var{string} may have more than one character, as in @option{-F @dots{}}. +Also, in the particular case when @var{string} is empty (@option{-F ""}), +truncation flagging is disabled, and no truncation marks are appended in +this case. + +As a matter of convenience to the user, many usual backslashed escape +sequences, as found in the C language, are recognized and converted to +the corresponding characters by @command{ptx} itself. + +@item -M @var{string} +@itemx --macro-name=@var{string} +@opindex -M +@opindex --macro-name + +Select another @var{string} to be used instead of @samp{xx}, while +generating output suitable for @command{nroff}, @command{troff} or @TeX{}. + +@item -O +@itemx --format=roff +@opindex -O +@opindex --format=roff + +Choose an output format suitable for @command{nroff} or @command{troff} +processing. Each output line will look like: + +@example +.xx "@var{tail}" "@var{before}" "@var{keyword_and_after}"@c + "@var{head}" "@var{ref}" +@end example + +so it will be possible to write a @samp{.xx} roff macro to take care of +the output typesetting. This is the default output format when GNU +extensions are disabled. Option @option{-M} can be used to change +@samp{xx} to another macro name. + +In this output format, each non-graphical character, like newline and +tab, is merely changed to exactly one space, with no special attempt to +compress consecutive spaces. Each quote character @samp{"} is doubled +so it will be correctly processed by @command{nroff} or @command{troff}. + +@item -T +@itemx --format=tex +@opindex -T +@opindex --format=tex + +Choose an output format suitable for @TeX{} processing. Each output +line will look like: + +@example +\xx @{@var{tail}@}@{@var{before}@}@{@var{keyword}@}@c +@{@var{after}@}@{@var{head}@}@{@var{ref}@} +@end example + +@noindent +so it will be possible to write a @code{\xx} definition to take care of +the output typesetting. Note that when references are not being +produced, that is, neither option @option{-A} nor option @option{-r} is +selected, the last parameter of each @code{\xx} call is inhibited. +Option @option{-M} can be used to change @samp{xx} to another macro +name. + +In this output format, some special characters, like @samp{$}, @samp{%}, +@samp{&}, @samp{#} and @samp{_} are automatically protected with a +backslash. Curly brackets @samp{@{}, @samp{@}} are protected with a +backslash and a pair of dollar signs (to force mathematical mode). The +backslash itself produces the sequence @code{\backslash@{@}}. +Circumflex and tilde diacritical marks produce the sequence @code{^\@{ @}} and +@code{~\@{ @}} respectively. Other diacriticized characters of the +underlying character set produce an appropriate @TeX{} sequence as far +as possible. The other non-graphical characters, like newline and tab, +and all other characters which are not part of ASCII, are merely +changed to exactly one space, with no special attempt to compress +consecutive spaces. Let me know how to improve this special character +processing for @TeX{}. + +@end table + + +@node Compatibility in ptx +@subsection The GNU extensions to @command{ptx} + +This version of @command{ptx} contains a few features which do not exist in +System V @command{ptx}. These extra features are suppressed by using the +@option{-G} command line option, unless overridden by other command line +options. Some GNU extensions cannot be recovered by overriding, so the +simple rule is to avoid @option{-G} if you care about GNU extensions. +Here are the differences between this program and System V @command{ptx}. + +@itemize @bullet + +@item +This program can read many input files at once, it always writes the +resulting concordance on standard output. On the other hand, System V +@command{ptx} reads only one file and sends the result to standard output +or, if a second @var{file} parameter is given on the command, to that +@var{file}. + +Having output parameters not introduced by options is a dangerous +practice which GNU avoids as far as possible. So, for using @command{ptx} +portably between GNU and System V, you should always use it with a +single input file, and always expect the result on standard output. You +might also want to automatically configure in a @option{-G} option to +@command{ptx} calls in products using @command{ptx}, if the configurator finds +that the installed @command{ptx} accepts @option{-G}. + +@item +The only options available in System V @command{ptx} are options @option{-b}, +@option{-f}, @option{-g}, @option{-i}, @option{-o}, @option{-r}, @option{-t} and +@option{-w}. All other options are GNU extensions and are not repeated in +this enumeration. Moreover, some options have a slightly different +meaning when GNU extensions are enabled, as explained below. + +@item +By default, concordance output is not formatted for @command{troff} or +@command{nroff}. It is rather formatted for a dumb terminal. @command{troff} +or @command{nroff} output may still be selected through option @option{-O}. + +@item +Unless @option{-R} option is used, the maximum reference width is +subtracted from the total output line width. With GNU extensions +disabled, width of references is not taken into account in the output +line width computations. + +@item +All 256 bytes, even ASCII NUL bytes, are always read and +processed from input file with no adverse effect, even if GNU extensions +are disabled. However, System V @command{ptx} does not accept 8-bit +characters, a few control characters are rejected, and the tilde +@samp{~} is also rejected. + +@item +Input line length is only limited by available memory, even if GNU +extensions are disabled. However, System V @command{ptx} processes only +the first 200 characters in each line. + +@item +The break (non-word) characters default to be every character except all +letters of the underlying character set, diacriticized or not. When GNU +extensions are disabled, the break characters default to space, tab and +newline only. + +@item +The program makes better use of output line width. If GNU extensions +are disabled, the program rather tries to imitate System V @command{ptx}, +but still, there are some slight disposition glitches this program does +not completely reproduce. + +@item +The user can specify both an Ignore file and an Only file. This is not +allowed with System V @command{ptx}. + +@end itemize + + +@node tsort invocation +@section @command{tsort}: Topological sort + +@pindex tsort +@cindex topological sort + +@command{tsort} performs a topological sort on the given @var{file}, or +standard input if no input file is given or for a @var{file} of +@samp{-}. For more details and some history, see @ref{tsort background}. +Synopsis: + +@example +tsort [@var{option}] [@var{file}] +@end example + +@command{tsort} reads its input as pairs of strings, separated by blanks, +indicating a partial ordering. The output is a total ordering that +corresponds to the given partial ordering. + +For example + +@example +tsort <<EOF +a b c +d +e f +b c d e +EOF +@end example + +@noindent +will produce the output + +@example +a +b +c +d +e +f +@end example + +Consider a more realistic example. +You have a large set of functions all in one file, and they may all be +declared static except one. Currently that one (say @code{main}) is the +first function defined in the file, and the ones it calls directly follow +it, followed by those they call, etc. Let's say that you are determined +to take advantage of prototypes, so you have to choose between declaring +all of those functions (which means duplicating a lot of information from +the definitions) and rearranging the functions so that as many as possible +are defined before they are used. One way to automate the latter process +is to get a list for each function of the functions it calls directly. +Many programs can generate such lists. They describe a call graph. +Consider the following list, in which a given line indicates that the +function on the left calls the one on the right directly. + +@example +main parse_options +main tail_file +main tail_forever +tail_file pretty_name +tail_file write_header +tail_file tail +tail_forever recheck +tail_forever pretty_name +tail_forever write_header +tail_forever dump_remainder +tail tail_lines +tail tail_bytes +tail_lines start_lines +tail_lines dump_remainder +tail_lines file_lines +tail_lines pipe_lines +tail_bytes xlseek +tail_bytes start_bytes +tail_bytes dump_remainder +tail_bytes pipe_bytes +file_lines dump_remainder +recheck pretty_name +@end example + +then you can use @command{tsort} to produce an ordering of those +functions that satisfies your requirement. + +@example +example$ tsort call-graph | tac +dump_remainder +start_lines +file_lines +pipe_lines +xlseek +start_bytes +pipe_bytes +tail_lines +tail_bytes +pretty_name +write_header +tail +recheck +parse_options +tail_file +tail_forever +main +@end example + +@command{tsort} detects any cycles in the input and writes the first cycle +encountered to standard error. + +Note that for a given partial ordering, generally there is no unique +total ordering. In the context of the call graph above, the function +@code{parse_options} may be placed anywhere in the list as long as it +precedes @code{main}. + +The only options are @option{--help} and @option{--version}. @xref{Common +options}. + +@exitstatus + +@menu +* tsort background:: Where tsort came from. +@end menu + +@node tsort background +@subsection @command{tsort}: Background + +@command{tsort} exists because very early versions of the Unix linker processed +an archive file exactly once, and in order. As @command{ld} read each object +in the archive, it decided whether it was needed in the program based on +whether it defined any symbols which were undefined at that point in +the link. + +This meant that dependencies within the archive had to be handled +specially. For example, @code{scanf} probably calls @code{read}. That means +that in a single pass through an archive, it was important for @code{scanf.o} +to appear before read.o, because otherwise a program which calls +@code{scanf} but not @code{read} might end up with an unexpected unresolved +reference to @code{read}. + +The way to address this problem was to first generate a set of +dependencies of one object file on another. This was done by a shell +script called @command{lorder}. The GNU tools don't provide a version of +lorder, as far as I know, but you can still find it in BSD +distributions. + +Then you ran @command{tsort} over the @command{lorder} output, and you used the +resulting sort to define the order in which you added objects to the archive. + +This whole procedure has been obsolete since about 1980, because +Unix archives now contain a symbol table (traditionally built by +@command{ranlib}, now generally built by @command{ar} itself), and the Unix +linker uses the symbol table to effectively make multiple passes over +an archive file. + +Anyhow, that's where tsort came from. To solve an old problem with +the way the linker handled archive files, which has since been solved +in different ways. + + +@node Operating on fields +@chapter Operating on fields + +@menu +* cut invocation:: Print selected parts of lines. +* paste invocation:: Merge lines of files. +* join invocation:: Join lines on a common field. +@end menu + + +@node cut invocation +@section @command{cut}: Print selected parts of lines + +@pindex cut +@command{cut} writes to standard output selected parts of each line of each +input file, or standard input if no files are given or for a file name of +@samp{-}. Synopsis: + +@example +cut @var{option}@dots{} [@var{file}]@dots{} +@end example + +In the table which follows, the @var{byte-list}, @var{character-list}, +and @var{field-list} are one or more numbers or ranges (two numbers +separated by a dash) separated by commas. Bytes, characters, and +fields are numbered starting at 1. Incomplete ranges may be +given: @option{-@var{m}} means @samp{1-@var{m}}; @samp{@var{n}-} means +@samp{@var{n}} through end of line or last field. The list elements +can be repeated, can overlap, and can be specified in any order; but +the selected input is written in the same order that it is read, and +is written exactly once. + +The program accepts the following options. Also see @ref{Common +options}. + +@table @samp + +@item -b @var{byte-list} +@itemx --bytes=@var{byte-list} +@opindex -b +@opindex --bytes +Select for printing only the bytes in positions listed in +@var{byte-list}. Tabs and backspaces are treated like any other +character; they take up 1 byte. If an output delimiter is specified, +(see the description of @option{--output-delimiter}), then output that +string between ranges of selected bytes. + +@item -c @var{character-list} +@itemx --characters=@var{character-list} +@opindex -c +@opindex --characters +Select for printing only the characters in positions listed in +@var{character-list}. The same as @option{-b} for now, but +internationalization will change that. Tabs and backspaces are +treated like any other character; they take up 1 character. If an +output delimiter is specified, (see the description of +@option{--output-delimiter}), then output that string between ranges +of selected bytes. + +@item -f @var{field-list} +@itemx --fields=@var{field-list} +@opindex -f +@opindex --fields +Select for printing only the fields listed in @var{field-list}. +Fields are separated by a TAB character by default. Also print any +line that contains no delimiter character, unless the +@option{--only-delimited} (@option{-s}) option is specified. + +Note @command{awk} supports more sophisticated field processing, +like reordering fields, and handling fields aligned with blank characters. +By default @command{awk} uses (and discards) runs of blank characters +to separate fields, and ignores leading and trailing blanks. +@example +@verbatim +awk '{print $2}' # print the second field +awk '{print $(NF-1)}' # print the penultimate field +awk '{print $2,$1}' # reorder the first two fields +@end verbatim +@end example +Note while @command{cut} accepts field specifications in +arbitrary order, output is always in the order encountered in the file. + +In the unlikely event that @command{awk} is unavailable, +one can use the @command{join} command, to process blank +characters as @command{awk} does above. +@example +@verbatim +join -a1 -o 1.2 - /dev/null # print the second field +join -a1 -o 1.2,1.1 - /dev/null # reorder the first two fields +@end verbatim +@end example + +@item -d @var{input_delim_byte} +@itemx --delimiter=@var{input_delim_byte} +@opindex -d +@opindex --delimiter +With @option{-f}, use the first byte of @var{input_delim_byte} as +the input fields separator (default is TAB). + +@item -n +@opindex -n +Do not split multi-byte characters (no-op for now). + +@item -s +@itemx --only-delimited +@opindex -s +@opindex --only-delimited +For @option{-f}, do not print lines that do not contain the field separator +character. Normally, any line without a field separator is printed verbatim. + +@item --output-delimiter=@var{output_delim_string} +@opindex --output-delimiter +With @option{-f}, output fields are separated by @var{output_delim_string}. +The default with @option{-f} is to use the input delimiter. +When using @option{-b} or @option{-c} to select ranges of byte or +character offsets (as opposed to ranges of fields), +output @var{output_delim_string} between non-overlapping +ranges of selected bytes. + +@item --complement +@opindex --complement +This option is a GNU extension. +Select for printing the complement of the bytes, characters or fields +selected with the @option{-b}, @option{-c} or @option{-f} options. +In other words, do @emph{not} print the bytes, characters or fields +specified via those options. This option is useful when you have +many fields and want to print all but a few of them. + +@optZeroTerminated + +@end table + +@exitstatus + + +@node paste invocation +@section @command{paste}: Merge lines of files + +@pindex paste +@cindex merging files + +@command{paste} writes to standard output lines consisting of sequentially +corresponding lines of each given file, separated by a TAB character. +Standard input is used for a file name of @samp{-} or if no input files +are given. + +Synopsis: + +@example +paste [@var{option}]@dots{} [@var{file}]@dots{} +@end example + +For example, with: +@example +$ cat num2 +1 +2 +$ cat let3 +a +b +c +@end example + +Take lines sequentially from each file: +@example +$ paste num2 let3 +1 a +2 b + @ c +@end example + +Duplicate lines from a file: +@example +$ paste num2 let3 num2 +1 a 1 +2 b 2 + @ c +@end example + +Intermix lines from standard input: +@example +$ paste - let3 - < num2 +1 a 2 + @ b + @ c +@end example + +Join consecutive lines with a space: +@example +$ seq 4 | paste -d ' ' - - +1 2 +3 4 +@end example + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -s +@itemx --serial +@opindex -s +@opindex --serial +Paste the lines of one file at a time rather than one line from each +file. Using the above example data: + +@example +$ paste -s num2 let3 +1 2 +a b c +@end example + +@item -d @var{delim-list} +@itemx --delimiters=@var{delim-list} +@opindex -d +@opindex --delimiters +Consecutively use the characters in @var{delim-list} instead of +TAB to separate merged lines. When @var{delim-list} is +exhausted, start again at its beginning. Using the above example data: + +@example +$ paste -d '%_' num2 let3 num2 +1%a_1 +2%b_2 +%c_ +@end example + +@optZeroTerminated + +@end table + +@exitstatus + + +@node join invocation +@section @command{join}: Join lines on a common field + +@pindex join +@cindex common field, joining on + +@command{join} writes to standard output a line for each pair of input +lines that have identical join fields. Synopsis: + +@example +join [@var{option}]@dots{} @var{file1} @var{file2} +@end example + +Either @var{file1} or @var{file2} (but not both) can be @samp{-}, +meaning standard input. @var{file1} and @var{file2} should be +sorted on the join fields. + +@example +@group +$ cat file1 +a 1 +b 2 +e 5 + +$ cat file2 +a X +e Y +f Z + +$ join file1 file2 +a 1 X +e 5 Y +@end group +@end example + + +@noindent +@command{join}'s default behavior (when no options are given): +@itemize +@item the join field is the first field in each line; +@item fields in the input are separated by one or more blanks, with leading +blanks on the line ignored; +@item fields in the output are separated by a space; +@item each output line consists of the join field, the remaining +fields from @var{file1}, then the remaining fields from @var{file2}. +@end itemize + + +@menu +* General options in join:: Options which affect general program behavior. +* Sorting files for join:: Using @command{sort} before @command{join}. +* Working with fields:: Joining on different fields. +* Paired and unpaired lines:: Controlling @command{join}'s field matching. +* Header lines:: Working with header lines in files. +* Set operations:: Union, Intersection and Difference of files. +@end menu + +@node General options in join +@subsection General options +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -a @var{file-number} +@opindex -a +Print a line for each unpairable line in file @var{file-number} (either +@samp{1} or @samp{2}), in addition to the normal output. + +@item --check-order +Fail with an error message if either input file is wrongly ordered. + +@item --nocheck-order +Do not check that both input files are in sorted order. This is the default. + +@item -e @var{string} +@opindex -e +Replace those output fields that are missing in the input with @var{string}. +I.e., missing fields specified with the @option{-12jo} options. + +@item --header +@opindex --header +Treat the first line of each input file as a header line. The header lines +will be joined and printed as the first output line. If @option{-o} is used to +specify output format, the header line will be printed according to the +specified format. The header lines will not be checked for ordering even if +@option{--check-order} is specified. Also if the header lines from each file +do not match, the heading fields from the first file will be used. + +@item -i +@itemx --ignore-case +@opindex -i +@opindex --ignore-case +Ignore differences in case when comparing keys. +With this option, the lines of the input files must be ordered in the same way. +Use @samp{sort -f} to produce this ordering. + +@item -1 @var{field} +@opindex -1 +Join on field @var{field} (a positive integer) of file 1. + +@item -2 @var{field} +@opindex -2 +Join on field @var{field} (a positive integer) of file 2. + +@item -j @var{field} +Equivalent to @option{-1 @var{field} -2 @var{field}}. + +@item -o @var{field-list} +@itemx -o auto +If the keyword @samp{auto} is specified, infer the output format from +the first line in each file. This is the same as the default output format +but also ensures the same number of fields are output for each line. +Missing fields are replaced with the @option{-e} option and extra fields +are discarded. + +Otherwise, construct each output line according to the format in +@var{field-list}. Each element in @var{field-list} is either the single +character @samp{0} or has the form @var{m.n} where the file number, @var{m}, +is @samp{1} or @samp{2} and @var{n} is a positive field number. + +A field specification of @samp{0} denotes the join field. +In most cases, the functionality of the @samp{0} field spec +may be reproduced using the explicit @var{m.n} that corresponds +to the join field. However, when printing unpairable lines +(using either of the @option{-a} or @option{-v} options), there is no way +to specify the join field using @var{m.n} in @var{field-list} +if there are unpairable lines in both files. +To give @command{join} that functionality, POSIX invented the @samp{0} +field specification notation. + +The elements in @var{field-list} +are separated by commas or blanks. +Blank separators typically need to be quoted for the shell. For +example, the commands @samp{join -o 1.2,2.2} and @samp{join -o '1.2 +2.2'} are equivalent. + +All output lines -- including those printed because of any @option{-a} +or @option{-v} option -- are subject to the specified @var{field-list}. + +@item -t @var{char} +Use character @var{char} as the input and output field separator. +Treat as significant each occurrence of @var{char} in the input file. +Use @samp{sort -t @var{char}}, without the @option{-b} option of +@samp{sort}, to produce this ordering. If @samp{join -t ''} is specified, +the whole line is considered, matching the default operation of sort. +If @samp{-t '\0'} is specified then the ASCII NUL +character is used to delimit the fields. + +@item -v @var{file-number} +Print a line for each unpairable line in file @var{file-number} +(either @samp{1} or @samp{2}), instead of the normal output. + +@optZeroTerminated +@newlineFieldSeparator + +@end table + +@exitstatus + +@set JOIN_COMMAND +@checkOrderOption{join} +@clear JOIN_COMMAND + + + +@node Sorting files for join +@subsection Pre-sorting + +@command{join} requires sorted input files. Each input file should be +sorted according to the key (=field/column number) used in +@command{join}. The recommended sorting option is @samp{sort -k 1b,1} +(assuming the desired key is in the first column). + +@noindent Typical usage: +@example +@group +$ sort -k 1b,1 file1 > file1.sorted +$ sort -k 1b,1 file2 > file2.sorted +$ join file1.sorted file2.sorted > file3 +@end group +@end example + +@vindex LC_COLLATE +Normally, the sort order is that of the +collating sequence specified by the @env{LC_COLLATE} locale. Unless +the @option{-t} option is given, the sort comparison ignores blanks at +the start of the join field, as in @code{sort -b}. If the +@option{--ignore-case} option is given, the sort comparison ignores +the case of characters in the join field, as in @code{sort -f}: + +@example +@group +$ sort -k 1bf,1 file1 > file1.sorted +$ sort -k 1bf,1 file2 > file2.sorted +$ join --ignore-case file1.sorted file2.sorted > file3 +@end group +@end example + +The @command{sort} and @command{join} commands should use consistent +locales and options if the output of @command{sort} is fed to +@command{join}. You can use a command like @samp{sort -k 1b,1} to +sort a file on its default join field, but if you select a non-default +locale, join field, separator, or comparison options, then you should +do so consistently between @command{join} and @command{sort}. + +@noindent To avoid any locale-related issues, it is recommended to use the +@samp{C} locale for both commands: + +@example +@group +$ LC_ALL=C sort -k 1b,1 file1 > file1.sorted +$ LC_ALL=C sort -k 1b,1 file2 > file2.sorted +$ LC_ALL=C join file1.sorted file2.sorted > file3 +@end group +@end example + + +@node Working with fields +@subsection Working with fields + +Use @option{-1},@option{-2} to set the key fields for each of the input files. +Ensure the preceding @command{sort} commands operated on the same fields. + +@noindent +The following example joins two files, using the values from seventh field +of the first file and the third field of the second file: + +@example +@group +$ sort -k 7b,7 file1 > file1.sorted +$ sort -k 3b,3 file2 > file2.sorted +$ join -1 7 -2 3 file1.sorted file2.sorted > file3 +@end group +@end example + +@noindent +If the field number is the same for both files, use @option{-j}: + +@example +@group +$ sort -k4b,4 file1 > file1.sorted +$ sort -k4b,4 file2 > file2.sorted +$ join -j4 file1.sorted file2.sorted > file3 +@end group +@end example + +@noindent +Both @command{sort} and @command{join} operate of whitespace-delimited +fields. To specify a different delimiter, use @option{-t} in @emph{both}: + +@example +@group +$ sort -t, -k3b,3 file1 > file1.sorted +$ sort -t, -k3b,3 file2 > file2.sorted +$ join -t, -j3 file1.sorted file2.sorted > file3 +@end group +@end example + +@noindent +To specify a tab (@sc{ascii} 0x09) character instead of whitespace, +use:@footnote{the @code{$'\t'} is supported in most modern shells. +For older shells, use a literal tab.} + +@example +@group +$ sort -t$'\t' -k3b,3 file1 > file1.sorted +$ sort -t$'\t' -k3b,3 file2 > file2.sorted +$ join -t$'\t' -j3 file1.sorted file2.sorted > file3 +@end group +@end example + + +@noindent +If @samp{join -t ''} is specified then the whole line is considered which +matches the default operation of sort: + +@example +@group +$ sort file1 > file1.sorted +$ sort file2 > file2.sorted +$ join -t '' file1.sorted file2.sorted > file3 +@end group +@end example + + +@node Paired and unpaired lines +@subsection Controlling @command{join}'s field matching + +In this section the @command{sort} commands are omitted for brevity. +Sorting the files before joining is still required. + +@command{join}'s default behavior is to print only lines common to +both input files. Use @option{-a} and @option{-v} to print unpairable lines +from one or both files. + +@noindent +All examples below use the following two (pre-sorted) input files: + +@multitable @columnfractions .5 .5 +@item +@example +$ cat file1 +a 1 +b 2 +@end example + +@tab +@example +$ cat file2 +a A +c C +@end example +@end multitable + + +@c TODO: Find better column widths that work for both HTML and PDF +@c and disable indentation of @example. +@multitable @columnfractions 0.5 0.5 + +@headitem Command @tab Outcome + + +@item +@example +$ join file1 file2 +a 1 A +@end example +@tab +common lines +(@emph{intersection}) + + + +@item +@example +$ join -a 1 file1 file2 +a 1 A +b 2 +@end example +@tab +common lines @emph{and} unpaired +lines from the first file + + +@item +@example +$ join -a 2 file1 file2 +a 1 A +c C +@end example +@tab +common lines @emph{and} unpaired lines from the second file + + +@item +@example +$ join -a 1 -a 2 file1 file2 +a 1 A +b 2 +c C +@end example +@tab +all lines (paired and unpaired) from both files +(@emph{union}). +@* +see note below regarding @code{-o auto}. + + +@item +@example +$ join -v 1 file1 file2 +b 2 +@end example +@tab +unpaired lines from the first file +(@emph{difference}) + + +@item +@example +$ join -v 2 file1 file2 +c C +@end example +@tab +unpaired lines from the second file +(@emph{difference}) + + +@item +@example +$ join -v 1 -v 2 file1 file2 +b 2 +c C +@end example +@tab +unpaired lines from both files, omitting common lines +(@emph{symmetric difference}). + + +@end multitable + +@noindent +The @option{-o auto -e X} options are useful when dealing with unpaired lines. +The following example prints all lines (common and unpaired) from both files. +Without @option{-o auto} it is not easy to discern which fields originate from +which file: + +@example +$ join -a 1 -a 2 file1 file2 +a 1 A +b 2 +c C + +$ join -o auto -e X -a 1 -a 2 file1 file2 +a 1 A +b 2 X +c X C +@end example + + +If the input has no unpairable lines, a GNU extension is +available; the sort order can be any order that considers two fields +to be equal if and only if the sort comparison described above +considers them to be equal. For example: + +@example +@group +$ cat file1 +a a1 +c c1 +b b1 + +$ cat file2 +a a2 +c c2 +b b2 + +$ join file1 file2 +a a1 a2 +c c1 c2 +b b1 b2 +@end group +@end example + + +@node Header lines +@subsection Header lines + +The @option{--header} option can be used when the files to join +have a header line which is not sorted: + +@example +@group +$ cat file1 +Name Age +Alice 25 +Charlie 34 + +$ cat file2 +Name Country +Alice France +Bob Spain + +$ join --header -o auto -e NA -a1 -a2 file1 file2 +Name Age Country +Alice 25 France +Bob NA Spain +Charlie 34 NA +@end group +@end example + + +To sort a file with a header line, use GNU @command{sed -u}. +The following example sort the files but keeps the first line of each +file in place: + +@example +@group +$ ( sed -u 1q ; sort -k2b,2 ) < file1 > file1.sorted +$ ( sed -u 1q ; sort -k2b,2 ) < file2 > file2.sorted +$ join --header -o auto -e NA -a1 -a2 file1.sorted file2.sorted > file3 +@end group +@end example + +@node Set operations +@subsection Union, Intersection and Difference of files + +Combine @command{sort}, @command{uniq} and @command{join} to +perform the equivalent of set operations on files: + +@c From https://www.pixelbeat.org/cmdline.html#sets +@multitable @columnfractions 0.5 0.5 +@headitem Command @tab outcome +@item @code{sort -u file1 file2} +@tab Union of unsorted files + +@item @code{sort file1 file2 | uniq -d} +@tab Intersection of unsorted files + +@item @code{sort file1 file1 file2 | uniq -u} +@tab Difference of unsorted files + +@item @code{sort file1 file2 | uniq -u} +@tab Symmetric Difference of unsorted files + +@item @code{join -t '' -a1 -a2 file1 file2} +@tab Union of sorted files + +@item @code{join -t '' file1 file2} +@tab Intersection of sorted files + +@item @code{join -t '' -v2 file1 file2} +@tab Difference of sorted files + +@item @code{join -t '' -v1 -v2 file1 file2} +@tab Symmetric Difference of sorted files + +@end multitable + +All examples above operate on entire lines and not on specific fields: +@command{sort} without @option{-k} and @command{join -t ''} both consider +entire lines as the key. + + +@node Operating on characters +@chapter Operating on characters + +@cindex operating on characters + +These commands operate on individual characters. + +@menu +* tr invocation:: Translate, squeeze, and/or delete characters. +* expand invocation:: Convert tabs to spaces. +* unexpand invocation:: Convert spaces to tabs. +@end menu + + +@node tr invocation +@section @command{tr}: Translate, squeeze, and/or delete characters + +@pindex tr + +Synopsis: + +@example +tr [@var{option}]@dots{} @var{string1} [@var{string2}] +@end example + +@command{tr} copies standard input to standard output, performing +one of the following operations: + +@itemize @bullet +@item +translate, and optionally squeeze repeated characters in the result, +@item +squeeze repeated characters, +@item +delete characters, +@item +delete characters, then squeeze repeated characters from the result. +@end itemize + +The @var{string1} and @var{string2} operands define arrays of +characters @var{array1} and @var{array2}. By default @var{array1} +lists input characters that @command{tr} operates on, and @var{array2} +lists corresponding translations. In some cases the second operand is +omitted. + +The program accepts the following options. Also see @ref{Common options}. +Options must precede operands. + +@table @samp + +@item -c +@itemx -C +@itemx --complement +@opindex -c +@opindex -C +@opindex --complement +Instead of @var{array1}, use its complement (all characters not +specified by @var{string1}), in ascending order. Use this option with +caution in multibyte locales where its meaning is not always clear +or portable; see @ref{Character arrays}. + +@item -d +@itemx --delete +@opindex -d +@opindex --delete +Delete characters in @var{array1}; do not translate. + +@item -s +@itemx --squeeze-repeats +@opindex -s +@opindex --squeeze-repeats +Replace each sequence of a repeated character that is listed in +the last specified @var{array}, with a single occurrence of that character. + +@item -t +@itemx --truncate-set1 +@opindex -t +@opindex --truncate-set1 +Truncate @var{array1} to the length of @var{array2}. + +@end table + + +@exitstatus + +@menu +* Character arrays:: Specifying arrays of characters. +* Translating:: Changing characters to other characters. +* Squeezing and deleting:: Removing characters. +@end menu + + +@node Character arrays +@subsection Specifying arrays of characters + +@cindex arrays of characters in @command{tr} + +The @var{string1} and @var{string2} operands are not regular +expressions, even though they may look similar. Instead, they +merely represent arrays of characters. As a GNU extension to POSIX, +an empty string operand represents an empty array of characters. + +The interpretation of @var{string1} and @var{string2} depends on locale. +GNU @command{tr} fully supports only safe single-byte locales, +where each possible input byte represents a single character. +Unfortunately, this means GNU @command{tr} will not handle commands +like @samp{tr @"o @L{}} the way you might expect, +since (assuming a UTF-8 encoding) this is equivalent to +@samp{tr '\303\266' '\305\201'} and GNU @command{tr} will +simply transliterate all @samp{\303} bytes to @samp{\305} bytes, etc. +POSIX does not clearly specify the behavior of @command{tr} in locales +where characters are represented by byte sequences instead of by +individual bytes, or where data might contain invalid bytes that are +encoding errors. To avoid problems in this area, you can run +@command{tr} in a safe single-byte locale by using a shell command +like @samp{LC_ALL=C tr} instead of plain @command{tr}. + +Although most characters simply represent themselves in @var{string1} +and @var{string2}, the strings can contain shorthands listed below, +for convenience. Some shorthands can be used only in @var{string1} or +@var{string2}, as noted below. + +@table @asis + +@item Backslash escapes +@cindex backslash escapes + +The following backslash escape sequences are recognized: + +@table @samp +@item \a +Bell (BEL, Control-G). +@item \b +Backspace (BS, Control-H). +@item \f +Form feed (FF, Control-L). +@item \n +Newline (LF, Control-J). +@item \r +Carriage return (CR, Control-M). +@item \t +Tab (HT, Control-I). +@item \v +Vertical tab (VT, Control-K). +@item \@var{ooo} +The eight-bit byte with the value given by @var{ooo}, which is the longest +sequence of one to three octal digits following the backslash. +For portability, @var{ooo} should represent a value that fits in eight bits. +As a GNU extension to POSIX, if the value would not fit, then only the +first two digits of @var{ooo} are used, e.g., @samp{\400} +is equivalent to @samp{\0400} and represents a two-byte sequence. +@item \\ +A backslash. +@end table + +It is an error if no character follows an unescaped backslash. +As a GNU extension, a backslash followed by a character not listed +above is interpreted as that character, removing any special +significance; this can be used to escape the characters +@samp{[} and @samp{-} when they would otherwise be special. + +@item Ranges +@cindex ranges + +The notation @samp{@var{m}-@var{n}} expands to the characters +from @var{m} through @var{n}, in ascending order. @var{m} should +not collate after @var{n}; if it does, an error results. As an example, +@samp{0-9} is the same as @samp{0123456789}. + +GNU @command{tr} does not support the System V syntax that uses square +brackets to enclose ranges. Translations specified in that format +sometimes work as expected, since the brackets are often transliterated +to themselves. However, they should be avoided because they sometimes +behave unexpectedly. For example, @samp{tr -d '[0-9]'} deletes brackets +as well as digits. + +Many historically common and even accepted uses of ranges are not fully +portable. For example, on EBCDIC hosts using the @samp{A-Z} +range will not do what most would expect because @samp{A} through @samp{Z} +are not contiguous as they are in ASCII@. +One way to work around this is to use character classes (see below). +Otherwise, it is most portable (and most ugly) to enumerate the members +of the ranges. + +@item Repeated characters +@cindex repeated characters + +The notation @samp{[@var{c}*@var{n}]} in @var{string2} expands to @var{n} +copies of character @var{c}. Thus, @samp{[y*6]} is the same as +@samp{yyyyyy}. The notation @samp{[@var{c}*]} in @var{string2} expands +to as many copies of @var{c} as are needed to make @var{array2} as long as +@var{array1}. If @var{n} begins with @samp{0}, it is interpreted in +octal, otherwise in decimal. A zero-valued @var{n} is treated as if +it were absent. + +@item Character classes +@cindex character classes + +The notation @samp{[:@var{class}:]} expands to all characters in +the (predefined) class @var{class}. When the @option{--delete} (@option{-d}) +and @option{--squeeze-repeats} (@option{-s}) options are both given, any +character class can be used in @var{string2}. Otherwise, only the +character classes @code{lower} and @code{upper} are accepted in +@var{string2}, and then only if the corresponding character class +(@code{upper} and @code{lower}, respectively) is specified in the same +relative position in @var{string1}. Doing this specifies case conversion. +Except for case conversion, a class's characters appear in no particular order. +The class names are given below; an error results when an invalid class +name is given. + +@table @code +@item alnum +@opindex alnum +Letters and digits. +@item alpha +@opindex alpha +Letters. +@item blank +@opindex blank +Horizontal whitespace. +@item cntrl +@opindex cntrl +Control characters. +@item digit +@opindex digit +Digits. +@item graph +@opindex graph +Printable characters, not including space. +@item lower +@opindex lower +Lowercase letters. +@item print +@opindex print +Printable characters, including space. +@item punct +@opindex punct +Punctuation characters. +@item space +@opindex space +Horizontal or vertical whitespace. +@item upper +@opindex upper +Uppercase letters. +@item xdigit +@opindex xdigit +Hexadecimal digits. +@end table + +@item Equivalence classes +@cindex equivalence classes + +The syntax @samp{[=@var{c}=]} expands to all characters equivalent to +@var{c}, in no particular order. These equivalence classes are +allowed in @var{string2} only when @option{--delete} (@option{-d}) and +@option{--squeeze-repeats} @option{-s} are both given. + +Although equivalence classes are intended to support non-English alphabets, +there seems to be no standard way to define them or determine their +contents. Therefore, they are not fully implemented in GNU @command{tr}; +each character's equivalence class consists only of that character, +which is of no particular use. + +@end table + + +@node Translating +@subsection Translating + +@cindex translating characters + +@command{tr} performs translation when @var{string1} and @var{string2} are +both given and the @option{--delete} (@option{-d}) option is not given. +@command{tr} translates each character of its input that is in @var{array1} +to the corresponding character in @var{array2}. Characters not in +@var{array1} are passed through unchanged. + +As a GNU extension to POSIX, when a character appears more than once +in @var{array1}, only the final instance is used. For example, these +two commands are equivalent: + +@example +tr aaa xyz +tr a z +@end example + +A common use of @command{tr} is to convert lowercase characters to +uppercase. This can be done in many ways. Here are three of them: + +@example +tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ +tr a-z A-Z +tr '[:lower:]' '[:upper:]' +@end example + +@noindent +However, ranges like @code{a-z} are not portable outside the C locale. + +When @command{tr} is performing translation, @var{array1} and @var{array2} +typically have the same length. If @var{array1} is shorter than +@var{array2}, the extra characters at the end of @var{array2} are ignored. + +On the other hand, making @var{array1} longer than @var{array2} is not +portable; POSIX says that the result is undefined. In this situation, +BSD @command{tr} pads @var{array2} to the length of @var{array1} by repeating +the last character of @var{array2} as many times as necessary. System V +@command{tr} truncates @var{array1} to the length of @var{array2}. + +By default, GNU @command{tr} handles this case like BSD @command{tr}. +When the @option{--truncate-set1} (@option{-t}) option is given, +GNU @command{tr} handles this case like the System V @command{tr} +instead. This option is ignored for operations other than translation. + +Acting like System V @command{tr} in this case breaks the relatively common +BSD idiom: + +@example +tr -cs A-Za-z0-9 '\012' +@end example + +@noindent +because it converts only zero bytes (the first element in the +complement of @var{array1}), rather than all non-alphanumerics, to +newlines. + +@noindent +By the way, the above idiom is not portable because it uses ranges, and +it assumes that the octal code for newline is 012. Here is a better +way to write it: + +@example +tr -cs '[:alnum:]' '[\n*]' +@end example + + +@node Squeezing and deleting +@subsection Squeezing repeats and deleting + +@cindex squeezing repeat characters +@cindex deleting characters +@cindex removing characters + +When given just the @option{--delete} (@option{-d}) option, @command{tr} +removes any input characters that are in @var{array1}. + +When given just the @option{--squeeze-repeats} (@option{-s}) option +and not translating, @command{tr} replaces each input sequence of a +repeated character that is in @var{array1} with a single occurrence of +that character. + +When given both @option{--delete} and @option{--squeeze-repeats}, @command{tr} +first performs any deletions using @var{array1}, then squeezes repeats +from any remaining characters using @var{array2}. + +The @option{--squeeze-repeats} option may also be used when translating, +in which case @command{tr} first performs translation, then squeezes +repeats from any remaining characters using @var{array2}. + +Here are some examples to illustrate various combinations of options: + +@itemize @bullet + +@item +Remove all zero bytes: + +@example +tr -d '\0' +@end example + +@item +Put all words on lines by themselves. This converts all +non-alphanumeric characters to newlines, then squeezes each string +of repeated newlines into a single newline: + +@example +tr -cs '[:alnum:]' '[\n*]' +@end example + +@item +Convert each sequence of repeated newlines to a single newline. +I.e., delete empty lines: + +@example +tr -s '\n' +@end example + +@item +Find doubled occurrences of words in a document. +@c Separate the following two "the"s, so typo checkers don't complain. +For example, people often write ``the @w{}the'' with the repeated words +separated by a newline. The Bourne shell script below works first +by converting each sequence of punctuation and blank characters to a +single newline. That puts each ``word'' on a line by itself. +Next it maps all uppercase characters to lower case, and finally it +runs @command{uniq} with the @option{-d} option to print out only the words +that were repeated. + +@example +#!/bin/sh +cat -- "$@@" \ + | tr -s '[:punct:][:blank:]' '[\n*]' \ + | tr '[:upper:]' '[:lower:]' \ + | uniq -d +@end example + +@item +Deleting a small set of characters is usually straightforward. For example, +to remove all @samp{a}s, @samp{x}s, and @samp{M}s you would do this: + +@example +tr -d axM +@end example + +However, when @samp{-} is one of those characters, it can be tricky because +@samp{-} has special meanings. Performing the same task as above but also +removing all @samp{-} characters, we might try @code{tr -d -axM}, but +that would fail because @command{tr} would try to interpret @option{-a} as +a command-line option. Alternatively, we could try putting the hyphen +inside the string, @code{tr -d a-xM}, but that wouldn't work either because +it would make @command{tr} interpret @code{a-x} as the range of characters +@samp{a}@dots{}@samp{x} rather than the three. +One way to solve the problem is to put the hyphen at the end of the list +of characters: + +@example +tr -d axM- +@end example + +Or you can use @samp{--} to terminate option processing: + +@example +tr -d -- -axM +@end example + +@end itemize + + +@node expand invocation +@section @command{expand}: Convert tabs to spaces + +@pindex expand +@cindex tabs to spaces, converting +@cindex converting tabs to spaces + +@command{expand} writes the contents of each given @var{file}, or standard +input if none are given or for a @var{file} of @samp{-}, to standard +output, with tab characters converted to the appropriate number of +spaces. Synopsis: + +@example +expand [@var{option}]@dots{} [@var{file}]@dots{} +@end example + +By default, @command{expand} converts all tabs to spaces. It preserves +backspace characters in the output; they decrement the column count for +tab calculations. The default action is equivalent to @option{-t 8} (set +tabs every 8 columns). + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -t @var{tab1}[,@var{tab2}]@dots{} +@itemx --tabs=@var{tab1}[,@var{tab2}]@dots{} +@opindex -t +@opindex --tabs +@cindex tab stops, setting +If only one tab stop is given, set the tabs @var{tab1} spaces apart +(default is 8). Otherwise, set the tabs at columns @var{tab1}, +@var{tab2}, @dots{} (numbered from 0), and replace any tabs beyond the +last tab stop given with single spaces. +@macro gnuExpandTabs +Tab stops can be separated by blanks as well as by commas. + +As a GNU extension the last @var{tab} specified can be prefixed +with a @samp{/} to indicate a tab size to use for remaining positions. +For example, @option{--tabs=2,4,/8} will set tab stops at position 2 and 4, +and every multiple of 8 after that. + +Also the last @var{tab} specified can be prefixed with a @samp{+} to indicate +a tab size to use for remaining positions, offset from the final explicitly +specified tab stop. +For example, to ignore the 1 character gutter present in diff output, +one can specify a 1 character offset using @option{--tabs=1,+8}, +which will set tab stops at positions 1,9,17,@dots{} +@end macro +@gnuExpandTabs + + +For compatibility, GNU @command{expand} also accepts the obsolete +option syntax, @option{-@var{t1}[,@var{t2}]@dots{}}. New scripts +should use @option{-t @var{t1}[,@var{t2}]@dots{}} instead. + +@item -i +@itemx --initial +@opindex -i +@opindex --initial +@cindex initial tabs, converting +Only convert initial tabs (those that precede all non-space or non-tab +characters) on each line to spaces. + +@end table + +@exitstatus + + +@node unexpand invocation +@section @command{unexpand}: Convert spaces to tabs + +@pindex unexpand + +@command{unexpand} writes the contents of each given @var{file}, or +standard input if none are given or for a @var{file} of @samp{-}, to +standard output, converting blanks at the beginning of each line into +as many tab characters as needed. In the default POSIX +locale, a @dfn{blank} is a space or a tab; other locales may specify +additional blank characters. Synopsis: + +@example +unexpand [@var{option}]@dots{} [@var{file}]@dots{} +@end example + +By default, @command{unexpand} converts only initial blanks (those +that precede all non-blank characters) on each line. It +preserves backspace characters in the output; they decrement the column +count for tab calculations. By default, tabs are set at every 8th +column. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -t @var{tab1}[,@var{tab2}]@dots{} +@itemx --tabs=@var{tab1}[,@var{tab2}]@dots{} +@opindex -t +@opindex --tabs +If only one tab stop is given, set the tabs @var{tab1} columns apart +instead of the default 8. Otherwise, set the tabs at columns +@var{tab1}, @var{tab2}, @dots{} (numbered from 0), and leave blanks +beyond the tab stops given unchanged. +@gnuExpandTabs + +This option implies the @option{-a} option. + +For compatibility, GNU @command{unexpand} supports the obsolete option syntax, +@option{-@var{tab1}[,@var{tab2}]@dots{}}, where tab stops must be +separated by commas. (Unlike @option{-t}, this obsolete option does +not imply @option{-a}.) New scripts should use @option{--first-only -t +@var{tab1}[,@var{tab2}]@dots{}} instead. + +@item -a +@itemx --all +@opindex -a +@opindex --all +Also convert all sequences of two or more blanks just before a tab stop, +even if they occur after non-blank characters in a line. + +@end table + +@exitstatus + + +@node Directory listing +@chapter Directory listing + +This chapter describes the @command{ls} command and its variants @command{dir} +and @command{vdir}, which list information about files. + +@menu +* ls invocation:: List directory contents. +* dir invocation:: Briefly ls. +* vdir invocation:: Verbosely ls. +* dircolors invocation:: Color setup for ls, etc. +@end menu + + +@node ls invocation +@section @command{ls}: List directory contents + +@pindex ls +@cindex directory listing + +The @command{ls} program lists information about files (of any type, +including directories). Options and file arguments can be intermixed +arbitrarily, as usual. Later options override earlier options that +are incompatible. + +For non-option command-line arguments that are directories, by default +@command{ls} lists the contents of directories, not recursively, and +omitting files with names beginning with @samp{.}. For other non-option +arguments, by default @command{ls} lists just the file name. If no +non-option argument is specified, @command{ls} operates on the current +directory, acting as if it had been invoked with a single argument of @samp{.}. + +@vindex LC_ALL +By default, the output is sorted alphabetically, according to the locale +settings in effect.@footnote{If you use a non-POSIX +locale (e.g., by setting @env{LC_ALL} to @samp{en_US}), then @command{ls} may +produce output that is sorted differently than you're accustomed to. +In that case, set the @env{LC_ALL} environment variable to @samp{C}.} +If standard output is +a terminal, the output is in columns (sorted vertically) and control +characters are output as question marks; otherwise, the output is listed +one per line and control characters are output as-is. + +Because @command{ls} is such a fundamental program, it has accumulated many +options over the years. They are described in the subsections below; +within each section, options are listed alphabetically (ignoring case). +The division of options into the subsections is not absolute, since some +options affect more than one aspect of @command{ls}'s operation. + +@cindex exit status of @command{ls} +Exit status: + +@display +0 success +1 minor problems (e.g., failure to access a file or directory not + specified as a command line argument. This happens when listing a + directory in which entries are actively being removed or renamed.) +2 serious trouble (e.g., memory exhausted, invalid option, failure + to access a file or directory specified as a command line argument + or a directory loop) +@end display + +Also see @ref{Common options}. + +@menu +* Which files are listed:: +* What information is listed:: +* Sorting the output:: +* General output formatting:: +* Formatting file timestamps:: +* Formatting the file names:: +@end menu + + +@node Which files are listed +@subsection Which files are listed + +These options determine which files @command{ls} lists information for. +By default, @command{ls} lists files and the contents of any +directories on the command line, except that in directories it ignores +files whose names start with @samp{.}. + +@table @samp + +@item -a +@itemx --all +@opindex -a +@opindex --all +In directories, do not ignore file names that start with @samp{.}. + +@item -A +@itemx --almost-all +@opindex -A +@opindex --almost-all +In directories, do not ignore all file names that start with @samp{.}; +ignore only @file{.} and @file{..}. The @option{--all} (@option{-a}) +option overrides this option. + +@item -B +@itemx --ignore-backups +@opindex -B +@opindex --ignore-backups +@cindex backup files, ignoring +In directories, ignore files that end with @samp{~}. This option is +equivalent to @samp{--ignore='*~' --ignore='.*~'}. + +@item -d +@itemx --directory +@opindex -d +@opindex --directory +List just the names of directories, as with other types of files, rather +than listing their contents. +@c The following sentence is the same as the one for -F. +Do not follow symbolic links listed on the +command line unless the @option{--dereference-command-line} (@option{-H}), +@option{--dereference} (@option{-L}), or +@option{--dereference-command-line-symlink-to-dir} options are specified. + +@item -H +@itemx --dereference-command-line +@opindex -H +@opindex --dereference-command-line +@cindex symbolic links, dereferencing +If a command line argument specifies a symbolic link, show information +for the file the link references rather than for the link itself. + +@item --dereference-command-line-symlink-to-dir +@opindex --dereference-command-line-symlink-to-dir +@cindex symbolic links, dereferencing +Do not dereference symbolic links, with one exception: +if a command line argument specifies a symbolic link that refers to +a directory, show information for that directory rather than for the +link itself. +This is the default behavior unless long format is being used +or any of the following options is in effect: +@option{--classify} (@option{-F}), +@option{--directory} (@option{-d}), +@option{--dereference} (@option{-L}), or +@option{--dereference-command-line} (@option{-H})). + +@item --group-directories-first +@opindex --group-directories-first +Group all the directories before the files and then sort the +directories and the files separately using the selected sort key +(see @option{--sort} option). +That is, this option specifies a primary sort key, +and the @option{--sort} option specifies a secondary key. +However, any use of @option{--sort=none} +(@option{-U}) disables this option altogether. + +@item --hide=PATTERN +@opindex --hide=@var{pattern} +In directories, ignore files whose names match the shell pattern +@var{pattern}, unless the @option{--all} (@option{-a}) or +@option{--almost-all} (@option{-A}) is also given. This +option acts like @option{--ignore=@var{pattern}} except that it has no +effect if @option{--all} (@option{-a}) or @option{--almost-all} +(@option{-A}) is also given. + +This option can be useful in shell aliases. For example, if +@command{lx} is an alias for @samp{ls --hide='*~'} and @command{ly} is +an alias for @samp{ls --ignore='*~'}, then the command @samp{lx -A} +lists the file @file{README~} even though @samp{ly -A} would not. + +@item -I @var{pattern} +@itemx --ignore=@var{pattern} +@opindex -I +@opindex --ignore=@var{pattern} +In directories, ignore files whose names match the shell pattern +(not regular expression) @var{pattern}. As +in the shell, an initial @samp{.} in a file name does not match a +wildcard at the start of @var{pattern}. Sometimes it is useful +to give this option several times. For example, + +@example +$ ls --ignore='.??*' --ignore='.[^.]' --ignore='#*' +@end example + +The first option ignores names of length 3 or more that start with @samp{.}, +the second ignores all two-character names that start with @samp{.} +except @samp{..}, and the third ignores names that start with @samp{#}. + +@item -L +@itemx --dereference +@opindex -L +@opindex --dereference +@cindex symbolic links, dereferencing +When showing file information for a symbolic link, show information +for the file the link references rather than the link itself. +However, even with this option, @command{ls} still prints the name +of the link itself, not the name of the file that the link points to. + +@item -R +@itemx --recursive +@opindex -R +@opindex --recursive +@cindex recursive directory listing +@cindex directory listing, recursive +List the contents of all directories recursively. + +@end table + + +@node What information is listed +@subsection What information is listed + +These options affect the information that @command{ls} displays. By +default, only file names are shown. + +@table @samp + +@item --author +@opindex --author +@cindex hurd, author, printing +In long format, list each file's author. +In GNU/Hurd, file authors can differ from their owners, but in other +operating systems the two are the same. + +@item -D +@itemx --dired +@opindex -D +@opindex --dired +@cindex dired Emacs mode support +Print an additional line after the main output: + +@example +//DIRED// @var{beg1} @var{end1} @var{beg2} @var{end2} @dots{} +@end example + +@noindent +The @var{begn} and @var{endn} are unsigned integers that record the +byte position of the beginning and end of each file name in the output. +This makes it easy for Emacs to find the names, even when they contain +unusual characters such as space or newline, without fancy searching. + +If directories are being listed recursively via +@option{--recursive} (@option{-R}), output a similar +line with offsets for each subdirectory name: + +@example +//SUBDIRED// @var{beg1} @var{end1} @dots{} +@end example + +Finally, output a line of the form: + +@example +//DIRED-OPTIONS// --quoting-style=@var{word} +@end example + +@noindent +where @var{word} is the quoting style (@pxref{Formatting the file names}). + +Here is an actual example: + +@example +$ mkdir -p a/sub/deeper a/sub2 +$ touch a/f1 a/f2 +$ touch a/sub/deeper/file +$ ls -gloRF --dired a + a: + total 8 + -rw-r--r-- 1 0 Jun 10 12:27 f1 + -rw-r--r-- 1 0 Jun 10 12:27 f2 + drwxr-xr-x 3 4096 Jun 10 12:27 sub/ + drwxr-xr-x 2 4096 Jun 10 12:27 sub2/ + + a/sub: + total 4 + drwxr-xr-x 2 4096 Jun 10 12:27 deeper/ + + a/sub/deeper: + total 0 + -rw-r--r-- 1 0 Jun 10 12:27 file + + a/sub2: + total 0 +//DIRED// 48 50 84 86 120 123 158 162 217 223 282 286 +//SUBDIRED// 2 3 167 172 228 240 290 296 +//DIRED-OPTIONS// --quoting-style=literal +@end example + +The pairs of offsets on the @samp{//DIRED//} line above delimit +these names: @file{f1}, @file{f2}, @file{sub}, @file{sub2}, @file{deeper}, +@file{file}. +The offsets on the @samp{//SUBDIRED//} line delimit the following +directory names: @file{a}, @file{a/sub}, @file{a/sub/deeper}, @file{a/sub2}. + +Here is an example of how to extract the fifth entry name, @samp{deeper}, +corresponding to the pair of offsets, 222 and 228: + +@example +$ ls -gloRF --dired a > out +$ dd bs=1 skip=222 count=6 < out 2>/dev/null; echo +deeper +@end example + +Although the listing above includes a trailing slash +for the @samp{deeper} entry, the offsets select the name without +the trailing slash. However, if you invoke @command{ls} with @option{--dired} +(@option{-D}) along with an option like +@option{--escape} (@option{-b}) and operate +on a file whose name contains special characters, the backslash +@emph{is} included: + +@example +$ touch 'a b' +$ ls -blog --dired 'a b' + -rw-r--r-- 1 0 Jun 10 12:28 a\ b +//DIRED// 30 34 +//DIRED-OPTIONS// --quoting-style=escape +@end example + +If you use a quoting style like @option{--quoting-style=c} (@option{-Q}) +that adds quote marks, then the offsets include the quote marks. +So beware that the user may select the quoting style via the environment +variable @env{QUOTING_STYLE}@. Hence, applications using @option{--dired} +should either specify an explicit @option{--quoting-style=literal} +(@option{-N}) option on the command line, or else be +prepared to parse the escaped names. + +The @option{--dired} (@option{-D}) option has well-defined behavior +only when long format is in effect and hyperlinks are disabled (e.g., +@option{--hyperlink=none}). + +@item --full-time +@opindex --full-time +Produce long format, and list times in full. It is +equivalent to using @option{--format=long} (@option{-l}) with +@option{--time-style=full-iso} (@pxref{Formatting file timestamps}). + +@item -g +@opindex -g +Produce long format, but omit owner information. + +@item -G +@itemx --no-group +@opindex -G +@opindex --no-group +Inhibit display of group information in long format. +(This is the default in some non-GNU versions of @command{ls}, so we +provide this option for compatibility.) + +@optHumanReadable + +@item -i +@itemx --inode +@opindex -i +@opindex --inode +@cindex inode number, printing +Print the inode number (also called the file serial number and index +number) of each file to the left of the file name. (This number +uniquely identifies each file within a particular file system.) + +@item -l +@itemx --format=long +@itemx --format=verbose +@opindex -l +@opindex --format +@opindex long ls @r{format} +@opindex verbose ls @r{format} +Produce long format. +In addition to the name of each file, print the file type, file mode bits, +number of hard links, owner name, group name, size, and +timestamp (@pxref{Formatting file timestamps}), normally +the modification timestamp (the mtime, @pxref{File timestamps}). +If the owner or group name cannot be determined, print +the owner or group ID instead, right-justified as a cue +that it is a number rather than a textual name. +Print question marks for other information that +cannot be determined. + +Normally the size is printed as a byte count without punctuation, but +this can be overridden (@pxref{Block size}). +For example, @option{--human-readable} (@option{-h}) +prints an abbreviated, human-readable count, and +@samp{--block-size="'1"} prints a byte count with the thousands +separator of the current locale. + +For each directory that is listed, preface the files with a line +@samp{total @var{blocks}}, where @var{blocks} is the file system allocation +for all files in that directory. The block size currently defaults to 1024 +bytes, but this can be overridden (@pxref{Block size}). +The @var{blocks} computed counts each hard link separately; +this is arguably a deficiency. + +The file type is one of the following characters: + +@c The commented-out entries are ones we're not sure about. + +@table @samp +@item - +regular file +@item b +block special file +@item c +character special file +@item C +high performance (``contiguous data'') file +@item d +directory +@item D +door (Solaris) +@c @item F +@c semaphore, if this is a distinct file type +@item l +symbolic link +@c @item m +@c multiplexed file (7th edition Unix; obsolete) +@item M +off-line (``migrated'') file (Cray DMF) +@item n +network special file (HP-UX) +@item p +FIFO (named pipe) +@item P +port (Solaris) +@c @item Q +@c message queue, if this is a distinct file type +@item s +socket +@c @item S +@c shared memory object, if this is a distinct file type +@c @item T +@c typed memory object, if this is a distinct file type +@c @item w +@c whiteout (4.4BSD; not implemented) +@item ? +some other file type +@end table + +@cindex permissions, output by @command{ls} +The file mode bits listed are similar to symbolic mode specifications +(@pxref{Symbolic Modes}). But @command{ls} combines multiple bits into the +third character of each set of permissions as follows: + +@table @samp +@item s +If the set-user-ID or set-group-ID bit and the corresponding executable bit +are both set. + +@item S +If the set-user-ID or set-group-ID bit is set but the corresponding +executable bit is not set. + +@item t +If the restricted deletion flag or sticky bit, and the +other-executable bit, are both set. The restricted deletion flag is +another name for the sticky bit. @xref{Mode Structure}. + +@item T +If the restricted deletion flag or sticky bit is set but the +other-executable bit is not set. + +@item x +If the executable bit is set and none of the above apply. + +@item - +Otherwise. +@end table + +Following the file mode bits is a single character that specifies +whether an alternate access method such as an access control list +applies to the file. When the character following the file mode bits is a +space, there is no alternate access method. When it is a printing +character, then there is such a method. + +GNU @command{ls} uses a @samp{.} character to indicate a file +with a security context, but no other alternate access method. + +A file with any other combination of alternate access methods +is marked with a @samp{+} character. + +@item -n +@itemx --numeric-uid-gid +@opindex -n +@opindex --numeric-uid-gid +@cindex numeric uid and gid +@cindex numeric user and group IDs +Produce long format, but +display right-justified numeric user and group IDs +instead of left-justified owner and group names. + +@item -o +@opindex -o +Produce long format, but omit group information. +It is equivalent to using @option{--format=long} (@option{-l}) +with @option{--no-group} (@option{-G}). + +@item -s +@itemx --size +@opindex -s +@opindex --size +@cindex file system allocation +@cindex size of files, reporting +Print the file system allocation of each file to the left of the file name. +This is the amount of file system space used by the file, which is usually a +bit more than the file's size, but it can be less if the file has holes. + +Normally the allocation is printed in units of +1024 bytes, but this can be overridden (@pxref{Block size}). + +@cindex NFS mounts from BSD to HP-UX +For files that are NFS-mounted from an HP-UX system to a BSD system, +this option reports sizes that are half the correct values. On HP-UX +systems, it reports sizes that are twice the correct values for files +that are NFS-mounted from BSD systems. This is due to a flaw in HP-UX; +it also affects the HP-UX @command{ls} program. + +@optSi + +@item -Z +@itemx --context +@opindex -Z +@opindex --context +@cindex SELinux +@cindex security context +Display the SELinux security context or @samp{?} if none is found. +In long format, print the security context to the left of the size column. + +@end table + + +@node Sorting the output +@subsection Sorting the output + +@cindex sorting @command{ls} output +These options change the order in which @command{ls} sorts the information +it outputs. By default, sorting is done by character code +(e.g., ASCII order). + +@table @samp + +@item -c +@itemx --time=ctime +@itemx --time=status +@opindex -c +@opindex --time +@opindex ctime@r{, printing or sorting by} +@opindex status time@r{, printing or sorting by} +@opindex use time@r{, printing or sorting files by} +In long format, +print the status change timestamp (the ctime) instead of the mtime. +When sorting by time or when not using long format, +sort according to the ctime. @xref{File timestamps}. + +@item -f +@opindex -f +@cindex unsorted directory listing +@cindex directory order, listing by +Produce an unsorted directory listing. +This is equivalent to the combination of @option{--all} (@option{-a}), +@option{--sort=none} (@option{-U}), @option{-1}, +@option{--color=none}, and @option{--hyperlink=none}, +while also disabling any previous use of @option{--size} (@option{-s}). + +@item -r +@itemx --reverse +@opindex -r +@opindex --reverse +@cindex reverse sorting +Reverse whatever the sorting method is -- e.g., list files in reverse +alphabetical order, youngest first, smallest first, or whatever. +This option has no effect when @option{--sort=none} (@option{-U}) +is in effect. + +@item -S +@itemx --sort=size +@opindex -S +@opindex --sort +@opindex size of files@r{, sorting files by} +Sort by file size, largest first. + +@item -t +@itemx --sort=time +@opindex -t +@opindex --sort +@opindex modification timestamp@r{, sorting files by} +Sort by modification timestamp (mtime) by default, newest first. +The timestamp to order by can be changed with the @option{--time} option. +@xref{File timestamps}. + +@item -u +@itemx --time=atime +@itemx --time=access +@itemx --time=use +@opindex -u +@opindex --time +@opindex use time@r{, printing or sorting files by} +@opindex atime@r{, printing or sorting files by} +@opindex access timestamp@r{, printing or sorting files by} +In long format, print the last access timestamp (the atime). +When sorting by time or when not using long format, +sort according to the atime. +@xref{File timestamps}. + +@item --time=mtime +@itemx --time=modification +@opindex --time +@opindex data modification time@r{, printing or sorting files by} +@opindex mtime@r{, printing or sorting files by} +This is the default timestamp display and sorting mode. +In long format, print the last data modification timestamp (the mtime). +When sorting by time or when not using long format, +sort according to the mtime. +@xref{File timestamps}. + +@item --time=birth +@itemx --time=creation +@opindex --time +@opindex birth time@r{, printing or sorting files by} +@opindex creation timestamp@r{, printing or sorting files by} +In long format, print the file creation timestamp if available, +falling back to the file modification timestamp (mtime) if not. +When sorting by time or when not using long format, +sort according to the birth time. +@xref{File timestamps}. + +@item -U +@itemx --sort=none +@opindex -U +@opindex --sort +@opindex none@r{, sorting option for @command{ls}} +Do not sort; list the files in whatever order they are +stored in the directory. (Do not do any of the other unrelated things +that @option{-f} does.) This can be useful when listing large +directories, where sorting can take some time. + +@item -v +@itemx --sort=version +@opindex -v +@opindex --sort +@opindex version@r{, sorting option for @command{ls}} +Sort by version name and number, lowest first. It behaves like a default +sort, except that each sequence of decimal digits is treated numerically +as an index/version number. @xref{Version sort ordering}. + +@item --sort=width +@opindex --sort +@opindex width@r{, sorting option for @command{ls}} +Sort by printed width of file names. +This can be useful with the @option{--format=vertical} (@option{-C}) +output format, to most densely display the listed files. + +@item -X +@itemx --sort=extension +@opindex -X +@opindex --sort +@opindex extension@r{, sorting files by} +Sort directory contents alphabetically by file extension (characters +after the last @samp{.}); files with no extension are sorted first. + +@end table + + +@node General output formatting +@subsection General output formatting + +These options affect the appearance of the overall output. + +@table @samp + +@item --format=single-column +@opindex --format +@opindex single-column @r{output of files} +List one file name per line, with no other information. +This is the default for @command{ls} when standard +output is not a terminal. See also the @option{--escape} (@option{-b}), +@option{--hide-control-chars} (@option{-q}), and @option{--zero} options +to disambiguate output of file names containing newline characters. + +@item -1 +@opindex -1 +List one file per line. This is like @option{--format=single-column} +except that it has no effect if long format is also in effect. + +@item -C +@itemx --format=vertical +@opindex -C +@opindex --format +@opindex vertical @r{sorted files in columns} +List files in columns, sorted vertically, with no other information. +This is the default for @command{ls} if standard output is a terminal. +It is always the default for the @command{dir} program. +GNU @command{ls} uses variable width columns to display as many files as +possible in the fewest lines. + +@item --color [=@var{when}] +@opindex --color +@cindex color, distinguishing file types with +Specify whether to use color for distinguishing file types; @var{when} +may be omitted, or one of: +@itemize @bullet +@item none +@vindex none @r{color option} +- Do not use color at all. This is the default. +@item auto +@vindex auto @r{color option} +@cindex terminal, using color iff +- Only use color if standard output is a terminal. +@item always +@vindex always @r{color option} +- Always use color. +@end itemize +Specifying @option{--color} and no @var{when} is equivalent to +@option{--color=always}. +If piping a colored listing through a pager like @command{less}, +use the pager's @option{-R} option to pass the color codes to the terminal. + +@vindex LS_COLORS +@vindex SHELL @r{environment variable, and color} +Using the @option{--color} option may incur a noticeable +performance penalty when run in a large directory, +because the default settings require that @command{ls} @code{stat} every +single file it lists. +However, if you would like most of the file-type coloring +but can live without the other coloring options (e.g., +executable, orphan, sticky, other-writable, capability), use +@command{dircolors} to set the @env{LS_COLORS} environment variable like this, +@example +eval $(dircolors -p | perl -pe \ + 's/^((CAP|S[ET]|O[TR]|M|E)\w+).*/$1 00/' | dircolors -) +@end example +and on a @code{dirent.d_type}-capable file system, @command{ls} +will perform only one @code{stat} call per command line argument. + +@item -F +@itemx --classify [=@var{when}] +@itemx --indicator-style=classify +@opindex -F +@opindex --classify +@opindex --indicator-style +@cindex file type and executables, marking +@cindex executables and file type, marking +Append a character to each file name indicating the file type. Also, +for regular files that are executable, append @samp{*}. The file type +indicators are @samp{/} for directories, @samp{@@} for symbolic links, +@samp{|} for FIFOs, @samp{=} for sockets, @samp{>} for doors, +and nothing for regular files. +@var{when} may be omitted, or one of: +@itemize @bullet +@item none +@vindex none @r{classify option} +- Do not classify. This is the default. +@item auto +@vindex auto @r{classify option} +@cindex terminal, using classify iff +- Only classify if standard output is a terminal. +@item always +@vindex always @r{classify option} +- Always classify. +@end itemize +Specifying @option{--classify} and no @var{when} is equivalent to +@option{--classify=always}. +@c The following sentence is the same as the one for -d. +Do not follow symbolic links listed on the +command line unless the @option{--dereference-command-line} (@option{-H}), +@option{--dereference} (@option{-L}), or +@option{--dereference-command-line-symlink-to-dir} options are specified. + +@item --file-type +@itemx --indicator-style=file-type +@opindex --file-type +@opindex --indicator-style +@cindex file type, marking +Append a character to each file name indicating the file type. This is +like @option{--classify} (@option{-F}, except that executables are not marked. + +@item --hyperlink [=@var{when}] +@opindex --hyperlink +@cindex hyperlink, linking to files +Output codes recognized by some terminals to link +to files using the @samp{file://} URI format. +@var{when} may be omitted, or one of: +@itemize @bullet +@item none +@vindex none @r{hyperlink option} +- Do not use hyperlinks at all. This is the default. +@item auto +@vindex auto @r{hyperlink option} +@cindex terminal, using hyperlink iff +- Only use hyperlinks if standard output is a terminal. +@item always +@vindex always @r{hyperlink option} +- Always use hyperlinks. +@end itemize +Specifying @option{--hyperlink} and no @var{when} is equivalent to +@option{--hyperlink=always}. + +@item --indicator-style=@var{word} +@opindex --indicator-style +Append a character indicator with style @var{word} to entry names, +as follows: + +@table @samp +@item none +Do not append any character indicator; this is the default. +@item slash +Append @samp{/} for directories. This is the same as the @option{-p} +option. +@item file-type +Append @samp{/} for directories, @samp{@@} for symbolic links, @samp{|} +for FIFOs, @samp{=} for sockets, and nothing for regular files. This is +the same as the @option{--file-type} option. +@item classify +Append @samp{*} for executable regular files, otherwise behave as for +@samp{file-type}. This is the same as the @option{--classify} +(@option{-F}) option. +@end table + +@item -k +@itemx --kibibytes +@opindex -k +@opindex --kibibytes +Set the default block size to its normal value of 1024 bytes, +overriding any contrary specification in environment variables +(@pxref{Block size}). If @option{--block-size}, +@option{--human-readable} (@option{-h}), or @option{--si} options are used, +they take precedence even if @option{--kibibytes} (@option{-k}) is placed after + +The @option{--kibibytes} (@option{-k}) option affects the +per-directory block count written in long format, +and the file system allocation written by the @option{--size} (@option{-s}) +option. It does not affect the file size in bytes that is written in +long format. + +@item -m +@itemx --format=commas +@opindex -m +@opindex --format +@opindex commas@r{, outputting between files} +List files horizontally, with as many as will fit on each line, +separated by @samp{, } (a comma and a space), +and with no other information. + +@item -p +@itemx --indicator-style=slash +@opindex -p +@opindex --indicator-style +@cindex file type, marking +Append a @samp{/} to directory names. + +@item -x +@itemx --format=across +@itemx --format=horizontal +@opindex -x +@opindex --format +@opindex across@r{, listing files} +@opindex horizontal@r{, listing files} +List the files in columns, sorted horizontally. + +@item -T @var{cols} +@itemx --tabsize=@var{cols} +@opindex -T +@opindex --tabsize +Assume that each tab stop is @var{cols} columns wide. The default is 8. +@command{ls} uses tabs where possible in the output, for efficiency. If +@var{cols} is zero, do not use tabs at all. + +Some terminal emulators might not properly align columns to the right of a +TAB following a non-ASCII byte. You can avoid that issue by using the +@option{-T0} option or put @code{TABSIZE=0} in your environment, to tell +@command{ls} to align using spaces, not tabs. + +If you set a terminal's hardware tabs to anything other than the default, +you should also use a @command{--tabsize} option or @env{TABSIZE} +environment variable either to match the hardware tabs, or to disable +the use of hardware tabs. Otherwise, the output of @command{ls} may +not line up. For example, if you run the shell command @samp{tabs -4} +to set hardware tabs to every four columns, you should also run +@samp{export TABSIZE=4} or @samp{export TABSIZE=0}, or use the +corresponding @option{--tabsize} options. + +@item -w @var{cols} +@itemx --width=@var{cols} +@opindex -w +@opindex --width +@vindex COLUMNS +Assume the screen is @var{cols} columns wide. The default is taken +from the terminal settings if possible; otherwise the environment +variable @env{COLUMNS} is used if it is set; otherwise the default +is 80. With a @var{cols} value of @samp{0}, there is no limit on +the length of the output line, and that single output line will +be delimited with spaces, not tabs. + +@item --zero +@opindex --zero +@outputNUL +This option is incompatible with the @option{--dired} (@option{-D}) option. +This option also implies the options @option{--show-control-chars}, +@option{-1}, @option{--color=none}, and +@option{--quoting-style=literal} (@option{-N}). + +@end table + + +@node Formatting file timestamps +@subsection Formatting file timestamps + +By default, file timestamps are listed in abbreviated form, using +a date like @samp{Mar 30@ @ 2020} for non-recent timestamps, and a +date-without-year and time like @samp{Mar 30 23:45} for recent timestamps. +This format can change depending on the current locale as detailed below. + +@cindex clock skew +A timestamp is considered to be @dfn{recent} if it is less than six +months old, and is not dated in the future. If a timestamp dated +today is not listed in recent form, the timestamp is in the future, +which means you probably have clock skew problems which may break +programs like @command{make} that rely on file timestamps. +@xref{File timestamps}. + +@vindex TZ +Timestamps are listed according to the time zone rules specified by +the @env{TZ} environment variable, or by the system default rules if +@env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone +with @env{TZ}, libc, The GNU C Library Reference Manual}. + +The following option changes how file timestamps are printed. + +@table @samp +@item --time-style=@var{style} +@opindex --time-style +@cindex time style +List timestamps in style @var{style}. The @var{style} should +be one of the following: + +@table @samp +@item +@var{format} +@vindex LC_TIME +List timestamps using @var{format}, where @var{format} is interpreted +like the format argument of @command{date} (@pxref{date invocation}). +For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes +@command{ls} to list timestamps like @samp{2020-03-30 23:45:56}. As +with @command{date}, @var{format}'s interpretation is affected by the +@env{LC_TIME} locale category. + +If @var{format} contains two format strings separated by a newline, +the former is used for non-recent files and the latter for recent +files; if you want output columns to line up, you may need to insert +spaces in one of the two formats. + +@item full-iso +List timestamps in full using ISO 8601-like date, time, and time zone +components with nanosecond precision, e.g., @samp{2020-07-21 +23:45:56.477817180 -0400}. This style is equivalent to +@samp{+%Y-%m-%d %H:%M:%S.%N %z}. + +This is useful because the time output includes all the information that +is available from the operating system. For example, this can help +explain @command{make}'s behavior, since GNU @command{make} +uses the full timestamp to determine whether a file is out of date. + +@item long-iso +List ISO 8601 date and time components with minute precision, e.g., +@samp{2020-03-30 23:45}. These timestamps are shorter than +@samp{full-iso} timestamps, and are usually good enough for everyday +work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}. + +@item iso +List ISO 8601 dates for non-recent timestamps (e.g., +@samp{2020-03-30@ }), and ISO 8601-like month, day, hour, and +minute for recent timestamps (e.g., @samp{03-30 23:45}). These +timestamps are uglier than @samp{long-iso} timestamps, but they carry +nearly the same information in a smaller space and their brevity helps +@command{ls} output fit within traditional 80-column output lines. +The following two @command{ls} invocations are equivalent: + +@example +newline=' +' +ls -l --time-style="+%Y-%m-%d $newline%m-%d %H:%M" +ls -l --time-style="iso" +@end example + +@item locale +@vindex LC_TIME +List timestamps in a locale-dependent form. For example, a French +locale might list non-recent timestamps like @samp{30 mars@ @ @ 2020} +and recent timestamps like @samp{30 mars@ @ 23:45}. Locale-dependent +timestamps typically consume more space than @samp{iso} timestamps and +are harder for programs to parse because locale conventions vary so +widely, but they are easier for many people to read. + +The @env{LC_TIME} locale category specifies the timestamp format. The +default POSIX locale uses timestamps like @samp{Mar 30@ +@ 2020} and @samp{Mar 30 23:45}; in this locale, the following two +@command{ls} invocations are equivalent: + +@example +newline=' +' +ls -l --time-style="+%b %e %Y$newline%b %e %H:%M" +ls -l --time-style="locale" +@end example + +Other locales behave differently. For example, in a German locale, +@option{--time-style="locale"} might be equivalent to +@option{--time-style="+%e. %b %Y $newline%e. %b %H:%M"} +and might generate timestamps like @samp{30. M@"ar 2020@ } and +@samp{30. M@"ar 23:45}. + +@item posix-@var{style} +@vindex LC_TIME +List POSIX-locale timestamps if the @env{LC_TIME} locale +category is POSIX, @var{style} timestamps otherwise. For +example, the @samp{posix-long-iso} style lists +timestamps like @samp{Mar 30@ @ 2020} and @samp{Mar 30 23:45} when in +the POSIX locale, and like @samp{2020-03-30 23:45} otherwise. +@end table +@end table + +@vindex TIME_STYLE +You can specify the default value of the @option{--time-style} option +with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set +the default style is @samp{locale}. GNU Emacs 21.3 and +later use the @option{--dired} option and therefore can parse any date +format, but if you are using Emacs 21.1 or 21.2 and specify a +non-POSIX locale you may need to set +@samp{TIME_STYLE="posix-long-iso"}. + +To avoid certain denial-of-service attacks, timestamps that would be +longer than 1000 bytes may be treated as errors. + + +@node Formatting the file names +@subsection Formatting the file names + +These options change how file names themselves are printed. + +@table @samp + +@item -b +@itemx --escape +@itemx --quoting-style=escape +@opindex -b +@opindex --escape +@opindex --quoting-style +@cindex backslash sequences for file names +Quote nongraphic characters in file names using alphabetic and octal +backslash sequences like those used in C. + +@item -N +@itemx --literal +@itemx --quoting-style=literal +@opindex -N +@opindex --literal +@opindex --quoting-style +Do not quote file names. However, with @command{ls} nongraphic +characters are still printed as question marks if the output is a +terminal and you do not specify the @option{--show-control-chars} +option. + +@item -q +@itemx --hide-control-chars +@opindex -q +@opindex --hide-control-chars +Print question marks instead of nongraphic characters in file names. +This is the default if the output is a terminal and the program is +@command{ls}. + +@item -Q +@itemx --quote-name +@itemx --quoting-style=c +@opindex -Q +@opindex --quote-name +@opindex --quoting-style +Enclose file names in double quotes and quote nongraphic characters as +in C. + +@item --quoting-style=@var{word} +@opindex --quoting-style +@cindex quoting style +Use style @var{word} to quote file names and other strings that may +contain arbitrary characters. The @var{word} should +be one of the following: + +@macro quotingStyles +@table @samp +@item literal +Output strings as-is; this is the same as the @option{--literal} (@option{-N}) +option. +@item shell +Quote strings for the shell if they contain shell metacharacters or would +cause ambiguous output. +The quoting is suitable for POSIX-compatible shells like +@command{bash}, but it does not always work for incompatible shells +like @command{csh}. +@item shell-always +Quote strings for the shell, even if they would normally not require quoting. +@item shell-escape +Like @samp{shell}, but also quoting non-printable characters using the POSIX +proposed @samp{$''} syntax suitable for most shells. +@item shell-escape-always +Like @samp{shell-escape}, but quote strings even if they would +normally not require quoting. +@item c +Quote strings as for C character string literals, including the +surrounding double-quote characters; this is the same as the +@option{--quote-name} (@option{-Q}) option. +@item escape +Quote strings as for C character string literals, except omit the +surrounding double-quote +characters; this is the same as the @option{--escape} (@option{-b}) option. +@item clocale +Quote strings as for C character string literals, except use +surrounding quotation marks appropriate for the +locale. +@item locale +@c Use @t instead of @samp to avoid duplicate quoting in some output styles. +Quote strings as for C character string literals, except use +surrounding quotation marks appropriate for the locale, and quote +@t{'like this'} instead of @t{"like +this"} in the default C locale. This looks nicer on many displays. +@end table +@end macro +@quotingStyles + +You can specify the default value of the @option{--quoting-style} option +with the environment variable @env{QUOTING_STYLE}@. If that environment +variable is not set, the default value is @samp{shell-escape} when the +output is a terminal, and @samp{literal} otherwise. + +@item --show-control-chars +@opindex --show-control-chars +Print nongraphic characters as-is in file names. +This is the default unless the output is a terminal and the program is +@command{ls}. + +@end table + + +@node dir invocation +@section @command{dir}: Briefly list directory contents + +@pindex dir +@cindex directory listing, brief + +@command{dir} is equivalent to @code{ls -C +-b}; that is, by default files are listed in columns, sorted vertically, +and special characters are represented by backslash escape sequences. + +@xref{ls invocation, @command{ls}}. + + +@node vdir invocation +@section @command{vdir}: Verbosely list directory contents + +@pindex vdir +@cindex directory listing, verbose + +@command{vdir} is equivalent to @code{ls -l +-b}; that is, by default files are listed in long format and special +characters are represented by backslash escape sequences. + +@xref{ls invocation, @command{ls}}. + +@node dircolors invocation +@section @command{dircolors}: Color setup for @command{ls} + +@pindex dircolors +@cindex color setup +@cindex setup for color + +@command{dircolors} outputs a sequence of shell commands to set up the +terminal for color output from @command{ls} (and @command{dir}, etc.). +Typical usage: + +@example +eval "$(dircolors [@var{option}]@dots{} [@var{file}])" +@end example + +If @var{file} is specified, @command{dircolors} reads it to determine which +colors to use for which file types and extensions. Otherwise, a +precompiled database is used. For details on the format of these files, +run @samp{dircolors --print-database}. + +To make @command{dircolors} read a @file{~/.dircolors} file if it +exists, you can put the following lines in your @file{~/.bashrc} (or +adapt them to your favorite shell): + +@example +d=.dircolors +test -r $d && eval "$(dircolors $d)" +@end example + +@vindex LS_COLORS +@vindex SHELL @r{environment variable, and color} +The output is a shell command to set the @env{LS_COLORS} environment +variable. You can specify the shell syntax to use on the command line, +or @command{dircolors} will guess it from the value of the @env{SHELL} +environment variable. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp +@item -b +@itemx --sh +@itemx --bourne-shell +@opindex -b +@opindex --sh +@opindex --bourne-shell +@cindex Bourne shell syntax for color setup +@cindex @command{sh} syntax for color setup +Output Bourne shell commands. This is the default if the @env{SHELL} +environment variable is set and does not end with @samp{csh} or +@samp{tcsh}. + +@item -c +@itemx --csh +@itemx --c-shell +@opindex -c +@opindex --csh +@opindex --c-shell +@cindex C shell syntax for color setup +@cindex @command{csh} syntax for color setup +Output C shell commands. This is the default if @code{SHELL} ends with +@command{csh} or @command{tcsh}. + +@item -p +@itemx --print-database +@opindex -p +@opindex --print-database +@cindex color database, printing +@cindex database for color setup, printing +@cindex printing color database +Print the (compiled-in) default color configuration database. This +output is itself a valid configuration file, and is fairly descriptive +of the possibilities. + +@item --print-ls-colors +@opindex --print-ls-colors +@cindex printing ls colors +Print the LS_COLORS entries on separate lines, +each colored as per the color they represent. + +@end table + +@exitstatus + + +@node Basic operations +@chapter Basic operations + +@cindex manipulating files + +This chapter describes the commands for basic file manipulation: +copying, moving (renaming), and deleting (removing). + +@menu +* cp invocation:: Copy files. +* dd invocation:: Convert and copy a file. +* install invocation:: Copy files and set attributes. +* mv invocation:: Move (rename) files. +* rm invocation:: Remove files or directories. +* shred invocation:: Remove files more securely. +@end menu + + +@node cp invocation +@section @command{cp}: Copy files and directories + +@pindex cp +@cindex copying files and directories +@cindex files, copying +@cindex directories, copying + +@command{cp} copies files (or, optionally, directories). The copy is +completely independent of the original. You can either copy one file to +another, or copy arbitrarily many files to a destination directory. +Synopses: + +@example +cp [@var{option}]@dots{} [-T] @var{source} @var{dest} +cp [@var{option}]@dots{} @var{source}@dots{} @var{directory} +cp [@var{option}]@dots{} -t @var{directory} @var{source}@dots{} +@end example + +@itemize @bullet +@item +If two file names are given, @command{cp} copies the first file to the +second. + +@item +If the @option{--target-directory} (@option{-t}) option is given, or +failing that if the last file is a directory and the +@option{--no-target-directory} (@option{-T}) option is not given, +@command{cp} copies each @var{source} file to the specified directory, +using the @var{source}s' names. +@end itemize + +Generally, files are written just as they are read. For exceptions, +see the @option{--sparse} option below. + +By default, @command{cp} does not copy directories. However, the +@option{-R}, @option{-a}, and @option{-r} options cause @command{cp} to +copy recursively by descending into source directories and copying files +to corresponding destination directories. + +When copying from a symbolic link, @command{cp} normally follows the +link only when not copying recursively or when @option{--link} +(@option{-l}) is used. This default can be overridden with the +@option{--archive} (@option{-a}), @option{-d}, @option{--dereference} +(@option{-L}), @option{--no-dereference} (@option{-P}), and +@option{-H} options. If more than one of these options is specified, +the last one silently overrides the others. + +When copying to a symbolic link, @command{cp} follows the +link only when it refers to an existing regular file. +However, when copying to a dangling symbolic link, @command{cp} +refuses by default, and fails with a diagnostic, since the operation +is inherently dangerous. This behavior is contrary to historical +practice and to POSIX@. +Set @env{POSIXLY_CORRECT} to make @command{cp} attempt to create +the target of a dangling destination symlink, in spite of the possible risk. +Also, when an option like +@option{--backup} or @option{--link} acts to rename or remove the +destination before copying, @command{cp} renames or removes the +symbolic link rather than the file it points to. + +By default, @command{cp} copies the contents of special files only +when not copying recursively. This default can be overridden with the +@option{--copy-contents} option. + +@cindex self-backups +@cindex backups, making only +@command{cp} generally refuses to copy a file onto itself, with the +following exception: if @option{--force --backup} is specified with +@var{source} and @var{dest} identical, and referring to a regular file, +@command{cp} will make a backup file, either regular or numbered, as +specified in the usual ways (@pxref{Backup options}). This is useful when +you simply want to make a backup of an existing file before changing it. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp +@item -a +@itemx --archive +@opindex -a +@opindex --archive +Preserve as much as possible of the structure and attributes of the +original files in the copy (but do not attempt to preserve internal +directory structure; i.e., @samp{ls -U} may list the entries in a copied +directory in a different order). +Try to preserve SELinux security context and extended attributes (xattr), +but ignore any failure to do that and print no corresponding diagnostic. +Equivalent to @option{-dR --preserve=all} with the reduced diagnostics. + +@item --attributes-only +@opindex --attributes-only +Copy only the specified attributes of the source file to the destination. +If the destination already exists, do not alter its contents. +See the @option{--preserve} option for controlling which attributes to copy. + +@item -b +@itemx --backup[=@var{method}] +@opindex -b +@opindex --backup +@vindex VERSION_CONTROL +@cindex backups, making +@xref{Backup options}. +Make a backup of each file that would otherwise be overwritten or removed. +As a special case, @command{cp} makes a backup of @var{source} when the force +and backup options are given and @var{source} and @var{dest} are the same +name for an existing, regular file. One useful application of this +combination of options is this tiny Bourne shell script: + +@example +#!/bin/sh +# Usage: backup FILE... +# Create a GNU-style backup of each listed FILE. +fail=0 +for i; do + cp --backup --force --preserve=all -- "$i" "$i" || fail=1 +done +exit $fail +@end example + +@item --copy-contents +@cindex directories, copying recursively +@cindex copying directories recursively +@cindex recursively copying directories +@cindex non-directories, copying as special files +If copying recursively, copy the contents of any special files (e.g., +FIFOs and device files) as if they were regular files. This means +trying to read the data in each source file and writing it to the +destination. It is usually a mistake to use this option, as it +normally has undesirable effects on special files like FIFOs and the +ones typically found in the @file{/dev} directory. In most cases, +@code{cp -R --copy-contents} will hang indefinitely trying to read +from FIFOs and special files like @file{/dev/console}, and it will +fill up your destination file system if you use it to copy @file{/dev/zero}. +This option has no effect unless copying recursively, and it does not +affect the copying of symbolic links. + +@item -d +@opindex -d +@cindex symbolic links, copying +@cindex hard links, preserving +Copy symbolic links as symbolic links rather than copying the files that +they point to, and preserve hard links between source files in the copies. +Equivalent to @option{--no-dereference --preserve=links}. + +@macro optDebugCopy +@item --debug +@opindex --debug +@cindex debugging, copying +Print extra information to stdout, explaining how files are copied. +This option implies the @option{--verbose} option. +@end macro +@optDebugCopy + +@item -f +@itemx --force +@opindex -f +@opindex --force +When copying without this option and an existing destination file cannot +be opened for writing, the copy fails. However, with @option{--force}, +when a destination file cannot be opened, @command{cp} then +tries to recreate the file by first removing it. Note @option{--force} +alone will not remove dangling symlinks. +When this option is combined with +@option{--link} (@option{-l}) or @option{--symbolic-link} +(@option{-s}), the destination link is replaced, and unless +@option{--backup} (@option{-b}) is also given there is no brief +moment when the destination does not exist. Also see the +description of @option{--remove-destination}. + +This option is independent of the @option{--interactive} or +@option{-i} option: neither cancels the effect of the other. + +This option is ignored when the @option{--no-clobber} or @option{-n} option +is also used. + +@item -H +@opindex -H +If a command line argument specifies a symbolic link, then copy the +file it points to rather than the symbolic link itself. However, +copy (preserving its nature) any symbolic link that is encountered +via recursive traversal. + +@item -i +@itemx --interactive +@opindex -i +@opindex --interactive +When copying a file other than a directory, prompt whether to +overwrite an existing destination file, and fail if the response +is not affirmative. The @option{-i} option overrides +a previous @option{-n} option. + +@item -l +@itemx --link +@opindex -l +@opindex --link +Make hard links instead of copies of non-directories. + +@item -L +@itemx --dereference +@opindex -L +@opindex --dereference +Follow symbolic links when copying from them. +With this option, @command{cp} cannot create a symbolic link. +For example, a symlink (to regular file) in the source tree will be copied to +a regular file in the destination tree. + +@item -n +@itemx --no-clobber +@opindex -n +@opindex --no-clobber +Do not overwrite an existing file; silently fail instead. +This option overrides a previous +@option{-i} option. This option is mutually exclusive with @option{-b} or +@option{--backup} option. + +@item -P +@itemx --no-dereference +@opindex -P +@opindex --no-dereference +@cindex symbolic links, copying +Copy symbolic links as symbolic links rather than copying the files that +they point to. This option affects only symbolic links in the source; +symbolic links in the destination are always followed if possible. + +@item -p +@itemx --preserve[=@var{attribute_list}] +@opindex -p +@opindex --preserve +@cindex file information, preserving, extended attributes, xattr +Preserve the specified attributes of the original files. +If specified, the @var{attribute_list} must be a comma-separated list +of one or more of the following strings: + +@table @samp +@item mode +@cindex access control lists (ACLs) +Preserve attributes relevant to access permissions, +including file mode bits and (if possible) access control lists (ACLs). +ACL preservation is system-dependent, and ACLs are not necessarily +translated when the source and destination are on file systems with +different ACL formats (e.g., NFSv4 versus POSIX formats). + +@item ownership +Preserve the owner and group. On most modern systems, +only users with appropriate privileges may change the owner of a file, +and ordinary users +may preserve the group ownership of a file only if they happen to be +a member of the desired group. +@item timestamps +Preserve the times of last access and last modification, when possible. +On older systems, it is not possible to preserve these attributes +when the affected file is a symbolic link. +However, many systems now provide the @code{utimensat} function, +which makes it possible even for symbolic links. +@item links +Preserve in the destination files +any links between corresponding source files. +Note that with @option{-L} or @option{-H}, this option can convert +symbolic links to hard links. For example, +@example +$ mkdir c; : > a; ln -s a b; cp -aH a b c; ls -i1 c +74161745 a +74161745 b +@end example +@noindent +Note the inputs: @file{b} is a symlink to regular file @file{a}, +yet the files in destination directory, @file{c/}, are hard-linked. +Since @option{-a} implies @option{--no-dereference} it would copy the symlink, +but the later @option{-H} tells @command{cp} to dereference the command line +arguments where it then sees two files with the same inode number. +Then the @option{--preserve=links} option also implied by @option{-a} +will preserve the perceived hard link. + +Here is a similar example that exercises @command{cp}'s @option{-L} option: +@example +$ mkdir b c; (cd b; : > a; ln -s a b); cp -aL b c; ls -i1 c/b +74163295 a +74163295 b +@end example + +@item context +Preserve SELinux security context of the file, or fail with full diagnostics. +@item xattr +@cindex access control lists (ACLs) +Preserve extended attributes of the file, or fail with full diagnostics. +If @command{cp} is built without xattr support, ignore this option. +If SELinux context, ACLs or Capabilities are implemented using xattrs, +they are preserved implicitly by this option as well, i.e., even without +specifying @option{--preserve=mode} or @option{--preserve=context}. +@item all +Preserve all file attributes. +Equivalent to specifying all of the above, but with the difference +that failure to preserve SELinux security context or extended attributes +does not change @command{cp}'s exit status. In contrast to @option{-a}, +all but @samp{Operation not supported} warnings are output. +@end table + +Using @option{--preserve} with no @var{attribute_list} is equivalent +to @option{--preserve=mode,ownership,timestamps}. + +In the absence of this option, the permissions of existing destination +files are unchanged. Each new file is created with the mode of the +corresponding source file minus the set-user-ID, set-group-ID, and +sticky bits as the create mode; the operating system then applies either +the umask or a default ACL, possibly resulting in a more restrictive +file mode. +@xref{File permissions}. + +@item --no-preserve=@var{attribute_list} +@cindex file information, preserving +Do not preserve the specified attributes. The @var{attribute_list} +has the same form as for @option{--preserve}. + +@item --parents +@opindex --parents +@cindex parent directories and @command{cp} +Form the name of each destination file by appending to the target +directory a slash and the specified name of the source file. The last +argument given to @command{cp} must be the name of an existing directory. +For example, the command: + +@example +cp --parents a/b/c existing_dir +@end example + +@noindent +copies the file @file{a/b/c} to @file{existing_dir/a/b/c}, creating +any missing intermediate directories. + +@item -R +@itemx -r +@itemx --recursive +@opindex -R +@opindex -r +@opindex --recursive +@cindex directories, copying recursively +@cindex copying directories recursively +@cindex recursively copying directories +@cindex non-directories, copying as special files +Copy directories recursively. By default, do not follow symbolic +links in the source unless used together with the @option{--link} +(@option{-l}) option; see the @option{--archive} (@option{-a}), @option{-d}, +@option{--dereference} (@option{-L}), @option{--no-dereference} +(@option{-P}), and @option{-H} options. Special files are copied by +creating a destination file of the same type as the source; see the +@option{--copy-contents} option. It is not portable to use +@option{-r} to copy symbolic links or special files. On some +non-GNU systems, @option{-r} implies the equivalent of +@option{-L} and @option{--copy-contents} for historical reasons. +Also, it is not portable to use @option{-R} to copy symbolic links +unless you also specify @option{-P}, as POSIX allows +implementations that dereference symbolic links by default. + +@item --reflink[=@var{when}] +@opindex --reflink[=@var{when}] +@cindex COW +@cindex clone +@cindex copy on write +Perform a lightweight, copy-on-write (COW) copy, if supported by the +file system. Once it has succeeded, beware that the source and destination +files share the same data blocks as long as they remain unmodified. +Thus, if an I/O error affects data blocks of one of the files, +the other suffers the same fate. + +The @var{when} value can be one of the following: + +@table @samp +@item always +If the copy-on-write operation is not supported +then report the failure for each file and exit with a failure status. +Plain @option{--reflink} is equivalent to @option{--reflink=always}. + +@item auto +If the copy-on-write operation is not supported then fall back +to the standard copy behavior. +This is the default if no @option{--reflink} option is given. + +@item never +Disable copy-on-write operation and use the standard copy behavior. +@end table + +This option is overridden by the @option{--link}, @option{--symbolic-link} +and @option{--attributes-only} options, thus allowing it to be used +to configure the default data copying behavior for @command{cp}. + +@item --remove-destination +@opindex --remove-destination +Remove each existing destination file before attempting to open it +(contrast with @option{-f} above). + +@item --sparse=@var{when} +@opindex --sparse=@var{when} +@cindex sparse files, copying +@cindex holes, copying files with +@findex read @r{system call, and holes} +A @dfn{sparse file} contains @dfn{holes} -- a sequence of zero bytes that +does not occupy any file system blocks; the @samp{read} system call +reads these as zeros. This can both save considerable space and +increase speed, since many binary files contain lots of consecutive zero +bytes. By default, @command{cp} detects holes in input source files via a crude +heuristic and makes the corresponding output file sparse as well. +Only regular files may be sparse. + +The @var{when} value can be one of the following: + +@table @samp +@item auto +The default behavior: if the input file is sparse, attempt to make +the output file sparse, too. However, if an output file exists but +refers to a non-regular file, then do not attempt to make it sparse. + +@item always +For each sufficiently long sequence of zero bytes in the input file, +attempt to create a corresponding hole in the output file, even if the +input file does not appear to be sparse. +This is useful when the input file resides on a file system +that does not support sparse files +(for example, @samp{efs} file systems in SGI IRIX 5.3 and earlier), +but the output file is on a type of file system that does support them. +Holes may be created only in regular files, so if the destination file +is of some other type, @command{cp} does not even try to make it sparse. + +@item never +Never make the output file sparse. +This is useful in creating a file for use with the @command{mkswap} command, +since such a file must not have any holes. +@end table + +For example, with the following alias, @command{cp} will use the +minimum amount of space supported by the file system. +(Older versions of @command{cp} can also benefit from +@option{--reflink=auto} here.) + +@example +alias cp='cp --sparse=always' +@end example + +@optStripTrailingSlashes + +@item -s +@itemx --symbolic-link +@opindex -s +@opindex --symbolic-link +@cindex symbolic links, copying with +Make symbolic links instead of copies of non-directories. All source +file names must be absolute (starting with @samp{/}) unless the +destination files are in the current directory. This option merely +results in an error message on systems that do not support symbolic links. + +@optBackupSuffix + +@optTargetDirectory + +@optNoTargetDirectory + +@item -u +@itemx --update[=@var{which}] +@opindex -u +@opindex --update[=@var{which}] +@cindex newer files, copying only +Do not copy a non-directory that has an existing destination with the +same or newer modification timestamp; instead, silently skip the file +without failing. If timestamps are being preserved, +the comparison is to the source timestamp truncated to the +resolutions of the destination file system and of the system calls +used to update timestamps; this avoids duplicate work if several +@samp{cp -pu} commands are executed with the same source and destination. +This option is ignored if the @option{-n} or @option{--no-clobber} +option is also specified. +Also, if @option{--preserve=links} is also specified (like with @samp{cp -au} +for example), that will take precedence; consequently, depending on the +order that files are processed from the source, newer files in the destination +may be replaced, to mirror hard links in the source. + +@macro whichUpdate +@var{which} gives more control over which existing files in the +destination are replaced, and its value can be one of the following: + +@table @samp +@item all +This is the default operation when an @option{--update} option is not specified, +and results in all existing files in the destination being replaced. + +@item none +This is similar to the @option{--no-clobber} option, in that no files in the +destination are replaced, but also skipping a file does not induce a failure. + +@item older +This is the default operation when @option{--update} is specified, and results +in files being replaced if they're older than the corresponding source file. +@end table +@end macro +@whichUpdate + +@item -v +@itemx --verbose +@opindex -v +@opindex --verbose +Print the name of each file before copying it. + +@item -x +@itemx --one-file-system +@opindex -x +@opindex --one-file-system +@cindex file systems, omitting copying to different +Skip subdirectories that are on different file systems from the one that +the copy started on. +However, mount point directories @emph{are} copied. + +@macro optContext +@item -Z +@itemx --context[=@var{context}] +@opindex -Z +@opindex --context +@cindex SELinux, setting/restoring security context +@cindex security context +Without a specified @var{context}, adjust the SELinux security context according +to the system default type for destination files, similarly to the +@command{restorecon} command. +The long form of this option with a specific context specified, +will set the context for newly created files only. +With a specified context, if both SELinux and SMACK are disabled, a warning is +issued. +@end macro +@optContext +This option is mutually exclusive with the @option{--preserve=context} +option, and overrides the @option{--preserve=all} and @option{-a} options. + +@end table + +@exitstatus + + +@node dd invocation +@section @command{dd}: Convert and copy a file + +@pindex dd +@cindex converting while copying a file + +@command{dd} copies input to output with a changeable I/O block size, +while optionally performing conversions on the data. Synopses: + +@example +dd [@var{operand}]@dots{} +dd @var{option} +@end example + +The only options are @option{--help} and @option{--version}. +@xref{Common options}. + +By default, @command{dd} copies standard input to standard output. +To copy, @command{dd} repeatedly does the following steps in order: + +@enumerate +@item +Read an input block. + +@item +If converting via @samp{sync}, pad as needed to meet the input block size. +Pad with spaces if converting via @samp{block} or @samp{unblock}, NUL +bytes otherwise. + +@item +If @samp{bs=} is given and no conversion mentioned in steps (4) or (5) +is given, output the data as a single block and skip all remaining steps. + +@item +If the @samp{swab} conversion is given, swap each pair of input bytes. +If the input data length is odd, preserve the last input byte +(since there is nothing to swap it with). + +@item +If any of the conversions @samp{swab}, @samp{block}, @samp{unblock}, +@samp{lcase}, @samp{ucase}, @samp{ascii}, @samp{ebcdic} and @samp{ibm} +are given, do these conversions. These conversions operate +independently of input blocking, and might deal with records that span +block boundaries. + +@item +Aggregate the resulting data into output blocks of the specified size, +and output each output block in turn. Do not pad the last output block; +it can be shorter than usual. +@end enumerate + +@command{dd} accepts the following operands, +whose syntax was inspired by the DD (data definition) statement of +OS/360 JCL. + +@table @samp + +@item if=@var{file} +@opindex if +Read from @var{file} instead of standard input. + +@item of=@var{file} +@opindex of +Write to @var{file} instead of standard output. Unless +@samp{conv=notrunc} is given, truncate @var{file} before writing it. + +@item ibs=@var{bytes} +@opindex ibs +@cindex block size of input +@cindex input block size +Set the input block size to @var{bytes}. +This makes @command{dd} read @var{bytes} per block. +The default is 512 bytes. + +@item obs=@var{bytes} +@opindex obs +@cindex block size of output +@cindex output block size +Set the output block size to @var{bytes}. +This makes @command{dd} write @var{bytes} per block. +The default is 512 bytes. + +@item bs=@var{bytes} +@opindex bs +@cindex block size +Set both input and output block sizes to @var{bytes}. +This makes @command{dd} read and write @var{bytes} per block, +overriding any @samp{ibs} and @samp{obs} settings. +In addition, if no data-transforming @option{conv} operand is specified, +input is copied to the output as soon as it's read, +even if it is smaller than the block size. + +@item cbs=@var{bytes} +@opindex cbs +@cindex block size of conversion +@cindex conversion block size +@cindex fixed-length records, converting to variable-length +@cindex variable-length records, converting to fixed-length +Set the conversion block size to @var{bytes}. +When converting variable-length records to fixed-length ones +(@option{conv=block}) or the reverse (@option{conv=unblock}), +use @var{bytes} as the fixed record length. + +@item skip=@var{n} +@itemx iseek=@var{n} +@opindex skip +@opindex iseek +Skip @var{n} @samp{ibs}-byte blocks in the input file before copying. +If @var{n} ends in the letter @samp{B}, interpret @var{n} +as a byte count rather than a block count. +(@samp{B} and the @samp{iseek=} spelling are GNU extensions to POSIX.) + +@item seek=@var{n} +@itemx oseek=@var{n} +@opindex seek +@opindex oseek +Skip @var{n} @samp{obs}-byte blocks in the output file before +truncating or copying. +If @var{n} ends in the letter @samp{B}, interpret @var{n} +as a byte count rather than a block count. +(@samp{B} and the @samp{oseek=} spelling are GNU extensions to POSIX.) + +@item count=@var{n} +@opindex count +Copy @var{n} @samp{ibs}-byte blocks from the input file, instead +of everything until the end of the file. +If @var{n} ends in the letter @samp{B}, +interpret @var{n} as a byte count rather than a block count; +this is a GNU extension to POSIX. +If short reads occur, as could be the case +when reading from a pipe for example, @samp{iflag=fullblock} +ensures that @samp{count=} counts complete input blocks +rather than input read operations. +As an extension to POSIX, @samp{count=0} copies zero blocks +instead of copying all blocks. + +@item status=@var{level} +@opindex status +Specify the amount of information printed. +If this operand is given multiple times, the last one takes precedence. +The @var{level} value can be one of the following: + +@table @samp + +@item none +@opindex none @r{dd status=} +Do not print any informational or warning messages to standard error. +Error messages are output as normal. + +@item noxfer +@opindex noxfer @r{dd status=} +Do not print the final transfer rate and volume statistics +that normally make up the last status line. + +@item progress +@opindex progress @r{dd status=} +Print the transfer rate and volume statistics on standard error, +when processing each input block. Statistics are output +on a single line at most once every second, but updates +can be delayed when waiting on I/O. + +@end table + +Transfer information is normally output to standard error upon +receipt of the @samp{INFO} signal or when @command{dd} exits, +and defaults to the following form in the C locale: + +@example +7287+1 records in +116608+0 records out +59703296 bytes (60 MB, 57 MiB) copied, 0.0427974 s, 1.4 GB/s +@end example + +The notation @samp{@var{w}+@var{p}} stands for @var{w} whole blocks +and @var{p} partial blocks. A partial block occurs when a read or +write operation succeeds but transfers less data than the block size. +An additional line like @samp{1 truncated record} or @samp{10 +truncated records} is output after the @samp{records out} line if +@samp{conv=block} processing truncated one or more input records. + +The @samp{status=} operand is a GNU extension to POSIX. + +@item conv=@var{conversion}[,@var{conversion}]@dots{} +@opindex conv +Convert the file as specified by the @var{conversion} argument(s). +(No spaces around any comma(s).) + +Conversions: + +@table @samp + +@item ascii +@opindex ascii@r{, converting to} +Convert EBCDIC to ASCII, +using the conversion table specified by POSIX@. +This provides a 1:1 translation for all 256 bytes. +This implies @samp{conv=unblock}; input is converted to +ASCII before trailing spaces are deleted. + +@item ebcdic +@opindex ebcdic@r{, converting to} +Convert ASCII to EBCDIC@. +This is the inverse of the @samp{ascii} conversion. +This implies @samp{conv=block}; trailing spaces are added +before being converted to EBCDIC@. + +@item ibm +@opindex alternate ebcdic@r{, converting to} +This acts like @samp{conv=ebcdic}, except it +uses the alternate conversion table specified by POSIX@. +This is not a 1:1 translation, but reflects common historical practice +for @samp{~}, @samp{[}, and @samp{]}. + +The @samp{ascii}, @samp{ebcdic}, and @samp{ibm} conversions are +mutually exclusive. If you use any of these conversions, you should also +use the @samp{cbs=} operand. + +@item block +@opindex block @r{(space-padding)} +For each line in the input, output @samp{cbs} bytes, replacing the +input newline with a space and truncating or padding input lines with +spaces as necessary. + +@item unblock +@opindex unblock +Remove any trailing spaces in each @samp{cbs}-sized input block, +and append a newline. + +The @samp{block} and @samp{unblock} conversions are mutually exclusive. +If you use either of these conversions, you should also use the +@samp{cbs=} operand. + +@item lcase +@opindex lcase@r{, converting to} +Change uppercase letters to lowercase. + +@item ucase +@opindex ucase@r{, converting to} +Change lowercase letters to uppercase. + +The @samp{lcase} and @samp{ucase} conversions are mutually exclusive. + +@item sparse +@opindex sparse +Try to seek rather than write NUL output blocks. +On a file system that supports sparse files, this will create +sparse output when extending the output file. +Be careful when using this conversion in conjunction with +@samp{conv=notrunc} or @samp{oflag=append}. +With @samp{conv=notrunc}, existing data in the output file +corresponding to NUL blocks from the input, will be untouched. +With @samp{oflag=append} the seeks performed will be ineffective. +Similarly, when the output is a device rather than a file, +NUL input blocks are not copied, and therefore this conversion +is most useful with virtual or pre zeroed devices. + +The @samp{sparse} conversion is a GNU extension to POSIX. + +@item swab +@opindex swab @r{(byte-swapping)} +@cindex byte-swapping +Swap every pair of input bytes. + +@item sync +@opindex sync @r{(padding with ASCII NULs)} +Pad every input block to size of @samp{ibs} with trailing zero bytes. +When used with @samp{block} or @samp{unblock}, pad with spaces instead of +zero bytes. + +@end table + +The following ``conversions'' are really file flags +and don't affect internal processing: + +@table @samp +@item excl +@opindex excl +@cindex creating output file, requiring +Fail if the output file already exists; @command{dd} must create the +output file itself. + +@item nocreat +@opindex nocreat +@cindex creating output file, avoiding +Do not create the output file; the output file must already exist. + +The @samp{excl} and @samp{nocreat} conversions are mutually exclusive, +and are GNU extensions to POSIX. + +@item notrunc +@opindex notrunc +@cindex truncating output file, avoiding +Do not truncate the output file. + +@item noerror +@opindex noerror +@cindex read errors, ignoring +Continue after read errors. + +@item fdatasync +@opindex fdatasync +@cindex synchronized data writes, before finishing +Synchronize output data just before finishing, +even if there were write errors. +This forces a physical write of output data, +so that even if power is lost the output data will be preserved. +If neither this nor @samp{fsync} are specified, output is treated as +usual with file systems, i.e., output data and metadata may be cached +in primary memory for some time before the operating system physically +writes it, and thus output data and metadata may be lost if power is lost. +@xref{sync invocation}. +This conversion is a GNU extension to POSIX. + +@item fsync +@opindex fsync +@cindex synchronized data and metadata writes, before finishing +Synchronize output data and metadata just before finishing, +even if there were write errors. +This acts like @samp{fdatasync} except it also preserves output metadata, +such as the last-modified time of the output file; for this reason it +may be a bit slower than @samp{fdatasync} although the performance +difference is typically insignificant for @command{dd}. +This conversion is a GNU extension to POSIX. + +@end table + +@item iflag=@var{flag}[,@var{flag}]@dots{} +@opindex iflag +Access the input file using the flags specified by the @var{flag} +argument(s). (No spaces around any comma(s).) + +@item oflag=@var{flag}[,@var{flag}]@dots{} +@opindex oflag +Access the output file using the flags specified by the @var{flag} +argument(s). (No spaces around any comma(s).) + +Here are the flags. + +@table @samp + +@item append +@opindex append +@cindex appending to the output file +Write in append mode, so that even if some other process is writing to +this file, every @command{dd} write will append to the current +contents of the file. This flag makes sense only for output. +If you combine this flag with the @samp{of=@var{file}} operand, +you should also specify @samp{conv=notrunc} unless you want the +output file to be truncated before being appended to. + +@item cio +@opindex cio +@cindex concurrent I/O +Use concurrent I/O mode for data. This mode performs direct I/O +and drops the POSIX requirement to serialize all I/O to the same file. +A file cannot be opened in CIO mode and with a standard open at the +same time. + +@item direct +@opindex direct +@cindex direct I/O +Use direct I/O for data, avoiding the buffer cache. +Note that the kernel may impose restrictions on read or write buffer sizes. +For example, with an ext4 destination file system and a Linux-based kernel, +using @samp{oflag=direct} will cause writes to fail with @code{EINVAL} if the +output buffer size is not a multiple of 512. + +@item directory +@opindex directory +@cindex directory I/O + +Fail unless the file is a directory. Most operating systems do not +allow I/O to a directory, so this flag has limited utility. + +@item dsync +@opindex dsync +@cindex synchronized data reads +Use synchronized I/O for data. For the output file, this forces a +physical write of output data on each write. For the input file, +this flag can matter when reading from a remote file that has been +written to synchronously by some other process. Metadata (e.g., +last-access and last-modified time) is not necessarily synchronized. + +@item sync +@opindex sync +@cindex synchronized data and metadata I/O +Use synchronized I/O for both data and metadata. + +@item nocache +@opindex nocache +@cindex discarding file cache +Request to discard the system data cache for a file. +When count=0 all cached data for the file is specified, +otherwise the cache is dropped for the processed +portion of the file. Also when count=0, +failure to discard the cache is diagnosed +and reflected in the exit status. + +Note data that is not already persisted to storage will not +be discarded from cache, so note the use of the @samp{sync} conversions +in the examples below, which are used to maximize the +effectiveness of the @samp{nocache} flag. + +Here are some usage examples: + +@example +# Advise to drop cache for whole file +dd if=ifile iflag=nocache count=0 + +# Ensure drop cache for the whole file +dd of=ofile oflag=nocache conv=notrunc,fdatasync count=0 + +# Advise to drop cache for part of file +# Note the kernel will only consider complete and +# already persisted pages. +dd if=ifile iflag=nocache skip=10 count=10 of=/dev/null + +# Stream data using just the read-ahead cache. +# See also the @samp{direct} flag. +dd if=ifile of=ofile iflag=nocache oflag=nocache,sync +@end example + +@item nonblock +@opindex nonblock +@cindex nonblocking I/O +Use non-blocking I/O. + +@item noatime +@opindex noatime +@cindex access timestamp +Do not update the file's access timestamp. +@xref{File timestamps}. +Some older file systems silently ignore this flag, so it is a good +idea to test it on your files before relying on it. + +@item noctty +@opindex noctty +@cindex controlling terminal +Do not assign the file to be a controlling terminal for @command{dd}. +This has no effect when the file is not a terminal. +On many hosts (e.g., GNU/Linux hosts), this flag has no effect +at all. + +@item nofollow +@opindex nofollow +@cindex symbolic links, following +Do not follow symbolic links. + +@item nolinks +@opindex nolinks +@cindex hard links +Fail if the file has multiple hard links. + +@item binary +@opindex binary +@cindex binary I/O +Use binary I/O@. This flag has an effect only on nonstandard +platforms that distinguish binary from text I/O. + +@item text +@opindex text +@cindex text I/O +Use text I/O@. Like @samp{binary}, this flag has no effect on +standard platforms. + +@item fullblock +@opindex fullblock +Accumulate full blocks from input. The @code{read} system call +may return early if a full block is not available. +When that happens, continue calling @code{read} to fill the remainder +of the block. +This flag can be used only with @code{iflag}. +This flag is useful with pipes for example +as they may return short reads. In that case, +this flag is needed to ensure that a @samp{count=} argument is +interpreted as a block count rather than a count of read operations. + +@end table + +These flags are all GNU extensions to POSIX. +They are not supported on all systems, and @samp{dd} rejects +attempts to use them when they are not supported. When reading from +standard input or writing to standard output, the @samp{nofollow} and +@samp{noctty} flags should not be specified, and the other flags +(e.g., @samp{nonblock}) can affect how other processes behave with the +affected file descriptors, even after @command{dd} exits. + +@end table + +The behavior of @command{dd} is unspecified if operands other than +@samp{conv=}, @samp{iflag=}, @samp{oflag=}, and @samp{status=} are +specified more than once. + +@cindex multipliers after numbers +The numeric-valued strings above (@var{n} and @var{bytes}) +are unsigned decimal integers that +can be followed by a multiplier: @samp{b}=512, @samp{c}=1, +@samp{w}=2, @samp{x@var{m}}=@var{m}, or any of the +standard block size suffixes like @samp{k}=1024 (@pxref{Block size}). +These multipliers are GNU extensions to POSIX, except that +POSIX allows @var{bytes} to be followed by @samp{k}, @samp{b}, and +@samp{x@var{m}}. Note @samp{x@var{m}} can be used more than once in a number. +Block sizes (i.e., specified by @var{bytes} strings) must be nonzero. + +Any block size you specify via @samp{bs=}, @samp{ibs=}, @samp{obs=}, @samp{cbs=} +should not be too large -- values larger than a few megabytes +are generally wasteful or (as in the gigabyte..exabyte case) downright +counterproductive or error-inducing. + +To process data with offset or size that is not a multiple of the I/O +block size, you can use a numeric string @var{n} that ends in the +letter @samp{B}. +For example, the following shell commands copy data +in 1 MiB blocks between a flash drive and a tape, but do not save +or restore a 512-byte area at the start of the flash drive: + +@example +flash=/dev/sda +tape=/dev/st0 + +# Copy all but the initial 512 bytes from flash to tape. +dd if=$flash iseek=512B bs=1MiB of=$tape + +# Copy from tape back to flash, leaving initial 512 bytes alone. +dd if=$tape bs=1MiB of=$flash oseek=512B +@end example + +@cindex ddrescue +@cindex storage devices, failing +For failing storage devices, other tools come with a great variety of extra +functionality to ease the saving of as much data as possible before the +device finally dies, e.g. +@uref{https://www.gnu.org/software/ddrescue/, GNU @command{ddrescue}}. +However, in some cases such a tool is not available or the administrator +feels more comfortable with the handling of @command{dd}. +As a simple rescue method, call @command{dd} as shown in the following +example: the operand @samp{conv=noerror,sync} is used to continue +after read errors and to pad out bad reads with NULs, while +@samp{iflag=fullblock} caters for short reads (which traditionally never +occur on flash or similar devices): + +@example +# Rescue data from an (unmounted!) partition of a failing device. +dd conv=noerror,sync iflag=fullblock </dev/sda1 > /mnt/rescue.img +@end example + +Sending an @samp{INFO} signal (or @samp{USR1} signal where that is unavailable) +to a running @command{dd} process makes it print I/O statistics to +standard error and then resume copying. In the example below, +@command{dd} is run in the background to copy 5GB of data. +The @command{kill} command makes it output intermediate I/O statistics, +and when @command{dd} completes normally or is killed by the +@code{SIGINT} signal, it outputs the final statistics. + +@example +# Ignore the signal so we never inadvertently terminate the dd child. +# Note this is not needed when SIGINFO is available. +trap '' USR1 + +# Run dd with the fullblock iflag to avoid short reads +# which can be triggered by reception of signals. +dd iflag=fullblock if=/dev/zero of=/dev/null count=5000000 bs=1000 & pid=$! + +# Output stats every second. +while kill -s USR1 $pid 2>/dev/null; do sleep 1; done +@end example + +The above script will output in the following format: + +@example +3441325+0 records in +3441325+0 records out +3441325000 bytes (3.4 GB, 3.2 GiB) copied, 1.00036 s, 3.4 GB/s +5000000+0 records in +5000000+0 records out +5000000000 bytes (5.0 GB, 4.7 GiB) copied, 1.44433 s, 3.5 GB/s +@end example + +The @samp{status=progress} operand periodically updates the last line +of the transfer statistics above. + +@vindex POSIXLY_CORRECT +On systems lacking the @samp{INFO} signal @command{dd} responds to the +@samp{USR1} signal instead, unless the @env{POSIXLY_CORRECT} +environment variable is set. + +@exitstatus + + +@node install invocation +@section @command{install}: Copy files and set attributes + +@pindex install +@cindex copying files and setting attributes + +@command{install} copies files while setting their file mode bits and, if +possible, their owner and group. Synopses: + +@example +install [@var{option}]@dots{} [-T] @var{source} @var{dest} +install [@var{option}]@dots{} @var{source}@dots{} @var{directory} +install [@var{option}]@dots{} -t @var{directory} @var{source}@dots{} +install [@var{option}]@dots{} -d @var{directory}@dots{} +@end example + +@itemize @bullet +@item +If two file names are given, @command{install} copies the first file to the +second. + +@item +If the @option{--target-directory} (@option{-t}) option is given, or +failing that if the last file is a directory and the +@option{--no-target-directory} (@option{-T}) option is not given, +@command{install} copies each @var{source} file to the specified +directory, using the @var{source}s' names. + +@item +If the @option{--directory} (@option{-d}) option is given, +@command{install} creates each @var{directory} and any missing parent +directories. Parent directories are created with mode +@samp{u=rwx,go=rx} (755), regardless of the @option{-m} option or the +current umask. @xref{Directory Setuid and Setgid}, for how the +set-user-ID and set-group-ID bits of parent directories are inherited. +@end itemize + +@cindex Makefiles, installing programs in +@command{install} is similar to @command{cp}, but allows you to control the +attributes of destination files. It is typically used in Makefiles to +copy programs into their destination directories. It refuses to copy +files onto themselves. + +@cindex extended attributes, xattr +@command{install} never preserves extended attributes (xattr). + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@optBackup + +@item -C +@itemx --compare +@opindex -C +@opindex --compare +Compare content of source and destination files, and if there would be no +change to the destination content, owner, group, permissions, and possibly +SELinux context, then do not modify the destination at all. +Note this option is best used in conjunction with @option{--user}, +@option{--group} and @option{--mode} options, lest @command{install} +incorrectly determines the default attributes that installed files would have +(as it doesn't consider setgid directories and POSIX default ACLs for example). +This could result in redundant copies or attributes that are not reset to the +correct defaults. + +@item -c +@opindex -c +Ignored; for compatibility with old Unix versions of @command{install}. + +@item -D +@opindex -D +Create any missing parent directories of @var{dest}, +then copy @var{source} to @var{dest}. +Explicitly specifying the @option{--target-directory=@var{dir}} will similarly +ensure the presence of that hierarchy before copying @var{source} arguments. + +@item -d +@itemx --directory +@opindex -d +@opindex --directory +@cindex directories, creating with given attributes +@cindex parent directories, creating missing +@cindex leading directories, creating missing +Create any missing parent directories, giving them the default +attributes. Then create each given directory, setting their owner, +group and mode as given on the command line or to the defaults. + +@optDebugCopy + +@item -g @var{group} +@itemx --group=@var{group} +@opindex -g +@opindex --group +@cindex group ownership of installed files, setting +Set the group ownership of installed files or directories to +@var{group}. The default is the process's current group. @var{group} +may be either a group name or a numeric group ID. + +@item -m @var{mode} +@itemx --mode=@var{mode} +@opindex -m +@opindex --mode +@cindex permissions of installed files, setting +Set the file mode bits for the installed file or directory to @var{mode}, +which can be either an octal number, or a symbolic mode as in +@command{chmod}, with @samp{a=} (no access allowed to anyone) as the +point of departure (@pxref{File permissions}). +The default mode is @samp{u=rwx,go=rx,a-s} -- read, write, and +execute for the owner, read and execute for group and other, and with +set-user-ID and set-group-ID disabled. +This default is not quite the same as @samp{755}, since it disables +instead of preserving set-user-ID and set-group-ID on directories. +@xref{Directory Setuid and Setgid}. + +@item -o @var{owner} +@itemx --owner=@var{owner} +@opindex -o +@opindex --owner +@cindex ownership of installed files, setting +@cindex appropriate privileges +@vindex root @r{as default owner} +If @command{install} has appropriate privileges (is run as root), set the +ownership of installed files or directories to @var{owner}. The default +is @code{root}. @var{owner} may be either a user name or a numeric user +ID. + +@item --preserve-context +@opindex --preserve-context +@cindex SELinux +@cindex security context +Preserve the SELinux security context of files and directories. +Failure to preserve the context in all of the files or directories +will result in an exit status of 1. If SELinux is disabled then +print a warning and ignore the option. + +@item -p +@itemx --preserve-timestamps +@opindex -p +@opindex --preserve-timestamps +@cindex timestamps of installed files, preserving +Set the time of last access and the time of last modification of each +installed file to match those of each corresponding original file. +When a file is installed without this option, its last access and +last modification timestamps are both set to the time of installation. +This option is useful if you want to use the last modification timestamps +of installed files to keep track of when they were last built as opposed +to when they were last installed. + +@item -s +@itemx --strip +@opindex -s +@opindex --strip +@cindex symbol table information, stripping +@cindex stripping symbol table information +Strip the symbol tables from installed binary executables. + +@item --strip-program=@var{program} +@opindex --strip-program +@cindex symbol table information, stripping, program +Program used to strip binaries. + +@optBackupSuffix + +@optTargetDirectory +Also specifying the @option{-D} option will ensure the directory is present. + +@optNoTargetDirectory + +@item -v +@itemx --verbose +@opindex -v +@opindex --verbose +Print the name of each file before copying it. + +@optContext +This option is mutually exclusive with the @option{--preserve-context} option. + + +@end table + +@exitstatus + + +@node mv invocation +@section @command{mv}: Move (rename) files + +@pindex mv + +@command{mv} moves or renames files (or directories). Synopses: + +@example +mv [@var{option}]@dots{} [-T] @var{source} @var{dest} +mv [@var{option}]@dots{} @var{source}@dots{} @var{directory} +mv [@var{option}]@dots{} -t @var{directory} @var{source}@dots{} +@end example + +@itemize @bullet +@item +If two file names are given, @command{mv} moves the first file to the +second. + +@item +If the @option{--target-directory} (@option{-t}) option is given, or +failing that if the last file is a directory and the +@option{--no-target-directory} (@option{-T}) option is not given, +@command{mv} moves each @var{source} file to the specified +directory, using the @var{source}s' names. +@end itemize + +To move a file, @command{mv} ordinarily simply renames it. +However, if renaming does not work because the destination's file +system differs, @command{mv} falls back on copying as if by @code{cp -a}, +then (assuming the copy succeeded) it removes the original. +If the copy fails, then @command{mv} removes any partially created +copy in the destination. If you were to copy three directories from +one file system to another and the copy of the first +directory succeeded, but the second didn't, the first would be left on +the destination file system and the second and third would be left on the +original file system. + +@cindex extended attributes, xattr +@command{mv} always tries to copy extended attributes (xattr), which may +include SELinux context, ACLs or Capabilities. +Upon failure all but @samp{Operation not supported} warnings are output. + +@cindex prompting, and @command{mv} +If a destination file exists but is normally unwritable, standard input +is a terminal, and the @option{-f} or @option{--force} option is not given, +@command{mv} prompts the user for whether to replace the file. (You might +own the file, or have write permission on its directory.) If the +response is not affirmative, the file is skipped. + +@emph{Warning}: Avoid specifying a source name with a trailing slash, +when it might be a symlink to a directory. +Otherwise, @command{mv} may do something very surprising, since +its behavior depends on the underlying rename system call. +On a system with a modern Linux-based kernel, it fails with +@code{errno=ENOTDIR}@. +However, on other systems (at least FreeBSD 6.1 and Solaris 10) it silently +renames not the symlink but rather the directory referenced by the symlink. +@xref{Trailing slashes}. + +@emph{Note}: @command{mv} will only replace empty directories in the +destination. Conflicting populated directories are skipped with a diagnostic. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@optBackup + +@optDebugCopy + +@item -f +@itemx --force +@opindex -f +@opindex --force +@cindex prompts, omitting +Do not prompt the user before removing a destination file. +@macro mvOptsIfn +If you specify more than one of the @option{-i}, @option{-f}, @option{-n} +options, only the final one takes effect. +@end macro +@mvOptsIfn + +@item -i +@itemx --interactive +@opindex -i +@opindex --interactive +@cindex prompts, forcing +Prompt whether to overwrite each existing destination file, regardless +of its permissions, and fail if the response is not affirmative. +@mvOptsIfn + +@item -n +@itemx --no-clobber +@opindex -n +@opindex --no-clobber +@cindex prompts, omitting +Do not overwrite an existing file; silently fail instead. +@mvOptsIfn +This option is mutually exclusive with @option{-b} or @option{--backup} option. +See also the @option{--update=none} option which will +skip existing files but not fail. + +@item --no-copy +@opindex --no-copy +@cindex renaming files without copying them +If a file cannot be renamed because the destination file system differs, +fail with a diagnostic instead of copying and then removing the file. + +@item -u +@itemx --update +@opindex -u +@opindex --update +@cindex newer files, moving only +Do not move a non-directory that has an existing destination with the +same or newer modification timestamp; +instead, silently skip the file without failing. +If the move is across file system boundaries, the comparison is to the +source timestamp truncated to the resolutions of the destination file +system and of the system calls used to update timestamps; this avoids +duplicate work if several @samp{mv -u} commands are executed with the +same source and destination. +This option is ignored if the @option{-n} or @option{--no-clobber} +option is also specified. + +@whichUpdate + +@item -v +@itemx --verbose +@opindex -v +@opindex --verbose +Print the name of each file before moving it. + +@optStripTrailingSlashes + +@optBackupSuffix + +@optTargetDirectory + +@optNoTargetDirectory + +@item -Z +@itemx --context +@opindex -Z +@opindex --context +@cindex SELinux, restoring security context +@cindex security context +This option functions similarly to the @command{restorecon} command, +by adjusting the SELinux security context according +to the system default type for destination files and each created directory. + +@end table + +@exitstatus + + +@node rm invocation +@section @command{rm}: Remove files or directories + +@pindex rm +@cindex removing files or directories + +@command{rm} removes each given @var{file}. By default, it does not remove +directories. Synopsis: + +@example +rm [@var{option}]@dots{} [@var{file}]@dots{} +@end example + +@cindex prompting, and @command{rm} +If the @option{-I} or @option{--interactive=once} option is given, +and there are more than three files or the @option{-r}, @option{-R}, +or @option{--recursive} are given, then @command{rm} prompts the user +for whether to proceed with the entire operation. If the response is +not affirmative, the entire command is aborted. + +Otherwise, if a file is unwritable, standard input is a terminal, and +the @option{-f} or @option{--force} option is not given, or the +@option{-i} or @option{--interactive=always} option @emph{is} given, +@command{rm} prompts the user for whether to remove the file. +If the response is not affirmative, the file is skipped. + +Any attempt to remove a file whose last file name component is +@file{.} or @file{..} is rejected without any prompting, as mandated +by POSIX. + +@emph{Warning}: If you use @command{rm} to remove a file, it is usually +possible to recover the contents of that file. If you want more assurance +that the contents are unrecoverable, consider using @command{shred}. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -d +@itemx --dir +@opindex -d +@opindex --dir +@cindex directories, removing +Remove the listed directories if they are empty. + +@item -f +@itemx --force +@opindex -f +@opindex --force +Ignore nonexistent files and missing operands, and never prompt the user. +Ignore any previous @option{--interactive} (@option{-i}) option. + +@item -i +@opindex -i +Prompt whether to remove each file. +If the response is not affirmative, silently skip the file without failing. +Ignore any previous @option{--force} (@option{-f}) option. +Equivalent to @option{--interactive=always}. + +@item -I +@opindex -I +Prompt once whether to proceed with the command, if more than three +files are named or if a recursive removal is requested. Ignore any +previous @option{--force} (@option{-f}) option. Equivalent to +@option{--interactive=once}. + +@item --interactive [=@var{when}] +@opindex --interactive +Specify when to issue an interactive prompt. @var{when} may be +omitted, or one of: +@itemize @bullet +@item never +@vindex never @r{interactive option} +- Do not prompt at all. +@item once +@vindex once @r{interactive option} +- Prompt once if more than three files are named or if a recursive +removal is requested. Equivalent to @option{-I}. +@item always +@vindex always @r{interactive option} +- Prompt for every file being removed. Equivalent to @option{-i}. +@end itemize +@option{--interactive} with no @var{when} is equivalent to +@option{--interactive=always}. + +@item --one-file-system +@opindex --one-file-system +@cindex one file system, restricting @command{rm} to +When removing a hierarchy recursively, do not remove any directory that is on a +file system different from that of the corresponding command line argument. +@cindex bind mount +This option is useful when removing a build ``chroot'' hierarchy, +which normally contains no valuable data. However, it is not uncommon +to bind-mount @file{/home} into such a hierarchy, to make it easier to +use one's start-up file. The catch is that it's easy to forget to +unmount @file{/home}. Then, when you use @command{rm -rf} to remove +your normally throw-away chroot, that command will remove everything +under @file{/home}, too. +Use the @option{--one-file-system} option, and it will +diagnose and skip directories on other file systems. +Of course, this will not save your @file{/home} if it and your +chroot happen to be on the same file system. +See also @option{--preserve-root=all} to protect command line arguments +themselves. + +@item --preserve-root [=all] +@opindex --preserve-root +@cindex root directory, disallow recursive destruction +Fail upon any attempt to remove the root directory, @file{/}, +when used with the @option{--recursive} option. +This is the default behavior. +@xref{Treating / specially}. +When @samp{all} is specified, reject any command line argument +that is not on the same file system as its parent. + +@item --no-preserve-root +@opindex --no-preserve-root +@cindex root directory, allow recursive destruction +Do not treat @file{/} specially when removing recursively. +This option is not recommended unless you really want to +remove all the files on your computer. +@xref{Treating / specially}. + +@item -r +@itemx -R +@itemx --recursive +@opindex -r +@opindex -R +@opindex --recursive +@cindex directories, removing (recursively) +Remove the listed directories and their contents recursively. + +@item -v +@itemx --verbose +@opindex -v +@opindex --verbose +Print the name of each file before removing it. + +@end table + +@cindex files beginning with @samp{-}, removing +@cindex @samp{-}, removing files beginning with +One common question is how to remove files whose names begin with a +@samp{-}. GNU @command{rm}, like every program that uses the @code{getopt} +function to parse its arguments, lets you use the @samp{--} option to +indicate that all following arguments are non-options. To remove a file +called @file{-f} in the current directory, you could type either: + +@example +rm -- -f +@end example + +@noindent +or: + +@example +rm ./-f +@end example + +@opindex - @r{and Unix @command{rm}} +The Unix @command{rm} program's use of a single @samp{-} for this purpose +predates the development of the @code{getopt} standard syntax. + +@exitstatus + + +@node shred invocation +@section @command{shred}: Remove files more securely + +@pindex shred +@cindex data, erasing +@cindex erasing data + +@command{shred} overwrites devices or files, to help prevent even +extensive forensics from recovering the data. + +Ordinarily when you remove a file (@pxref{rm invocation}), its data +and metadata are not actually destroyed. Only the file's directory +entry is removed, and the file's storage is reclaimed only when no +process has the file open and no other directory entry links to the +file. And even if file's data and metadata's storage space is freed +for further reuse, there are undelete utilities that will attempt to +reconstruct the file from the data in freed storage, and that can +bring the file back if the storage was not rewritten. + +On a busy system with a nearly-full device, space can get reused in a few +seconds. But there is no way to know for sure. And although the +undelete utilities and already-existing processes require insider or +superuser access, you may be wary of the superuser, +of processes running on your behalf, or of attackers +that can physically access the storage device. So if you have sensitive +data, you may want to be sure that recovery is not possible +by plausible attacks like these. + +The best way to remove something irretrievably is to destroy the media +it's on with acid, melt it down, or the like. For cheap removable media +this is often the preferred method. However, some storage devices +are expensive or are harder to destroy, so the @command{shred} utility tries +to achieve a similar effect non-destructively, by overwriting the file +with non-sensitive data. + +@strong{Please note} that @command{shred} relies on a crucial +assumption: that the file system and hardware overwrite data in place. +Although this is common and is the traditional +way to do things, many modern file system designs do not satisfy this +assumption. Exceptions include: + +@itemize @bullet + +@item +Log-structured or journaled file systems, such as ext3/ext4 (in +@code{data=journal} mode), Btrfs, NTFS, ReiserFS, XFS, ZFS, file +systems supplied with AIX and Solaris, etc., when they are configured to +journal data. + +@item +File systems that write redundant data and carry on even if some writes +fail, such as RAID-based file systems. + +@item +File systems that make snapshots, such as Network Appliance's NFS server. + +@item +File systems that cache in temporary locations, such as NFS version 3 +clients. + +@item +Compressed file systems. +@end itemize + +For ext3 and ext4 file systems, @command{shred} is less effective +when the file system is in @code{data=journal} +mode, which journals file data in addition to just metadata. In both +the @code{data=ordered} (default) and @code{data=writeback} modes, +@command{shred} works as usual. The ext3/ext4 journaling modes can be changed +by adding the @code{data=something} option to the mount options for a +particular file system in the @file{/etc/fstab} file, as documented in +the @command{mount} man page (@samp{man mount}). Alternatively, if +you know how large the journal is, you can shred the journal by +shredding enough file data so that the journal cycles around and fills +up with shredded data. + +If you are not sure how your file system operates, then you should assume +that it does not overwrite data in place, which means @command{shred} cannot +reliably operate on regular files in your file system. + +Generally speaking, it is more reliable to shred a device than a file, +since this bypasses file system design issues mentioned above. +However, devices are also problematic for shredding, for reasons +such as the following: + +@itemize @bullet + +@item +Solid-state storage devices (SSDs) typically do wear leveling to +prolong service life, and this means writes are distributed to other +blocks by the hardware, so ``overwritten'' data blocks are still +present in the underlying device. + +@item +Most storage devices map out bad blocks invisibly to +the application; if the bad blocks contain sensitive data, +@command{shred} won't be able to destroy it. + +@item +With some obsolete storage technologies, +it may be possible to take (say) a floppy disk back +to a laboratory and use a lot of sensitive (and expensive) equipment +to look for the faint ``echoes'' of the original data underneath the +overwritten data. With these older technologies, if the file has been +overwritten only once, it's reputedly not even that hard. Luckily, +this kind of data recovery has become difficult, and there is no +public evidence that today's higher-density storage devices can be +analyzed in this way. + +The @command{shred} command can use many overwrite passes, +with data patterns chosen to +maximize the damage they do to the old data. +By default the patterns are designed for best effect on hard drives using +now-obsolete technology; for newer devices, a single pass should suffice. +For more details, see the source code and Peter Gutmann's paper +@uref{https://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html, +@cite{Secure Deletion of Data from Magnetic and Solid-State Memory}}, +from the proceedings of the Sixth USENIX Security Symposium (San Jose, +California, July 22--25, 1996). +@end itemize + +@command{shred} makes no attempt to detect or report these problems, just as +it makes no attempt to do anything about backups. However, since it is +more reliable to shred devices than files, @command{shred} by default does +not deallocate or remove the output file. This default is more suitable +for devices, which typically cannot be deallocated and should not be +removed. + +Finally, consider the risk of backups and mirrors. +File system backups and remote mirrors may contain copies of the +file that cannot be removed, and that will allow a shredded file +to be recovered later. So if you keep any data you may later want +to destroy using @command{shred}, be sure that it is not backed up or mirrored. + +@example +shred [@var{option}]@dots{} @var{file}[@dots{}] +@end example + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -f +@itemx --force +@opindex -f +@opindex --force +@cindex force deletion +Override file permissions if necessary to allow overwriting. + +@item -n @var{number} +@itemx --iterations=@var{number} +@opindex -n @var{number} +@opindex --iterations=@var{number} +@cindex iterations, selecting the number of +By default, @command{shred} uses @value{SHRED_DEFAULT_PASSES} passes of +overwrite. You can reduce this to save time, or increase it if you think it's +appropriate. After 25 passes all of the internal overwrite patterns will have +been used at least once. + +@item --random-source=@var{file} +@opindex --random-source +@cindex random source for shredding +Use @var{file} as a source of random data used to overwrite and to +choose pass ordering. @xref{Random sources}. + +@item -s @var{bytes} +@itemx --size=@var{bytes} +@opindex -s @var{bytes} +@opindex --size=@var{bytes} +@cindex size of file to shred +Shred the first @var{bytes} bytes of the file. The default is to shred +the whole file. @var{bytes} can be followed by a size specification like +@samp{K}, @samp{M}, or @samp{G} to specify a multiple. @xref{Block size}. + +@item -u +@itemx --remove[=@var{how}] +@opindex -u +@opindex --remove +@opindex --remove=unlink +@opindex --remove=wipe +@opindex --remove=wipesync +@cindex removing files after shredding +After shredding a file, deallocate it (if possible) and then remove it. +If a file has multiple links, only the named links will be removed. +Often the file name is less sensitive than the file data, in which case +the optional @var{how} parameter, supported with the long form option, +gives control of how to more efficiently remove each directory entry. +The @samp{unlink} parameter will just use a standard unlink call, +@samp{wipe} will also first obfuscate bytes in the name, and +@samp{wipesync} will also sync each obfuscated byte in the name to +the file system. +Note @samp{wipesync} is the default method, but can be expensive, +requiring a sync for every character in every file. This can become +significant with many files, or is redundant if your file system provides +synchronous metadata updates. + +@item -v +@itemx --verbose +@opindex -v +@opindex --verbose +Display to standard error all status updates as sterilization proceeds. + +@item -x +@itemx --exact +@opindex -x +@opindex --exact +By default, @command{shred} rounds the size of a regular file up to the next +multiple of the file system block size to fully erase the slack space in +the last block of the file. This space may contain portions of the current +system memory on some systems for example. +Use @option{--exact} to suppress that behavior. +Thus, by default if you shred a 10-byte regular file on a system with 512-byte +blocks, the resulting file will be 512 bytes long. With this option, +shred does not increase the apparent size of the file. + +@item -z +@itemx --zero +@opindex -z +@opindex --zero +Normally, the last pass that @command{shred} writes is made up of +random data. If this would be conspicuous on your storage device (for +example, because it looks like encrypted data), or you just think +it's tidier, the @option{--zero} option adds an additional overwrite pass with +all zero bits. This is in addition to the number of passes specified +by the @option{--iterations} option. + +@end table + +You might use the following command to erase the file system you +created on a USB flash drive. This command typically takes several +minutes, depending on the drive's size and write speed. On modern +storage devices a single pass should be adequate, and will take one +third the time of the default three-pass approach. + +@example +shred -v -n 1 /dev/sdd1 +@end example + +Similarly, to erase all data on a selected partition of +your device, you could give a command like the following. + +@example +# 1 pass, write pseudo-random data; 3x faster than the default +shred -v -n1 /dev/sda5 +@end example + +To be on the safe side, use at least one pass that overwrites using +pseudo-random data. I.e., don't be tempted to use @samp{-n0 --zero}, +in case some device controller optimizes the process of writing blocks +of all zeros, and thereby does not clear all bytes in a block. +Some SSDs may do just that. + +A @var{file} of @samp{-} denotes standard output. +The intended use of this is to shred a removed temporary file. +For example: + +@example +i=$(mktemp) +exec 3<>"$i" +rm -- "$i" +echo "Hello, world" >&3 +shred - >&3 +exec 3>- +@end example + +However, the command @samp{shred - >file} does not shred the contents +of @var{file}, since the shell truncates @var{file} before invoking +@command{shred}. Use the command @samp{shred file} or (if using a +Bourne-compatible shell) the command @samp{shred - 1<>file} instead. + +@exitstatus + + +@node Special file types +@chapter Special file types + +@cindex special file types +@cindex file types, special + +This chapter describes commands which create special types of files (and +@command{rmdir}, which removes directories, one special file type). + +@cindex special file types +@cindex file types +Although Unix-like operating systems have markedly fewer special file +types than others, not @emph{everything} can be treated only as the +undifferentiated byte stream of @dfn{normal files}. For example, when a +file is created or removed, the system must record this information, +which it does in a @dfn{directory} -- a special type of file. Although +you can read directories as normal files, if you're curious, in order +for the system to do its job it must impose a structure, a certain +order, on the bytes of the file. Thus it is a ``special'' type of file. + +Besides directories, other special file types include named pipes +(FIFOs), symbolic links, sockets, and so-called @dfn{special files}. + +@menu +* link invocation:: Make a hard link via the link syscall +* ln invocation:: Make links between files. +* mkdir invocation:: Make directories. +* mkfifo invocation:: Make FIFOs (named pipes). +* mknod invocation:: Make block or character special files. +* readlink invocation:: Print value of a symlink or canonical file name. +* rmdir invocation:: Remove empty directories. +* unlink invocation:: Remove files via the unlink syscall +@end menu + + +@node link invocation +@section @command{link}: Make a hard link via the link syscall + +@pindex link +@cindex links, creating +@cindex hard links, creating +@cindex creating links (hard only) + +@command{link} creates a single hard link at a time. +It is a minimalist interface to the system-provided +@code{link} function. @xref{Hard Links, , , libc, +The GNU C Library Reference Manual}. +It avoids the bells and whistles of the more commonly-used +@command{ln} command (@pxref{ln invocation}). +Synopsis: + +@example +link @var{filename} @var{linkname} +@end example + +@var{filename} must specify an existing file, and @var{linkname} +must specify a nonexistent entry in an existing directory. +@command{link} simply calls @code{link (@var{filename}, @var{linkname})} +to create the link. + +On a GNU system, this command acts like @samp{ln --directory +--no-target-directory @var{filename} @var{linkname}}. However, the +@option{--directory} and @option{--no-target-directory} options are +not specified by POSIX, and the @command{link} command is +more portable in practice. + +If @var{filename} is a symbolic link, it is unspecified whether +@var{linkname} will be a hard link to the symbolic link or to the +target of the symbolic link. Use @command{ln -P} or @command{ln -L} +to specify which behavior is desired. + +@exitstatus + + +@node ln invocation +@section @command{ln}: Make links between files + +@pindex ln +@cindex links, creating +@cindex hard links, creating +@cindex symbolic (soft) links, creating +@cindex creating links (hard or soft) + +@cindex file systems and hard links +@command{ln} makes links between files. By default, it makes hard links; +with the @option{-s} option, it makes symbolic (or @dfn{soft}) links. +Synopses: + +@example +ln [@var{option}]@dots{} [-T] @var{target} @var{linkname} +ln [@var{option}]@dots{} @var{target} +ln [@var{option}]@dots{} @var{target}@dots{} @var{directory} +ln [@var{option}]@dots{} -t @var{directory} @var{target}@dots{} +@end example + +@itemize @bullet + +@item +If two file names are given, @command{ln} creates a link to the first +file from the second. + +@item +If one @var{target} is given, @command{ln} creates a link to that file +in the current directory. + +@item +If the @option{--target-directory} (@option{-t}) option is given, or +failing that if the last file is a directory and the +@option{--no-target-directory} (@option{-T}) option is not given, +@command{ln} creates a link to each @var{target} file in the specified +directory, using the @var{target}s' names. + +@end itemize + +Normally @command{ln} does not replace existing files. Use the +@option{--force} (@option{-f}) option to replace them unconditionally, +the @option{--interactive} (@option{-i}) option to replace them +conditionally, and the @option{--backup} (@option{-b}) option to +rename them. Unless the @option{--backup} (@option{-b}) option is +used there is no brief moment when the destination does not exist; +this is an extension to POSIX. + +@cindex hard link, defined +@cindex inode, and hard links +A @dfn{hard link} is another name for an existing file; the link and the +original are indistinguishable. Technically speaking, they share the +same inode, and the inode contains all the information about a +file -- indeed, it is not incorrect to say that the inode @emph{is} the +file. Most systems prohibit making a hard link to +a directory; on those where it is allowed, only the super-user can do +so (and with caution, since creating a cycle will cause problems to many +other utilities). Hard links cannot cross file system boundaries. (These +restrictions are not mandated by POSIX, however.) + +@cindex dereferencing symbolic links +@cindex symbolic link, defined +@dfn{Symbolic links} (@dfn{symlinks} for short), on the other hand, are +a special file type (which not all kernels support: System V release 3 +(and older) systems lack symlinks) in which the link file actually +refers to a different file, by name. When most operations (opening, +reading, writing, and so on) are passed the symbolic link file, the +kernel automatically @dfn{dereferences} the link and operates on the +target of the link. But some operations (e.g., removing) work on the +link file itself, rather than on its target. The owner and group of a +symlink are not significant to file access performed through +the link, but do have implications on deleting a symbolic link from a +directory with the restricted deletion bit set. On the GNU system, +the mode of a symlink has no significance and cannot be changed, but +on some BSD systems, the mode can be changed and will affect whether +the symlink will be traversed in file name resolution. @xref{Symbolic Links,,, +libc, The GNU C Library Reference Manual}. + +Symbolic links can contain arbitrary strings; a @dfn{dangling symlink} +occurs when the string in the symlink does not resolve to a file. +There are no restrictions against creating dangling symbolic links. +There are trade-offs to using absolute or relative symlinks. An +absolute symlink always points to the same file, even if the directory +containing the link is moved. However, if the symlink is visible from +more than one machine (such as on a networked file system), the file +pointed to might not always be the same. A relative symbolic link is +resolved in relation to the directory that contains the link, and is +often useful in referring to files on the same device without regards +to what name that device is mounted on when accessed via networked +machines. + +When creating a relative symlink in a different location than the +current directory, the resolution of the symlink will be different +than the resolution of the same string from the current directory. +Therefore, many users prefer to first change directories to the +location where the relative symlink will be created, so that +tab-completion or other file resolution will find the same target as +what will be placed in the symlink. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@optBackup + +@item -d +@itemx -F +@itemx --directory +@opindex -d +@opindex -F +@opindex --directory +@cindex hard links to directories +Allow users with appropriate privileges to attempt to make hard links +to directories. +However, note that this will probably fail due to +system restrictions, even for the super-user. + +@item -f +@itemx --force +@opindex -f +@opindex --force +Remove existing destination files. + +@item -i +@itemx --interactive +@opindex -i +@opindex --interactive +@cindex prompting, and @command{ln} +Prompt whether to remove existing destination files, +and fail if the response is not affirmative. + +@item -L +@itemx --logical +@opindex -L +@opindex --logical +If @option{-s} is not in effect, and the source file is a symbolic +link, create the hard link to the file referred to by the symbolic +link, rather than the symbolic link itself. + +@item -n +@itemx --no-dereference +@opindex -n +@opindex --no-dereference +Do not treat the last operand specially when it is a symbolic link to +a directory. Instead, treat it as if it were a normal file. + +When the destination is an actual directory (not a symlink to one), +there is no ambiguity. The link is created in that directory. +But when the specified destination is a symlink to a directory, +there are two ways to treat the user's request. @command{ln} can +treat the destination just as it would a normal directory and create +the link in it. On the other hand, the destination can be viewed as a +non-directory -- as the symlink itself. In that case, @command{ln} +must delete or backup that symlink before creating the new link. +The default is to treat a destination that is a symlink to a directory +just like a directory. + +This option is weaker than the @option{--no-target-directory} +(@option{-T}) option, so it has no effect if both options are given. + +@item -P +@itemx --physical +@opindex -P +@opindex --physical +If @option{-s} is not in effect, and the source file is a symbolic +link, create the hard link to the symbolic link itself. On platforms +where this is not supported by the kernel, this option creates a +symbolic link with identical contents; since symbolic link contents +cannot be edited, any file name resolution performed through either +link will be the same as if a hard link had been created. + +@item -r +@itemx --relative +@opindex -r +@opindex --relative +Make symbolic links relative to the link location. +This option is only valid with the @option{--symbolic} option. + +Example: + +@example +ln -srv /a/file /tmp +'/tmp/file' -> '../a/file' +@end example + +Relative symbolic links are generated based on their canonicalized +containing directory, and canonicalized targets. I.e., all symbolic +links in these file names will be resolved. +@xref{realpath invocation}, which gives greater control +over relative file name generation, as demonstrated in the following example: + +@example +@verbatim +ln--relative() { + test "$1" = --no-symlinks && { nosym=$1; shift; } + target="$1"; + test -d "$2" && link="$2/." || link="$2" + rtarget="$(realpath $nosym -m "$target" \ + --relative-to "$(dirname "$link")")" + ln -s -v "$rtarget" "$link" +} +@end verbatim +@end example + +@item -s +@itemx --symbolic +@opindex -s +@opindex --symbolic +Make symbolic links instead of hard links. This option merely produces +an error message on systems that do not support symbolic links. + +@optBackupSuffix + +@optTargetDirectory + +@optNoTargetDirectory + +@item -v +@itemx --verbose +@opindex -v +@opindex --verbose +Print the name of each file after linking it successfully. + +@end table + +@cindex hard links to symbolic links +@cindex symbolic links and @command{ln} +If @option{-L} and @option{-P} are both given, the last one takes +precedence. If @option{-s} is also given, @option{-L} and @option{-P} +are silently ignored. If neither option is given, then this +implementation defaults to @option{-P} if the system @code{link} supports +hard links to symbolic links (such as the GNU system), and @option{-L} +if @code{link} follows symbolic links (such as on BSD). + +@exitstatus + +Examples: + +@example +Bad Example: + +# Create link ../a pointing to a in that directory. +# Not really useful because it points to itself. +ln -s a .. + +Better Example: + +# Change to the target before creating symlinks to avoid being confused. +cd .. +ln -s adir/a . + +Bad Example: + +# Hard coded file names don't move well. +ln -s $(pwd)/a /some/dir/ + +Better Example: + +# Relative file names survive directory moves and also +# work across networked file systems. +ln -s afile anotherfile +ln -s ../adir/afile yetanotherfile +@end example + + +@node mkdir invocation +@section @command{mkdir}: Make directories + +@pindex mkdir +@cindex directories, creating +@cindex creating directories + +@command{mkdir} creates directories with the specified names. Synopsis: + +@example +mkdir [@var{option}]@dots{} @var{name}@dots{} +@end example + +@command{mkdir} creates each directory @var{name} in the order given. +It reports an error if @var{name} already exists, unless the +@option{-p} option is given and @var{name} is a directory. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -m @var{mode} +@itemx --mode=@var{mode} +@opindex -m +@opindex --mode +@cindex modes of created directories, setting +Set the file permission bits of created directories to @var{mode}, +which uses the same syntax as +in @command{chmod} and uses @samp{a=rwx} (read, write and execute allowed for +everyone) for the point of the departure. @xref{File permissions}. +This option affects only directories given on the command line; +it does not affect any parents that may be created via the @option{-p} option. + +Normally the directory has the desired file mode bits at the moment it +is created. As a GNU extension, @var{mode} may also mention +special mode bits, but in this case there may be a temporary window +during which the directory exists but its special mode bits are +incorrect. @xref{Directory Setuid and Setgid}, for how the +set-user-ID and set-group-ID bits of directories are inherited unless +overridden in this way. + +@item -p +@itemx --parents +@opindex -p +@opindex --parents +@cindex parent directories, creating +Make any missing parent directories for each argument, setting their +file permission bits to @samp{=rwx,u+wx}, +that is, with the umask modified by @samp{u+wx}. Ignore +existing parent directories, and do not change their file permission +bits. + +If the @option{-m} option is also given, it does not affect +file permission bits of any newly-created parent directories. +To control these bits, set the +umask before invoking @command{mkdir}. For example, if the shell +command @samp{(umask u=rwx,go=rx; mkdir -p P/Q)} creates the parent +@file{P} it sets the parent's file permission bits to @samp{u=rwx,go=rx}. +(The umask must include @samp{u=wx} for this method to work.) +To set a parent's special mode bits as well, you can invoke +@command{chmod} after @command{mkdir}. @xref{Directory Setuid and +Setgid}, for how the set-user-ID and set-group-ID bits of +newly-created parent directories are inherited. + +@item -v +@itemx --verbose +@opindex -v +@opindex --verbose +Print a message for each created directory. This is most useful with +@option{--parents}. + +@optContext + +@end table + +@exitstatus + + +@node mkfifo invocation +@section @command{mkfifo}: Make FIFOs (named pipes) + +@pindex mkfifo +@cindex FIFOs, creating +@cindex named pipes, creating +@cindex creating FIFOs (named pipes) + +@command{mkfifo} creates FIFOs (also called @dfn{named pipes}) with the +specified names. Synopsis: + +@example +mkfifo [@var{option}] @var{name}@dots{} +@end example + +A @dfn{FIFO} is a special file type that permits independent processes +to communicate. One process opens the FIFO file for writing, and +another for reading, after which data can flow as with the usual +anonymous pipe in shells or elsewhere. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -m @var{mode} +@itemx --mode=@var{mode} +@opindex -m +@opindex --mode +@cindex modes of created FIFOs, setting +Set the mode of created FIFOs to @var{mode}, which is symbolic as in +@command{chmod} and uses @samp{a=rw} (read and write allowed for everyone) +for the point of departure. @var{mode} should specify only file +permission bits. @xref{File permissions}. + +@optContext + +@end table + +@exitstatus + + +@node mknod invocation +@section @command{mknod}: Make block or character special files + +@pindex mknod +@cindex block special files, creating +@cindex character special files, creating + +@command{mknod} creates a FIFO, character special file, or block special +file with the specified name. Synopsis: + +@example +mknod [@var{option}]@dots{} @var{name} @var{type} [@var{major} @var{minor}] +@end example + +@cindex special files +@cindex block special files +@cindex character special files +Unlike the phrase ``special file type'' above, the term @dfn{special +file} has a technical meaning on Unix: something that can generate or +receive data. Usually this corresponds to a physical piece of hardware, +e.g., a printer or a flash drive. (These files are typically created at +system-configuration time.) The @command{mknod} command is what creates +files of this type. Such devices can be read either a character at a +time or a ``block'' (many characters) at a time, hence we say there are +@dfn{block special} files and @dfn{character special} files. + +@c mknod is a shell built-in at least with OpenBSD's /bin/sh +@mayConflictWithShellBuiltIn{mknod} + +The arguments after @var{name} specify the type of file to make: + +@table @samp + +@item p +@opindex p @r{for FIFO file} +for a FIFO + +@item b +@opindex b @r{for block special file} +for a block special file + +@item c +@c Don't document the 'u' option -- it's just a synonym for 'c'. +@c Do *any* versions of mknod still use it? +@c @itemx u +@opindex c @r{for character special file} +@c @opindex u @r{for character special file} +for a character special file + +@end table + +When making a block or character special file, the major and minor +device numbers must be given after the file type. +If a major or minor device number begins with @samp{0x} or @samp{0X}, +it is interpreted as hexadecimal; otherwise, if it begins with @samp{0}, +as octal; otherwise, as decimal. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -m @var{mode} +@itemx --mode=@var{mode} +@opindex -m +@opindex --mode +Set the mode of created files to @var{mode}, which is symbolic as in +@command{chmod} and uses @samp{a=rw} as the point of departure. +@var{mode} should specify only file permission bits. +@xref{File permissions}. + +@optContext + +@end table + +@exitstatus + + +@node readlink invocation +@section @command{readlink}: Print value of a symlink or canonical file name + +@pindex readlink +@cindex displaying value of a symbolic link +@cindex canonical file name +@cindex canonicalize a file name +@cindex realpath + +@command{readlink} may work in one of two supported modes: + +@table @samp + +@item Readlink mode + +@command{readlink} outputs the value of the given symbolic links. +If @command{readlink} is invoked with an argument other than the name +of a symbolic link, it produces no output and exits with a nonzero exit code. + +@item Canonicalize mode + +@command{readlink} outputs the absolute name of the given files which contain +no @file{.}, @file{..} components nor any repeated separators +(@file{/}) or symbolic links. Note the @command{realpath} command is the +preferred command to use for canonicalization. @xref{realpath invocation}. + +@end table + +@example +readlink [@var{option}]@dots{} @var{file}@dots{} +@end example + +By default, @command{readlink} operates in readlink mode. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -f +@itemx --canonicalize +@opindex -f +@opindex --canonicalize +Activate canonicalize mode. +If any component of the file name except the last one is missing or unavailable, +@command{readlink} produces no output and exits with a nonzero exit +code. A trailing slash is ignored. + +@item -e +@itemx --canonicalize-existing +@opindex -e +@opindex --canonicalize-existing +Activate canonicalize mode. +If any component is missing or unavailable, @command{readlink} produces +no output and exits with a nonzero exit code. A trailing slash +requires that the name resolve to a directory. + +@item -m +@itemx --canonicalize-missing +@opindex -m +@opindex --canonicalize-missing +Activate canonicalize mode. +If any component is missing or unavailable, @command{readlink} treats it +as a directory. + +@item -n +@itemx --no-newline +@opindex -n +@opindex --no-newline +Do not print the output delimiter, when a single @var{file} is specified. +Print a warning if specified along with multiple @var{file}s. + +@item -s +@itemx -q +@itemx --silent +@itemx --quiet +@opindex -s +@opindex -q +@opindex --silent +@opindex --quiet +Suppress most error messages. On by default. + +@item -v +@itemx --verbose +@opindex -v +@opindex --verbose +Report error messages. + +@optZero + +@end table + +The @command{readlink} utility first appeared in OpenBSD 2.1. + +The @command{realpath} command without options, operates like +@command{readlink} in canonicalize mode. + +@exitstatus + + +@node rmdir invocation +@section @command{rmdir}: Remove empty directories + +@pindex rmdir +@cindex removing empty directories +@cindex directories, removing empty + +@command{rmdir} removes empty directories. Synopsis: + +@example +rmdir [@var{option}]@dots{} @var{directory}@dots{} +@end example + +If any @var{directory} argument does not refer to an existing empty +directory, it is an error. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item --ignore-fail-on-non-empty +@opindex --ignore-fail-on-non-empty +@cindex directory deletion, ignoring failures +Ignore each failure to remove a directory that is non-empty. + +@item -p +@itemx --parents +@opindex -p +@opindex --parents +@cindex parent directories, removing +Remove @var{directory}, then try to remove each component of @var{directory}. +So, for example, @samp{rmdir -p a/b/c} is similar to @samp{rmdir a/b/c a/b a}. +As such, it fails if any of those directories turns out not to be empty. +Use the @option{--ignore-fail-on-non-empty} option to make it so such +a failure does not evoke a diagnostic and does not cause @command{rmdir} to +exit unsuccessfully. + +@item -v +@itemx --verbose +@opindex -v +@opindex --verbose +@cindex directory deletion, reporting +Give a diagnostic for each successful removal. +@var{directory} is removed. + +@end table + +@xref{rm invocation}, for how to remove non-empty directories recursively. + +To remove all empty directories under @var{dirname}, including +directories that become empty because other directories are removed, +you can use either of the following commands: + +@example +# This uses GNU extensions. +find @var{dirname} -type d -empty -delete + +# This runs on any POSIX platform. +find @var{dirname} -depth -type d -exec rmdir @{@} + +@end example + +@exitstatus + + +@node unlink invocation +@section @command{unlink}: Remove files via the unlink syscall + +@pindex unlink +@cindex removing files or directories (via the unlink syscall) + +@command{unlink} deletes a single specified file name. +It is a minimalist interface to the system-provided +@code{unlink} function. @xref{Deleting Files, , , libc, +The GNU C Library Reference Manual}. Synopsis: +It avoids the bells and whistles of the more commonly-used +@command{rm} command (@pxref{rm invocation}). + +@example +unlink @var{filename} +@end example + +On some systems @code{unlink} can be used to delete the name of a +directory. On others, it can be used that way only by a privileged user. +In the GNU system @code{unlink} can never delete the name of a directory. + +The @command{unlink} command honors the @option{--help} and +@option{--version} options. To remove a file whose name begins with +@samp{-}, prefix the name with @samp{./}, e.g., @samp{unlink ./--help}. + +@exitstatus + + +@node Changing file attributes +@chapter Changing file attributes + +@cindex changing file attributes +@cindex file attributes, changing +@cindex attributes, file + +A file is not merely its contents, a name, and a file type +(@pxref{Special file types}). A file also has an owner (a user ID), a +group (a group ID), permissions (what the owner can do with the file, +what people in the group can do, and what everyone else can do), various +timestamps, and other information. Collectively, we call these a file's +@dfn{attributes}. + +These commands change file attributes. + +@menu +* chown invocation:: Change file owners and groups. +* chgrp invocation:: Change file groups. +* chmod invocation:: Change access permissions. +* touch invocation:: Change file timestamps. +@end menu + + +@node chown invocation +@section @command{chown}: Change file owner and group + +@pindex chown +@cindex file ownership, changing +@cindex group ownership, changing +@cindex changing file ownership +@cindex changing group ownership + +@command{chown} changes the user and/or group ownership of each given @var{file} +to @var{new-owner} or to the user and group of an existing reference file. +Synopsis: + +@example +chown [@var{option}]@dots{} @{@var{new-owner} | --reference=@var{ref_file}@}@c + @var{file}@dots{} +@end example + +If used, @var{new-owner} specifies the new owner and/or group as follows +(with no embedded white space): + +@example +[@var{owner}] [ : [@var{group}] ] +@end example + +Specifically: + +@table @var +@item owner +If only an @var{owner} (a user name or numeric user ID) is given, that +user is made the owner of each given file, and the files' group is not +changed. + +@item owner@samp{:}group +If the @var{owner} is followed by a colon and a @var{group} (a +group name or numeric group ID), with no spaces between them, the group +ownership of the files is changed as well (to @var{group}). + +@item owner@samp{:} +If a colon but no group name follows @var{owner}, that user is +made the owner of the files and the group of the files is changed to +@var{owner}'s login group. + +@item @samp{:}group +If the colon and following @var{group} are given, but the owner +is omitted, only the group of the files is changed; in this case, +@command{chown} performs the same function as @command{chgrp}. + +@item @samp{:} +If only a colon is given, or if @var{new-owner} is empty, neither the +owner nor the group is changed. + +@end table + +If @var{owner} or @var{group} is intended to represent a numeric user +or group ID, then you may specify it with a leading @samp{+}. +@xref{Disambiguating names and IDs}. + +Some older scripts may still use @samp{.} in place of the @samp{:} separator. +POSIX 1003.1-2001 (@pxref{Standards conformance}) does not +require support for that, but for backward compatibility GNU +@command{chown} supports @samp{.} so long as no ambiguity results, +although it issues a warning and support may be removed in future versions. +New scripts should avoid the use of @samp{.} because it is not +portable, and because it has undesirable results if the entire +@var{owner@samp{.}group} happens to identify a user whose name +contains @samp{.}. + +@macro chownGroupRestrictions +It is system dependent whether a user can change the group to an arbitrary one, +or the more portable behavior of being restricted to setting a group of +which the user is a member. +@end macro +@chownGroupRestrictions + +The @command{chown} command sometimes clears the set-user-ID or +set-group-ID permission bits. This behavior depends on the policy and +functionality of the underlying @code{chown} system call, which may +make system-dependent file mode modifications outside the control of +the @command{chown} command. For example, the @command{chown} command +might not affect those bits when invoked by a user with appropriate +privileges, or when the +bits signify some function other than executable permission (e.g., +mandatory locking). +When in doubt, check the underlying system behavior. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -c +@itemx --changes +@opindex -c +@opindex --changes +@cindex changed owners, verbosely describing +Verbosely describe the action for each @var{file} whose ownership +actually changes. + +@item -f +@itemx --silent +@itemx --quiet +@opindex -f +@opindex --silent +@opindex --quiet +@cindex error messages, omitting +Do not print error messages about files whose ownership cannot be +changed. + +@item --from=@var{old-owner} +@opindex --from +@cindex symbolic links, changing owner +Change a @var{file}'s ownership only if it has current attributes specified +by @var{old-owner}. @var{old-owner} has the same form as @var{new-owner} +described above. +This option is useful primarily from a security standpoint in that +it narrows considerably the window of potential abuse. +For example, to reflect a user ID numbering change for one user's files +without an option like this, @code{root} might run + +@example +find / -owner OLDUSER -print0 | xargs -0 chown -h NEWUSER +@end example + +But that is dangerous because the interval between when the @command{find} +tests the existing file's owner and when the @command{chown} is actually run +may be quite large. +One way to narrow the gap would be to invoke chown for each file +as it is found: + +@example +find / -owner OLDUSER -exec chown -h NEWUSER @{@} \; +@end example + +But that is very slow if there are many affected files. +With this option, it is safer (the gap is narrower still) +though still not perfect: + +@example +chown -h -R --from=OLDUSER NEWUSER / +@end example + +@item --dereference +@opindex --dereference +@cindex symbolic links, changing owner +@findex lchown +Do not act on symbolic links themselves but rather on what they point to. +This is the default when not operating recursively. +@warnOptDerefWithRec + +@item -h +@itemx --no-dereference +@opindex -h +@opindex --no-dereference +@cindex symbolic links, changing owner +@findex lchown +Act on symbolic links themselves instead of what they point to. +This mode relies on the @code{lchown} system call. +On systems that do not provide the @code{lchown} system call, +@command{chown} fails when a file specified on the command line +is a symbolic link. +By default, no diagnostic is issued for symbolic links encountered +during a recursive traversal, but see @option{--verbose}. + +@item --preserve-root +@opindex --preserve-root +@cindex root directory, disallow recursive modification +Fail upon any attempt to recursively change the root directory, @file{/}. +Without @option{--recursive}, this option has no effect. +@xref{Treating / specially}. + +@item --no-preserve-root +@opindex --no-preserve-root +@cindex root directory, allow recursive modification +Cancel the effect of any preceding @option{--preserve-root} option. +@xref{Treating / specially}. + +@item --reference=@var{ref_file} +@opindex --reference +Change the user and group of each @var{file} to be the same as those of +@var{ref_file}. If @var{ref_file} is a symbolic link, do not use the +user and group of the symbolic link, but rather those of the file it +refers to. + +@item -v +@itemx --verbose +@opindex -v +@opindex --verbose +Output a diagnostic for every file processed. +If a symbolic link is encountered during a recursive traversal +on a system without the @code{lchown} system call, and @option{--no-dereference} +is in effect, then issue a diagnostic saying neither the symbolic link nor +its referent is being changed. + +@item -R +@itemx --recursive +@opindex -R +@opindex --recursive +@cindex recursively changing file ownership +Recursively change ownership of directories and their contents. + +@choptH +@xref{Traversing symlinks}. + +@choptL +@warnOptDerefWithRec +@xref{Traversing symlinks}. + +@choptP +@xref{Traversing symlinks}. + +@end table + +@exitstatus + +Examples: + +@example +# Change the owner of /u to "root". +chown root /u + +# Likewise, but also change its group to "staff". +chown root:staff /u + +# Change the owner of /u and subfiles to "root". +chown -hR root /u +@end example + + +@node chgrp invocation +@section @command{chgrp}: Change group ownership + +@pindex chgrp +@cindex group ownership, changing +@cindex changing group ownership + +@command{chgrp} changes the group ownership of each given @var{file} +to @var{group} (which can be either a group name or a numeric group ID) +or to the group of an existing reference file. @xref{chown invocation}. +Synopsis: + +@example +chgrp [@var{option}]@dots{} @{@var{group} | --reference=@var{ref_file}@}@c + @var{file}@dots{} +@end example + +If @var{group} is intended to represent a +numeric group ID, then you may specify it with a leading @samp{+}. +@xref{Disambiguating names and IDs}. + +@chownGroupRestrictions + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -c +@itemx --changes +@opindex -c +@opindex --changes +@cindex changed files, verbosely describing +Verbosely describe the action for each @var{file} whose group actually +changes. + +@item -f +@itemx --silent +@itemx --quiet +@opindex -f +@opindex --silent +@opindex --quiet +@cindex error messages, omitting +Do not print error messages about files whose group cannot be +changed. + +@item --dereference +@opindex --dereference +@cindex symbolic links, changing owner +@findex lchown +Do not act on symbolic links themselves but rather on what they point to. +This is the default when not operating recursively. +@warnOptDerefWithRec + +@item -h +@itemx --no-dereference +@opindex -h +@opindex --no-dereference +@cindex symbolic links, changing group +@findex lchown +Act on symbolic links themselves instead of what they point to. +This mode relies on the @code{lchown} system call. +On systems that do not provide the @code{lchown} system call, +@command{chgrp} fails when a file specified on the command line +is a symbolic link. +By default, no diagnostic is issued for symbolic links encountered +during a recursive traversal, but see @option{--verbose}. + +@item --preserve-root +@opindex --preserve-root +@cindex root directory, disallow recursive modification +Fail upon any attempt to recursively change the root directory, @file{/}. +Without @option{--recursive}, this option has no effect. +@xref{Treating / specially}. + +@item --no-preserve-root +@opindex --no-preserve-root +@cindex root directory, allow recursive modification +Cancel the effect of any preceding @option{--preserve-root} option. +@xref{Treating / specially}. + +@item --reference=@var{ref_file} +@opindex --reference +Change the group of each @var{file} to be the same as that of +@var{ref_file}. If @var{ref_file} is a symbolic link, do not use the +group of the symbolic link, but rather that of the file it refers to. + +@item -v +@itemx --verbose +@opindex -v +@opindex --verbose +Output a diagnostic for every file processed. +If a symbolic link is encountered during a recursive traversal +on a system without the @code{lchown} system call, and @option{--no-dereference} +is in effect, then issue a diagnostic saying neither the symbolic link nor +its referent is being changed. + +@item -R +@itemx --recursive +@opindex -R +@opindex --recursive +@cindex recursively changing group ownership +Recursively change the group ownership of directories and their contents. + +@choptH +@xref{Traversing symlinks}. + +@choptL +@warnOptDerefWithRec +@xref{Traversing symlinks}. + +@choptP +@xref{Traversing symlinks}. + +@end table + +@exitstatus + +Examples: + +@example +# Change the group of /u to "staff". +chgrp staff /u + +# Change the group of /u and subfiles to "staff". +chgrp -hR staff /u +@end example + + +@node chmod invocation +@section @command{chmod}: Change access permissions + +@pindex chmod +@cindex changing access permissions +@cindex access permissions, changing +@cindex permissions, changing access + +@command{chmod} changes the access permissions of the named files. Synopsis: + +@example +chmod [@var{option}]@dots{} @{@var{mode} | --reference=@var{ref_file}@}@c + @var{file}@dots{} +@end example + +@cindex symbolic links, permissions of +@command{chmod} never changes the permissions of symbolic links, since +the @command{chmod} system call cannot change their permissions. +This is not a problem since the permissions of symbolic links are +never used. However, for each symbolic link listed on the command +line, @command{chmod} changes the permissions of the pointed-to file. +In contrast, @command{chmod} ignores symbolic links encountered during +recursive directory traversals. + +Only a process whose effective user ID matches the user ID of the file, +or a process with appropriate privileges, is permitted to change the +file mode bits of a file. + +A successful use of @command{chmod} clears the set-group-ID bit of a +regular file if the file's group ID does not match the user's +effective group ID or one of the user's supplementary group IDs, +unless the user has appropriate privileges. Additional restrictions +may cause the set-user-ID and set-group-ID bits of @var{mode} or +@var{ref_file} to be ignored. This behavior depends on the policy and +functionality of the underlying @code{chmod} system call. When in +doubt, check the underlying system behavior. + +If used, @var{mode} specifies the new file mode bits. +For details, see the section on @ref{File permissions}. +If you really want @var{mode} to have a leading @samp{-}, you should +use @option{--} first, e.g., @samp{chmod -- -w file}. Typically, +though, @samp{chmod a-w file} is preferable, and @command{chmod -w +file} (without the @option{--}) complains if it behaves differently +from what @samp{chmod a-w file} would do. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -c +@itemx --changes +@opindex -c +@opindex --changes +Verbosely describe the action for each @var{file} whose permissions +actually change. + +@item -f +@itemx --silent +@itemx --quiet +@opindex -f +@opindex --silent +@opindex --quiet +@cindex error messages, omitting +Do not print error messages about files whose permissions cannot be +changed. + +@item --preserve-root +@opindex --preserve-root +@cindex root directory, disallow recursive modification +Fail upon any attempt to recursively change the root directory, @file{/}. +Without @option{--recursive}, this option has no effect. +@xref{Treating / specially}. + +@item --no-preserve-root +@opindex --no-preserve-root +@cindex root directory, allow recursive modification +Cancel the effect of any preceding @option{--preserve-root} option. +@xref{Treating / specially}. + +@item -v +@itemx --verbose +@opindex -v +@opindex --verbose +Verbosely describe the action or non-action taken for every @var{file}. + +@item --reference=@var{ref_file} +@opindex --reference +Change the mode of each @var{file} to be the same as that of @var{ref_file}. +@xref{File permissions}. +If @var{ref_file} is a symbolic link, do not use the mode +of the symbolic link, but rather that of the file it refers to. + +@item -R +@itemx --recursive +@opindex -R +@opindex --recursive +@cindex recursively changing access permissions +Recursively change permissions of directories and their contents. + +@end table + +@exitstatus + +Examples: + +@smallexample +# Change file permissions of FOO to be world readable +# and user writable, with no other permissions. +chmod 644 foo +chmod a=r,u+w foo + +# Add user and group execute permissions to FOO. +chmod +110 file +chmod ug+x file + +# Set file permissions of DIR and subsidiary files to +# be the umask default, assuming execute permissions for +# directories and for files already executable. +chmod -R a=,+rwX dir +@end smallexample + + +@node touch invocation +@section @command{touch}: Change file timestamps + +@pindex touch +@cindex changing file timestamps +@cindex file timestamps, changing +@cindex timestamps, changing file + +@command{touch} changes the access and/or modification timestamps of the +specified files. Synopsis: + +@example +touch [@var{option}]@dots{} @var{file}@dots{} +@end example + +@cindex empty files, creating +Any @var{file} argument that does not exist is created empty, unless +option @option{--no-create} (@option{-c}) or @option{--no-dereference} +(@option{-h}) was in effect. + +A @var{file} argument string of @samp{-} is handled specially and +causes @command{touch} to change the times of the file associated with +standard output. + +By default, @command{touch} sets file timestamps to the current time. +Because @command{touch} acts on its operands left to right, the +resulting timestamps of earlier and later operands may disagree. + +@cindex permissions, for changing file timestamps +When setting file timestamps to the current time, @command{touch} can +change the timestamps for files that the user does not own but has +write permission for. Otherwise, the user must own the files. Some +older systems have a further restriction: the user must own the files +unless both the access and modification timestamps are being set to the +current time. + +The @command{touch} command cannot set a file's status change timestamp to +a user-specified value, and cannot change the file's birth time (if +supported) at all. Also, @command{touch} has issues similar to those +affecting all programs that update file timestamps. For example, +@command{touch} may set a file's timestamp to a value that differs +slightly from the requested time. @xref{File timestamps}. + +@vindex TZ +Timestamps assume the time zone rules specified by the @env{TZ} +environment variable, or by the system default rules if @env{TZ} is +not set. @xref{TZ Variable,, Specifying the Time Zone with @env{TZ}, +libc, The GNU C Library Reference Manual}. +You can avoid ambiguities during +daylight saving transitions by using UTC timestamps. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -a +@itemx --time=atime +@itemx --time=access +@itemx --time=use +@opindex -a +@opindex --time +@opindex atime@r{, changing} +@opindex access @r{time, changing} +@opindex use @r{time, changing} +Change the access timestamp only. @xref{File timestamps}. + +@item -c +@itemx --no-create +@opindex -c +@opindex --no-create +Do not warn about or create files that do not exist. + +@item -d @var{time} +@itemx --date=@var{time} +@opindex -d +@opindex --date +@opindex time +Use @var{time} instead of the current time. It can contain month names, +time zones, @samp{am} and @samp{pm}, @samp{yesterday}, etc. For +example, @option{--date="2020-07-21 14:19:13.489392193 +0530"} +specifies the instant of time that is 489,392,193 nanoseconds after +July 21, 2020 at 2:19:13 PM in a time zone that is 5 hours and 30 +minutes east of UTC@. @xref{Date input formats}. +File systems that do not support high-resolution timestamps +silently ignore any excess precision here. + +@item -f +@opindex -f +@cindex BSD @command{touch} compatibility +Ignored; for compatibility with BSD versions of @command{touch}. + +@item -h +@itemx --no-dereference +@opindex -h +@opindex --no-dereference +@cindex symbolic links, changing time +@findex lutimes +Attempt to change the timestamps of a symbolic link, rather than what +the link refers to. When using this option, empty files are not +created, but option @option{-c} must also be used to avoid warning +about files that do not exist. Not all systems support changing the +timestamps of symlinks, since underlying system support for this +action was not required until POSIX 2008. Also, on some +systems, the mere act of examining a symbolic link changes the access +timestamp, such that only changes to the modification timestamp will persist +long enough to be observable. When coupled with option @option{-r}, a +reference timestamp is taken from a symbolic link rather than the file +it refers to. + +@item -m +@itemx --time=mtime +@itemx --time=modify +@opindex -m +@opindex --time +@opindex mtime@r{, changing} +@opindex modify @r{time, changing} +Change the modification timestamp only. + +@item -r @var{file} +@itemx --reference=@var{file} +@opindex -r +@opindex --reference +Use the times of the reference @var{file} instead of the current time. +If this option is combined with the @option{--date=@var{time}} +(@option{-d @var{time}}) option, the reference @var{file}'s time is +the origin for any relative @var{time}s given, but is otherwise ignored. +For example, @samp{-r foo -d '-5 seconds'} specifies a timestamp +equal to five seconds before the corresponding timestamp for @file{foo}. +If @var{file} is a symbolic link, the reference timestamp is taken +from the target of the symlink, unless @option{-h} was also in effect. + +@item -t [[@var{cc}]@var{yy}]@var{mmddhhmm}[.@var{ss}] +@cindex leap seconds +Use the argument (optional four-digit or two-digit years, months, +days, hours, minutes, optional seconds) instead of the current time. +If the year is specified with only two digits, then @var{cc} +is 20 for years in the range 0 @dots{} 68, and 19 for years in +69 @dots{} 99. If no digits of the year are specified, +the argument is interpreted as a date in the current year. +On the atypical systems that support leap seconds, @var{ss} may be +@samp{60}. + +@end table + +@vindex _POSIX2_VERSION +On systems predating POSIX 1003.1-2001, +@command{touch} supports an obsolete syntax, as follows. +If no timestamp is given with any of the @option{-d}, @option{-r}, or +@option{-t} options, and if there are two or more @var{file}s and the +first @var{file} is of the form @samp{@var{mmddhhmm}[@var{yy}]} and this +would be a valid argument to the @option{-t} option (if the @var{yy}, if +any, were moved to the front), and if the represented year +is in the range 1969--1999, that argument is interpreted as the time +for the other files instead of as a file name. +Although this obsolete behavior can be controlled with the +@env{_POSIX2_VERSION} environment variable (@pxref{Standards +conformance}), portable scripts should avoid commands whose +behavior depends on this variable. +For example, use @samp{touch ./12312359 main.c} or @samp{touch -t +12312359 main.c} rather than the ambiguous @samp{touch 12312359 main.c}. + +@exitstatus + + +@node File space usage +@chapter File space usage + +@cindex File space usage +@cindex disk usage + +No file system can hold an infinite amount of data. These commands report +how much storage is in use or available, report other file and +file status information, and write buffers to file systems. + +@menu +* df invocation:: Report file system space usage. +* du invocation:: Estimate file space usage. +* stat invocation:: Report file or file system status. +* sync invocation:: Synchronize cached writes to persistent storage. +* truncate invocation:: Shrink or extend the size of a file. +@end menu + + +@node df invocation +@section @command{df}: Report file system space usage + +@pindex df +@cindex file system usage +@cindex disk usage by file system + +@command{df} reports the amount of space used and available on +file systems. Synopsis: + +@example +df [@var{option}]@dots{} [@var{file}]@dots{} +@end example + +With no arguments, @command{df} reports the space used and available on all +currently mounted file systems (of all types). Otherwise, @command{df} +reports on the file system containing each argument @var{file}. + +Normally the space is printed in units of +1024 bytes, but this can be overridden (@pxref{Block size}). +Non-integer quantities are rounded up to the next higher unit. + +For bind mounts and without arguments, @command{df} only outputs the statistics +for that device with the shortest mount point name in the list of file systems +(@var{mtab}), i.e., it hides duplicate entries, unless the @option{-a} option is +specified. + +With the same logic, @command{df} elides a mount entry of a dummy pseudo device +if there is another mount entry of a real block device for that mount point with +the same device number, e.g. the early-boot pseudo file system @samp{rootfs} is +not shown per default when already the real root device has been mounted. + +@cindex disk device file +@cindex device file +If an argument @var{file} resolves to a special file containing +a mounted file system, @command{df} shows the space available on that +file system rather than on the file system containing the device node. +GNU @command{df} does not attempt to determine the usage +on unmounted file systems, because on most kinds of systems doing so +requires extremely non-portable intimate knowledge of file system structures. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -a +@itemx --all +@opindex -a +@opindex --all +@cindex ignore file systems +Include in the listing dummy, duplicate, or inaccessible file systems, which +are omitted by default. Dummy file systems are typically special purpose +pseudo file systems such as @samp{/proc}, with no associated storage. +Duplicate file systems are local or remote file systems that are mounted +at separate locations in the local file hierarchy, or bind mounted locations. +Inaccessible file systems are those which are mounted but subsequently +over-mounted by another file system at that point, or otherwise inaccessible +due to permissions of the mount point etc. + +@item -B @var{size} +@itemx --block-size=@var{size} +@opindex -B +@opindex --block-size +@cindex file system sizes +Scale sizes by @var{size} before printing them (@pxref{Block size}). +For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes. + +@optHumanReadable + +@item -H +@opindex -H +Equivalent to @option{--si}. + +@item -i +@itemx --inodes +@opindex -i +@opindex --inodes +@cindex inode usage +List inode usage information instead of block usage. An inode (short +for index node) contains information about a file such as its owner, +permissions, timestamps, and location on the file system. + +@item -k +@opindex -k +@cindex kibibytes for file system sizes +Print sizes in 1024-byte blocks, overriding the default block size +(@pxref{Block size}). +This option is equivalent to @option{--block-size=1K}. + +@item -l +@itemx --local +@opindex -l +@opindex --local +@cindex file system types, limiting output to certain +Limit the listing to local file systems. By default, remote file systems +are also listed. + +@item --no-sync +@opindex --no-sync +@cindex file system space, retrieving old data more quickly +Do not invoke the @code{sync} system call before getting any usage data. +This may make @command{df} run significantly faster on systems with many +file systems, but on some systems (notably Solaris) the results may be slightly +out of date. This is the default. + +@item --output +@itemx --output[=@var{field_list}] +@opindex --output +Use the output format defined by @var{field_list}, or print all fields if +@var{field_list} is omitted. In the latter case, the order of the columns +conforms to the order of the field descriptions below. + +The use of the @option{--output} together with each of the options @option{-i}, +@option{-P}, and @option{-T} is mutually exclusive. + +FIELD_LIST is a comma-separated list of columns to be included in @command{df}'s +output and therefore effectively controls the order of output columns. +Each field can thus be used at the place of choice, but yet must only be +used once. + +Valid field names in the @var{field_list} are: +@table @samp +@item source +The source of the mount point, usually a device. +@item fstype +File system type. + +@item itotal +Total number of inodes. +@item iused +Number of used inodes. +@item iavail +Number of available inodes. +@item ipcent +Percentage of @var{iused} divided by @var{itotal}. + +@item size +Total number of blocks. +@item used +Number of used blocks. +@item avail +Number of available blocks. +@item pcent +Percentage of @var{used} divided by @var{size}. + +@item file +The file name if specified on the command line. +@item target +The mount point. +@end table + +The fields for block and inodes statistics are affected by the scaling +options like @option{-h} as usual. + +The definition of the @var{field_list} can even be split among several +@option{--output} uses. + +@example +#!/bin/sh +# Print the TARGET (i.e., the mount point) along with their percentage +# statistic regarding the blocks and the inodes. +df --out=target --output=pcent,ipcent + +# Print all available fields. +df --o +@end example + + +@item -P +@itemx --portability +@opindex -P +@opindex --portability +@cindex one-line output format +@cindex POSIX output format +@cindex portable output format +@cindex output format, portable +Use the POSIX output format. This is like the default format except +for the following: + +@enumerate +@item +The information about each file system is always printed on exactly +one line; a mount device is never put on a line by itself. This means +that if the mount device name is more than 20 characters long (e.g., for +some network mounts), the columns are misaligned. + +@item +The labels in the header output line are changed to conform to POSIX. + +@item +The default block size and output format are unaffected by the +@env{DF_BLOCK_SIZE}, @env{BLOCK_SIZE} and @env{BLOCKSIZE} environment +variables. However, the default block size is still affected by +@env{POSIXLY_CORRECT}: it is 512 if @env{POSIXLY_CORRECT} is set, 1024 +otherwise. @xref{Block size}. +@end enumerate + +@optSi + +@item --sync +@opindex --sync +@cindex file system space, retrieving current data more slowly +Invoke the @code{sync} system call before getting any usage data. On +some systems (notably Solaris), doing this yields more up to date results, +but in general this option makes @command{df} much slower, especially when +there are many or very busy file systems. + +@item --total +@opindex --total +@cindex grand total of file system size, usage and available space +Print a grand total of all arguments after all arguments have +been processed. This can be used to find out the total size, usage +and available space of all listed devices. If no arguments are specified +df will try harder to elide file systems insignificant to the total +available space, by suppressing duplicate remote file systems. + +For the grand total line, @command{df} prints @samp{"total"} into the +@var{source} column, and @samp{"-"} into the @var{target} column. +If there is no @var{source} column (see @option{--output}), then +@command{df} prints @samp{"total"} into the @var{target} column, +if present. + +@item -t @var{fstype} +@itemx --type=@var{fstype} +@opindex -t +@opindex --type +@cindex file system types, limiting output to certain +Limit the listing to file systems of type @var{fstype}. Multiple +file system types can be specified by giving multiple @option{-t} options. +By default, nothing is omitted. + +@item -T +@itemx --print-type +@opindex -T +@opindex --print-type +@cindex file system types, printing +Print each file system's type. The types printed here are the same ones +you can include or exclude with @option{-t} and @option{-x}. The particular +types printed are whatever is supported by the system. Here are some of +the common names (this list is certainly not exhaustive): + +@table @samp + +@item nfs +@cindex NFS file system type +An NFS file system, i.e., one mounted over a network from another +machine. This is the one type name which seems to be used uniformly by +all systems. + +@item ext2@r{, }ext3@r{, }ext4@r{, }xfs@r{, }btrfs@dots{} +@cindex Linux file system types +@cindex local file system types +@opindex ext2 @r{file system type} +@opindex ext3 @r{file system type} +@opindex ext4 @r{file system type} +@opindex xfs @r{file system type} +@opindex btrfs @r{file system type} +A file system on a locally-mounted device. (The system might even +support more than one type here; GNU/Linux does.) + +@item iso9660@r{, }cdfs +@cindex CD-ROM file system type +@cindex DVD file system type +@cindex ISO9660 file system type +@opindex iso9660 @r{file system type} +@opindex cdfs @r{file system type} +A file system on a CD or DVD drive. HP-UX uses @samp{cdfs}, most other +systems use @samp{iso9660}. + +@item ntfs@r{,}fat +@cindex NTFS file system +@cindex DOS file system +@cindex MS-DOS file system +@cindex MS-Windows file system +@opindex ntfs @r{file system file} +@opindex fat @r{file system file} +File systems used by MS-Windows / MS-DOS. + +@end table + +@item -x @var{fstype} +@itemx --exclude-type=@var{fstype} +@opindex -x +@opindex --exclude-type +Limit the listing to file systems not of type @var{fstype}. +Multiple file system types can be eliminated by giving multiple +@option{-x} options. By default, no file system types are omitted. + +@item -v +Ignored; for compatibility with System V versions of @command{df}. + +@end table + +@command{df} is installed only on systems that have usable mount tables, +so portable scripts should not rely on its existence. + +@exitstatus +Failure includes the case where no output is generated, so you can +inspect the exit status of a command like @samp{df -t ext3 -t reiserfs +@var{dir}} to test whether @var{dir} is on a file system of type +@samp{ext3} or @samp{reiserfs}. + +Since the list of file systems (@var{mtab}) is needed to determine the +file system type, failure includes the cases when that list cannot +be read and one or more of the options @option{-a}, @option{-l}, @option{-t} +or @option{-x} is used together with a file name argument. + + +@node du invocation +@section @command{du}: Estimate file space usage + +@pindex du +@cindex file space usage +@cindex disk usage for files + +@command{du} reports the space needed to represent a set of files. +Synopsis: + +@example +du [@var{option}]@dots{} [@var{file}]@dots{} +@end example + +With no arguments, @command{du} reports the space needed to represent +the files at or under the current directory. +Normally the space is printed in units of +1024 bytes, but this can be overridden (@pxref{Block size}). +Non-integer quantities are rounded up to the next higher unit. + +If two or more hard links point to the same file, only one of the hard +links is counted. The @var{file} argument order affects which links +are counted, and changing the argument order may change the numbers +and entries that @command{du} outputs. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@optNull + +@item -a +@itemx --all +@opindex -a +@opindex --all +Show counts for all files, not just directories. + +@item --apparent-size +@opindex --apparent-size +Print apparent sizes, rather than file system usage. The apparent size of a +file is the number of bytes reported by @code{wc -c} on regular files, +or more generally, @code{ls -l --block-size=1} or @code{stat --format=%s}. +For example, a file containing the word @samp{zoo} with no newline would, +of course, have an apparent size of 3. Such a small file may require +anywhere from 0 to 16 KiB or more of file system space, depending on +the type and configuration of the file system on which the file resides. +However, a sparse file created with this command: + +@example +dd bs=1 seek=2GiB if=/dev/null of=big +@end example + +@noindent +has an apparent size of 2 GiB, yet on most modern +file systems, it actually uses almost no space. + +Apparent sizes are meaningful only for regular files and symbolic links. +Other file types do not contribute to apparent size. + +@item -B @var{size} +@itemx --block-size=@var{size} +@opindex -B +@opindex --block-size +@cindex file sizes +Scale sizes by @var{size} before printing them (@pxref{Block size}). +For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes. + +@item -b +@itemx --bytes +@opindex -b +@opindex --bytes +Equivalent to @code{--apparent-size --block-size=1}. + +@item -c +@itemx --total +@opindex -c +@opindex --total +@cindex grand total of file system space +Print a grand total of all arguments after all arguments have +been processed. This can be used to find out the total file system usage of +a given set of files or directories. + +@item -D +@itemx --dereference-args +@opindex -D +@opindex --dereference-args +Dereference symbolic links that are command line arguments. +Does not affect other symbolic links. This is helpful for finding +out the file system usage of directories, such as @file{/usr/tmp}, which +are often symbolic links. + +@item -d @var{depth} +@itemx --max-depth=@var{depth} +@opindex -d @var{depth} +@opindex --max-depth=@var{depth} +@cindex limiting output of @command{du} +Show the total for each directory (and file if @option{--all}) that is at +most MAX_DEPTH levels down from the root of the hierarchy. The root +is at level 0, so @code{du --max-depth=0} is equivalent to @code{du -s}. + +@c --files0-from=FILE +@filesZeroFromOption{du,, with the @option{--total} (@option{-c}) option} + +@item -H +@opindex -H +Equivalent to @option{--dereference-args} (@option{-D}). + +@optHumanReadable + +@item --inodes +@opindex --inodes +@cindex inode usage, dereferencing in @command{du} +List inode usage information instead of block usage. +This option is useful for finding directories which contain many files, and +therefore eat up most of the inodes space of a file system (see @command{df}, +option @option{--inodes}). +It can well be combined with the options @option{-a}, @option{-c}, +@option{-h}, @option{-l}, @option{-s}, @option{-S}, @option{-t} and +@option{-x}; however, passing other options regarding the block size, for +example @option{-b}, @option{-m} and @option{--apparent-size}, is ignored. + +@item -k +@opindex -k +@cindex kibibytes for file sizes +Print sizes in 1024-byte blocks, overriding the default block size +(@pxref{Block size}). +This option is equivalent to @option{--block-size=1K}. + +@item -L +@itemx --dereference +@opindex -L +@opindex --dereference +@cindex symbolic links, dereferencing in @command{du} +Dereference symbolic links (show the file system space used by the file +or directory that the link points to instead of the space used by +the link). + +@item -l +@itemx --count-links +@opindex -l +@opindex --count-links +@cindex hard links, counting in @command{du} +Count the size of all files, even if they have appeared already (as a +hard link). + +@item -m +@opindex -m +@cindex mebibytes for file sizes +Print sizes in 1,048,576-byte blocks, overriding the default block size +(@pxref{Block size}). +This option is equivalent to @option{--block-size=1M}. + +@item -P +@itemx --no-dereference +@opindex -P +@opindex --no-dereference +@cindex symbolic links, dereferencing in @command{du} +For each symbolic link encountered by @command{du}, +consider the file system space used by the symbolic link itself. + +@item -S +@itemx --separate-dirs +@opindex -S +@opindex --separate-dirs +Normally, in the output of @command{du} (when not using @option{--summarize}), +the size listed next to a directory name, @var{d}, represents the sum +of sizes of all entries beneath @var{d} as well as the size of @var{d} itself. +With @option{--separate-dirs}, the size reported for a directory name, +@var{d}, will exclude the size of any subdirectories. + +@optSi + +@item -s +@itemx --summarize +@opindex -s +@opindex --summarize +Display only a total for each argument. + +@item -t @var{size} +@itemx --threshold=@var{size} +@opindex -t +@opindex --threshold +Exclude entries based on a given @var{size}. The @var{size} refers to used +blocks in normal mode (@pxref{Block size}), or inodes count in conjunction +with the @option{--inodes} option. + +If @var{size} is positive, then @command{du} will only print entries with a size +greater than or equal to that. + +If @var{size} is negative, then @command{du} will only print entries with a size +smaller than or equal to that. + +Although GNU @command{find} can be used to find files of a certain size, +@command{du}'s @option{--threshold} option can be used to also filter +directories based on a given size. + +When combined with the @option{--apparent-size} option, the +@option{--threshold} option elides entries based on apparent size. +When combined with the @option{--inodes} option, it elides entries +based on inode counts. + +Here's how you would use @option{--threshold} to find directories with a size +greater than or equal to 200 megabytes: + +@example +du --threshold=200MB +@end example + +Here's how you would use @option{--threshold} to find directories and +files -- note the @option{-a} -- with an apparent size smaller than or +equal to 500 bytes: + +@example +du -a -t -500 --apparent-size +@end example + +Here's how you would use @option{--threshold} to find directories on the root +file system with more than 20000 inodes used in the directory tree below: + +@example +du --inodes -x --threshold=20000 / +@end example + + +@item --time +@opindex --time +@cindex last modified dates, displaying in @command{du} +Show the most recent modification timestamp (mtime) of any file in the +directory, or any of its subdirectories. @xref{File timestamps}. + +@item --time=ctime +@itemx --time=status +@itemx --time=use +@opindex --time +@opindex ctime@r{, show the most recent} +@opindex status time@r{, show the most recent} +@opindex use time@r{, show the most recent} +Show the most recent status change timestamp (ctime) of any file in +the directory, or any of its subdirectories. @xref{File timestamps}. + +@item --time=atime +@itemx --time=access +@opindex --time +@opindex atime@r{, show the most recent} +@opindex access timestamp@r{, show the most recent} +Show the most recent access timestamp (atime) of any file in the +directory, or any of its subdirectories. @xref{File timestamps}. + +@item --time-style=@var{style} +@opindex --time-style +@cindex time style +List timestamps in style @var{style}. This option has an effect only if +the @option{--time} option is also specified. The @var{style} should +be one of the following: + +@table @samp +@item +@var{format} +@vindex LC_TIME +List timestamps using @var{format}, where @var{format} is interpreted +like the format argument of @command{date} (@pxref{date invocation}). +For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes +@command{du} to list timestamps like @samp{2020-07-21 23:45:56}. As +with @command{date}, @var{format}'s interpretation is affected by the +@env{LC_TIME} locale category. + +@item full-iso +List timestamps in full using ISO 8601-like date, time, and time zone +components with nanosecond precision, e.g., @samp{2020-07-21 +23:45:56.477817180 -0400}. This style is equivalent to +@samp{+%Y-%m-%d %H:%M:%S.%N %z}. + +@item long-iso +List ISO 8601 date and time components with minute precision, e.g., +@samp{2020-07-21 23:45}. These timestamps are shorter than +@samp{full-iso} timestamps, and are usually good enough for everyday +work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}. + +@item iso +List ISO 8601 dates for timestamps, e.g., @samp{2020-07-21}. +This style is equivalent to @samp{+%Y-%m-%d}. +@end table + +@vindex TIME_STYLE +You can specify the default value of the @option{--time-style} option +with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set +the default style is @samp{long-iso}. For compatibility with @command{ls}, +if @env{TIME_STYLE} begins with @samp{+} and contains a newline, +the newline and any later characters are ignored; if @env{TIME_STYLE} +begins with @samp{posix-} the @samp{posix-} is ignored; and if +@env{TIME_STYLE} is @samp{locale} it is ignored. + +@item -X @var{file} +@itemx --exclude-from=@var{file} +@opindex -X @var{file} +@opindex --exclude-from=@var{file} +@cindex excluding files from @command{du} +Like @option{--exclude}, except take the patterns to exclude from @var{file}, +one per line. If @var{file} is @samp{-}, take the patterns from standard +input. + +@item --exclude=@var{pattern} +@opindex --exclude=@var{pattern} +@cindex excluding files from @command{du} +When recursing, skip subdirectories or files matching @var{pattern}. +For example, @code{du --exclude='*.o'} excludes files whose names +end in @samp{.o}. + +@item -x +@itemx --one-file-system +@opindex -x +@opindex --one-file-system +@cindex one file system, restricting @command{du} to +Skip directories that are on different file systems from the one that +the argument being processed is on. + +@end table + +Since @command{du} relies on information reported by the operating +system, its output might not reflect the space consumed in the +underlying devices. For example; + +@itemize @bullet +@item +Operating systems normally do not report device space consumed by +duplicate or backup blocks, error correction bits, and so forth. +This causes @command{du} to underestimate the device space actually used. + +@item +@cindex copy-on-write and @command{du} +In file systems that use copy-on-write, if two distinct files share +space the output of @command{du} typically counts the space that would +be consumed if all files' non-holes were rewritten, not the space +currently consumed. + +@item +@cindex compression and @command{du} +In file systems that use compression, the operating system might +report the uncompressed space. (If it does report the compressed space, +that report might change after one merely overwrites existing file data.) + +@item +@cindex networked file systems and @command{du} +Networked file systems historically have had difficulty communicating +accurate file system information from server to client. +@end itemize + +@noindent +For these reasons @command{du} might better be thought of as an +estimate of the size of a @command{tar} or other conventional backup +for a set of files, rather than as a measure of space consumed in the +underlying devices. + +@exitstatus + + +@node stat invocation +@section @command{stat}: Report file or file system status + +@pindex stat +@cindex file status +@cindex file system status + +@command{stat} displays information about the specified file(s). Synopsis: + +@example +stat [@var{option}]@dots{} [@var{file}]@dots{} +@end example + +With no option, @command{stat} reports all information about the given files. +But it also can be used to report the information of the file systems the +given files are located on. If the files are links, @command{stat} can +also give information about the files the links point to. + +@mayConflictWithShellBuiltIn{stat} + +@table @samp + +@item -L +@itemx --dereference +@opindex -L +@opindex --dereference +@cindex symbolic links, dereferencing in @command{stat} +Change how @command{stat} treats symbolic links. +With this option, @command{stat} acts on the file referenced +by each symbolic link argument. +Without it, @command{stat} acts on any symbolic link argument directly. + +@item -f +@itemx --file-system +@opindex -f +@opindex --file-system +@cindex file systems +Report information about the file systems where the given files are located +instead of information about the files themselves. +This option implies the @option{-L} option. + +@item --cached=@var{mode} +@opindex --cached=@var{mode} +@cindex attribute caching +Control how attributes are read from the file system; +if supported by the system. This allows one to +control the trade-off between freshness and efficiency +of attribute access, especially useful with remote file systems. +@var{mode} can be: + +@table @samp +@item always +Always read the already cached attributes if available. + +@item never +Always synchronize with the latest file system attributes. +This also mounts automounted files. + +@item default +Leave the caching behavior to the underlying file system. + +@end table + +@item -c +@itemx --format=@var{format} +@opindex -c +@opindex --format=@var{format} +@cindex output format +Use @var{format} rather than the default format. +@var{format} is automatically newline-terminated, so +running a command like the following with two or more @var{file} +operands produces a line of output for each operand: +@example +$ stat --format=%d:%i / /usr +2050:2 +2057:2 +@end example + +@item --printf=@var{format} +@opindex --printf=@var{format} +@cindex output format +Use @var{format} rather than the default format. +Like @option{--format}, but interpret backslash escapes, +and do not output a mandatory trailing newline. +If you want a newline, include @samp{\n} in the @var{format}. +Here's how you would use @option{--printf} to print the device +and inode numbers of @file{/} and @file{/usr}: +@example +$ stat --printf='%d:%i\n' / /usr +2050:2 +2057:2 +@end example + +@item -t +@itemx --terse +@opindex -t +@opindex --terse +@cindex terse output +Print the information in terse form, suitable for parsing by other programs. + +The output of the following commands are identical and the @option{--format} +also identifies the items printed (in fuller form) in the default format. +Note the format string would include another @samp{%C} at the end with an +active SELinux security context. +@example +$ stat --format="%n %s %b %f %u %g %D %i %h %t %T %X %Y %Z %W %o" ... +$ stat --terse ... +@end example + +The same illustrating terse output in @option{--file-system} mode: +@example +$ stat -f --format="%n %i %l %t %s %S %b %f %a %c %d" ... +$ stat -f --terse ... +@end example +@end table + +The valid @var{format} directives for files with @option{--format} and +@option{--printf} are: + +@itemize @bullet +@item %a -- Permission bits in octal (note @samp{#} and @samp{0} printf flags) +@item %A -- Permission bits in symbolic form (similar to @command{ls -ld}) +@item %b -- Number of blocks allocated (see @samp{%B}) +@item %B -- The size in bytes of each block reported by @samp{%b} +@item %C -- The SELinux security context of a file, if available +@item %d -- Device number in decimal (st_dev) +@item %D -- Device number in hex (st_dev) +@item %Hd -- Major device number in decimal +@item %Ld -- Minor device number in decimal +@item %f -- Raw mode in hex +@item %F -- File type +@item %g -- Group ID of owner +@item %G -- Group name of owner +@item %h -- Number of hard links +@item %i -- Inode number +@item %m -- Mount point (See note below) +@item %n -- File name +@item %N -- Quoted file name with dereference if symbolic link (see below) +@item %o -- Optimal I/O transfer size hint +@item %s -- Total size, in bytes +@item %r -- Device type in decimal (st_rdev) +@item %R -- Device type in hex (st_rdev) +@item %Hr -- Major device type in decimal (see below) +@item %Lr -- Minor device type in decimal (see below) +@item %t -- Major device type in hex (see below) +@item %T -- Minor device type in hex (see below) +@item %u -- User ID of owner +@item %U -- User name of owner +@item %w -- Time of file birth, or @samp{-} if unknown +@item %W -- Time of file birth as seconds since Epoch, or @samp{0} +@item %x -- Time of last access +@item %X -- Time of last access as seconds since Epoch +@item %y -- Time of last data modification +@item %Y -- Time of last data modification as seconds since Epoch +@item %z -- Time of last status change +@item %Z -- Time of last status change as seconds since Epoch +@end itemize + +The @samp{%a} format prints the octal mode, and so it is useful +to control the zero padding of the output with the @samp{#} and @samp{0} +printf flags. For example to pad to at least 3 wide while making larger +numbers unambiguously octal, you can use @samp{%#03a}. + +The @samp{%N} format can be set with the environment variable +@env{QUOTING_STYLE}@. If that environment variable is not set, +the default value is @samp{shell-escape-always}. Valid quoting styles are: +@quotingStyles + +The @samp{r}, @samp{R}, @samp{%t}, and @samp{%T} formats operate on the st_rdev +member of the stat(2) structure, i.e., the represented device rather than +the containing device, and so are only defined for character and block +special files. On some systems or file types, st_rdev may be used to +represent other quantities. + +The @samp{%W}, @samp{%X}, @samp{%Y}, and @samp{%Z} formats accept a +precision preceded by a period to specify the number of digits to +print after the decimal point. For example, @samp{%.3X} outputs the +access timestamp to millisecond precision. If a period is given but no +precision, @command{stat} uses 9 digits, so @samp{%.X} is equivalent to +@samp{%.9X}@. When discarding excess precision, timestamps are truncated +toward minus infinity. + +@example +zero pad: + $ stat -c '[%015Y]' /usr + [000001288929712] +space align: + $ stat -c '[%15Y]' /usr + [ 1288929712] + $ stat -c '[%-15Y]' /usr + [1288929712 ] +precision: + $ stat -c '[%.3Y]' /usr + [1288929712.114] + $ stat -c '[%.Y]' /usr + [1288929712.114951834] +@end example + +The mount point printed by @samp{%m} is similar to that output +by @command{df}, except that: +@itemize @bullet +@item +stat does not dereference symlinks by default +(unless @option{-L} is specified) +@item +stat does not search for specified device nodes in the +file system list, instead operating on them directly +@item +@cindex bind mount +stat outputs the alias for a bind mounted file, rather than +the initial mount point of its backing device. +One can recursively call stat until there is no change in output, +to get the current base mount point +@end itemize + +When listing file system information (@option{--file-system} (@option{-f})), +you must use a different set of @var{format} directives: + +@itemize @bullet +@item %a -- Free blocks available to non-super-user +@item %b -- Total data blocks in file system +@item %c -- Total file nodes in file system +@item %d -- Free file nodes in file system +@item %f -- Free blocks in file system +@item %i -- File System ID in hex +@item %l -- Maximum length of file names +@item %n -- File name +@item %s -- Block size (for faster transfers) +@item %S -- Fundamental block size (for block counts) +@item %t -- Type in hex +@item %T -- Type in human readable form +@end itemize + +@vindex TZ +Timestamps are listed according to the time zone rules specified by +the @env{TZ} environment variable, or by the system default rules if +@env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone +with @env{TZ}, libc, The GNU C Library Reference Manual}. + +@exitstatus + + +@node sync invocation +@section @command{sync}: Synchronize cached writes to persistent storage + +@pindex sync +@cindex synchronize file system and memory +@cindex Synchronize cached writes to persistent storage + +@command{sync} synchronizes in memory files or file systems to persistent +storage. Synopsis: + +@example +sync [@var{option}] [@var{file}]@dots{} +@end example + +@cindex superblock, writing +@cindex inodes, written buffered +@command{sync} writes any data buffered in memory out to the storage device. +This can +include (but is not limited to) modified superblocks, modified inodes, +and delayed reads and writes. This must be implemented by the kernel; +The @command{sync} program does nothing but exercise the @code{sync}, +@code{syncfs}, @code{fsync}, and @code{fdatasync} system calls. + +@cindex crashes and corruption +The kernel keeps data in memory to avoid doing (relatively slow) device +reads and writes. This improves performance, but if the computer +crashes, data may be lost or the file system corrupted as a +result. The @command{sync} command instructs the kernel to write +data in memory to persistent storage. + +If any argument is specified then only those files will be +synchronized using the fsync(2) syscall by default. + +If at least one file is specified, it is possible to change the +synchronization method with the following options. Also see +@ref{Common options}. + +@table @samp +@item -d +@itemx --data +@opindex --data +Use fdatasync(2) to sync only the data for the file, +and any metadata required to maintain file system consistency. + +@item -f +@itemx --file-system +@opindex --file-system +Synchronize all the I/O waiting for the file systems that contain the file, +using the syscall syncfs(2). Note you would usually @emph{not} specify +this option if passing a device node like @samp{/dev/sda} for example, +as that would sync the containing file system rather than the referenced one. +Note also that depending on the system, passing individual device nodes or files +may have different sync characteristics than using no arguments. +I.e., arguments passed to fsync(2) may provide greater guarantees through +write barriers, than a global sync(2) used when no arguments are provided. +@end table + +@exitstatus + + +@node truncate invocation +@section @command{truncate}: Shrink or extend the size of a file + +@pindex truncate +@cindex truncating, file sizes + +@command{truncate} shrinks or extends the size of each @var{file} to the +specified size. Synopsis: + +@example +truncate @var{option}@dots{} @var{file}@dots{} +@end example + +@cindex files, creating +Any @var{file} that does not exist is created. + +@cindex sparse files, creating +@cindex holes, creating files with +If a @var{file} is larger than the specified size, the extra data is lost. +If a @var{file} is shorter, it is extended and the sparse extended part +(or hole) reads as zero bytes. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -c +@itemx --no-create +@opindex -c +@opindex --no-create +Do not create files that do not exist. + +@item -o +@itemx --io-blocks +@opindex -o +@opindex --io-blocks +Treat @var{size} as number of I/O blocks of the @var{file} rather than bytes. + +@item -r @var{rfile} +@itemx --reference=@var{rfile} +@opindex -r +@opindex --reference +Base the size of each @var{file} on the size of @var{rfile}. + +@item -s @var{size} +@itemx --size=@var{size} +@opindex -s +@opindex --size +Set or adjust the size of each @var{file} according to @var{size}. +@var{size} is in bytes unless @option{--io-blocks} is specified. +@multiplierSuffixesNoBlocks{size} + +@var{size} may also be prefixed by one of the following to adjust +the size of each @var{file} based on its current size: +@example +@samp{+} => extend by +@samp{-} => reduce by +@samp{<} => at most +@samp{>} => at least +@samp{/} => round down to multiple of +@samp{%} => round up to multiple of +@end example + +@end table + +@exitstatus + + +@node Printing text +@chapter Printing text + +@cindex printing text, commands for +@cindex commands for printing text + +This section describes commands that display text strings. + +@menu +* echo invocation:: Print a line of text. +* printf invocation:: Format and print data. +* yes invocation:: Print a string until interrupted. +@end menu + + +@node echo invocation +@section @command{echo}: Print a line of text + +@pindex echo +@cindex displaying text +@cindex printing text +@cindex text, displaying +@cindex arbitrary text, displaying + +@command{echo} writes each given @var{string} to standard output, with a +space between each and a newline after the last one. Synopsis: + +@example +echo [@var{option}]@dots{} [@var{string}]@dots{} +@end example + +@mayConflictWithShellBuiltIn{echo} + +Due to historical and backwards compatibility reasons, certain bare option-like +strings cannot be passed to @command{echo} as non-option arguments. +It is therefore not advisable to use @command{echo} for printing unknown or +variable arguments. The @command{printf} command is recommended as a more +portable and flexible replacement for tasks historically performed by +@command{echo}. @xref{printf invocation}. + +The program accepts the following options. Also see @ref{Common options}. +Options must precede operands, and the normally-special argument +@samp{--} has no special meaning and is treated like any other +@var{string}. + +@table @samp +@item -n +@opindex -n +Do not output the trailing newline. + +@item -e +@opindex -e +@cindex backslash escapes +Enable interpretation of the following backslash-escaped characters in +each @var{string}: + +@table @samp +@item \a +alert (bell) +@item \b +backspace +@item \c +produce no further output +@item \e +escape +@item \f +form feed +@item \n +newline +@item \r +carriage return +@item \t +horizontal tab +@item \v +vertical tab +@item \\ +backslash +@item \0@var{nnn} +the eight-bit value that is the octal number @var{nnn} +(zero to three octal digits), if @var{nnn} is +a nine-bit value, the ninth bit is ignored +@item \@var{nnn} +the eight-bit value that is the octal number @var{nnn} +(one to three octal digits), if @var{nnn} is +a nine-bit value, the ninth bit is ignored +@item \x@var{hh} +the eight-bit value that is the hexadecimal number @var{hh} +(one or two hexadecimal digits) +@end table + +@item -E +@opindex -E +@cindex backslash escapes +Disable interpretation of backslash escapes in each @var{string}. +This is the default. If @option{-e} and @option{-E} are both +specified, the last one given takes effect. + +@end table + +@vindex POSIXLY_CORRECT +If the @env{POSIXLY_CORRECT} environment variable is set, then when +@command{echo}'s first argument is not @option{-n} it outputs +option-like arguments instead of treating them as options. For +example, @code{echo -ne hello} outputs @samp{-ne hello} instead of +plain @samp{hello}. Also backslash escapes are always enabled. +Note to echo the string @samp{-n}, one of the characters +can be escaped in either octal or hexadecimal representation. +For example, @code{echo -e '\x2dn'}. + +POSIX does not require support for any options, and says +that the behavior of @command{echo} is implementation-defined if any +@var{string} contains a backslash or if the first argument is @option{-n}. +Portable programs should use the @command{printf} command instead. +@xref{printf invocation}. + +@exitstatus + + +@node printf invocation +@section @command{printf}: Format and print data + +@pindex printf +@command{printf} does formatted printing of text. Synopsis: + +@example +printf @var{format} [@var{argument}]@dots{} +@end example + +@command{printf} prints the @var{format} string, interpreting @samp{%} +directives and @samp{\} escapes to format numeric and string arguments +in a way that is mostly similar to the C @samp{printf} function. +@xref{Output Conversion Syntax,, @command{printf} format directives, +libc, The GNU C Library Reference Manual}, for details. +The differences are listed below. + +@mayConflictWithShellBuiltIn{printf} + +@itemize @bullet + +@item +The @var{format} argument is reused as necessary to convert all the +given @var{argument}s. For example, the command @samp{printf %s a b} +outputs @samp{ab}. + +@item +Missing @var{argument}s are treated as null strings or as zeros, +depending on whether the context expects a string or a number. For +example, the command @samp{printf %sx%d} prints @samp{x0}. + +@item +@kindex \c +An additional escape, @samp{\c}, causes @command{printf} to produce no +further output. For example, the command @samp{printf 'A%sC\cD%sF' B +E} prints @samp{ABC}. + +@item +The hexadecimal escape sequence @samp{\x@var{hh}} has at most two +digits, as opposed to C where it can have an unlimited number of +digits. For example, the command @samp{printf '\x07e'} prints two +bytes, whereas the C statement @samp{printf ("\x07e")} prints just +one. + +@item +@kindex %b +An additional directive @samp{%b}, prints its +argument string with @samp{\} escapes interpreted in the same way as in +the @var{format} string, except that octal escapes are of the form +@samp{\0@var{ooo}} where @var{ooo} is 0 to 3 octal digits. If +@samp{\@var{ooo}} is nine-bit value, ignore the ninth bit. +If a precision is also given, it limits the number of bytes printed +from the converted string. + +@item +@kindex %q +An additional directive @samp{%q}, prints its argument string +in a format that can be reused as input by most shells. +Non-printable characters are escaped with the POSIX proposed @samp{$''} syntax, +and shell metacharacters are quoted appropriately. +This is an equivalent format to @command{ls --quoting=shell-escape} output. + +@item +Numeric arguments must be single C constants, possibly with leading +@samp{+} or @samp{-}. For example, @samp{printf %.4d -3} outputs +@samp{-0003}. + +@item +@vindex POSIXLY_CORRECT +If the leading character of a numeric argument is @samp{"} or @samp{'} +then its value is the numeric value of the immediately following +character. Any remaining characters are silently ignored if the +@env{POSIXLY_CORRECT} environment variable is set; otherwise, a +warning is printed. For example, @samp{printf "%d" "'a"} outputs +@samp{97} on hosts that use the ASCII character set, since +@samp{a} has the numeric value 97 in ASCII. + +@end itemize + +@vindex LC_NUMERIC +A floating point argument is interpreted according to +the @env{LC_NUMERIC} category of either the current or the C locale, +and is printed according to the current locale. +For example, in a locale whose decimal point character is a comma, +the command @samp{printf '%g %g' 2,5 2.5} outputs @samp{2,5 2,5}. +@xref{Floating point}. + +@kindex \@var{ooo} +@kindex \x@var{hh} +@command{printf} interprets @samp{\@var{ooo}} in @var{format} as an octal number +(if @var{ooo} is 1 to 3 octal digits) specifying a byte to print, +and @samp{\x@var{hh}} as a hexadecimal number (if @var{hh} is 1 to 2 hex +digits) specifying a character to print. +Note however that when @samp{\@var{ooo}} specifies a number larger than 255, +@command{printf} ignores the ninth bit. +For example, @samp{printf '\400'} is equivalent to @samp{printf '\0'}. + +@kindex \uhhhh +@kindex \Uhhhhhhhh +@cindex Unicode +@cindex ISO/IEC 10646 +@vindex LC_CTYPE +@command{printf} interprets two syntax forms for specifying Unicode +(ISO/IEC 10646) characters. +@samp{\u} for 16-bit Unicode characters, specified as +four hexadecimal digits @var{hhhh}, and @samp{\U} for 32-bit Unicode +characters, specified as eight hexadecimal digits @var{hhhhhhhh}. +@command{printf} outputs the Unicode characters +according to the @env{LC_CTYPE} locale. Unicode characters in the range +U+D800@dots{}U+DFFF cannot be specified by this syntax. +This syntax fully supports the universal character subset +introduced in ISO C 99. + +The processing of @samp{\u} and @samp{\U} requires a full-featured +@code{iconv} facility. It is activated on systems with glibc 2.2 (or newer), +or when @code{libiconv} is installed prior to this package. Otherwise +@samp{\u} and @samp{\U} will print as-is. + +Unicode character syntax is useful for writing strings in a locale +independent way. For example, a string containing the Euro currency symbol + +@example +$ env printf '\u20AC 14.95' +@end example + +@noindent +will be output correctly in all locales supporting the Euro symbol +(ISO-8859-15, UTF-8, and others). Similarly, a Chinese string + +@example +$ env printf '\u4e2d\u6587' +@end example + +@noindent +will be output correctly in all Chinese locales (GB2312, BIG5, UTF-8, etc). + +Note that in these examples, the @command{printf} command has been +invoked via @command{env} to ensure that we run the program found via +your shell's search path, and not a shell alias or a built-in function. + +For larger strings, you don't need to look up the hexadecimal code +values of each character one by one. ASCII characters mixed with \u +escape sequences is also known as the JAVA source file encoding. You can +use GNU recode 3.5c (or newer) to convert strings to this encoding. Here +is how to convert a piece of text into a shell script which will output +this text in a locale-independent way: + +@example +$ LC_CTYPE=zh_TW.big5 env printf \ + '\u4e2d\u6587\n' > sample.txt +$ recode BIG5..JAVA < sample.txt \ + | sed -e "s|^|env printf '|" -e "s|%|%%|g" -e "s|$|\\\\n'|" \ + > sample.sh +@end example + +The only options are a lone @option{--help} or +@option{--version}. @xref{Common options}. +Options must precede operands. + +@exitstatus + + +@node yes invocation +@section @command{yes}: Print a string until interrupted + +@pindex yes +@cindex repeated output of a string + +@command{yes} prints the command line arguments, separated by spaces and +followed by a newline, forever until it is killed. If no arguments are +given, it prints @samp{y} followed by a newline forever until killed. + +Upon a write error, @command{yes} exits with status @samp{1}. + +The only options are a lone @option{--help} or @option{--version}. +To output an argument that begins with +@samp{-}, precede it with @option{--}, e.g., @samp{yes -- --help}. +@xref{Common options}. + + +@node Conditions +@chapter Conditions + +@cindex conditions +@cindex commands for exit status +@cindex exit status commands + +This section describes commands that are primarily useful for their exit +status, rather than their output. Thus, they are often used as the +condition of shell @code{if} statements, or as the last command in a +pipeline. + +@menu +* false invocation:: Do nothing, unsuccessfully. +* true invocation:: Do nothing, successfully. +* test invocation:: Check file types and compare values. +* expr invocation:: Evaluate expressions. +@end menu + + +@node false invocation +@section @command{false}: Do nothing, unsuccessfully + +@pindex false +@cindex do nothing, unsuccessfully +@cindex failure exit status +@cindex exit status of @command{false} + +@command{false} does nothing except return an exit status of 1, meaning +@dfn{failure}. It can be used as a place holder in shell scripts +where an unsuccessful command is needed. +In most modern shells, @command{false} is a built-in command, so when +you use @samp{false} in a script, you're probably using the built-in +command, not the one documented here. + +@command{false} honors the @option{--help} and @option{--version} options. + +This version of @command{false} is implemented as a C program, and is thus +more secure and faster than a shell script implementation, and may safely +be used as a dummy shell for the purpose of disabling accounts. + +Note that @command{false} (unlike all other programs documented herein) +exits unsuccessfully, even when invoked with +@option{--help} or @option{--version}. + +Portable programs should not assume that the exit status of +@command{false} is 1, as it is greater than 1 on some +non-GNU hosts. + + +@node true invocation +@section @command{true}: Do nothing, successfully + +@pindex true +@cindex do nothing, successfully +@cindex no-op +@cindex successful exit +@cindex exit status of @command{true} + +@command{true} does nothing except return an exit status of 0, meaning +@dfn{success}. It can be used as a place holder in shell scripts +where a successful command is needed, although the shell built-in +command @code{:} (colon) may do the same thing faster. +In most modern shells, @command{true} is a built-in command, so when +you use @samp{true} in a script, you're probably using the built-in +command, not the one documented here. + +@command{true} honors the @option{--help} and @option{--version} options. + +Note, however, that it is possible to cause @command{true} +to exit with nonzero status: with the @option{--help} or @option{--version} +option, and with standard +output already closed or redirected to a file that evokes an I/O error. +For example, using a Bourne-compatible shell: + +@example +$ ./true --version >&- +./true: write error: Bad file number +$ ./true --version > /dev/full +./true: write error: No space left on device +@end example + +This version of @command{true} is implemented as a C program, and is thus +more secure and faster than a shell script implementation, and may safely +be used as a dummy shell for the purpose of disabling accounts. + +@node test invocation +@section @command{test}: Check file types and compare values + +@pindex test +@cindex check file types +@cindex compare values +@cindex expression evaluation + +@command{test} returns a status of 0 (true) or 1 (false) depending on the +evaluation of the conditional expression @var{expr}. Each part of the +expression must be a separate argument. + +@command{test} has file status checks, string operators, and numeric +comparison operators. + +@command{test} has an alternate form that uses opening and closing +square brackets instead a leading @samp{test}. For example, instead +of @samp{test -d /}, you can write @samp{[ -d / ]}. The square +brackets must be separate arguments; for example, @samp{[-d /]} does +not have the desired effect. Since @samp{test @var{expr}} and @samp{[ +@var{expr} ]} have the same meaning, only the former form is discussed +below. + +Synopses: + +@example +test @var{expression} +test +[ @var{expression} ] +[ ] +[ @var{option} +@end example + +@mayConflictWithShellBuiltIn{test} + +If @var{expression} is omitted, @command{test} returns false. +If @var{expression} is a single argument, +@command{test} returns false if the argument is null and true +otherwise. The argument +can be any string, including strings like @samp{-d}, @samp{-1}, +@samp{--}, @samp{--help}, and @samp{--version} that most other +programs would treat as options. To get help and version information, +invoke the commands @samp{[ --help} and @samp{[ --version}, without +the usual closing brackets. @xref{Common options}. + +@cindex exit status of @command{test} +Exit status: + +@display +0 if the expression is true, +1 if the expression is false, +2 if an error occurred. +@end display + +@menu +* File type tests:: @code{-[bcdfhLpSt]} +* Access permission tests:: @code{-[gkruwxOG]} +* File characteristic tests:: @code{-e -s -nt -ot -ef} +* String tests:: @code{-z -n = == !=} +* Numeric tests:: @code{-eq -ne -lt -le -gt -ge} +* Connectives for test:: @code{! -a -o} +@end menu + + +@node File type tests +@subsection File type tests + +@cindex file type tests + +These options test for particular types of files. (Everything's a file, +but not all files are the same!) + +@table @samp + +@item -b @var{file} +@opindex -b +@cindex block special check +True if @var{file} exists and is a block special device. + +@item -c @var{file} +@opindex -c +@cindex character special check +True if @var{file} exists and is a character special device. + +@item -d @var{file} +@opindex -d +@cindex directory check +True if @var{file} exists and is a directory. + +@item -f @var{file} +@opindex -f +@cindex regular file check +True if @var{file} exists and is a regular file. + +@item -h @var{file} +@itemx -L @var{file} +@opindex -L +@opindex -h +@cindex symbolic link check +True if @var{file} exists and is a symbolic link. +Unlike all other file-related tests, this test does not dereference +@var{file} if it is a symbolic link. + +@item -p @var{file} +@opindex -p +@cindex named pipe check +True if @var{file} exists and is a named pipe. + +@item -S @var{file} +@opindex -S +@cindex socket check +True if @var{file} exists and is a socket. + +@item -t @var{fd} +@opindex -t +@cindex terminal check +True if @var{fd} is a file descriptor that is associated with a +terminal. + +@end table + + +@node Access permission tests +@subsection Access permission tests + +@cindex access permission tests +@cindex permission tests + +These options test for particular access permissions. + +@table @samp + +@item -g @var{file} +@opindex -g +@cindex set-group-ID check +True if @var{file} exists and has its set-group-ID bit set. + +@item -k @var{file} +@opindex -k +@cindex sticky bit check +True if @var{file} exists and has its @dfn{sticky} bit set. + +@item -r @var{file} +@opindex -r +@cindex readable file check +True if @var{file} exists and the user has read access. + +@item -u @var{file} +@opindex -u +@cindex set-user-ID check +True if @var{file} exists and has its set-user-ID bit set. + +@item -w @var{file} +@opindex -w +@cindex writable file check +True if @var{file} exists and the user has write access. + +@item -x @var{file} +@opindex -x +@cindex executable file check +True if @var{file} exists and the user has execute access +(or search permission, if it is a directory). + +@item -O @var{file} +@opindex -O +@cindex owned by effective user ID check +True if @var{file} exists and is owned by the current effective user ID. + +@item -G @var{file} +@opindex -G +@cindex owned by effective group ID check +True if @var{file} exists and is owned by the current effective group ID. + +@end table + +@node File characteristic tests +@subsection File characteristic tests + +@cindex file characteristic tests + +These options test other file characteristics. + +@table @samp + +@item -e @var{file} +@opindex -e +@cindex existence-of-file check +True if @var{file} exists. + +@item -s @var{file} +@opindex -s +@cindex nonempty file check +True if @var{file} exists and has a size greater than zero. + +@item @var{file1} -nt @var{file2} +@opindex -nt +@cindex newer-than file check +True if @var{file1} is newer (according to modification date) than +@var{file2}, or if @var{file1} exists and @var{file2} does not. + +@item @var{file1} -ot @var{file2} +@opindex -ot +@cindex older-than file check +True if @var{file1} is older (according to modification date) than +@var{file2}, or if @var{file2} exists and @var{file1} does not. + +@item @var{file1} -ef @var{file2} +@opindex -ef +@cindex same file check +@cindex hard link check +True if @var{file1} and @var{file2} have the same device and inode +numbers, i.e., if they are hard links to each other. + +@item -N @var{file} +@opindex -N +@cindex mtime-greater-atime file check +True if @var{file} exists and has been modified (mtime) since it was +last read (atime). + +@end table + + +@node String tests +@subsection String tests + +@cindex string tests + +These options test string characteristics. You may need to quote +@var{string} arguments for the shell. For example: + +@example +test -n "$V" +@end example + +The quotes here prevent the wrong arguments from being passed to +@command{test} if @samp{$V} is empty or contains special characters. + +@table @samp + +@item -z @var{string} +@opindex -z +@cindex zero-length string check +True if the length of @var{string} is zero. + +@item -n @var{string} +@itemx @var{string} +@opindex -n +@cindex nonzero-length string check +True if the length of @var{string} is nonzero. + +@item @var{string1} = @var{string2} +@opindex = +@cindex equal string check +True if the strings are equal. + +@item @var{string1} == @var{string2} +@opindex == +@cindex equal string check +True if the strings are equal (synonym for =). +Note this form is not as portable to other +shells and systems. + +@item @var{string1} != @var{string2} +@opindex != +@cindex not-equal string check +True if the strings are not equal. + +@end table + + +@node Numeric tests +@subsection Numeric tests + +@cindex numeric tests +@cindex arithmetic tests + +Numeric relational operators. The arguments must be entirely numeric +(possibly negative), or the special expression @w{@code{-l @var{string}}}, +which evaluates to the length of @var{string}. + +@table @samp + +@item @var{arg1} -eq @var{arg2} +@itemx @var{arg1} -ne @var{arg2} +@itemx @var{arg1} -lt @var{arg2} +@itemx @var{arg1} -le @var{arg2} +@itemx @var{arg1} -gt @var{arg2} +@itemx @var{arg1} -ge @var{arg2} +@opindex -eq +@opindex -ne +@opindex -lt +@opindex -le +@opindex -gt +@opindex -ge +These arithmetic binary operators return true if @var{arg1} is equal, +not-equal, less-than, less-than-or-equal, greater-than, or +greater-than-or-equal than @var{arg2}, respectively. + +@end table + +For example: + +@example +test -1 -gt -2 && echo yes +@result{} yes +test -l abc -gt 1 && echo yes +@result{} yes +test 0x100 -eq 1 +@error{} test: integer expression expected before -eq +@end example + + +@node Connectives for test +@subsection Connectives for @command{test} + +@cindex logical connectives +@cindex connectives, logical + +Note it's preferred to use shell logical primitives +rather than these logical connectives internal to @command{test}, +because an expression may become ambiguous +depending on the expansion of its parameters. + +For example, this becomes ambiguous when @samp{$1} +is set to @samp{'!'} and @samp{$2} to the empty string @samp{''}: + +@example +test "$1" -a "$2" +@end example + +and should be written as: + +@example +test "$1" && test "$2" +@end example + +Note the shell logical primitives also benefit from +short circuit operation, which can be significant +for file attribute tests. + +@table @samp + +@item ! @var{expr} +@opindex ! +True if @var{expr} is false. +@samp{!} has lower precedence than all parts of @var{expr}. +Note @samp{!} needs to be specified to the left +of a binary expression, I.e., @samp{'!' 1 -gt 2} +rather than @samp{1 '!' -gt 2}. +Also @samp{!} is often a shell special character +and is best used quoted. + + +@item @var{expr1} -a @var{expr2} +@opindex -a +@cindex logical and operator +@cindex and operator +True if both @var{expr1} and @var{expr2} are true. +@samp{-a} is left associative, +and has a higher precedence than @samp{-o}. + +@item @var{expr1} -o @var{expr2} +@opindex -o +@cindex logical or operator +@cindex or operator +True if either @var{expr1} or @var{expr2} is true. +@samp{-o} is left associative. + +@end table + + +@node expr invocation +@section @command{expr}: Evaluate expressions + +@pindex expr +@cindex expression evaluation +@cindex evaluation of expressions + +@command{expr} evaluates an expression and writes the result on standard +output. Each token of the expression must be a separate argument. + +Operands are either integers or strings. Integers consist of one or +more decimal digits, with an optional leading @samp{-}. +@command{expr} converts +anything appearing in an operand position to an integer or a string +depending on the operation being applied to it. + +Strings are not quoted for @command{expr} itself, though you may need to +quote them to protect characters with special meaning to the shell, +e.g., spaces. However, regardless of whether it is quoted, a string +operand should not be a parenthesis or any of @command{expr}'s +operators like @code{+}, so you cannot safely pass an arbitrary string +@code{$str} to expr merely by quoting it to the shell. One way to +work around this is to use the GNU extension @code{+}, +(e.g., @code{+ "$str" = foo}); a more portable way is to use +@code{@w{" $str"}} and to adjust the rest of the expression to take +the leading space into account (e.g., @code{@w{" $str" = " foo"}}). + +You should not pass a negative integer or a string with leading +@samp{-} as @command{expr}'s first argument, as it might be +misinterpreted as an option; this can be avoided by parenthesization. +Also, portable scripts should not use a string operand that happens to +take the form of an integer; this can be worked around by inserting +leading spaces as mentioned above. + +@cindex parentheses for grouping +Operators may be given as infix symbols or prefix keywords. Parentheses +may be used for grouping in the usual manner. You must quote +parentheses and many operators to avoid the shell evaluating them, +however. + +Because @command{expr} uses multiple-precision arithmetic, it works +with integers wider than those of machine registers. + +The only options are @option{--help} and @option{--version}. @xref{Common +options}. Options must precede operands. + +@cindex exit status of @command{expr} +Exit status: + +@display +0 if the expression is neither null nor 0, +1 if the expression is null or 0, +2 if the expression is invalid, +3 if an internal error occurred (e.g., arithmetic overflow). +@end display + +@menu +* String expressions:: @code{+ : match substr index length} +* Numeric expressions:: @code{+ - * / %} +* Relations for expr:: @code{| & < <= = == != >= >} +* Examples of expr:: Examples. +@end menu + + +@node String expressions +@subsection String expressions + +@cindex string expressions +@cindex expressions, string + +@command{expr} supports pattern matching and other string operators. These +have higher precedence than both the numeric and relational operators (in +the next sections). + +@table @samp + +@item @var{string} : @var{regex} +@cindex pattern matching +@cindex regular expression matching +@cindex matching patterns +Perform pattern matching. The arguments are converted to strings and the +second is considered to be a (basic, a la GNU @code{grep}) regular +expression, with a @code{^} implicitly prepended. The first argument is +then matched against this regular expression. + +If @var{regex} does not use @samp{\(} and @samp{\)}, the @code{:} +expression returns the number of characters matched, or 0 if the match +fails. + +If @var{regex} uses @samp{\(} and @samp{\)}, the @code{:} expression +returns the part of @var{string} that matched the subexpression, or +the null string if the match failed or the subexpression did not +contribute to the match. + +@kindex \( @r{regexp operator} +Only the first @samp{\( @dots{} \)} pair is relevant to the return +value; additional pairs are meaningful only for grouping the regular +expression operators. + +@kindex \+ @r{regexp operator} +@kindex \? @r{regexp operator} +@kindex \| @r{regexp operator} +In the regular expression, @code{\+}, @code{\?}, and @code{\|} are +operators which respectively match one or more, zero or one, or separate +alternatives. These operators are GNU extensions. @xref{Regular Expressions,, +Regular Expressions, grep, The GNU Grep Manual}, for details of +regular expression syntax. Some examples are in @ref{Examples of expr}. + +@item match @var{string} @var{regex} +@findex match +An alternative way to do pattern matching. This is the same as +@w{@samp{@var{string} : @var{regex}}}. + +@item substr @var{string} @var{position} @var{length} +@findex substr +Returns the substring of @var{string} beginning at @var{position} +with length at most @var{length}. If either @var{position} or +@var{length} is negative, zero, or non-numeric, returns the null string. + +@item index @var{string} @var{charset} +@findex index +Returns the first position in @var{string} where the first character in +@var{charset} was found. If no character in @var{charset} is found in +@var{string}, return 0. + +@item length @var{string} +@findex length +Returns the length of @var{string}. + +@item + @var{token} +@kindex + +Interpret @var{token} as a string, even if it is a keyword like @var{match} +or an operator like @code{/}. +This makes it possible to test @code{expr length + "$x"} or +@code{expr + "$x" : '.*/\(.\)'} and have it do the right thing even if +the value of @var{$x} happens to be (for example) @code{/} or @code{index}. +This operator is a GNU extension. Portable shell scripts should use +@code{@w{" $token"} : @w{' \(.*\)'}} instead of @code{+ "$token"}. + +@end table + +To make @command{expr} interpret keywords as strings, you must use the +@code{quote} operator. + + +@node Numeric expressions +@subsection Numeric expressions + +@cindex numeric expressions +@cindex expressions, numeric + +@command{expr} supports the usual numeric operators, in order of increasing +precedence. These numeric operators have lower precedence than the +string operators described in the previous section, and higher precedence +than the connectives (next section). + +@table @samp + +@item + - +@kindex + +@kindex - +@cindex addition +@cindex subtraction +Addition and subtraction. Both arguments are converted to integers; +an error occurs if this cannot be done. + +@item * / % +@kindex * +@kindex / +@kindex % +@cindex multiplication +@cindex division +@cindex remainder +Multiplication, division, remainder. Both arguments are converted to +integers; an error occurs if this cannot be done. + +@end table + + +@node Relations for expr +@subsection Relations for @command{expr} + +@cindex connectives, logical +@cindex logical connectives +@cindex relations, numeric or string + +@command{expr} supports the usual logical connectives and relations. These +have lower precedence than the string and numeric operators +(previous sections). Here is the list, lowest-precedence operator first. + +@table @samp + +@item | +@kindex | +@cindex logical or operator +@cindex or operator +Returns its first argument if that is neither null nor zero, otherwise +its second argument if it is neither null nor zero, otherwise 0. It +does not evaluate its second argument if its first argument is neither +null nor zero. + +@item & +@kindex & +@cindex logical and operator +@cindex and operator +Return its first argument if neither argument is null or zero, otherwise +0. It does not evaluate its second argument if its first argument is +null or zero. + +@item < <= = == != >= > +@kindex < +@kindex <= +@kindex = +@kindex == +@kindex > +@kindex >= +@cindex comparison operators +@vindex LC_COLLATE +Compare the arguments and return 1 if the relation is true, 0 otherwise. +@code{==} is a synonym for @code{=}. @command{expr} first tries to convert +both arguments to integers and do a numeric comparison; if either +conversion fails, it does a lexicographic comparison using the character +collating sequence specified by the @env{LC_COLLATE} locale. + +@end table + + +@node Examples of expr +@subsection Examples of using @command{expr} + +@cindex examples of @command{expr} +Here are a few examples, including quoting for shell metacharacters. + +To add 1 to the shell variable @code{foo}, in Bourne-compatible shells: + +@example +foo=$(expr $foo + 1) +@end example + +To print the non-directory part of the file name stored in +@code{$fname}, which need not contain a @code{/}: + +@example +expr $fname : '.*/\(.*\)' '|' $fname +@end example + +An example showing that @code{\+} is an operator: + +@example +expr aaa : 'a\+' +@result{} 3 +@end example + +@example +expr abc : 'a\(.\)c' +@result{} b +expr index abcdef cz +@result{} 3 +expr index index a +@error{} expr: syntax error +expr index + index a +@result{} 0 +@end example + + +@node Redirection +@chapter Redirection + +@cindex redirection +@cindex commands for redirection + +Unix shells commonly provide several forms of @dfn{redirection} -- ways +to change the input source or output destination of a command. But one +useful redirection is performed by a separate command, not by the shell; +it's described here. + +@menu +* tee invocation:: Redirect output to multiple files or processes. +@end menu + + +@node tee invocation +@section @command{tee}: Redirect output to multiple files or processes + +@pindex tee +@cindex pipe fitting +@cindex destinations, multiple output +@cindex read from standard input and write to standard output and files + +The @command{tee} command copies standard input to standard output and also +to any files given as arguments. This is useful when you want not only +to send some data down a pipe, but also to save a copy. Synopsis: + +@example +tee [@var{option}]@dots{} [@var{file}]@dots{} +@end example + +If a file being written to does not already exist, it is created. If a +file being written to already exists, the data it previously contained +is overwritten unless the @option{-a} option is used. + +In previous versions of GNU Coreutils (5.3.0--8.23), +a @var{file} of @samp{-} +caused @command{tee} to send another copy of input to standard output. +However, as the interleaved output was not very useful, @command{tee} now +conforms to POSIX and treats @samp{-} as a file name. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp +@item -a +@itemx --append +@opindex -a +@opindex --append +Append standard input to the given files rather than overwriting +them. + +@item -i +@itemx --ignore-interrupts +@opindex -i +@opindex --ignore-interrupts +Ignore interrupt signals. + +@item -p +@itemx --output-error[=@var{mode}] +@opindex -p +@opindex --output-error +Adjust the behavior with errors on the outputs. +In summary @option{-p} allows @command{tee} to operate in a more +appropriate manner with pipes, and to continue to process data +to any remaining outputs, if any pipe outputs exit early. +The default operation when @option{--output-error} is @emph{not} +specified is to exit immediately on error writing to a pipe, +and diagnose errors writing to a non-pipe. +The long form @option{--output-error} option supports selection +between the following @var{mode}s: + +@table @samp +@item warn +Warn on error opening or writing any output, including pipes. +Writing is continued to still open files/pipes. +Exit status indicates failure if any output has an error. + +@item warn-nopipe +This is the default @var{mode} when not specified, +or when the short form @option{-p} is used. +Warn on error opening or writing any output, except pipes. +Writing is continued to still open files/pipes. +Exit immediately if all remaining outputs become broken pipes. +Exit status indicates failure if any non pipe output had an error. + +@item exit +Exit on error opening or writing any output, including pipes. + +@item exit-nopipe +Exit on error opening or writing any output, except pipes. +Exit immediately if all remaining outputs become broken pipes. +@end table + +@end table + +The @command{tee} command is useful when you happen to be transferring a large +amount of data and also want to summarize that data without reading +it a second time. For example, when you are downloading a DVD image, +you often want to verify its signature or checksum right away. +The inefficient way to do it is simply: + +@example +wget https://example.com/some.iso && sha1sum some.iso +@end example + +One problem with the above is that it makes you wait for the +download to complete before starting the time-consuming SHA1 computation. +Perhaps even more importantly, the above requires reading +the DVD image a second time (the first was from the network). + +The efficient way to do it is to interleave the download +and SHA1 computation. Then, you'll get the checksum for +free, because the entire process parallelizes so well: + +@example +# slightly contrived, to demonstrate process substitution +wget -O - https://example.com/dvd.iso \ + | tee >(sha1sum > dvd.sha1) > dvd.iso +@end example + +That makes @command{tee} write not just to the expected output file, +but also to a pipe running @command{sha1sum} and saving the final +checksum in a file named @file{dvd.sha1}. + +Note, however, that this example relies on a feature of modern shells +called @dfn{process substitution} +(the @samp{>(command)} syntax, above; +@xref{Process Substitution,,Process Substitution, bash, +The Bash Reference Manual}.), +so it works with @command{zsh}, @command{bash}, and @command{ksh}, +but not with @command{/bin/sh}. So if you write code like this +in a shell script, be sure to start the script with @samp{#!/bin/bash}. + +Note also that if any of the process substitutions (or piped standard output) +might exit early without consuming all the data, the @option{-p} option +is needed to allow @command{tee} to continue to process the input +to any remaining outputs. + +Since the above example writes to one file and one process, +a more conventional and portable use of @command{tee} is even better: + +@example +wget -O - https://example.com/dvd.iso \ + | tee dvd.iso | sha1sum > dvd.sha1 +@end example + +You can extend this example to make @command{tee} write to two processes, +computing MD5 and SHA1 checksums in parallel. In this case, +process substitution is required: + +@example +wget -O - https://example.com/dvd.iso \ + | tee >(sha1sum > dvd.sha1) \ + >(md5sum > dvd.md5) \ + > dvd.iso +@end example + +This technique is also useful when you want to make a @emph{compressed} +copy of the contents of a pipe. +Consider a tool to graphically summarize file system usage data from +@samp{du -ak}. +For a large hierarchy, @samp{du -ak} can run for a long time, +and can easily produce terabytes of data, so you won't want to +rerun the command unnecessarily. Nor will you want to save +the uncompressed output. + +Doing it the inefficient way, you can't even start the GUI +until after you've compressed all of the @command{du} output: + +@example +du -ak | gzip -9 > /tmp/du.gz +gzip -d /tmp/du.gz | checkspace -a +@end example + +With @command{tee} and process substitution, you start the GUI +right away and eliminate the decompression completely: + +@example +du -ak | tee >(gzip -9 > /tmp/du.gz) | checkspace -a +@end example + +Finally, if you regularly create more than one type of +compressed tarball at once, for example when @code{make dist} creates +both @command{gzip}-compressed and @command{bzip2}-compressed tarballs, +there may be a better way. +Typical @command{automake}-generated @file{Makefile} rules create +the two compressed tar archives with commands in sequence, like this +(slightly simplified): + +@example +tardir=your-pkg-M.N +tar chof - "$tardir" | gzip -9 -c > your-pkg-M.N.tar.gz +tar chof - "$tardir" | bzip2 -9 -c > your-pkg-M.N.tar.bz2 +@end example + +However, if the hierarchy you are archiving and compressing is larger +than a couple megabytes, and especially if you are using a multi-processor +system with plenty of memory, then you can do much better by reading the +directory contents only once and running the compression programs in parallel: + +@example +tardir=your-pkg-M.N +tar chof - "$tardir" \ + | tee >(gzip -9 -c > your-pkg-M.N.tar.gz) \ + | bzip2 -9 -c > your-pkg-M.N.tar.bz2 +@end example + +If you want to further process the output from process substitutions, +and those processes write atomically (i.e., write less than the system's +PIPE_BUF size at a time), that's possible with a construct like: + +@example +tardir=your-pkg-M.N +tar chof - "$tardir" \ + | tee >(md5sum --tag) > >(sha256sum --tag) \ + | sort | gpg --clearsign > your-pkg-M.N.tar.sig +@end example + +@exitstatus + + +@node File name manipulation +@chapter File name manipulation + +@cindex file name manipulation +@cindex manipulation of file names +@cindex commands for file name manipulation + +This section describes commands that manipulate file names. + +@menu +* basename invocation:: Strip directory and suffix from a file name. +* dirname invocation:: Strip last file name component. +* pathchk invocation:: Check file name validity and portability. +* mktemp invocation:: Create temporary file or directory. +* realpath invocation:: Print resolved file names. +@end menu + + +@node basename invocation +@section @command{basename}: Strip directory and suffix from a file name + +@pindex basename +@cindex strip directory and suffix from file names +@cindex directory, stripping from file names +@cindex suffix, stripping from file names +@cindex file names, stripping directory and suffix +@cindex leading directory components, stripping + +@command{basename} removes any leading directory components from +@var{name}. Synopsis: + +@example +basename @var{name} [@var{suffix}] +basename @var{option}@dots{} @var{name}@dots{} +@end example + +If @var{suffix} is specified and is identical to the end of @var{name}, +it is removed from @var{name} as well. Note that since trailing slashes +are removed prior to suffix matching, @var{suffix} will do nothing if it +contains slashes. @command{basename} prints the result on standard +output. + +@c This test is used both here and in the section on dirname. +@macro basenameAndDirname +Together, @command{basename} and @command{dirname} are designed such +that if @samp{ls "$name"} succeeds, then the command sequence @samp{cd +"$(dirname "$name")"; ls "$(basename "$name")"} will, too. This works +for everything except file names containing a trailing newline. +@end macro +@basenameAndDirname + +POSIX allows the implementation to define the results if +@var{name} is empty or @samp{//}. In the former case, GNU +@command{basename} returns the empty string. In the latter case, the +result is @samp{//} on platforms where @var{//} is distinct from +@var{/}, and @samp{/} on platforms where there is no difference. + +The program accepts the following options. Also see @ref{Common options}. +Options must precede operands. + +@table @samp + +@item -a +@itemx --multiple +@opindex -a +@opindex --multiple +Support more than one argument. Treat every argument as a @var{name}. +With this, an optional @var{suffix} must be specified using the +@option{-s} option. + +@item -s @var{suffix} +@itemx --suffix=@var{suffix} +@opindex -s +@opindex --suffix +Remove a trailing @var{suffix}. +This option implies the @option{-a} option. + +@optZero + +@end table + +@exitstatus + +Examples: + +@example +# Output "sort". +basename /usr/bin/sort + +# Output "stdio". +basename include/stdio.h .h + +# Output "stdio". +basename -s .h include/stdio.h + +# Output "stdio" followed by "stdlib" +basename -a -s .h include/stdio.h include/stdlib.h +@end example + + +@node dirname invocation +@section @command{dirname}: Strip last file name component + +@pindex dirname +@cindex directory components, printing +@cindex stripping non-directory suffix +@cindex non-directory suffix, stripping + +@command{dirname} prints all but the final slash-delimited component +of each @var{name}. Slashes on either side of the final component are +also removed. If the string contains no slash, @command{dirname} +prints @samp{.} (meaning the current directory). Synopsis: + +@example +dirname [@var{option}] @var{name}@dots{} +@end example + +@var{name} need not be a file name, but if it is, this operation +effectively lists the directory that contains the final component, +including the case when the final component is itself a directory. + +@basenameAndDirname + +POSIX allows the implementation to define the results if +@var{name} is @samp{//}. With GNU @command{dirname}, the +result is @samp{//} on platforms where @var{//} is distinct from +@var{/}, and @samp{/} on platforms where there is no difference. + +The program accepts the following option. Also see @ref{Common options}. + +@table @samp + +@optZero + +@end table + +@exitstatus + +Examples: + +@example +# Output "/usr/bin". +dirname /usr/bin/sort +dirname /usr/bin//.// + +# Output "dir1" followed by "dir2" +dirname dir1/str dir2/str + +# Output ".". +dirname stdio.h +@end example + + +@node pathchk invocation +@section @command{pathchk}: Check file name validity and portability + +@pindex pathchk +@cindex file names, checking validity and portability +@cindex valid file names, checking for +@cindex portable file names, checking for + +@command{pathchk} checks validity and portability of file names. Synopsis: + +@example +pathchk [@var{option}]@dots{} @var{name}@dots{} +@end example + +For each @var{name}, @command{pathchk} prints an error message if any of +these conditions is true: + +@enumerate +@item +One of the existing directories in @var{name} does not have search +(execute) permission, +@item +The length of @var{name} is larger than the maximum supported by the +operating system. +@item +The length of one component of @var{name} is longer than +its file system's maximum. +@end enumerate + +A nonexistent @var{name} is not an error, so long as a file with that +name could be created under the above conditions. + +The program accepts the following options. Also see @ref{Common options}. +Options must precede operands. + +@table @samp + +@item -p +@opindex -p +Instead of performing checks based on the underlying file system, +print an error message if any of these conditions is true: + +@enumerate +@item +A file name is empty. + +@item +A file name contains a character outside the POSIX portable file +name character set, namely, the ASCII letters and digits, @samp{.}, +@samp{_}, @samp{-}, and @samp{/}. + +@item +The length of a file name or one of its components exceeds the +POSIX minimum limits for portability. +@end enumerate + +@item -P +@opindex -P +Print an error message if a file name is empty, or if it contains a component +that begins with @samp{-}. + +@item --portability +@opindex --portability +Print an error message if a file name is not portable to all POSIX +hosts. This option is equivalent to @samp{-p -P}. + +@end table + +@cindex exit status of @command{pathchk} +Exit status: + +@display +0 if all specified file names passed all checks, +1 otherwise. +@end display + +@node mktemp invocation +@section @command{mktemp}: Create temporary file or directory + +@pindex mktemp +@cindex file names, creating temporary +@cindex directory, creating temporary +@cindex temporary files and directories + +@command{mktemp} manages the creation of temporary files and +directories. Synopsis: + +@example +mktemp [@var{option}]@dots{} [@var{template}] +@end example + +Safely create a temporary file or directory based on @var{template}, +and print its name. If given, @var{template} must include at least +three consecutive @samp{X}s in the last component. If omitted, the template +@samp{tmp.XXXXXXXXXX} is used, and option @option{--tmpdir} is +implied. The final run of @samp{X}s in the @var{template} will be replaced +by alpha-numeric characters; thus, on a case-sensitive file system, +and with a @var{template} including a run of @var{n} instances of @samp{X}, +there are @samp{62**@var{n}} potential file names. + +Older scripts used to create temporary files by simply joining the +name of the program with the process id (@samp{$$}) as a suffix. +However, that naming scheme is easily predictable, and suffers from a +race condition where the attacker can create an appropriately named +symbolic link, such that when the script then opens a handle to what +it thought was an unused file, it is instead modifying an existing +file. Using the same scheme to create a directory is slightly safer, +since the @command{mkdir} will fail if the target already exists, but +it is still inferior because it allows for denial of service attacks. +Therefore, modern scripts should use the @command{mktemp} command to +guarantee that the generated name will be unpredictable, and that +knowledge of the temporary file name implies that the file was created +by the current script and cannot be modified by other users. + +When creating a file, the resulting file has read and write +permissions for the current user, but no permissions for the group or +others; these permissions are reduced if the current umask is more +restrictive. + +Here are some examples (although note that if you repeat them, you +will most likely get different file names): + +@itemize @bullet + +@item +Create a temporary file in the current directory. +@example +$ mktemp file.XXXX +file.H47c +@end example + +@item +Create a temporary file with a known suffix. +@example +$ mktemp --suffix=.txt file-XXXX +file-H08W.txt +$ mktemp file-XXXX-XXXX.txt +file-XXXX-eI9L.txt +@end example + +@item +Create a secure fifo relative to the user's choice of @env{TMPDIR}, +but falling back to the current directory rather than @file{/tmp}. +Note that @command{mktemp} does not create fifos, but can create a +secure directory in which the fifo can live. Exit the shell if the +directory or fifo could not be created. +@example +$ dir=$(mktemp -p "$@{TMPDIR:-.@}" -d dir-XXXX) || exit 1 +$ fifo=$dir/fifo +$ mkfifo "$fifo" || @{ rmdir "$dir"; exit 1; @} +@end example + +@item +Create and use a temporary file if possible, but ignore failure. The +file will reside in the directory named by @env{TMPDIR}, if specified, +or else in @file{/tmp}. +@example +$ file=$(mktemp -q) && @{ +> # Safe to use $file only within this block. Use quotes, +> # since $TMPDIR, and thus $file, may contain whitespace. +> echo ... > "$file" +> rm "$file" +> @} +@end example + +@item +Act as a semi-random character generator (it is not fully random, +since it is impacted by the contents of the current directory). To +avoid security holes, do not use the resulting names to create a file. +@example +$ mktemp -u XXX +Gb9 +$ mktemp -u XXX +nzC +@end example + +@end itemize + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -d +@itemx --directory +@opindex -d +@opindex --directory +Create a directory rather than a file. The directory will have read, +write, and search permissions for the current user, but no permissions +for the group or others; these permissions are reduced if the current +umask is more restrictive. + +@item -q +@itemx --quiet +@opindex -q +@opindex --quiet +Suppress diagnostics about failure to create a file or directory. The +exit status will still reflect whether a file was created. + +@item -u +@itemx --dry-run +@opindex -u +@opindex --dry-run +Generate a temporary name that does not name an existing file, without +changing the file system contents. Using the output of this command +to create a new file is inherently unsafe, as there is a window of +time between generating the name and using it where another process +can create an object by the same name. + +@item -p @var{dir} +@itemx --tmpdir[=@var{dir}] +@opindex -p +@opindex --tmpdir +Treat @var{template} relative to the directory @var{dir}. If +@var{dir} is not specified (only possible with the long option +@option{--tmpdir}) or is the empty string, use the value of +@env{TMPDIR} if available, otherwise use @samp{/tmp}. If this is +specified, @var{template} must not be absolute. However, +@var{template} can still contain slashes, although intermediate +directories must already exist. + +@item --suffix=@var{suffix} +@opindex --suffix +Append @var{suffix} to the @var{template}. @var{suffix} must not +contain slash. If @option{--suffix} is specified, @var{template} must +end in @samp{X}; if it is not specified, then an appropriate +@option{--suffix} is inferred by finding the last @samp{X} in +@var{template}. This option exists for use with the default +@var{template} and for the creation of a @var{suffix} that starts with +@samp{X}. + +@item -t +@opindex -t +Treat @var{template} as a single file relative to the value of +@env{TMPDIR} if available, or to the directory specified by +@option{-p}, otherwise to @samp{/tmp}. @var{template} must not +contain slashes. This option is deprecated; the use of @option{-p} +without @option{-t} offers better defaults (by favoring the command +line over @env{TMPDIR}) and more flexibility (by allowing intermediate +directories). + +@end table + +@cindex exit status of @command{mktemp} +Exit status: + +@display +0 if the file was created, +1 otherwise. +@end display + + +@node realpath invocation +@section @command{realpath}: Print the resolved file name. + +@pindex realpath +@cindex file names, canonicalization +@cindex symlinks, resolution +@cindex canonical file name +@cindex canonicalize a file name +@pindex realpath +@findex realpath + +@command{realpath} expands all symbolic links and resolves references to +@samp{/./}, @samp{/../} and extra @samp{/} characters. By default, +all but the last component of the specified files must exist. Synopsis: + +@example +realpath [@var{option}]@dots{} @var{file}@dots{} +@end example + +The file name canonicalization functionality overlaps with that of the +@command{readlink} command. This is the preferred command for +canonicalization as it's a more suitable and standard name. In addition +this command supports relative file name processing functionality. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -e +@itemx --canonicalize-existing +@opindex -e +@opindex --canonicalize-existing +Ensure that all components of the specified file names exist. +If any component is missing or unavailable, @command{realpath} will output +a diagnostic unless the @option{-q} option is specified, and exit with a +nonzero exit code. A trailing slash requires that the name resolve to a +directory. + +@item -m +@itemx --canonicalize-missing +@opindex -m +@opindex --canonicalize-missing +If any component of a specified file name is missing or unavailable, +treat it as a directory. + +@item -L +@itemx --logical +@opindex -L +@opindex --logical +Symbolic links are resolved in the specified file names, +but they are resolved after any subsequent @samp{..} components are processed. + +@item -P +@itemx --physical +@opindex -P +@opindex --physical +Symbolic links are resolved in the specified file names, +and they are resolved before any subsequent @samp{..} components are processed. +This is the default mode of operation. + +@item -q +@itemx --quiet +@opindex -q +@opindex --quiet +Suppress diagnostic messages for specified file names. + +@item --relative-to=@var{dir} +@opindex --relative-to +@cindex relpath +Print the resolved file names relative to the specified directory. +Note this option honors the @option{-m} and @option{-e} options +pertaining to file existence. + +@item --relative-base=@var{dir} +@opindex --relative-base +Print the resolved file names as relative @emph{if} the files +are descendants of @var{dir}. +Otherwise, print the resolved file names as absolute. +Note this option honors the @option{-m} and @option{-e} options +pertaining to file existence. +For details about combining @option{--relative-to} and @option{--relative-base}, +@pxref{Realpath usage examples}. + +@item -s +@itemx --strip +@itemx --no-symlinks +@opindex -s +@opindex --strip +@opindex --no-symlinks +Do not resolve symbolic links. Only resolve references to +@samp{/./}, @samp{/../} and remove extra @samp{/} characters. +When combined with the @option{-m} option, realpath operates +only on the file name, and does not touch any actual file. + +@optZero + +@end table + +@cindex exit status of @command{realpath} +Exit status: + +@display +0 if all file names were printed without issue. +1 otherwise. +@end display + +@menu +* Realpath usage examples:: Realpath usage examples. +@end menu + + +@node Realpath usage examples +@subsection Realpath usage examples + +@opindex --relative-to +@opindex --relative-base + +By default, @command{realpath} prints the absolute file name of given files +(symlinks are resolved, @file{words} is resolved to @file{american-english}): + +@example +@group +cd /home/user +realpath /usr/bin/sort /tmp/foo /usr/share/dict/words 1.txt +@result{} /usr/bin/sort +@result{} /tmp/foo +@result{} /usr/share/dict/american-english +@result{} /home/user/1.txt +@end group +@end example + +With @option{--relative-to}, file names are printed relative to +the given directory: + +@example +@group +realpath --relative-to=/usr/bin \ + /usr/bin/sort /tmp/foo /usr/share/dict/words 1.txt +@result{} sort +@result{} ../../tmp/foo +@result{} ../share/dict/american-english +@result{} ../../home/user/1.txt +@end group +@end example + +With @option{--relative-base}, relative file names are printed @emph{if} +the resolved file name is below the given base directory. For files outside the +base directory absolute file names are printed: + +@example +@group +realpath --relative-base=/usr \ + /usr/bin/sort /tmp/foo /usr/share/dict/words 1.txt +@result{} bin/sort +@result{} /tmp/foo +@result{} share/dict/american-english +@result{} /home/user/1.txt +@end group +@end example + +When both @option{--relative-to=DIR1} and @option{--relative-base=DIR2} +are used, file names are printed relative to @var{dir1} @emph{if} they are +located below @var{dir2}. If the files are not below @var{dir2}, they are +printed as absolute file names: + +@example +@group +realpath --relative-to=/usr/bin --relative-base=/usr \ + /usr/bin/sort /tmp/foo /usr/share/dict/words 1.txt +@result{} sort +@result{} /tmp/foo +@result{} ../share/dict/american-english +@result{} /home/user/1.txt +@end group +@end example + +When both @option{--relative-to=DIR1} and @option{--relative-base=DIR2} +are used, @var{dir1} @emph{must} be a subdirectory of @var{dir2}. Otherwise, +@command{realpath} prints absolutes file names. + + +@node Working context +@chapter Working context + +@cindex working context +@cindex commands for printing the working context + +This section describes commands that display or alter the context in +which you are working: the current directory, the terminal settings, and +so forth. See also the user-related commands in the next section. + +@menu +* pwd invocation:: Print working directory. +* stty invocation:: Print or change terminal characteristics. +* printenv invocation:: Print environment variables. +* tty invocation:: Print file name of terminal on standard input. +@end menu + + +@node pwd invocation +@section @command{pwd}: Print working directory + +@pindex pwd +@cindex print name of current directory +@cindex current working directory, printing +@cindex working directory, printing + + +@command{pwd} prints the name of the current directory. Synopsis: + +@example +pwd [@var{option}]@dots{} +@end example + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp +@item -L +@itemx --logical +@opindex -L +@opindex --logical +If the contents of the environment variable @env{PWD} provide an +absolute name of the current directory with no @samp{.} or @samp{..} +components, but possibly with symbolic links, then output those +contents. Otherwise, fall back to default @option{-P} handling. + +@item -P +@itemx --physical +@opindex -P +@opindex --physical +Print a fully resolved name for the current directory. That is, all +components of the printed name will be actual directory names -- none +will be symbolic links. +@end table + +@cindex symbolic links and @command{pwd} +If @option{-L} and @option{-P} are both given, the last one takes +precedence. If neither option is given, then this implementation uses +@option{-P} as the default unless the @env{POSIXLY_CORRECT} +environment variable is set. + +@mayConflictWithShellBuiltIn{pwd} + +@exitstatus + + +@node stty invocation +@section @command{stty}: Print or change terminal characteristics + +@pindex stty +@cindex change or print terminal settings +@cindex terminal settings +@cindex line settings of terminal + +@command{stty} prints or changes terminal characteristics, such as baud rate. +Synopses: + +@example +stty [@var{option}] [@var{setting}]@dots{} +stty [@var{option}] +@end example + +If given no line settings, @command{stty} prints the baud rate, line +discipline number (on systems that support it), and line settings +that have been changed from the values set by @samp{stty sane}. +By default, mode reading and setting are performed on the tty line +connected to standard input, although this can be modified by the +@option{--file} option. + +@command{stty} accepts many non-option arguments that change aspects of +the terminal line operation, as described below. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp +@item -a +@itemx --all +@opindex -a +@opindex --all +Print all current settings in human-readable form. This option may not +be used in combination with any line settings. + +@item -F @var{device} +@itemx --file=@var{device} +@opindex -F +@opindex --file +Set the line opened by the file name specified in @var{device} instead of +the tty line connected to standard input. This option is necessary +because opening a POSIX tty requires use of the +@code{O_NONDELAY} flag to prevent a POSIX tty from blocking +until the carrier detect line is high if +the @code{clocal} flag is not set. Hence, it is not always possible +to allow the shell to open the device in the traditional manner. + +@item -g +@itemx --save +@opindex -g +@opindex --save +@cindex machine-readable @command{stty} output +Print all current settings in a form that can be used as an argument to +another @command{stty} command to restore the current settings. This option +may not be used in combination with any line settings. + +@end table + +Many settings can be turned off by preceding them with a @samp{-}. +Such arguments are marked below with ``May be negated'' in their +description. The descriptions themselves refer to the positive +case, that is, when @emph{not} negated (unless stated otherwise, +of course). + +Some settings are not available on all POSIX systems, since they use +extensions. Such arguments are marked below with +``Non-POSIX'' in their description. On non-POSIX +systems, those or other settings also may not +be available, but it's not feasible to document all the variations: just +try it and see. + +@command{stty} is installed only on platforms with the POSIX terminal +interface, so portable scripts should not rely on its existence on +non-POSIX platforms. + +@exitstatus + +@menu +* Control:: Control settings +* Input:: Input settings +* Output:: Output settings +* Local:: Local settings +* Combination:: Combination settings +* Characters:: Special characters +* Special:: Special settings +@end menu + + +@node Control +@subsection Control settings + +@cindex control settings +Control settings: + +@table @samp +@item parenb +@opindex parenb +@cindex two-way parity +Generate parity bit in output and expect parity bit in input. +May be negated. + +@item parodd +@opindex parodd +@cindex odd parity +@cindex even parity +Set odd parity (even if negated). May be negated. + +@item cmspar +@opindex cmspar +@cindex constant parity +@cindex stick parity +@cindex mark parity +@cindex space parity +Use "stick" (mark/space) parity. If parodd is set, the parity bit is +always 1; if parodd is not set, the parity bit is always zero. +Non-POSIX@. May be negated. + +@item cs5 +@itemx cs6 +@itemx cs7 +@itemx cs8 +@opindex cs@var{n} +@cindex character size +@cindex eight-bit characters +Set character size to 5, 6, 7, or 8 bits. + +@item hup +@itemx hupcl +@opindex hup[cl] +Send a hangup signal when the last process closes the tty. May be +negated. + +@item cstopb +@opindex cstopb +@cindex stop bits +Use two stop bits per character (one if negated). May be negated. + +@item cread +@opindex cread +Allow input to be received. May be negated. + +@item clocal +@opindex clocal +@cindex modem control +Disable modem control signals. May be negated. + +@item crtscts +@opindex crtscts +@cindex hardware flow control +@cindex flow control, hardware +@cindex RTS/CTS flow control +Enable RTS/CTS flow control. Non-POSIX@. May be negated. + +@item cdtrdsr +@opindex cdtrdsr +@cindex hardware flow control +@cindex flow control, hardware +@cindex DTR/DSR flow control +Enable DTR/DSR flow control. Non-POSIX@. May be negated. +@end table + + +@node Input +@subsection Input settings + +@cindex input settings +These settings control operations on data received from the terminal. + +@table @samp +@item ignbrk +@opindex ignbrk +@cindex breaks, ignoring +Ignore break characters. May be negated. + +@item brkint +@opindex brkint +@cindex breaks, cause interrupts +Make breaks cause an interrupt signal. May be negated. + +@item ignpar +@opindex ignpar +@cindex parity, ignoring +Ignore characters with parity errors. May be negated. + +@item parmrk +@opindex parmrk +@cindex parity errors, marking +Mark parity errors (with a 255-0-character sequence). May be negated. + +@item inpck +@opindex inpck +Enable input parity checking. May be negated. + +@item istrip +@opindex istrip +@cindex eight-bit input +Clear high (8th) bit of input characters. May be negated. + +@item inlcr +@opindex inlcr +@cindex newline, translating to return +Translate newline to carriage return. May be negated. + +@item igncr +@opindex igncr +@cindex return, ignoring +Ignore carriage return. May be negated. + +@item icrnl +@opindex icrnl +@cindex return, translating to newline +Translate carriage return to newline. May be negated. + +@item iutf8 +@opindex iutf8 +@cindex input encoding, UTF-8 +Assume input characters are UTF-8 encoded. May be negated. + +@item ixon +@opindex ixon +@kindex C-s/C-q flow control +@cindex XON/XOFF flow control +Enable XON/XOFF flow control (that is, @kbd{Ctrl-S}/@kbd{Ctrl-Q}). May +be negated. + +@item ixoff +@itemx tandem +@opindex ixoff +@opindex tandem +@cindex software flow control +@cindex flow control, software +Enable sending of @code{stop} character when the system input buffer +is almost full, and @code{start} character when it becomes almost +empty again. May be negated. + +@item iuclc +@opindex iuclc +@cindex uppercase, translating to lowercase +Translate uppercase characters to lowercase. Non-POSIX@. May be +negated. Note ilcuc is not implemented, as one would not be able to issue +almost any (lowercase) Unix command, after invoking it. + +@item ixany +@opindex ixany +Allow any character to restart output (only the start character +if negated). Non-POSIX@. May be negated. + +@item imaxbel +@opindex imaxbel +@cindex beeping at input buffer full +Enable beeping and not flushing input buffer if a character arrives +when the input buffer is full. Non-POSIX@. May be negated. +@end table + + +@node Output +@subsection Output settings + +@cindex output settings +These settings control operations on data sent to the terminal. + +@table @samp +@item opost +@opindex opost +Postprocess output. May be negated. + +@item olcuc +@opindex olcuc +@cindex lowercase, translating to output +Translate lowercase characters to uppercase. Non-POSIX@. May be +negated. (Note ouclc is not currently implemented.) + +@item ocrnl +@opindex ocrnl +@cindex return, translating to newline +Translate carriage return to newline. Non-POSIX@. May be negated. + +@item onlcr +@opindex onlcr +@cindex newline, translating to crlf +Translate newline to carriage return-newline. Non-POSIX@. May be +negated. + +@item onocr +@opindex onocr +Do not print carriage returns in the first column. Non-POSIX@. +May be negated. + +@item onlret +@opindex onlret +Newline performs a carriage return. Non-POSIX@. May be negated. + +@item ofill +@opindex ofill +@cindex pad instead of timing for delaying +Use fill (padding) characters instead of timing for delays. +Non-POSIX@. +May be negated. + +@item ofdel +@opindex ofdel +@cindex pad character +Use ASCII DEL characters for fill instead of +ASCII NUL characters. Non-POSIX@. +May be negated. + +@item nl1 +@itemx nl0 +@opindex nl@var{n} +Newline delay style. Non-POSIX. + +@item cr3 +@itemx cr2 +@itemx cr1 +@itemx cr0 +@opindex cr@var{n} +Carriage return delay style. Non-POSIX. + +@item tab3 +@itemx tab2 +@itemx tab1 +@itemx tab0 +@opindex tab@var{n} +Horizontal tab delay style. Non-POSIX. + +@item bs1 +@itemx bs0 +@opindex bs@var{n} +Backspace delay style. Non-POSIX. + +@item vt1 +@itemx vt0 +@opindex vt@var{n} +Vertical tab delay style. Non-POSIX. + +@item ff1 +@itemx ff0 +@opindex ff@var{n} +Form feed delay style. Non-POSIX. +@end table + + +@node Local +@subsection Local settings + +@cindex local settings + +@table @samp +@item isig +@opindex isig +Enable @code{interrupt}, @code{quit}, and @code{suspend} special +characters. May be negated. + +@item icanon +@opindex icanon +Enable @code{erase}, @code{kill}, @code{werase}, and @code{rprnt} +special characters. May be negated. + +@item iexten +@opindex iexten +Enable non-POSIX special characters. May be negated. + +@item echo +@opindex echo +Echo input characters. May be negated. + +@item echoe +@itemx crterase +@opindex echoe +@opindex crterase +Echo @code{erase} characters as backspace-space-backspace. May be +negated. + +@item echok +@opindex echok +@cindex newline echoing after @code{kill} +Echo a newline after a @code{kill} character. May be negated. + +@item echonl +@opindex echonl +@cindex newline, echoing +Echo newline even if not echoing other characters. May be negated. + +@item noflsh +@opindex noflsh +@cindex flushing, disabling +Disable flushing after @code{interrupt} and @code{quit} special +characters. May be negated. + +@item xcase +@opindex xcase +@cindex case translation +Enable input and output of uppercase characters by preceding their +lowercase equivalents with @samp{\}, when @code{icanon} is set. +Non-POSIX@. May be negated. + +@item tostop +@opindex tostop +@cindex background jobs, stopping at terminal write +Stop background jobs that try to write to the terminal. Non-POSIX@. +May be negated. + +@item echoprt +@itemx prterase +@opindex echoprt +@opindex prterase +Echo erased characters backward, between @samp{\} and @samp{/}. +Non-POSIX@. May be negated. + +@item echoctl +@itemx ctlecho +@opindex echoctl +@opindex ctlecho +@cindex control characters, using @samp{^@var{c}} +@cindex hat notation for control characters +Echo control characters in hat notation (@samp{^@var{c}}) instead +of literally. Non-POSIX@. May be negated. + +@item echoke +@itemx crtkill +@opindex echoke +@opindex crtkill +Echo the @code{kill} special character by erasing each character on +the line as indicated by the @code{echoprt} and @code{echoe} settings, +instead of by the @code{echoctl} and @code{echok} settings. +Non-POSIX@. +May be negated. + +@item extproc +@opindex extproc +Enable @samp{LINEMODE}, which is used to avoid echoing +each character over high latency links. See also +@uref{https://tools.ietf.org/search/rfc1116, Internet RFC 1116}. +Non-POSIX@. +May be negated. + +@item flusho +@opindex flusho +Discard output. +Note this setting is currently ignored on GNU/Linux systems. +Non-POSIX@. +May be negated. +@end table + + +@node Combination +@subsection Combination settings + +@cindex combination settings +Combination settings: + +@table @samp +@item evenp +@opindex evenp +@itemx parity +@opindex parity +Same as @code{parenb -parodd cs7}. May be negated. If negated, same +as @code{-parenb cs8}. + +@item oddp +@opindex oddp +Same as @code{parenb parodd cs7}. May be negated. If negated, same +as @code{-parenb cs8}. + +@item nl +@opindex nl +Same as @code{-icrnl -onlcr}. May be negated. If negated, same as +@code{icrnl -inlcr -igncr onlcr -ocrnl -onlret}. + +@item ek +@opindex ek +Reset the @code{erase} and @code{kill} special characters to their default +values. + +@item sane +@opindex sane +Same as: + +@c This is too long to write inline. +@example +cread -ignbrk brkint -inlcr -igncr icrnl +icanon iexten echo echoe echok -echonl -noflsh +-ixoff -iutf8 -iuclc -ixany imaxbel -xcase -olcuc -ocrnl +opost -ofill onlcr -onocr -onlret nl0 cr0 tab0 bs0 vt0 ff0 +isig -tostop -ofdel -echoprt echoctl echoke -extproc +@end example + +@noindent +and also sets all special characters to their default values. + +@item cooked +@opindex cooked +Same as @code{brkint ignpar istrip icrnl ixon opost isig icanon}, plus +sets the @code{eof} and @code{eol} characters to their default values +if they are the same as the @code{min} and @code{time} characters. +May be negated. If negated, same as @code{raw}. + +@item raw +@opindex raw +Same as: + +@example +-ignbrk -brkint -ignpar -parmrk -inpck -istrip +-inlcr -igncr -icrnl -ixon -ixoff -icanon -opost +-isig -iuclc -ixany -imaxbel -xcase min 1 time 0 +@end example + +@noindent +May be negated. If negated, same as @code{cooked}. + +@item cbreak +@opindex cbreak +Same as @option{-icanon}. May be negated. If negated, same as +@code{icanon}. + +@item pass8 +@opindex pass8 +@cindex eight-bit characters +Same as @code{-parenb -istrip cs8}. May be negated. If negated, +same as @code{parenb istrip cs7}. + +@item litout +@opindex litout +Same as @option{-parenb -istrip -opost cs8}. May be negated. +If negated, same as @code{parenb istrip opost cs7}. + +@item decctlq +@opindex decctlq +Same as @option{-ixany}. Non-POSIX@. May be negated. + +@item tabs +@opindex tabs +Same as @code{tab0}. Non-POSIX@. May be negated. If negated, same +as @code{tab3}. + +@item lcase +@itemx LCASE +@opindex lcase +@opindex LCASE +Same as @code{xcase iuclc olcuc}. Non-POSIX@. May be negated. +(Used for terminals with uppercase characters only.) + +@item crt +@opindex crt +Same as @code{echoe echoctl echoke}. + +@item dec +@opindex dec +Same as @code{echoe echoctl echoke -ixany intr ^C erase ^? kill C-u}. +@end table + + +@node Characters +@subsection Special characters + +@cindex special characters +@cindex characters, special + +The special characters' default values vary from system to system. +They are set with the syntax @samp{name value}, where the names are +listed below and the value can be given either literally, in hat +notation (@samp{^@var{c}}), or as an integer which may start with +@samp{0x} to indicate hexadecimal, @samp{0} to indicate octal, or +any other digit to indicate decimal. + +@cindex disabling special characters +@kindex u@r{, and disabling special characters} +For GNU stty, giving a value of @code{^-} or @code{undef} disables that +special character. (This is incompatible with Ultrix @command{stty}, +which uses a value of @samp{u} to disable a special character. GNU +@command{stty} treats a value @samp{u} like any other, namely to set that +special character to @key{U}.) + +@table @samp + +@item intr +@opindex intr +Send an interrupt signal. + +@item quit +@opindex quit +Send a quit signal. + +@item erase +@opindex erase +Erase the last character typed. + +@item kill +@opindex kill +Erase the current line. + +@item eof +@opindex eof +Send an end of file (terminate the input). + +@item eol +@opindex eol +End the line. + +@item eol2 +@opindex eol2 +Alternate character to end the line. Non-POSIX. + +@item discard +@opindex discard +@opindex flush +Alternate character to toggle discarding of output. Non-POSIX. + +@item swtch +@opindex swtch +Switch to a different shell layer. Non-POSIX. + +@item status +@opindex status +Send an info signal. Not currently supported on GNU/Linux. Non-POSIX. + +@item start +@opindex start +Restart the output after stopping it. + +@item stop +@opindex stop +Stop the output. + +@item susp +@opindex susp +Send a terminal stop signal. + +@item dsusp +@opindex dsusp +Send a terminal stop signal after flushing the input. Non-POSIX. + +@item rprnt +@opindex rprnt +Redraw the current line. Non-POSIX. + +@item werase +@opindex werase +Erase the last word typed. Non-POSIX. + +@item lnext +@opindex lnext +Enter the next character typed literally, even if it is a special +character. Non-POSIX. +@end table + + +@node Special +@subsection Special settings + +@cindex special settings + +@table @samp +@item min @var{n} +@opindex min +Set the minimum number of characters that will satisfy a read until +the time value has expired, when @option{-icanon} is set. + +@item time @var{n} +@opindex time +Set the number of tenths of a second before reads time out if the minimum +number of characters have not been read, when @option{-icanon} is set. + +@item ispeed @var{n} +@opindex ispeed +Set the input speed to @var{n}. + +@item ospeed @var{n} +@opindex ospeed +Set the output speed to @var{n}. + +@item rows @var{n} +@opindex rows +Tell the tty kernel driver that the terminal has @var{n} rows. +Non-POSIX. + +@item cols @var{n} +@itemx columns @var{n} +@opindex cols +@opindex columns +Tell the kernel that the terminal has @var{n} columns. Non-POSIX. + +@item drain +@opindex drain +@cindex nonblocking @command{stty} setting +Apply settings after first waiting for pending output to be transmitted. +This is enabled by default for GNU @command{stty}. +Note this is treated as an option rather than a line setting, +and will follow the option processing rules described in the summary above. +It is useful to disable this option +in cases where the system may be in a state where serial transmission +is not possible. +For example, if the system has received the @samp{DC3} character +with @code{ixon} (software flow control) enabled, then @command{stty} would +block without @code{-drain} being specified. +May be negated. Non-POSIX. + +@item size +@opindex size +@vindex LINES +@vindex COLUMNS +Print the number of rows and columns that the kernel thinks the +terminal has. (Systems that don't support rows and columns in the kernel +typically use the environment variables @env{LINES} and @env{COLUMNS} +instead; however, GNU @command{stty} does not know anything about them.) +Non-POSIX. + +@item line @var{n} +@opindex line +Use line discipline @var{n}. Non-POSIX. + +@item speed +@opindex speed +Print the terminal speed. + +@item @var{n} +@cindex baud rate, setting +Set the input and output speeds to @var{n}. @var{n} can be one of: 0 +50 75 110 134 134.5 150 200 300 600 1200 1800 2400 4800 9600 19200 +38400 @code{exta} @code{extb}. @code{exta} is the same as 19200; +@code{extb} is the same as 38400. Many systems, including GNU/Linux, +support higher speeds. The @command{stty} command includes support +for speeds of +57600, +115200, +230400, +460800, +500000, +576000, +921600, +1000000, +1152000, +1500000, +2000000, +2500000, +3000000, +3500000, +or +4000000 where the system supports these. +0 hangs up the line if @option{-clocal} is set. +@end table + + +@node printenv invocation +@section @command{printenv}: Print all or some environment variables + +@pindex printenv +@cindex printing all or some environment variables +@cindex environment variables, printing + +@command{printenv} prints environment variable values. Synopsis: + +@example +printenv [@var{option}] [@var{variable}]@dots{} +@end example + +If no @var{variable}s are specified, @command{printenv} prints the value of +every environment variable. Otherwise, it prints the value of each +@var{variable} that is set, and nothing for those that are not set. + +The program accepts the following option. Also see @ref{Common options}. + +@table @samp + +@optNull + +@end table + +@cindex exit status of @command{printenv} +Exit status: + +@display +0 if all variables specified were found +1 if at least one specified variable was not found +2 if a write error occurred +@end display + + +@node tty invocation +@section @command{tty}: Print file name of terminal on standard input + +@pindex tty +@cindex print terminal file name +@cindex terminal file name, printing + +@command{tty} prints the file name of the terminal connected to its standard +input. It prints @samp{not a tty} if standard input is not a terminal. +Synopsis: + +@example +tty [@var{option}]@dots{} +@end example + +The program accepts the following option. Also see @ref{Common options}. + +@table @samp + +@item -s +@itemx --silent +@itemx --quiet +@opindex -s +@opindex --silent +@opindex --quiet +Print nothing; only return an exit status. + +@end table + +@cindex exit status of @command{tty} +Exit status: + +@display +0 if standard input is a terminal +1 if standard input is a non-terminal file +2 if given incorrect arguments +3 if a write error occurs +@end display + + +@node User information +@chapter User information + +@cindex user information, commands for +@cindex commands for printing user information + +This section describes commands that print user-related information: +logins, groups, and so forth. + +@menu +* id invocation:: Print user identity. +* logname invocation:: Print current login name. +* whoami invocation:: Print effective user ID. +* groups invocation:: Print group names a user is in. +* users invocation:: Print login names of users currently logged in. +* who invocation:: Print who is currently logged in. +@end menu + + +@node id invocation +@section @command{id}: Print user identity + +@pindex id +@cindex real user and group IDs, printing +@cindex effective user and group IDs, printing +@cindex printing real and effective user and group IDs + +@command{id} prints information about the given user, or the process +running it if no user is specified. Synopsis: + +@example +id [@var{option}]@dots{} [@var{user}]@dots{} +@end example + +@var{user} can be either a user ID or a name, with name look-up +taking precedence unless the ID is specified with a leading @samp{+}. +@xref{Disambiguating names and IDs}. + +@vindex POSIXLY_CORRECT +By default, it prints the real user ID, real group ID, effective user ID +if different from the real user ID, effective group ID if different from +the real group ID, and supplemental group IDs. +In addition, if SELinux +is enabled and the @env{POSIXLY_CORRECT} environment variable is not set, +then print @samp{context=@var{c}}, where @var{c} is the security context. + +Each of these numeric values is preceded by an identifying string and +followed by the corresponding user or group name in parentheses. + +The options cause @command{id} to print only part of the above information. +Also see @ref{Common options}. + +@table @samp +@item -g +@itemx --group +@opindex -g +@opindex --group +Print only the group ID. + +@item -G +@itemx --groups +@opindex -G +@opindex --groups +Print only the group ID and the supplementary groups. + +@item -n +@itemx --name +@opindex -n +@opindex --name +Print the user or group name instead of the ID number. Requires +@option{-u}, @option{-g}, or @option{-G}. + +@item -r +@itemx --real +@opindex -r +@opindex --real +Print the real, instead of effective, user or group ID@. Requires +@option{-u}, @option{-g}, or @option{-G}. + +@item -u +@itemx --user +@opindex -u +@opindex --user +Print only the user ID. + +@item -Z +@itemx --context +@opindex -Z +@opindex --context +@cindex SELinux +@cindex security context +Print only the security context of the process, which is generally +the user's security context inherited from the parent process. +If neither SELinux or SMACK is enabled then print a warning and +set the exit status to 1. + +@item -z +@itemx --zero +@opindex -z +@opindex --zero +Delimit output items with ASCII NUL characters. +This option is not permitted when using the default format. +When multiple users are specified, and the @option{--groups} option +is also in effect, groups are delimited with a single NUL character, +while users are delimited with two NUL characters. + +Example: +@example +$ id -Gn --zero +users <NUL> devs <NUL> +@end example + +@end table + +@macro primaryAndSupplementaryGroups{cmd,arg} +Primary and supplementary groups for a process are normally inherited +from its parent and are usually unchanged since login. This means +that if you change the group database after logging in, @command{\cmd\} +will not reflect your changes within your existing login session. +Running @command{\cmd\} with a \arg\ causes the user and group +database to be consulted afresh, and so will give a different result. +@end macro +@primaryAndSupplementaryGroups{id,user argument} + +@exitstatus + +@node logname invocation +@section @command{logname}: Print current login name + +@pindex logname +@cindex printing user's login name +@cindex login name, printing +@cindex user name, printing + +@flindex utmp +@command{logname} prints the calling user's name, as found in a +system-maintained file (often @file{/var/run/utmp} or +@file{/etc/utmp}), and exits with a status of 0. If there is no entry +for the calling process, @command{logname} prints +an error message and exits with a status of 1. + +The only options are @option{--help} and @option{--version}. @xref{Common +options}. + +@exitstatus + + +@node whoami invocation +@section @command{whoami}: Print effective user name + +@pindex whoami +@cindex effective user name, printing +@cindex printing the effective user ID + +@command{whoami} prints the user name associated with the current +effective user ID@. It is equivalent to the command @samp{id -un}. + +The only options are @option{--help} and @option{--version}. @xref{Common +options}. + +@exitstatus + + +@node groups invocation +@section @command{groups}: Print group names a user is in + +@pindex groups +@cindex printing groups a user is in +@cindex supplementary groups, printing + +@command{groups} prints the names of the primary and any supplementary +groups for each given @var{username}, or the current process if no names +are given. If more than one name is given, the name of each user is +printed before +the list of that user's groups and the user name is separated from the +group list by a colon. Synopsis: + +@example +groups [@var{username}]@dots{} +@end example + +The group lists are equivalent to the output of the command @samp{id -Gn}. + +The only options are @option{--help} and @option{--version}. @xref{Common +options}. + +@primaryAndSupplementaryGroups{groups,list of users} + +@exitstatus + +@node users invocation +@section @command{users}: Print login names of users currently logged in + +@pindex users +@cindex printing current usernames +@cindex usernames, printing current + +@cindex login sessions, printing users with +@command{users} prints on a single line a blank-separated list of user +names of users currently logged in to the current host. Each user name +corresponds to a login session, so if a user has more than one login +session, that user's name will appear the same number of times in the +output. Synopsis: + +@example +users [@var{file}] +@end example + +@flindex utmp +@flindex wtmp +With no @var{file} argument, @command{users} extracts its information from +a system-maintained file (often @file{/var/run/utmp} or +@file{/etc/utmp}). If a file argument is given, @command{users} uses +that file instead. A common choice is @file{/var/log/wtmp}. + +The only options are @option{--help} and @option{--version}. @xref{Common +options}. + +The @command{users} command is installed only on platforms with the +POSIX @code{<utmpx.h>} include file or equivalent, so portable scripts +should not rely on its existence on non-POSIX platforms. + +@exitstatus + + +@node who invocation +@section @command{who}: Print who is currently logged in + +@pindex who +@cindex printing current user information +@cindex information, about current users + +@command{who} prints information about users who are currently logged on. +Synopsis: + +@example +@command{who} [@var{option}] [@var{file}] [am i] +@end example + +@cindex terminal lines, currently used +@cindex login time +@cindex remote hostname +If given no non-option arguments, @command{who} prints the following +information for each user currently logged on: login name, terminal +line, login time, and remote hostname or X display. + +@flindex utmp +@flindex wtmp +If given one non-option argument, @command{who} uses that instead of +a default system-maintained file (often @file{/var/run/utmp} or +@file{/etc/utmp}) as the name of the file containing the record of +users logged on. @file{/var/log/wtmp} is commonly given as an argument +to @command{who} to look at who has previously logged on. + +@opindex am i +@opindex who am i +If given two non-option arguments, @command{who} prints only the entry +for the user running it (determined from its standard input), preceded +by the hostname. Traditionally, the two arguments given are @samp{am +i}, as in @samp{who am i}. + +@vindex TZ +Timestamps are listed according to the time zone rules specified by +the @env{TZ} environment variable, or by the system default rules if +@env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone +with @env{TZ}, libc, The GNU C Library Reference Manual}. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -a +@itemx --all +@opindex -a +@opindex --all +Same as @samp{-b -d --login -p -r -t -T -u}. + +@item -b +@itemx --boot +@opindex -b +@opindex --boot +Print the date and time of last system boot. + +@item -d +@itemx --dead +@opindex -d +@opindex --dead +Print information corresponding to dead processes. + +@item -H +@itemx --heading +@opindex -H +@opindex --heading +Print a line of column headings. + +@item -l +@itemx --login +@opindex -l +@opindex --login +List only the entries that correspond to processes via which the +system is waiting for a user to login. The user name is always @samp{LOGIN}. + +@item --lookup +@opindex --lookup +Attempt to canonicalize hostnames found in utmp through a DNS lookup. This +is not the default because it can cause significant delays on systems with +automatic dial-up internet access. + +@item -m +@opindex -m +Same as @samp{who am i}. + +@item -p +@itemx --process +@opindex -p +@opindex --process +List active processes spawned by init. + +@item -q +@itemx --count +@opindex -q +@opindex --count +Print only the login names and the number of users logged on. +Overrides all other options. + +@item -r +@itemx --runlevel +@opindex -r +@opindex --runlevel +Print the current (and maybe previous) run-level of the init process. + +@item -s +@opindex -s +Ignored; for compatibility with other versions of @command{who}. + +@item -t +@itemx --time +@opindex -t +@opindex --time +Print last system clock change. + +@item -u +@opindex -u +@cindex idle time +After the login time, print the number of hours and minutes that the +user has been idle. @samp{.} means the user was active in the last minute. +@samp{old} means the user has been idle for more than 24 hours. + +@item -w +@itemx -T +@itemx --mesg +@itemx --message +@itemx --writable +@opindex -w +@opindex -T +@opindex --mesg +@opindex --message +@opindex --writable +@cindex message status +@pindex write@r{, allowed} +After each login name print a character indicating the user's message status: + +@display +@samp{+} allowing @code{write} messages +@samp{-} disallowing @code{write} messages +@samp{?} cannot find terminal device +@end display + +@end table + +The @command{who} command is installed only on platforms with the +POSIX @code{<utmpx.h>} include file or equivalent, so portable scripts +should not rely on its existence on non-POSIX platforms. + +@exitstatus + + +@node System context +@chapter System context + +@cindex system context +@cindex context, system +@cindex commands for system context + +This section describes commands that print or change system-wide +information. + +@menu +* date invocation:: Print or set system date and time. +* arch invocation:: Print machine hardware name. +* nproc invocation:: Print the number of processors. +* uname invocation:: Print system information. +* hostname invocation:: Print or set system name. +* hostid invocation:: Print numeric host identifier. +* uptime invocation:: Print system uptime and load. +@end menu + +@node date invocation +@section @command{date}: Print or set system date and time + +@pindex date +@cindex time, printing or setting +@cindex printing the current time + +Synopses: + +@example +date [@var{option}]@dots{} [+@var{format}] +date [-u|--utc|--universal] @c this avoids a newline in the output +[ MMDDhhmm[[CC]YY][.ss] ] +@end example + +The @command{date} command displays the date and time. +With the @option{--set} (@option{-s}) option, or with +@samp{MMDDhhmm[[CC]YY][.ss]}, +it sets the date and time. + +@vindex LC_TIME +Invoking @command{date} with no @var{format} argument is equivalent to invoking +it with a default format that depends on the @env{LC_TIME} locale category. +In the default C locale, this format is @samp{'+%a %b %e %H:%M:%S %Z %Y'}, +so the output looks like @samp{Thu Jul @ 9 17:00:00 EDT 2020}. + +@vindex TZ +Normally, @command{date} uses the time zone rules indicated by the +@env{TZ} environment variable, or the system default rules if @env{TZ} +is not set. @xref{TZ Variable,, Specifying the Time Zone with +@env{TZ}, libc, The GNU C Library Reference Manual}. + +@exitstatus + +@menu +* Date format specifiers:: Used in @samp{date '+...'} +* Setting the time:: Changing the system clock. +* Options for date:: Instead of the current time. +@detailmenu +* Date input formats:: Specifying date strings. +@end detailmenu +* Examples of date:: Examples. +@end menu + +@node Date format specifiers +@subsection Specifying the format of @command{date} output + +@findex strftime @r{and @command{date}} +@cindex time formats +@cindex formatting times +If given an argument that starts with a @samp{+}, @command{date} prints the +current date and time (or the date and time specified by the +@option{--date} option, see below) in the format defined by that argument, +which is similar to that of the @code{strftime} function. Except for +conversion specifiers, which start with @samp{%}, characters in the +format string are printed unchanged. The conversion specifiers are +described below. + +@menu +* Time conversion specifiers:: %[HIklMNpPrRsSTXzZ] +* Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY] +* Literal conversion specifiers:: %[%nt] +* Padding and other flags:: Pad with zeros, spaces, etc. +@end menu + +@node Time conversion specifiers +@subsubsection Time conversion specifiers + +@cindex time conversion specifiers +@cindex conversion specifiers, time + +@command{date} conversion specifiers related to times. + +@table @samp +@item %H +hour (@samp{00}@dots{}@samp{23}) +@item %I +hour (@samp{01}@dots{}@samp{12}) +@item %k +hour, space padded (@samp{ 0}@dots{}@samp{23}); equivalent to @samp{%_H}@. +This is a GNU extension. +@item %l +hour, space padded (@samp{ 1}@dots{}@samp{12}); equivalent to @samp{%_I}@. +This is a GNU extension. +@item %M +minute (@samp{00}@dots{}@samp{59}) +@item %N +nanoseconds (@samp{000000000}@dots{}@samp{999999999}). +This is a GNU extension. +@item %p +locale's equivalent of either @samp{AM} or @samp{PM}; +blank in many locales. +Noon is treated as @samp{PM} and midnight as @samp{AM}. +@item %P +like @samp{%p}, except lower case. +This is a GNU extension. +@item %r +locale's 12-hour clock time (e.g., @samp{11:11:04 PM}) +@item %R +24-hour hour and minute. Same as @samp{%H:%M}. +@item %s +@cindex Epoch, seconds since +@cindex seconds since the Epoch +@cindex beginning of time +@cindex leap seconds +seconds since the Epoch, i.e., since 1970-01-01 00:00 UTC@. +Leap seconds are not counted unless leap second support is available. +@xref{%s-examples}, for examples. +This is a GNU extension. +@item %S +@cindex leap seconds +second (@samp{00}@dots{}@samp{60}). +This may be @samp{60} if leap seconds are supported. +@item %T +24-hour hour, minute, and second. Same as @samp{%H:%M:%S}. +@item %X +locale's time representation (e.g., @samp{23:13:48}) +@item %z +Four-digit numeric time zone, e.g., @samp{-0600} or @samp{+0530}, or +@samp{-0000} if no +time zone is determinable. This value reflects the numeric time zone +appropriate for the current time, using the time zone rules specified +by the @env{TZ} environment variable. A time zone is not determinable if +its numeric offset is zero and its abbreviation begins with @samp{-}. +The time (and optionally, the time zone rules) can be overridden +by the @option{--date} option. +@item %:z +Numeric time zone with @samp{:}, e.g., @samp{-06:00} or +@samp{+05:30}), or @samp{-00:00} if no time zone is determinable. +This is a GNU extension. +@item %::z +Numeric time zone to the nearest second with @samp{:} (e.g., +@samp{-06:00:00} or @samp{+05:30:00}), or @samp{-00:00:00} if no time zone is +determinable. +This is a GNU extension. +@item %:::z +Numeric time zone with @samp{:} using the minimum necessary precision +(e.g., @samp{-06}, @samp{+05:30}, or @samp{-04:56:02}), or @samp{-00} if +no time zone is determinable. +This is a GNU extension. +@item %Z +alphabetic time zone abbreviation (e.g., @samp{EDT}), or nothing if no +time zone is determinable. See @samp{%z} for how it is determined. +@end table + + +@node Date conversion specifiers +@subsubsection Date conversion specifiers + +@cindex date conversion specifiers +@cindex conversion specifiers, date + +@command{date} conversion specifiers related to dates. + +@table @samp +@item %a +locale's abbreviated weekday name (e.g., @samp{Sun}) +@item %A +locale's full weekday name, variable length (e.g., @samp{Sunday}) +@item %b +locale's abbreviated month name (e.g., @samp{Jan}) +@item %B +locale's full month name, variable length (e.g., @samp{January}) +@item %c +locale's date and time (e.g., @samp{Thu Mar @ 3 23:05:25 2020}) +@item %C +century. This is like @samp{%Y}, except the last two digits are omitted. +For example, it is @samp{20} if @samp{%Y} is @samp{2019}, +and is @samp{-0} if @samp{%Y} is @samp{-001}. +It is normally at least two characters, but it may be more. +@item %d +day of month (e.g., @samp{01}) +@item %D +date; same as @samp{%m/%d/%y} +@item %e +day of month, space padded; same as @samp{%_d} +@item %F +full date in ISO 8601 format; like @samp{%+4Y-%m-%d} +except that any flags or field width override the @samp{+} +and (after subtracting 6) the @samp{4}. +This is a good choice for a date format, as it is standard and +is easy to sort in the usual case where years are in the range +0000@dots{}9999. +@item %g +year corresponding to the ISO week number, but without the century +(range @samp{00} through @samp{99}). This has the same format and value +as @samp{%y}, except that if the ISO week number (see +@samp{%V}) belongs +to the previous or next year, that year is used instead. +@item %G +year corresponding to the ISO week number. This has the +same format and value as @samp{%Y}, except that if the ISO +week number (see +@samp{%V}) belongs to the previous or next year, that year is used +instead. +It is normally useful only if @samp{%V} is also used; +for example, the format @samp{%G-%m-%d} is probably a mistake, +since it combines the ISO week number year with the conventional month and day. +@item %h +same as @samp{%b} +@item %j +day of year (@samp{001}@dots{}@samp{366}) +@item %m +month (@samp{01}@dots{}@samp{12}) +@item %q +quarter of year (@samp{1}@dots{}@samp{4}) +@item %u +day of week (@samp{1}@dots{}@samp{7}) with @samp{1} corresponding to Monday +@item %U +week number of year, with Sunday as the first day of the week +(@samp{00}@dots{}@samp{53}). +Days in a new year preceding the first Sunday are in week zero. +@item %V +ISO week number, that is, the +week number of year, with Monday as the first day of the week +(@samp{01}@dots{}@samp{53}). +If the week containing January 1 has four or more days in +the new year, then it is considered week 1; otherwise, it is week 53 of +the previous year, and the next week is week 1. (See the ISO 8601 +standard.) +@item %w +day of week (@samp{0}@dots{}@samp{6}) with 0 corresponding to Sunday +@item %W +week number of year, with Monday as first day of week +(@samp{00}@dots{}@samp{53}). +Days in a new year preceding the first Monday are in week zero. +@item %x +locale's date representation (e.g., @samp{12/31/99}) +@item %y +last two digits of year (@samp{00}@dots{}@samp{99}) +@item %Y +year. This is normally at least four characters, but it may be more. +Year @samp{0000} precedes year @samp{0001}, and year @samp{-001} +precedes year @samp{0000}. +@end table + + +@node Literal conversion specifiers +@subsubsection Literal conversion specifiers + +@cindex literal conversion specifiers +@cindex conversion specifiers, literal + +@command{date} conversion specifiers that produce literal strings. + +@table @samp +@item %% +a literal % +@item %n +a newline +@item %t +a horizontal tab +@end table + + +@node Padding and other flags +@subsubsection Padding and other flags + +@cindex numeric field padding +@cindex padding of numeric fields +@cindex fields, padding numeric + +Unless otherwise specified, @command{date} normally pads numeric fields +with zeros, so that, for +example, numeric months are always output as two digits. +Most numeric fields are padded on the left. +However, nanoseconds are padded on the right since they are commonly +used after decimal points in formats like @samp{%s.%-N}. +Also, seconds since the Epoch are not padded +since there is no natural width for them. + +The following optional flags can appear after the @samp{%}: + +@table @samp +@item - +(hyphen) Do not pad the field; useful if the output is intended for +human consumption. +This is a GNU extension. +As a special case, @samp{%-N} outputs only enough trailing digits to +not lose information, assuming that the timestamp's resolution is the +same as the current hardware clock. For example, if the hardware +clock resolution is 1 microsecond, @samp{%s.%-N} outputs something +like @samp{1640890100.395710}. + +@item _ +(underscore) Pad with spaces; useful if you need a fixed +number of characters in the output, but zeros are too distracting. +This is a GNU extension. +@item 0 +(zero) Pad with zeros even if the conversion specifier +would normally pad with spaces. +@item + +Pad with zeros, like @samp{0}. In addition, precede any year number +with @samp{+} if it exceeds 9999 or if its field width exceeds 4; +similarly, precede any century number with @samp{+} if it exceeds 99 +or if its field width exceeds 2. This supports ISO 8601 formats +for dates far in the future; for example, the command @code{date +--date=12019-02-25 +%+13F} outputs the string @samp{+012019-02-25}. +@item ^ +Use upper case characters if possible. +This is a GNU extension. +@item # +Use opposite case characters if possible. +A field that is normally upper case becomes lower case, and vice versa. +This is a GNU extension. +@end table + +@noindent +Here are some examples of padding: + +@example +date +%d/%m -d "Feb 1" +@result{} 01/02 +date +%-d/%-m -d "Feb 1" +@result{} 1/2 +date +%_d/%_m -d "Feb 1" +@result{} 1/ 2 +@end example + +You can optionally specify the field width +(after any flag, if present) as a decimal number. If the natural size of the +output of the field has less than the specified number of characters, +the result is normally written right adjusted and padded to the given +size. For example, @samp{%9B} prints the right adjusted month name in +a field of width 9. Nanoseconds are left adjusted, and are truncated +or padded to the field width. + +An optional modifier can follow the optional flag and width +specification. The modifiers are: + +@table @samp +@item E +Use the locale's alternate representation for date and time. This +modifier applies to the @samp{%c}, @samp{%C}, @samp{%x}, @samp{%X}, +@samp{%y} and @samp{%Y} conversion specifiers. In a Japanese locale, for +example, @samp{%Ex} might yield a date format based on the Japanese +Emperors' reigns. + +@item O +Use the locale's alternate numeric symbols for numbers. This modifier +applies only to numeric conversion specifiers. +@end table + +If the format supports the modifier but no alternate representation +is available, it is ignored. + +POSIX specifies the behavior of flags and field widths only for +@samp{%C}, @samp{%F}, @samp{%G}, and @samp{%Y} (all without +modifiers), and requires a flag to be present if and only if a field +width is also present. Other combinations of flags, field widths and +modifiers are GNU extensions. + + +@node Setting the time +@subsection Setting the time + +@cindex setting the time +@cindex time setting +@cindex appropriate privileges + +You must have appropriate privileges to set the +system clock. For changes to persist across a reboot, the +hardware clock may need to be updated from the system clock, which +might not happen automatically on your system. + +To set the clock, you can use the @option{--set} (@option{-s}) option +(@pxref{Options for date}). To set the clock without using GNU +extensions, you can give @command{date} an argument of the form +@samp{MMDDhhmm[[CC]YY][.ss]} where each two-letter +component stands for two digits with the following meanings: + +@table @var +@item MM +month +@item DD +day within month +@item hh +hour +@item mm +minute +@item CC +first two digits of year (optional) +@item YY +last two digits of year (optional) +@item ss +second (optional) +@end table + +Note, the @option{--date} and @option{--set} options may not be used with an +argument in the above format. The @option{--universal} option may be used +with such an argument to indicate that the specified date and time are +relative to Universal Time rather than to the local time zone. + + +@node Options for date +@subsection Options for @command{date} + +@cindex @command{date} options +@cindex options for @command{date} + +The program accepts the following options. Also see @ref{Common options}. +Except for @option{-u}, these options are all GNU extensions to POSIX. + +All options that specify the date to display are mutually exclusive. +I.e.: @option{--date}, @option{--file}, @option{--reference}, +@option{--resolution}. + +@table @samp + +@item -d @var{datestr} +@itemx --date=@var{datestr} +@opindex -d +@opindex --date +@cindex parsing date strings +@cindex date strings, parsing +@cindex arbitrary date strings, parsing +@opindex yesterday +@opindex tomorrow +@opindex next @var{day} +@opindex last @var{day} +Display the date and time specified in @var{datestr} instead of the +current date and time. @var{datestr} can be in almost any common +format. It can contain month names, time zones, @samp{am} and @samp{pm}, +@samp{yesterday}, etc. For example, @option{--date="2020-07-21 +14:19:13.489392193 +0530"} specifies the instant of time that is +489,392,193 nanoseconds after July 21, 2020 at 2:19:13 PM in a +time zone that is 5 hours and 30 minutes east of UTC.@* +Note: input currently must be in locale independent format. E.g., the +LC_TIME=C below is needed to print back the correct date in many locales: +@example +date -d "$(LC_TIME=C date)" +@end example +@xref{Date input formats}. + +@item --debug +@opindex --debug +@cindex debugging date strings +@cindex date strings, debugging +@cindex arbitrary date strings, debugging +Annotate the parsed date, display the effective time zone, and warn about +potential misuse. + +@item -f @var{datefile} +@itemx --file=@var{datefile} +@opindex -f +@opindex --file +Parse each line in @var{datefile} as with @option{-d} and display the +resulting date and time. If @var{datefile} is @samp{-}, use standard +input. This is useful when you have many dates to process, because the +system overhead of starting up the @command{date} executable many times can +be considerable. + +@item -I[@var{timespec}] +@itemx --iso-8601[=@var{timespec}] +@opindex -I[@var{timespec}] +@opindex --iso-8601[=@var{timespec}] +Display the date using an ISO 8601 format, @samp{%Y-%m-%d}. + +The argument @var{timespec} specifies the number of additional +terms of the time to include. It can be one of the following: +@table @samp +@item auto +Print just the date. This is the default if @var{timespec} is omitted. +This is like the format @code{%Y-%m-%d}. + +@item hours +Also print hours and time zone. +This is like the format @code{%Y-%m-%dT%H%:z}. + +@item minutes +Also print minutes. +This is like the format @code{%Y-%m-%dT%H:%M%:z}. + +@item seconds +Also print seconds. +This is like the format @code{%Y-%m-%dT%H:%M:%S%:z}. + +@item ns +Also print nanoseconds. +This is like the format @code{%Y-%m-%dT%H:%M:%S,%N%:z}. +@end table + +@macro dateParseNote +This format is always suitable as input +for the @option{--date} (@option{-d}) and @option{--file} +(@option{-f}) options, regardless of the current locale. +@end macro +@dateParseNote + +@item -r @var{file} +@itemx --reference=@var{file} +@opindex -r +@opindex --reference +Display the date and time of the last modification of @var{file}, +instead of the current date and time. + +@item --resolution +@opindex --resolution +Display the timestamp resolution instead of the time. +Current clock timestamps that are output by @command{date} +are integer multiples of the timestamp resolution. +With this option, the format defaults to @samp{%s.%N}. +For example, if the clock resolution is 1 millisecond, +the output is: + +@example +0.001000000 +@end example + +@item -R +@itemx --rfc-email +@opindex -R +@opindex --rfc-email +Display the date and time using the format @samp{%a, %d %b %Y %H:%M:%S +%z}, evaluated in the C locale so abbreviations are always in English. +For example: + +@example +Mon, 09 Jul 2020 17:00:00 -0400 +@end example + +@opindex --rfc-822 +@opindex --rfc-2822 +This format conforms to Internet RFCs +@uref{https://tools.ietf.org/search/rfc5322, 5322}, +@uref{https://tools.ietf.org/search/rfc2822, 2822} and +@uref{https://tools.ietf.org/search/rfc822, 822}, the +current and previous standards for Internet email. +For compatibility with older versions of @command{date}, +@option{--rfc-2822} and @option{--rfc-822} are aliases for +@option{--rfc-email}. + +@item --rfc-3339=@var{timespec} +@opindex --rfc-3339=@var{timespec} +Display the date using a format specified by +@uref{https://tools.ietf.org/search/rfc3339, Internet +RFC 3339}. This is like @option{--iso-8601}, except that a space rather +than a @samp{T} separates dates from times, and a period rather than +a comma separates seconds from subseconds. +@dateParseNote + +The argument @var{timespec} specifies how much of the time to include. +It can be one of the following: + +@table @samp +@item date +Print just the full-date, e.g., @samp{2020-07-21}. +This is like the format @samp{%Y-%m-%d}. + +@item seconds +Print the full-date and full-time separated by a space, e.g., +@samp{2020-07-21 04:30:37+05:30}. The output ends with a numeric +time-offset; here the @samp{+05:30} means that local time is five +hours and thirty minutes east of UTC@. This is like +the format @samp{%Y-%m-%d %H:%M:%S%:z}. + +@item ns +Like @samp{seconds}, but also print nanoseconds, e.g., +@samp{2020-07-21 04:30:37.998458565+05:30}. +This is like the format @samp{%Y-%m-%d %H:%M:%S.%N%:z}. + +@end table + +@item -s @var{datestr} +@itemx --set=@var{datestr} +@opindex -s +@opindex --set +Set the date and time to @var{datestr}. See @option{-d} above. +See also @ref{Setting the time}. + +@item -u +@itemx --utc +@itemx --universal +@opindex -u +@opindex --utc +@opindex --universal +@cindex Coordinated Universal Time +@cindex UTC +@cindex Greenwich Mean Time +@cindex GMT +@cindex leap seconds +@vindex TZ +@cindex Universal Time +Use Universal Time by operating as if the +@env{TZ} environment variable were set to the string @samp{UTC0}. +UTC stands for Coordinated Universal Time, established in 1960. +Universal Time is often called ``Greenwich Mean Time'' (GMT) for +historical reasons. +Typically, systems ignore leap seconds and thus implement an +approximation to UTC rather than true UTC. +@end table + + +@node Examples of date +@subsection Examples of @command{date} + +@cindex examples of @command{date} + +Here are a few examples. Also see the documentation for the @option{-d} +option in the previous section. + +@itemize @bullet + +@item +To print the date of the day before yesterday: + +@example +date --date='2 days ago' +@end example + +@item +To print the date of the day three months and one day hence: + +@example +date --date='3 months 1 day' +@end example + +@item +To print the day of year of Christmas in the current year: + +@example +date --date='25 Dec' +%j +@end example + +@item +To print the current full month name and the day of the month: + +@example +date '+%B %d' +@end example + +But this may not be what you want because for the first nine days of +the month, the @samp{%d} expands to a zero-padded two-digit field, +for example @samp{date -d 1may '+%B %d'} will print @samp{May 01}. + +@item +To print a date without the leading zero for one-digit days +of the month, you can use the (GNU extension) +@samp{-} flag to suppress +the padding altogether: + +@example +date -d 1may '+%B %-d' +@end example + +@item +To print the current date and time in the format required by many +non-GNU versions of @command{date} when setting the system clock: + +@example +date +%m%d%H%M%Y.%S +@end example + +@item +To set the system clock forward by two minutes: + +@example +date --set='+2 minutes' +@end example + +@item +To print the date in Internet RFC 5322 format, +use @samp{date --rfc-email}. Here is some example output: + +@example +Tue, 09 Jul 2020 19:00:37 -0400 +@end example + +@anchor{%s-examples} +@item +To convert a date string to the number of seconds since the Epoch +(which is 1970-01-01 00:00 UTC), use the @option{--date} option with +the @samp{%s} format. That can be useful in sorting and/or graphing +and/or comparing data by date. The following command outputs the +number of the seconds since the Epoch for the time two minutes after the +Epoch: + +@example +date --date='1970-01-01 00:02:00 +0000' +%s +120 +@end example + +To convert a date string from one time zone @var{from} to another @var{to}, +specify @samp{TZ="@var{from}"} in the environment and @samp{TZ="@var{to}"} +in the @option{--date} option. @xref{Specifying time zone rules}. +For example: + +@smallexample +TZ="Asia/Tokyo" date --date='TZ="America/New_York" 2023-05-07 12:23' +Mon May @ 8 01:23:00 JST 2023 +@end smallexample + +If you do not specify time zone information in the date string, +@command{date} uses your computer's idea of the time zone when +interpreting the string. For example, if your computer's time zone is +that of Cambridge, Massachusetts, which was then 5 hours (i.e., 18,000 +seconds) behind UTC: + +@example +# local time zone used +date --date='1970-01-01 00:02:00' +%s +18120 +@end example + +@item +If you're sorting or graphing dated data, your raw date values may be +represented as seconds since the Epoch. But few people can look at +the date @samp{1577836800} and casually note ``Oh, that's the first +second of the year 2020 in Greenwich, England.'' + +@example +date --date='2020-01-01 UTC' +%s +1577836800 +@end example + +An alternative is to use the @option{--utc} (@option{-u}) option. +Then you may omit @samp{UTC} from the date string. Although this +produces the same result for @samp{%s} and many other format sequences, +with a time zone offset different from zero, it would give a different +result for zone-dependent formats like @samp{%z}. + +@example +date -u --date=2020-07-21 +%s +1595289600 +@end example + +To convert such an unwieldy number of seconds back to +a more readable form, use a command like this: + +@example +date -d @@1595289600 +"%F %T %z" +2020-07-20 20:00:00 -0400 +@end example + +Often it is better to output UTC-relative date and time: + +@example +date -u -d @@1595289600 +"%F %T %z" +2020-07-21 00:00:00 +0000 +@end example + +@item +@cindex leap seconds +Typically the seconds count omits leap seconds, but some systems are +exceptions. Because leap seconds are not predictable, the mapping +between the seconds count and a future timestamp is not reliable on +the atypical systems that include leap seconds in their counts. + +Here is how the two kinds of systems handle the leap second at +the end of the year 2016: + +@example +# Typical systems ignore leap seconds: +date --date='2016-12-31 23:59:59 +0000' +%s +1483228799 +date --date='2016-12-31 23:59:60 +0000' +%s +date: invalid date '2016-12-31 23:59:60 +0000' +date --date='2017-01-01 00:00:00 +0000' +%s +1483228800 +@end example + +@example +# Atypical systems count leap seconds: +date --date='2016-12-31 23:59:59 +0000' +%s +1483228825 +date --date='2016-12-31 23:59:60 +0000' +%s +1483228826 +date --date='2017-01-01 00:00:00 +0000' +%s +1483228827 +@end example + +@end itemize + + +@node arch invocation +@section @command{arch}: Print machine hardware name + +@pindex arch +@cindex print machine hardware name +@cindex system information, printing + +@command{arch} prints the machine hardware name, +and is equivalent to @samp{uname -m}. +Synopsis: + +@example +arch [@var{option}] +@end example + +The program accepts the @ref{Common options} only. + +@command{arch} is not installed by default, so portable scripts should +not rely on its existence. + +@exitstatus + + +@node nproc invocation +@section @command{nproc}: Print the number of available processors + +@pindex nproc +@cindex Print the number of processors +@cindex system information, printing + +Print the number of processing units available to the current process, +which may be less than the number of online processors. +If this information is not accessible, then print the number of +processors installed. If the @env{OMP_NUM_THREADS} or @env{OMP_THREAD_LIMIT} +environment variables are set, then they will determine the minimum +and maximum returned value respectively. The result is guaranteed to be +greater than zero. Synopsis: + +@example +nproc [@var{option}] +@end example + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item --all +@opindex --all +Print the number of installed processors on the system, which may +be greater than the number online or available to the current process. +The @env{OMP_NUM_THREADS} or @env{OMP_THREAD_LIMIT} environment variables +are not honored in this case. + +@item --ignore=@var{number} +@opindex --ignore +If possible, exclude this @var{number} of processing units. + +@end table + +@exitstatus + + +@node uname invocation +@section @command{uname}: Print system information + +@pindex uname +@cindex print system information +@cindex system information, printing + +@command{uname} prints information about the machine and operating system +it is run on. If no options are given, @command{uname} acts as if the +@option{-s} option were given. Synopsis: + +@example +uname [@var{option}]@dots{} +@end example + +If multiple options or @option{-a} are given, the selected information is +printed in this order: + +@example +@var{kernel-name} @var{nodename} @var{kernel-release} @var{kernel-version} +@var{machine} @var{processor} @var{hardware-platform} @var{operating-system} +@end example + +The information may contain internal spaces, so such output cannot be +parsed reliably. In the following example, @var{kernel-version} is +@samp{#1 SMP Fri Jul 17 17:18:38 UTC 2020}: + +@example +uname -a +@result{} Linux dumdum.example.org 5.9.16-200.fc33.x86_64@c + #1 SMP Mon Dec 21 14:08:22 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux +@end example + + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -a +@itemx --all +@opindex -a +@opindex --all +Print all of the below information, except omit the processor type +and the hardware platform name if they are unknown. + +@item -i +@itemx --hardware-platform +@opindex -i +@opindex --hardware-platform +@cindex implementation, hardware +@cindex hardware platform +@cindex platform, hardware +Print the hardware platform name +(sometimes called the hardware implementation). +Print @samp{unknown} if this information is not available. +Note this is non-portable (even across GNU/Linux distributions). + +@item -m +@itemx --machine +@opindex -m +@opindex --machine +@cindex machine type +@cindex hardware class +@cindex hardware type +Print the machine hardware name (sometimes called the hardware class +or hardware type). + +@item -n +@itemx --nodename +@opindex -n +@opindex --nodename +@cindex hostname +@cindex node name +@cindex network node name +Print the network node hostname. + +@item -p +@itemx --processor +@opindex -p +@opindex --processor +@cindex host processor type +Print the processor type (sometimes called the instruction set +architecture or ISA). +Print @samp{unknown} if this information is not available. +Note this is non-portable (even across GNU/Linux distributions). + +@item -o +@itemx --operating-system +@opindex -o +@opindex --operating-system +@cindex operating system name +Print the name of the operating system. + +@item -r +@itemx --kernel-release +@opindex -r +@opindex --kernel-release +@cindex kernel release +@cindex release of kernel +Print the kernel release. + +@item -s +@itemx --kernel-name +@opindex -s +@opindex --kernel-name +@cindex kernel name +@cindex name of kernel +Print the kernel name. +POSIX 1003.1-2001 (@pxref{Standards conformance}) calls this +``the implementation of the operating system'', because the +POSIX specification itself has no notion of ``kernel''. +The kernel name might be the same as the operating system name printed +by the @option{-o} or @option{--operating-system} option, but it might +differ. Some operating systems (e.g., FreeBSD, HP-UX) have the same +name as their underlying kernels; others (e.g., GNU/Linux, Solaris) +do not. + +@item -v +@itemx --kernel-version +@opindex -v +@opindex --kernel-version +@cindex kernel version +@cindex version of kernel +Print the kernel version. + +@end table + +@exitstatus + + +@node hostname invocation +@section @command{hostname}: Print or set system name + +@pindex hostname +@cindex setting the hostname +@cindex printing the hostname +@cindex system name, printing +@cindex appropriate privileges + +With no arguments, @command{hostname} prints the name of the current host +system. With one argument, it sets the current host name to the +specified string. You must have appropriate privileges to set the host +name. Synopsis: + +@example +hostname [@var{name}] +@end example + +The only options are @option{--help} and @option{--version}. @xref{Common +options}. + +@command{hostname} is not installed by default, and other packages +also supply a @command{hostname} command, so portable scripts should +not rely on its existence or on the exact behavior documented above. + +@exitstatus + + +@node hostid invocation +@section @command{hostid}: Print numeric host identifier + +@pindex hostid +@cindex printing the host identifier + +@command{hostid} prints the numeric identifier of the current host +in hexadecimal. This command accepts no arguments. +The only options are @option{--help} and @option{--version}. +@xref{Common options}. + +For example, here's what it prints on one system I use: + +@example +$ hostid +1bac013d +@end example + +On that system, the 32-bit quantity happens to be closely +related to the system's Internet address, but that isn't always +the case. + +@command{hostid} is installed only on systems that have the +@code{gethostid} function, so portable scripts should not rely on its +existence. + +@exitstatus + +@node uptime invocation +@section @command{uptime}: Print system uptime and load + +@pindex uptime +@cindex printing the system uptime and load + +@command{uptime} prints the current time, the system's uptime, the +number of logged-in users and the current load average. + +If an argument is specified, it is used as the file to be read +to discover how many users are logged in. If no argument is +specified, a system default is used (@command{uptime --help} indicates +the default setting). + +The only options are @option{--help} and @option{--version}. +@xref{Common options}. + +For example, here's what it prints right now on one system I use: + +@example +$ uptime + 14:07 up 3:35, 3 users, load average: 1.39, 1.15, 1.04 +@end example + +The precise method of calculation of load average varies somewhat +between systems. Some systems calculate it as the average number of +runnable processes over the last 1, 5 and 15 minutes, but some systems +also include processes in the uninterruptible sleep state (that is, +those processes which are waiting for device I/O). The Linux kernel +includes uninterruptible processes. + +@command{uptime} is installed only on platforms with infrastructure +for obtaining the boot time, and other packages also supply an +@command{uptime} command, so portable scripts should not rely on its +existence or on the exact behavior documented above. + +@exitstatus + +@node SELinux context +@chapter SELinux context + +@cindex SELinux context +@cindex SELinux, context +@cindex commands for SELinux context + +This section describes commands for operations with SELinux +contexts. + +@menu +* chcon invocation:: Change SELinux context of file +* runcon invocation:: Run a command in specified SELinux context +@end menu + +@node chcon invocation +@section @command{chcon}: Change SELinux context of file + +@pindex chcon +@cindex changing security context +@cindex change SELinux context + +@command{chcon} changes the SELinux security context of the selected files. +Synopses: + +@example +chcon [@var{option}]@dots{} @var{context} @var{file}@dots{} +chcon [@var{option}]@dots{} [-u @var{user}] [-r @var{role}] [-l @var{range}]@c + [-t @var{type}] @var{file}@dots{} +chcon [@var{option}]@dots{} --reference=@var{rfile} @var{file}@dots{} +@end example + +Change the SELinux security context of each @var{file} to @var{context}. +With @option{--reference}, change the security context of each @var{file} +to that of @var{rfile}. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item --dereference +@opindex --dereference +Do not affect symbolic links but what they refer to; this is the default. + +@item -h +@itemx --no-dereference +@opindex -h +@opindex --no-dereference +@cindex no dereference +Affect the symbolic links themselves instead of any referenced file. + +@item --reference=@var{rfile} +@opindex --reference +@cindex reference file +Use @var{rfile}'s security context rather than specifying a @var{context} value. + +@item -R +@itemx --recursive +@opindex -R +@opindex --recursive +Operate on files and directories recursively. + +@item --preserve-root +@opindex --preserve-root +Refuse to operate recursively on the root directory, @file{/}, +when used together with the @option{--recursive} option. +@xref{Treating / specially}. + +@item --no-preserve-root +@opindex --no-preserve-root +Do not treat the root directory, @file{/}, specially when operating +recursively; this is the default. +@xref{Treating / specially}. + +@choptH +@xref{Traversing symlinks}. + +@choptL +@xref{Traversing symlinks}. + +@choptP +@xref{Traversing symlinks}. + +@item -v +@itemx --verbose +@opindex -v +@opindex --verbose +@cindex diagnostic +Output a diagnostic for every file processed. + +@item -u @var{user} +@itemx --user=@var{user} +@opindex -u +@opindex --user +Set user @var{user} in the target security context. + +@item -r @var{role} +@itemx --role=@var{role} +@opindex -r +@opindex --role +Set role @var{role} in the target security context. + +@item -t @var{type} +@itemx --type=@var{type} +@opindex -t +@opindex --type +Set type @var{type} in the target security context. + +@item -l @var{range} +@itemx --range=@var{range} +@opindex -l +@opindex --range +Set range @var{range} in the target security context. + +@end table + +@exitstatus + +@node runcon invocation +@section @command{runcon}: Run a command in specified SELinux context + +@pindex runcon +@cindex run with security context + + +@command{runcon} runs file in specified SELinux security context. + +Synopses: +@example +runcon @var{context} @var{command} [@var{args}] +runcon [ -c ] [-u @var{user}] [-r @var{role}] [-t @var{type}]@c + [-l @var{range}] @var{command} [@var{args}] +@end example + +Run @var{command} with completely-specified @var{context}, or with +current or transitioned security context modified by one or more of @var{level}, +@var{role}, @var{type} and @var{user}. + +If none of @option{-c}, @option{-t}, @option{-u}, @option{-r}, or @option{-l} +is specified, the first argument is used as the complete context. +Any additional arguments after @var{command} +are interpreted as arguments to the command. + +With neither @var{context} nor @var{command}, print the current +security context. + +@cindex restricted security context +@cindex NO_NEW_PRIVS +Note also the @command{setpriv} command which can be used to set the +NO_NEW_PRIVS bit using @command{setpriv --no-new-privs runcon ...}, +thus disallowing usage of a security context with more privileges +than the process would normally have. + +@command{runcon} accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -c +@itemx --compute +@opindex -c +@opindex --compute +Compute process transition context before modifying. + +@item -u @var{user} +@itemx --user=@var{user} +@opindex -u +@opindex --user +Set user @var{user} in the target security context. + +@item -r @var{role} +@itemx --role=@var{role} +@opindex -r +@opindex --role +Set role @var{role} in the target security context. + +@item -t @var{type} +@itemx --type=@var{type} +@opindex -t +@opindex --type +Set type @var{type} in the target security context. + +@item -l @var{range} +@itemx --range=@var{range} +@opindex -l +@opindex --range +Set range @var{range} in the target security context. + +@end table + +@cindex exit status of @command{runcon} +Exit status: + +@display +125 if @command{runcon} itself fails +126 if @var{command} is found but cannot be invoked +127 if @var{command} cannot be found +the exit status of @var{command} otherwise +@end display + +@node Modified command invocation +@chapter Modified command invocation + +@cindex modified command invocation +@cindex invocation of commands, modified +@cindex commands for invoking other commands + +This section describes commands that run other commands in some context +different than the current one: a modified environment, as a different +user, etc. + +@menu +* chroot invocation:: Modify the root directory. +* env invocation:: Modify environment variables. +* nice invocation:: Modify niceness. +* nohup invocation:: Immunize to hangups. +* stdbuf invocation:: Modify buffering of standard streams. +* timeout invocation:: Run with time limit. +@end menu + + +@node chroot invocation +@section @command{chroot}: Run a command with a different root directory + +@pindex chroot +@cindex running a program in a specified root directory +@cindex root directory, running a program in a specified + +@command{chroot} runs a command with a specified root directory. +On many systems, only the super-user can do this.@footnote{However, +some systems (e.g., FreeBSD) can be configured to allow certain regular +users to use the @code{chroot} system call, and hence to run this program. +Also, on Cygwin, anyone can run the @command{chroot} command, because the +underlying function is non-privileged due to lack of support in MS-Windows. +Furthermore, the @command{chroot} command avoids the @code{chroot} system call +when @var{newroot} is identical to the old @file{/} directory for consistency +with systems where this is allowed for non-privileged users.}. +Synopses: + +@example +chroot @var{option} @var{newroot} [@var{command} [@var{args}]@dots{}] +chroot @var{option} +@end example + +Ordinarily, file names are looked up starting at the root of the +directory structure, i.e., @file{/}. @command{chroot} changes the root to +the directory @var{newroot} (which must exist), then changes the working +directory to @file{/}, and finally runs @var{command} with optional @var{args}. +If @var{command} is not specified, the default is the value of the @env{SHELL} +environment variable or @command{/bin/sh} if not set, invoked with the +@option{-i} option. +@var{command} must not be a special built-in utility +(@pxref{Special built-in utilities}). + +The program accepts the following options. Also see @ref{Common options}. +Options must precede operands. + +@table @samp + +@item --groups=@var{groups} +@opindex --groups +Use this option to override the supplementary @var{groups} to be +used by the new process. +The items in the list (names or numeric IDs) must be separated by commas. +Use @samp{--groups=''} to disable the supplementary group look-up +implicit in the @option{--userspec} option. + +@item --userspec=@var{user}[:@var{group}] +@opindex --userspec +By default, @var{command} is run with the same credentials +as the invoking process. +Use this option to run it as a different @var{user} and/or with a +different primary @var{group}. +If a @var{user} is specified then the supplementary groups +are set according to the system defined list for that user, +unless overridden with the @option{--groups} option. + +@item --skip-chdir +@opindex --skip-chdir +Use this option to not change the working directory to @file{/} after changing +the root directory to @var{newroot}, i.e., inside the chroot. +This option is only permitted when @var{newroot} is the old @file{/} directory, +and therefore is mostly useful together with the @option{--groups} and +@option{--userspec} options to retain the previous working directory. + +@end table + +The user and group name look-up performed by the @option{--userspec} +and @option{--groups} options, is done both outside and inside +the chroot, with successful look-ups inside the chroot taking precedence. +If the specified user or group items are intended to represent a numeric ID, +then a name to ID resolving step is avoided by specifying a leading @samp{+}. +@xref{Disambiguating names and IDs}. + +Here are a few tips to help avoid common problems in using chroot. +To start with a simple example, make @var{command} refer to a statically +linked binary. If you were to use a dynamically linked executable, then +you'd have to arrange to have the shared libraries in the right place under +your new root directory. + +For example, if you create a statically linked @command{ls} executable, +and put it in @file{/tmp/empty}, you can run this command as root: + +@example +$ chroot /tmp/empty /ls -Rl / +@end example + +Then you'll see output like this: + +@example +/: +total 1023 +-rwxr-xr-x 1 0 0 1041745 Aug 16 11:17 ls +@end example + +If you want to use a dynamically linked executable, say @command{bash}, +then first run @samp{ldd bash} to see what shared objects it needs. +Then, in addition to copying the actual binary, also copy the listed +files to the required positions under your intended new root directory. +Finally, if the executable requires any other files (e.g., data, state, +device files), copy them into place, too. + +@command{chroot} is installed only on systems that have the +@code{chroot} function, so portable scripts should not rely on its +existence. + +@cindex exit status of @command{chroot} +Exit status: + +@display +125 if @command{chroot} itself fails +126 if @var{command} is found but cannot be invoked +127 if @var{command} cannot be found +the exit status of @var{command} otherwise +@end display + + +@node env invocation +@section @command{env}: Run a command in a modified environment + +@pindex env +@cindex environment, running a program in a modified +@cindex modified environment, running a program in a +@cindex running a program in a modified environment + +@command{env} runs a command with a modified environment. Synopses: + +@example +env [@var{option}]@dots{} [@var{name}=@var{value}]@dots{} @c +[@var{command} [@var{args}]@dots{}] +env -[v]S'[@var{option}]@dots{} [@var{name}=@var{value}]@dots{} @c +[@var{command} [@var{args}]@dots{}]' +env +@end example + +@command{env} is commonly used on first line of scripts (shebang line): +@example +#!/usr/bin/env @var{command} +#!/usr/bin/env -[v]S[@var{option}]@dots{} [@var{name}=@var{value}]@dots{} @c +@var{command} [@var{args}]@dots{} +@end example + +Operands of the form @samp{@var{variable}=@var{value}} set +the environment variable @var{variable} to value @var{value}. +@var{value} may be empty (@samp{@var{variable}=}). Setting a variable +to an empty value is different from unsetting it. +These operands are evaluated left-to-right, so if two operands +mention the same variable the earlier is ignored. + +Environment variable names can be empty, and can contain any +characters other than @samp{=} and ASCII NUL. +However, it is wise to limit yourself to names that +consist solely of underscores, digits, and ASCII letters, +and that begin with a non-digit, as applications like the shell do not +work well with other names. + +@vindex PATH +The first operand that does not contain the character @samp{=} +specifies the program to invoke; it is +searched for according to the @env{PATH} environment variable. Any +remaining arguments are passed as arguments to that program. +The program should not be a special built-in utility +(@pxref{Special built-in utilities}). + +Modifications to @env{PATH} take effect prior to searching for +@var{command}. Use caution when reducing @env{PATH}; behavior is +not portable when @env{PATH} is undefined or omits key directories +such as @file{/bin}. + +In the rare case that a utility contains a @samp{=} in the name, the +only way to disambiguate it from a variable assignment is to use an +intermediate command for @var{command}, and pass the problematic +program name via @var{args}. For example, if @file{./prog=} is an +executable in the current @env{PATH}: + +@example +env prog= true # runs 'true', with prog= in environment +env ./prog= true # runs 'true', with ./prog= in environment +env -- prog= true # runs 'true', with prog= in environment +env sh -c '\prog= true' # runs 'prog=' with argument 'true' +env sh -c 'exec "$@@"' sh prog= true # also runs 'prog=' +@end example + +@cindex environment, printing + +If no command name is specified following the environment +specifications, the resulting environment is printed. This is like +specifying the @command{printenv} program. + +For some examples, suppose the environment passed to @command{env} +contains @samp{LOGNAME=rms}, @samp{EDITOR=emacs}, and +@samp{PATH=.:/gnubin:/hacks}: + +@itemize @bullet + +@item +Output the current environment. +@example +$ env | LC_ALL=C sort +EDITOR=emacs +LOGNAME=rms +PATH=.:/gnubin:/hacks +@end example + +@item +Run @command{foo} with a reduced environment, preserving only the +original @env{PATH} to avoid problems in locating @command{foo}. +@example +env - PATH="$PATH" foo +@end example + +@item +Run @command{foo} with the environment containing @samp{LOGNAME=rms}, +@samp{EDITOR=emacs}, and @samp{PATH=.:/gnubin:/hacks}, and guarantees +that @command{foo} was found in the file system rather than as a shell +built-in. +@example +env foo +@end example + +@item +Run @command{nemacs} with the environment containing @samp{LOGNAME=foo}, +@samp{EDITOR=emacs}, @samp{PATH=.:/gnubin:/hacks}, and +@samp{DISPLAY=gnu:0}. +@example +env DISPLAY=gnu:0 LOGNAME=foo nemacs +@end example + +@item +Attempt to run the program @command{/energy/--} (as that is the only +possible path search result); if the command exists, the environment +will contain @samp{LOGNAME=rms} and @samp{PATH=/energy}, and the +arguments will be @samp{e=mc2}, @samp{bar}, and @samp{baz}. +@example +env -u EDITOR PATH=/energy -- e=mc2 bar baz +@end example + +@end itemize + + +@subsection General options + +The program accepts the following options. Also see @ref{Common options}. +Options must precede operands. + +@table @samp + +@optNull + +@item -u @var{name} +@itemx --unset=@var{name} +@opindex -u +@opindex --unset +Remove variable @var{name} from the environment, if it was in the +environment. + +@item - +@itemx -i +@itemx --ignore-environment +@opindex - +@opindex -i +@opindex --ignore-environment +Start with an empty environment, ignoring the inherited environment. + +@item -C @var{dir} +@itemx --chdir=@var{dir} +@opindex -C +@opindex --chdir +Change the working directory to @var{dir} before invoking @var{command}. +This differs from the shell built-in @command{cd} in that it starts +@var{command} as a subprocess rather than altering the shell's own working +directory; this allows it to be chained with other commands that run commands +in a different context. For example: + +@example +# Run 'true' with /chroot as its root directory and /srv as its working +# directory. +chroot /chroot env --chdir=/srv true +# Run 'true' with /build as its working directory, FOO=bar in its +# environment, and a time limit of five seconds. +env --chdir=/build FOO=bar timeout 5 true +@end example + +@item --default-signal[=@var{sig}] +Unblock and reset signal @var{sig} to its default signal handler. +Without @var{sig} all known signals are unblocked and reset to their defaults. +Multiple signals can be comma-separated. An empty @var{sig} argument is a no-op. +The following command runs @command{seq} with SIGINT and SIGPIPE set to their +default (which is to terminate the program): + +@example +env --default-signal=PIPE,INT seq 1000 | head -n1 +@end example + +In the following example, we see how this is not +possible to do with traditional shells. +Here the first trap command sets SIGPIPE to ignore. +The second trap command ostensibly sets it back to its default, +but POSIX mandates that the shell must not change inherited +state of the signal -- so it is a no-op. + +@example +trap '' PIPE && sh -c 'trap - PIPE ; seq inf | head -n1' +@end example + +Using @option{--default-signal=PIPE} we can +ensure the signal handling is set to its default behavior: + +@example +trap '' PIPE && sh -c 'env --default-signal=PIPE seq inf | head -n1' +@end example + + +@item --ignore-signal[=@var{sig}] +Ignore signal @var{sig} when running a program. Without @var{sig} all +known signals are set to ignore. Multiple signals can be comma-separated. +An empty @var{sig} argument is a no-op. The following command runs @command{seq} +with SIGINT set to be ignored -- pressing @kbd{Ctrl-C} will not terminate it: + +@example +env --ignore-signal=INT seq inf > /dev/null +@end example + +@samp{SIGCHLD} is special, in that @option{--ignore-signal=CHLD} might have +no effect (POSIX says it's unspecified). + +Most operating systems do not allow ignoring @samp{SIGKILL}, @samp{SIGSTOP} +(and possibly other signals). Attempting to ignore these signals will fail. + +Multiple (and contradictory) @option{--default-signal=SIG} and +@option{--ignore-signal=SIG} options are processed left-to-right, +with the latter taking precedence. In the following example, @samp{SIGPIPE} is +set to default while @samp{SIGINT} is ignored: + +@example +env --default-signal=INT,PIPE --ignore-signal=INT +@end example + +@item --block-signal[=@var{sig}] +Block signal(s) @var{sig} from being delivered. Without @var{sig} all +known signals are set to blocked. Multiple signals can be comma-separated. +An empty @var{sig} argument is a no-op. + +@item --list-signal-handling +List blocked or ignored signals to standard error, before executing a command. + +@item -v +@itemx --debug +@opindex -v +@opindex --debug +Show verbose information for each processing step. + +@example +$ env -v -uTERM A=B uname -s +unset: TERM +setenv: A=B +executing: uname + arg[0]= 'uname' + arg[1]= '-s' +Linux +@end example + +When combined with @option{-S} it is recommended to list @option{-v} +first, e.g. @command{env -vS'string'}. + +@item -S @var{string} +@itemx --split-string=@var{string} +@opindex -S +@opindex --split-string +@cindex shebang arguments +@cindex scripts arguments +@cindex env in scripts +process and split @var{string} into separate arguments used to pass +multiple arguments on shebang lines. @command{env} supports FreeBSD's +syntax of several escape sequences and environment variable +expansions. See below for details and examples. + +@end table + +@cindex exit status of @command{env} +Exit status: + +@display +0 if no @var{command} is specified and the environment is output +125 if @command{env} itself fails +126 if @var{command} is found but cannot be invoked +127 if @var{command} cannot be found +the exit status of @var{command} otherwise +@end display + +@subsection @option{-S}/@option{--split-string} usage in scripts + +The @option{-S}/@option{--split-string} option enables use of multiple +arguments on the first line of scripts (the shebang line, @samp{#!}). + +When a script's interpreter is in a known location, scripts typically +contain the absolute file name in their first line: + +@multitable {Python Script:} {#!/usr/bin/python3} +@item Shell script: +@tab +@example +#!/bin/sh +echo hello +@end example + +@item Perl script: +@tab +@example +#!/usr/bin/perl +print "hello\n"; +@end example + +@item Python script: +@tab +@example +#!/usr/bin/python3 +print("hello") +@end example + +@end multitable + +When a script's interpreter is in a non-standard location +in the @env{PATH} environment variable, it is recommended +to use @command{env} on the first line of the script to +find the executable and run it: + +@multitable {Python Script:} {#!/usr/bin/env python3} +@item Shell script: +@tab +@example +#!/usr/bin/env bash +echo hello +@end example + +@item Perl script: +@tab +@example +#!/usr/bin/env perl +print "hello\n"; +@end example + +@item Python script: +@tab +@example +#!/usr/bin/env python3 +print("hello") +@end example + +@end multitable + +Most operating systems (e.g. GNU/Linux, BSDs) treat all text after the +first space as a single argument. When using @command{env} in a script +it is thus not possible to specify multiple arguments. + +In the following example: +@example +#!/usr/bin/env perl -T -w +print "hello\n"; +@end example + +The operating system treats @samp{perl -T -w} as one argument (the +program's name), and executing the script fails with: + +@example +/usr/bin/env: 'perl -T -w': No such file or directory +@end example + +The @option{-S} option instructs @command{env} to split the single string +into multiple arguments. The following example works as expected: + +@example +$ cat hello.pl +#!/usr/bin/env -S perl -T -w +print "hello\n"; + +$ chmod a+x hello.pl +$ ./hello.pl +hello +@end example + +And is equivalent to running @command{perl -T -w hello.pl} on the command line +prompt. + +@unnumberedsubsubsec Testing and troubleshooting + +@cindex single quotes, and @command{env -S} +@cindex @command{env -S}, and single quotes +@cindex @option{-S}, env and single quotes +To test @command{env -S} on the command line, use single quotes for the +@option{-S} string to emulate a single parameter. Single quotes are not +needed when using @command{env -S} in a shebang line on the first line of a +script (the operating system already treats it as one argument). + +The following command is equivalent to the @file{hello.pl} script above: + +@example +$ env -S'perl -T -w' hello.pl +@end example + +@cindex @command{env -S}, debugging +@cindex debugging, @command{env -S} + +To troubleshoot @option{-S} usage add the @option{-v} as the first +argument (before @option{-S}). + +Using @option{-vS} on a shebang line in a script: + +@example +$ cat hello-debug.pl +#!/usr/bin/env -vS perl -T -w +print "hello\n"; + +$ chmod a+x hello-debug.pl +$ ./hello-debug.pl +split -S: 'perl -T -w' + into: 'perl' + & '-T' + & '-w' +executing: perl + arg[0]= 'perl' + arg[1]= '-T' + arg[2]= '-w' + arg[3]= './hello-debug.pl' +hello +@end example + +Using @option{-vS} on the command line prompt (adding single quotes): + +@example +$ env -vS'perl -T -w' hello-debug.pl +split -S: 'perl -T -w' + into: 'perl' + & '-T' + & '-w' +executing: perl + arg[0]= 'perl' + arg[1]= '-T' + arg[2]= '-w' + arg[3]= 'hello-debug.pl' +hello +@end example + +@subsection @option{-S}/@option{--split-string} syntax + +@unnumberedsubsubsec Splitting arguments by whitespace + +Running @command{env -Sstring} splits the @var{string} into +arguments based on unquoted spaces or tab characters. +(Newlines, carriage returns, vertical tabs and form feeds are treated +like spaces and tabs.) + +In the following contrived example the @command{awk} variable +@samp{OFS} will be @code{<space>xyz<space>} as these spaces are inside +double quotes. The other space characters are used as argument separators: + +@example +$ cat one.awk +#!/usr/bin/env -S awk -v OFS=" xyz " -f +BEGIN @{print 1,2,3@} + +$ chmod a+x one.awk +$ ./one.awk +1 xyz 2 xyz 3 +@end example + +When using @option{-S} on the command line prompt, remember to add +single quotes around the entire string: + +@example +$ env -S'awk -v OFS=" xyz " -f' one.awk +1 xyz 2 xyz 3 +@end example + +@unnumberedsubsubsec Escape sequences + +@command{env} supports several escape sequences. These sequences +are processed when unquoted or inside double quotes (unless otherwise noted). +Single quotes disable escape sequences except @samp{\'} and @samp{\\}. + +@multitable @columnfractions .10 .90 + +@item @code{\c} +@tab Ignore the remaining characters in the string. +Cannot be used inside double quotes. + +@item @code{\f} +@tab form-feed character (ASCII 0x0C) + +@item @code{\n} +@tab new-line character (ASCII 0x0A) + +@item @code{\r} +@tab carriage-return character (ASCII 0x0D) + +@item @code{\t} +@tab tab character (ASCII 0x09) + +@item @code{\v} +@tab vertical tab character (ASCII 0x0B) + +@item @code{\#} +@tab A hash @samp{#} character. Used when a @samp{#} character +is needed as the first character of an argument (see 'comments' section +below). + +@item @code{\$} +@tab A dollar-sign character @samp{$}. Unescaped @samp{$} characters +are used to expand environment variables (see 'variables' section below). + +@item @code{\_} +@tab Inside double-quotes, replaced with a single space character. +Outside quotes, treated as an argument separator. @samp{\_} can be used +to avoid space characters in a shebang line (see examples below). + +@item @code{\"} +@tab A double-quote character. + +@item @code{\'} +@tab A single-quote character. +This escape sequence works inside single-quoted strings. + +@item @code{\\} +@tab A backslash character. +This escape sequence works inside single-quoted strings. + +@end multitable + +The following @command{awk} script will use tab character as input and output +field separator (instead of spaces and tabs): + +@example +$ cat tabs.awk +#!/usr/bin/env -S awk -v FS="\t" -v OFS="\t" -f +... +@end example + +@unnumberedsubsubsec Comments + +The escape sequence @samp{\c} (used outside single/double quotes) +causes @command{env} to ignore the rest of the string. + +The @samp{#} character causes @command{env} to ignore the rest of +the string when it appears as the first character of an argument. +Use @samp{\#} to reverse this behavior. + +@example +$ env -S'printf %s\n A B C' +A +B +C + +$ env -S'printf %s\n A# B C' +A# +B +C + +$ env -S'printf %s\n A #B C' +A + +$ env -S'printf %s\n A \#B C' +A +#B +C + +$ env -S'printf %s\n A\cB C' +A +@end example + +NOTE: The above examples use single quotes as they are executed +on the command-line. + + + +@unnumberedsubsubsec Environment variable expansion + +The pattern @samp{$@{VARNAME@}} is used to substitute a value from +the environment variable. The pattern must include the curly braces +(@samp{@{},@samp{@}}). Without them @command{env} will reject the string. +Special shell variables (such as @samp{$@@}, @samp{$*}, @samp{$$}) are +not supported. + +If the environment variable is empty or not set, the pattern will be replaced +by an empty string. The value of @samp{$@{VARNAME@}} will be that of +the executed @command{env}, before any modifications using +@option{-i}/@option{--ignore-environment}/@option{-u}/@option{--unset} or +setting new values using @samp{VAR=VALUE}. + +The following python script prepends @file{/opt/custom/modules} to the python +module search path environment variable (@samp{PYTHONPATH}): + +@example +$ cat custom.py +#!/usr/bin/env -S PYTHONPATH=/opt/custom/modules/:$@{PYTHONPATH@} python +print "hello" +... +@end example + +The expansion of @samp{$@{PYTHONPATH@}} is performed by @command{env}, +not by a shell. If the curly braces are omitted, @command{env} will fail: + +@example +$ cat custom.py +#!/usr/bin/env -S PYTHONPATH=/opt/custom/modules/:$PYTHONPATH python +print "hello" +... + +$ chmod a+x custom.py +$ custom.py +/usr/bin/env: only $@{VARNAME@} expansion is supported, error at: $PYTHONPATH @c +python +@end example + +Environment variable expansion happens before clearing the environment +(with @option{-i}) or unsetting specific variables (with @option{-u}): + +@example +$ env -S'-i OLDUSER=$@{USER@} env' +OLDUSER=gordon +@end example + +Use @option{-v} to diagnose the operations step-by-step: + +@example +$ env -vS'-i OLDUSER=$@{USER@} env' +expanding $@{USER@} into 'gordon' +split -S: '-i OLDUSER=$@{USER@} env' + into: '-i' + & 'OLDUSER=gordon' + & 'env' +cleaning environ +setenv: OLDUSER=gordon +executing: env + arg[0]= 'env' +OLDUSER=gordon +@end example + + + +@node nice invocation +@section @command{nice}: Run a command with modified niceness + +@pindex nice +@cindex niceness +@cindex scheduling, affecting +@cindex appropriate privileges + +@command{nice} prints a process's @dfn{niceness}, or runs +a command with modified niceness. @dfn{niceness} affects how +favorably the process is scheduled in the system. +Synopsis: + +@example +nice [@var{option}]@dots{} [@var{command} [@var{arg}]@dots{}] +@end example + +If no arguments are given, @command{nice} prints the current niceness. +Otherwise, @command{nice} runs the given @var{command} with its +niceness adjusted. By default, its niceness is incremented by 10. + +Niceness values range at least from @minus{}20 (process has high priority +and gets more resources, thus slowing down other processes) through 19 +(process has lower priority and runs slowly itself, but has less impact +on the speed of other running processes). Some systems +may have a wider range of niceness values; conversely, other systems may +enforce more restrictive limits. An attempt to set the niceness +outside the supported range is treated as an attempt to use the +minimum or maximum supported value. + +A niceness should not be confused with a scheduling priority, which +lets applications determine the order in which threads are scheduled +to run. Unlike a priority, a niceness is merely advice to the +scheduler, which the scheduler is free to ignore. Also, as a point of +terminology, POSIX defines the behavior of @command{nice} in +terms of a @dfn{nice value}, which is the non-negative difference +between a niceness and the minimum niceness. Though @command{nice} +conforms to POSIX, its documentation and diagnostics use the +term ``niceness'' for compatibility with historical practice. + +@var{command} must not be a special built-in utility (@pxref{Special +built-in utilities}). + +@mayConflictWithShellBuiltIn{nice} + +Note to change the @dfn{niceness} of an existing process, +one needs to use the @command{renice} command. + +The program accepts the following option. Also see @ref{Common options}. +Options must precede operands. + +@table @samp +@item -n @var{adjustment} +@itemx --adjustment=@var{adjustment} +@opindex -n +@opindex --adjustment +Add @var{adjustment} instead of 10 to the command's niceness. If +@var{adjustment} is negative and you lack appropriate privileges, +@command{nice} issues a warning but otherwise acts as if you specified +a zero adjustment. + +For compatibility @command{nice} also supports an obsolete +option syntax @option{-@var{adjustment}}. New scripts should use +@option{-n @var{adjustment}} instead. + +@end table + +@command{nice} is installed only on systems that have the POSIX +@code{setpriority} function, so portable scripts should not rely on +its existence on non-POSIX platforms. + +@cindex exit status of @command{nice} +Exit status: + +@display +0 if no @var{command} is specified and the niceness is output +125 if @command{nice} itself fails +126 if @var{command} is found but cannot be invoked +127 if @var{command} cannot be found +the exit status of @var{command} otherwise +@end display + +It is sometimes useful to run a non-interactive program with reduced niceness. + +@example +$ nice factor 4611686018427387903 +@end example + +Since @command{nice} prints the current niceness, +you can invoke it through itself to demonstrate how it works. + +The default behavior is to increase the niceness by @samp{10}: + +@example +$ nice +0 +$ nice nice +10 +$ nice -n 10 nice +10 +@end example + +The @var{adjustment} is relative to the current niceness. In the +next example, the first @command{nice} invocation runs the second one +with niceness 10, and it in turn runs the final one with a niceness +that is 3 more: + +@example +$ nice nice -n 3 nice +13 +@end example + +Specifying a niceness larger than the supported range +is the same as specifying the maximum supported value: + +@example +$ nice -n 10000000000 nice +19 +@end example + +Only a privileged user may run a process with lower niceness: + +@example +$ nice -n -1 nice +nice: cannot set niceness: Permission denied +0 +$ sudo nice -n -1 nice +-1 +@end example + + +@node nohup invocation +@section @command{nohup}: Run a command immune to hangups + +@pindex nohup +@cindex hangups, immunity to +@cindex immunity to hangups +@cindex logging out and continuing to run + +@flindex nohup.out +@command{nohup} runs the given @var{command} with hangup signals ignored, +so that the command can continue running in the background after you log +out. Synopsis: + +@example +nohup @var{command} [@var{arg}]@dots{} +@end example + +If standard input is a terminal, redirect it so that terminal sessions +do not mistakenly consider the terminal to be used by the command. +Make the substitute file descriptor unreadable, so that commands that +mistakenly attempt to read from standard input can report an error. +This redirection is a GNU extension; programs intended to be portable +to non-GNU hosts can use @samp{nohup @var{command} [@var{arg}]@dots{} +0>/dev/null} instead. + +@flindex nohup.out +If standard output is a terminal, the command's standard output is appended +to the file @file{nohup.out}; if that cannot be written to, it is appended +to the file @file{$HOME/nohup.out}; and if that cannot be written to, the +command is not run. +Any @file{nohup.out} or @file{$HOME/nohup.out} file created by +@command{nohup} is made readable and writable only to the user, +regardless of the current umask settings. + +If standard error is a terminal, it is normally redirected to the same file +descriptor as the (possibly-redirected) standard output. +However, if standard output is closed, standard error terminal output +is instead appended to the file @file{nohup.out} or +@file{$HOME/nohup.out} as above. + +To capture the command's output to a file other than @file{nohup.out} +you can redirect it. For example, to capture the output of +@command{make}: + +@example +nohup make > make.log +@end example + +@command{nohup} does not automatically put the command it runs in the +background; you must do that explicitly, by ending the command line +with an @samp{&}. Also, @command{nohup} does not alter the +niceness of @var{command}; use @command{nice} for that, +e.g., @samp{nohup nice @var{command}}. + +@var{command} must not be a special built-in utility (@pxref{Special +built-in utilities}). + +The only options are @option{--help} and @option{--version}. @xref{Common +options}. Options must precede operands. + +@cindex exit status of @command{nohup} +Exit status: + +@display +125 if @command{nohup} itself fails, and @env{POSIXLY_CORRECT} is not set +126 if @var{command} is found but cannot be invoked +127 if @var{command} cannot be found +the exit status of @var{command} otherwise +@end display + +If @env{POSIXLY_CORRECT} is set, internal failures give status 127 +instead of 125. + + +@node stdbuf invocation +@section @command{stdbuf}: Run a command with modified I/O stream buffering + +@pindex stdbuf +@cindex standard streams, buffering +@cindex line buffered + +@command{stdbuf} allows one to modify the buffering operations of the +three standard I/O streams associated with a program. Synopsis: + +@example +stdbuf @var{option}@dots{} @var{command} +@end example + +@var{command} must start with the name of a program that +@enumerate +@item +uses the ISO C @code{FILE} streams for input/output (note the +programs @command{dd} and @command{cat} don't do that), + +@item +does not adjust the buffering of its standard streams (note the +program @command{tee} is not in this category). +@end enumerate + +Any additional @var{arg}s are passed as additional arguments to the +@var{command}. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item -i @var{mode} +@itemx --input=@var{mode} +@opindex -i +@opindex --input +Adjust the standard input stream buffering. + +@item -o @var{mode} +@itemx --output=@var{mode} +@opindex -o +@opindex --output +Adjust the standard output stream buffering. + +@item -e @var{mode} +@itemx --error=@var{mode} +@opindex -e +@opindex --error +Adjust the standard error stream buffering. + +@end table + +The @var{mode} can be specified as follows: + +@table @samp + +@item L +Set the stream to line buffered mode. +In this mode data is coalesced until a newline is output or +input is read from any stream attached to a terminal device. +This option is invalid with standard input. + +@item 0 +Disable buffering of the selected stream. +In this mode, data is output immediately and only the +amount of data requested is read from input. +Note the difference in function for input and output. +Disabling buffering for input will not influence the responsiveness +or blocking behavior of the stream input functions. +For example @code{fread} will still block until @code{EOF} or error, +even if the underlying @code{read} returns less data than requested. + +@item @var{size} +Specify the size of the buffer to use in fully buffered mode. +@multiplierSuffixesNoBlocks{size} + +@end table + +@command{stdbuf} is installed only on platforms that use the +Executable and Linkable Format (ELF) and support the +@code{constructor} attribute, so portable scripts should not rely on +its existence. + +@cindex exit status of @command{stdbuf} +Exit status: + +@display +125 if @command{stdbuf} itself fails +126 if @var{command} is found but cannot be invoked +127 if @var{command} cannot be found +the exit status of @var{command} otherwise +@end display + + +@node timeout invocation +@section @command{timeout}: Run a command with a time limit + +@pindex timeout +@cindex time limit +@cindex run commands with bounded time + +@command{timeout} runs the given @var{command} and kills it if it is +still running after the specified time interval. Synopsis: + +@example +timeout [@var{option}] @var{duration} @var{command} [@var{arg}]@dots{} +@end example + +@var{command} must not be a special built-in utility (@pxref{Special +built-in utilities}). + +The program accepts the following options. Also see @ref{Common options}. +Options must precede operands. + +@table @samp +@item --preserve-status +@opindex --preserve-status +Return the exit status of the managed @var{command} on timeout, rather than +a specific exit status indicating a timeout. This is useful if the +managed @var{command} supports running for an indeterminate amount of time. + +@item --foreground +@opindex --foreground +Don't create a separate background program group, so that +the managed @var{command} can use the foreground TTY normally. +This is needed to support two situations when timing out commands, +when not invoking @command{timeout} from an interactive shell. +@enumerate +@item +@var{command} is interactive and needs to read from the terminal for example +@item +the user wants to support sending signals directly to @var{command} +from the terminal (like Ctrl-C for example) +@end enumerate + +Note in this mode of operation, any children of @var{command} +will not be timed out. Also SIGCONT will not be sent to @var{command}, +as it's generally not needed with foreground processes, and can +cause intermittent signal delivery issues with programs that are monitors +themselves (like GDB for example). + +@item -k @var{duration} +@itemx --kill-after=@var{duration} +@opindex -k +@opindex --kill-after +Ensure the monitored @var{command} is killed by also sending a @samp{KILL} +signal. + +The specified @var{duration} starts from the point in time when +@command{timeout} sends the initial signal to @var{command}, i.e., +not from the beginning when the @var{command} is started. + +This option has no effect if either the main @var{duration} +of the @command{timeout} command, or the @var{duration} specified +to this option, is 0. + +This option may be useful if the selected signal did not kill the @var{command}, +either because the signal was blocked or ignored, or if the @var{command} takes +too long (e.g. for cleanup work) to terminate itself within a certain amount +of time. + +@item -s @var{signal} +@itemx --signal=@var{signal} +@opindex -s +@opindex --signal +Send this @var{signal} to @var{command} on timeout, rather than the +default @samp{TERM} signal. @var{signal} may be a name like @samp{HUP} +or a number. @xref{Signal specifications}. + +@item -v +@itemx --verbose +@opindex -v +@opindex --verbose +Diagnose to standard error, any signal sent upon timeout. +@end table + +@cindex time units +@var{duration} is a floating point number in either the current or the +C locale (@pxref{Floating point}) followed by an optional unit: +@display +@samp{s} for seconds (the default) +@samp{m} for minutes +@samp{h} for hours +@samp{d} for days +@end display +A duration of 0 disables the associated timeout. +Note that the actual timeout duration is dependent on system conditions, +which should be especially considered when specifying sub-second timeouts. + +@cindex exit status of @command{timeout} +Exit status: + +@display +124 if @var{command} times out, and @option{--preserve-status} is not specified +125 if @command{timeout} itself fails +126 if @var{command} is found but cannot be invoked +127 if @var{command} cannot be found +137 if @var{command} or @command{timeout} is sent the KILL(9) signal (128+9) +the exit status of @var{command} otherwise +@end display + +In the case of the @samp{KILL(9)} signal, @command{timeout} returns with +exit status 137, regardless of whether that signal is sent to @var{command} +or to @command{timeout} itself, i.e., these cases cannot be distinguished. +In the latter case, the @var{command} process may still be alive after +@command{timeout} has forcefully been terminated. + +Examples: + +@example +# Send the default TERM signal after 20s to a short-living 'sleep 1'. +# As that terminates long before the given duration, 'timeout' returns +# with the same exit status as the command, 0 in this case. +timeout 20 sleep 1 + +# Send the INT signal after 5s to the 'sleep' command. Returns after +# 5 seconds with exit status 124 to indicate the sending of the signal. +timeout -s INT 5 sleep 20 + +# Likewise, but the command ignoring the INT signal due to being started +# via 'env --ignore-signal'. Thus, 'sleep' terminates regularly after +# the full 20 seconds, still 'timeout' returns with exit status 124. +timeout -s INT 5s env --ignore-signal=INT sleep 20 + +# Likewise, but sending the KILL signal 3 seconds after the initial +# INT signal. Hence, 'sleep' is forcefully terminated after about +# 8 seconds (5+3), and 'timeout' returns with an exit status of 137. +timeout -s INT -k 3s 5s env --ignore-signal=INT sleep 20 +@end example + +@node Process control +@chapter Process control + +@cindex processes, commands for controlling +@cindex commands for controlling processes + +@menu +* kill invocation:: Sending a signal to processes. +@end menu + + +@node kill invocation +@section @command{kill}: Send a signal to processes + +@pindex kill +@cindex send a signal to processes + +The @command{kill} command sends a signal to processes, causing them +to terminate or otherwise act upon receiving the signal in some way. +Alternatively, it lists information about signals. Synopses: + +@example +kill [-s @var{signal} | --signal @var{signal} | -@var{signal}] @var{pid}@dots{} +kill [-l | --list | -t | --table] [@var{signal}]@dots{} +@end example + +@mayConflictWithShellBuiltIn{kill} + +The first form of the @command{kill} command sends a signal to all +@var{pid} arguments. The default signal to send if none is specified +is @samp{TERM}@. The special signal number @samp{0} does not denote a +valid signal, but can be used to test whether the @var{pid} arguments +specify processes to which a signal could be sent. + +If @var{pid} is positive, the signal is sent to the process with the +process ID @var{pid}. If @var{pid} is zero, the signal is sent to all +processes in the process group of the current process. If @var{pid} +is @minus{}1, the signal is sent to all processes for which the user has +permission to send a signal. If @var{pid} is less than @minus{}1, the signal +is sent to all processes in the process group that equals the absolute +value of @var{pid}. + +If @var{pid} is not positive, a system-dependent set of system +processes is excluded from the list of processes to which the signal +is sent. + +If a negative @var{pid} argument is desired as the first one, it +should be preceded by @option{--}. However, as a common extension to +POSIX, @option{--} is not required with @samp{kill +-@var{signal} -@var{pid}}. The following commands are equivalent: + +@example +kill -15 -1 +kill -TERM -1 +kill -s TERM -- -1 +kill -- -1 +@end example + +The first form of the @command{kill} command succeeds if every @var{pid} +argument specifies at least one process that the signal was sent to. + +The second form of the @command{kill} command lists signal information. +Either the @option{-l} or @option{--list} option, or the @option{-t} +or @option{--table} option must be specified. Without any +@var{signal} argument, all supported signals are listed. The output +of @option{-l} or @option{--list} is a list of the signal names, one +per line; if @var{signal} is already a name, the signal number is +printed instead. The output of @option{-t} or @option{--table} is a +table of signal numbers, names, and descriptions. This form of the +@command{kill} command succeeds if all @var{signal} arguments are valid +and if there is no output error. + +The @command{kill} command also supports the @option{--help} and +@option{--version} options. @xref{Common options}. + +A @var{signal} may be a signal name like @samp{HUP}, or a signal +number like @samp{1}, or an exit status of a process terminated by the +signal. A signal name can be given in canonical form or prefixed by +@samp{SIG}@. The case of the letters is ignored, except for the +@option{-@var{signal}} option which must use upper case to avoid +ambiguity with lower case option letters. +@xref{Signal specifications}, for a list of supported +signal names and numbers. + +@node Delaying +@chapter Delaying + +@cindex delaying commands +@cindex commands for delaying + +@c Perhaps @command{wait} or other commands should be described here also? + +@menu +* sleep invocation:: Delay for a specified time. +@end menu + + +@node sleep invocation +@section @command{sleep}: Delay for a specified time + +@pindex sleep +@cindex delay for a specified time + +@command{sleep} pauses for an amount of time specified by the sum of +the values of the command line arguments. +Synopsis: + +@example +sleep @var{number}[smhd]@dots{} +@end example + +@cindex time units +Each argument is a non-negative number followed by an optional unit; the default +is seconds. The units are: + +@table @samp +@item s +seconds +@item m +minutes +@item h +hours +@item d +days +@end table + +Although portable POSIX scripts must give @command{sleep} a single +non-negative integer argument without a suffix, GNU @command{sleep} +also accepts two or more arguments, unit suffixes, and floating-point +numbers in either the current or the C locale. @xref{Floating point}. + +For instance, the following could be used to @command{sleep} for +1 second, 234 milli-, 567 micro- and 890 nanoseconds: + +@example +sleep 1234e-3 567.89e-6 +@end example + +Also one could sleep indefinitely like: + +@example +sleep inf +@end example + +The only options are @option{--help} and @option{--version}. @xref{Common +options}. + +@c sleep is a shell built-in at least with Solaris 11's /bin/sh +@mayConflictWithShellBuiltIn{sleep} + +@exitstatus + + +@node Numeric operations +@chapter Numeric operations + +@cindex numeric operations +These programs do numerically-related operations. + +@menu +* factor invocation:: Show factors of numbers. +* numfmt invocation:: Reformat numbers. +* seq invocation:: Print sequences of numbers. +@end menu + + +@node factor invocation +@section @command{factor}: Print prime factors + +@pindex factor +@cindex prime factors + +@command{factor} prints prime factors. Synopsis: + +@example +factor [@var{option}]@dots{} [@var{number}]@dots{} +@end example + +If no @var{number} is specified on the command line, @command{factor} reads +numbers from standard input, delimited by newlines, tabs, or spaces. + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp +@item -h +@itemx --exponents +@opindex -h +@opindex --exponents +print factors in the form @math{p^e}, rather than repeating +the prime @samp{p}, @samp{e} times. If the exponent @samp{e} is 1, +then it is omitted. + +@example +$ factor --exponents 3000 +3000: 2^3 3 5^3 +@end example +@end table + +If the number to be factored is small (less than @math{2^{127}} on +typical machines), @command{factor} uses a faster algorithm. +For example, on a circa-2017 Intel Xeon Silver 4116, factoring the +product of the eighth and ninth Mersenne primes (approximately +@math{2^{92}}) takes about 4 ms of CPU time: + +@example +$ M8=$(echo 2^31-1 | bc) +$ M9=$(echo 2^61-1 | bc) +$ n=$(echo "$M8 * $M9" | bc) +$ bash -c "time factor $n" +4951760154835678088235319297: 2147483647 2305843009213693951 + +real 0m0.004s +user 0m0.004s +sys 0m0.000s +@end example + +For larger numbers, @command{factor} uses a slower algorithm. On the +same platform, factoring the eighth Fermat number @math{2^{256} + 1} +takes about 14 seconds, and the slower algorithm would have taken +about 750 ms to factor @math{2^{127} - 3} instead of the 50 ms needed by +the faster algorithm. + +Factoring large numbers is, in general, hard. The Pollard-Brent rho +algorithm used by @command{factor} is particularly effective for +numbers with relatively small factors. If you wish to factor large +numbers which do not have small factors (for example, numbers which +are the product of two large primes), other methods are far better. + +@exitstatus + + +@node numfmt invocation +@section @command{numfmt}: Reformat numbers + +@pindex numfmt + +@command{numfmt} reads numbers in various representations and reformats them +as requested. The most common usage is converting numbers to/from @emph{human} +representation (e.g. @samp{4G} @expansion{} @samp{4,000,000,000}). + +@example +numfmt [@var{option}]@dots{} [@var{number}] +@end example + +@command{numfmt} converts each @var{number} on the command-line according to the +specified options (see below). If no @var{number}s are given, it reads numbers +from standard input. @command{numfmt} can optionally extract numbers from +specific columns, maintaining proper line padding and alignment. + +@exitstatus + +See @option{--invalid} for additional information regarding exit status. + +@subsection General options + +The program accepts the following options. Also see @ref{Common options}. + +@table @samp + +@item --debug +@opindex --debug +Print (to standard error) warning messages about possible erroneous usage. + +@item -d @var{d} +@itemx --delimiter=@var{d} +@opindex -d +@opindex --delimiter +Use the character @var{d} as input field separator (default: whitespace). +@emph{Note}: Using non-default delimiter turns off automatic padding. + +@item --field=@var{fields} +@opindex --field +Convert the number in input field @var{fields} (default: 1). +@var{fields} supports @command{cut} style field ranges: + +@example +N N'th field, counted from 1 +N- from N'th field, to end of line +N-M from N'th to M'th field (inclusive) +-M from first to M'th field (inclusive) +- all fields +@end example + + +@item --format=@var{format} +@opindex --format +Use printf-style floating FORMAT string. The @var{format} string must contain +one @samp{%f} directive, optionally with @samp{'}, @samp{-}, @samp{0}, width +or precision modifiers. The @samp{'} modifier will enable @option{--grouping}, +the @samp{-} modifier will enable left-aligned @option{--padding} and the width +modifier will enable right-aligned @option{--padding}. The @samp{0} width +modifier (without the @samp{-} modifier) will generate leading zeros on the +number, up to the specified width. A precision specification like @samp{%.1f} +will override the precision determined from the input data or set due to +@option{--to} option auto scaling. + +@item --from=@var{unit} +@opindex --from +Auto-scales input numbers according to @var{unit}. See UNITS below. +The default is no scaling, meaning suffixes (e.g. @samp{M}, @samp{G}) will +trigger an error. + +@item --from-unit=@var{n} +@opindex --from-unit +Specify the input unit size (instead of the default 1). Use this option when +the input numbers represent other units (e.g. if the input number @samp{10} +represents 10 units of 512 bytes, use @samp{--from-unit=512}). +Suffixes are handled as with @samp{--from=auto}. + +@item --grouping +@opindex --grouping +Group digits in output numbers according to the current locale's grouping rules +(e.g @emph{Thousands Separator} character, commonly @samp{.} (dot) or @samp{,} +comma). This option has no effect in @samp{POSIX/C} locale. + +@item --header[=@var{n}] +@opindex --header +@opindex --header=N +Print the first @var{n} (default: 1) lines without any conversion. + +@item --invalid=@var{mode} +@opindex --invalid +The default action on input errors is to exit immediately with status code 2. +@option{--invalid=@samp{abort}} explicitly specifies this default mode. +With a @var{mode} of @samp{fail}, print a warning for @emph{each} conversion +error, and exit with status 2. With a @var{mode} of @samp{warn}, exit with +status 0, even in the presence of conversion errors, and with a @var{mode} of +@samp{ignore} do not even print diagnostics. + +@item --padding=@var{n} +@opindex --padding +Pad the output numbers to @var{n} characters, by adding spaces. If @var{n} is +a positive number, numbers will be right-aligned. If @var{n} is a negative +number, numbers will be left-aligned. By default, numbers are automatically +aligned based on the input line's width (only with the default delimiter). + +@item --round=@var{method} +@opindex --round +@opindex --round=up +@opindex --round=down +@opindex --round=from-zero +@opindex --round=towards-zero +@opindex --round=nearest +When converting number representations, round the number according to +@var{method}, which can be @samp{up}, @samp{down}, +@samp{from-zero} (the default), @samp{towards-zero}, @samp{nearest}. + +@item --suffix=@var{suffix} +@opindex --suffix +Add @samp{SUFFIX} to the output numbers, and accept optional @samp{SUFFIX} in +input numbers. + +@item --to=@var{unit} +@opindex --to +Auto-scales output numbers according to @var{unit}. See @emph{Units} below. +The default is no scaling, meaning all the digits of the number are printed. + +@item --to-unit=@var{n} +@opindex --to-unit +Specify the output unit size (instead of the default 1). Use this option when +the output numbers represent other units (e.g. to represent @samp{4,000,000} +bytes in blocks of 1KB, use @samp{--to=si --to-unit=1000}). +Suffixes are handled as with @samp{--from=auto}. + +@optZeroTerminated +@newlineFieldSeparator + +@end table + +@subsection Possible @var{unit}s: + +The following are the possible @var{unit} options with @option{--from=UNITS} and +@option{--to=UNITS}: + +@table @var + +@item none +No scaling is performed. For input numbers, no suffixes are accepted, and any +trailing characters following the number will trigger an error. For output +numbers, all digits of the numbers will be printed. + +@item si +Auto-scale numbers according to the @emph{International System of Units (SI)} +standard. +For input numbers, accept one of the following suffixes. +For output numbers, values larger than 1000 will be rounded, and printed with +one of the following suffixes: + +@example +@samp{K} => @math{1000^1 = 10^3} (Kilo) +@samp{M} => @math{1000^2 = 10^6} (Mega) +@samp{G} => @math{1000^3 = 10^9} (Giga) +@samp{T} => @math{1000^4 = 10^{12}} (Tera) +@samp{P} => @math{1000^5 = 10^{15}} (Peta) +@samp{E} => @math{1000^6 = 10^{18}} (Exa) +@samp{Z} => @math{1000^7 = 10^{21}} (Zetta) +@samp{Y} => @math{1000^8 = 10^{24}} (Yotta) +@samp{R} => @math{1000^9 = 10^{27}} (Ronna) +@samp{Q} => @math{1000^{10} = 10^{30}} (Quetta) +@end example + +@item iec +Auto-scale numbers according to the @emph{International Electrotechnical +Commission (IEC)} standard. +For input numbers, accept one of the following suffixes. +For output numbers, values larger than 1024 will be rounded, and printed with +one of the following suffixes: + +@example +@samp{K} => @math{1024^1 = 2^{10}} (Kibi) +@samp{M} => @math{1024^2 = 2^{20}} (Mebi) +@samp{G} => @math{1024^3 = 2^{30}} (Gibi) +@samp{T} => @math{1024^4 = 2^{40}} (Tebi) +@samp{P} => @math{1024^5 = 2^{50}} (Pebi) +@samp{E} => @math{1024^6 = 2^{60}} (Exbi) +@samp{Z} => @math{1024^7 = 2^{70}} (Zebi) +@samp{Y} => @math{1024^8 = 2^{80}} (Yobi) +@samp{R} => @math{1024^9 = 2^{90}} (Robi) +@samp{Q} => @math{1024^{10} = 2^{100}} (Quebi) +@end example + +The @option{iec} option uses a single letter suffix (e.g. @samp{G}), which is +not fully standard, as the @emph{iec} standard recommends a two-letter symbol +(e.g @samp{Gi}) -- but in practice, this method is common. Compare with +the @option{iec-i} option. + +@item iec-i +Auto-scale numbers according to the @emph{International Electrotechnical +Commission (IEC)} standard. +For input numbers, accept one of the following suffixes. +For output numbers, values larger than 1024 will be rounded, and printed with +one of the following suffixes: + +@example +@samp{Ki} => @math{1024^1 = 2^{10}} (Kibi) +@samp{Mi} => @math{1024^2 = 2^{20}} (Mebi) +@samp{Gi} => @math{1024^3 = 2^{30}} (Gibi) +@samp{Ti} => @math{1024^4 = 2^{40}} (Tebi) +@samp{Pi} => @math{1024^5 = 2^{50}} (Pebi) +@samp{Ei} => @math{1024^6 = 2^{60}} (Exbi) +@samp{Zi} => @math{1024^7 = 2^{70}} (Zebi) +@samp{Yi} => @math{1024^8 = 2^{80}} (Yobi) +@samp{Ri} => @math{1024^9 = 2^{90}} (Robi) +@samp{Qi} => @math{1024^{10} = 2^{100}} (Quebi) +@end example + +The @option{iec-i} option uses a two-letter suffix symbol (e.g. @samp{Gi}), +as the @emph{iec} standard recommends, but this is not always common in +practice. Compare with the @option{iec} option. + +@item auto +@samp{auto} can only be used with @option{--from}. With this method, numbers +with single-letter suffixes like @samp{K} +suffixes are interpreted as @emph{SI} values, and numbers with +two-letter suffixes like @samp{Ki} +are interpreted as @emph{IEC} values. + +@end table + +@subsection Examples of using @command{numfmt} + +Converting a single number from/to @emph{human} representation: +@example +$ numfmt --to=si 500000 +500K + +$ numfmt --to=iec 500000 +489K + +$ numfmt --to=iec-i 500000 +489Ki + +$ numfmt --from=si 1M +1000000 + +$ numfmt --from=iec 1M +1048576 + +# with '--from=auto', M=Mega, Mi=Mebi +$ numfmt --from=auto 1M +1000000 +$ numfmt --from=auto 1Mi +1048576 +@end example + +Converting from @samp{SI} to @samp{IEC} scales (e.g. when a drive's capacity is +advertised as @samp{1TB}, while checking the drive's capacity gives lower +values): + +@example +$ numfmt --from=si --to=iec 1T +932G +@end example + +With both input and output scales specified, +the largest defined prefixes are supported: + +@example +$ numfmt --from=si --to=iec-i 2000R +1.6Qi +@end example + +Converting a single field from an input file / piped input (these contrived +examples are for demonstration purposes only, as both @command{ls} and +@command{df} support the @option{--human-readable} option to +output sizes in human-readable format): + +@example +# Third field (file size) will be shown in SI representation +$ ls -log | numfmt --field 3 --header --to=si | head -n4 +-rw-r--r-- 1 94K Aug 23 2011 ABOUT-NLS +-rw-r--r-- 1 3.7K Jan 7 16:15 AUTHORS +-rw-r--r-- 1 36K Jun 1 2011 COPYING +-rw-r--r-- 1 0 Jan 7 15:15 ChangeLog + +# Second field (size) will be shown in IEC representation +$ df --block-size=1 | numfmt --field 2 --header --to=iec | head -n4 +File system 1B-blocks Used Available Use% Mounted on +rootfs 132G 104741408 26554036 80% / +tmpfs 794M 7580 804960 1% /run/shm +/dev/sdb1 694G 651424756 46074696 94% /home +@end example + + +Output can be tweaked using @option{--padding} or @option{--format}: + +@example +# Pad to 10 characters, right-aligned +$ du -s * | numfmt --to=si --padding=10 + 2.5K config.log + 108 config.status + 1.7K configure + 20 configure.ac + +# Pad to 10 characters, left-aligned +$ du -s * | numfmt --to=si --padding=-10 +2.5K config.log +108 config.status +1.7K configure +20 configure.ac + +# Pad to 10 characters, left-aligned, using 'format' +$ du -s * | numfmt --to=si --format="%10f" + 2.5K config.log + 108 config.status + 1.7K configure + 20 configure.ac + +# Pad to 10 characters, left-aligned, using 'format' +$ du -s * | numfmt --to=si --padding="%-10f" +2.5K config.log +108 config.status +1.7K configure +20 configure.ac +@end example + +With locales that support grouping digits, using @option{--grouping} or +@option{--format} enables grouping. In @samp{POSIX} locale, grouping is +silently ignored: + +@example +$ LC_ALL=C numfmt --from=iec --grouping 2G +2147483648 + +$ LC_ALL=en_US.utf8 numfmt --from=iec --grouping 2G +2,147,483,648 + +$ LC_ALL=ta_IN numfmt --from=iec --grouping 2G +2,14,74,83,648 + +$ LC_ALL=C numfmt --from=iec --format="==%'15f==" 2G +== 2147483648== + +$ LC_ALL=en_US.utf8 numfmt --from=iec --format="==%'15f==" 2G +== 2,147,483,648== + +$ LC_ALL=en_US.utf8 numfmt --from=iec --format="==%'-15f==" 2G +==2,147,483,648 == + +$ LC_ALL=ta_IN numfmt --from=iec --format="==%'15f==" 2G +== 2,14,74,83,648== +@end example + + +@node seq invocation +@section @command{seq}: Print numeric sequences + +@pindex seq +@cindex numeric sequences +@cindex sequence of numbers + +@command{seq} prints a sequence of numbers to standard output. Synopses: + +@example +seq [@var{option}]@dots{} @var{last} +seq [@var{option}]@dots{} @var{first} @var{last} +seq [@var{option}]@dots{} @var{first} @var{increment} @var{last} +@end example + +@command{seq} prints the numbers from @var{first} to @var{last} by +@var{increment}. By default, each number is printed on a separate line. +When @var{increment} is not specified, it defaults to @samp{1}, +even when @var{first} is larger than @var{last}. +@var{first} also defaults to @samp{1}. So @code{seq 1} prints +@samp{1}, but @code{seq 0} and @code{seq 10 5} produce no output. +The sequence of numbers ends when the sum of the current number and +@var{increment} would become greater than @var{last}, +so @code{seq 1 10 10} only produces @samp{1}. +@var{increment} must not be @samp{0}; use the tool @command{yes} to get +repeated output of a constant number. +@var{first}, @var{increment} and @var{last} must not be @code{NaN}, +but @code{inf} is supported. +Floating-point numbers may be specified in either the current or +the C locale. @xref{Floating point}. + +The program accepts the following options. Also see @ref{Common options}. +Options must precede operands. + +@table @samp +@item -f @var{format} +@itemx --format=@var{format} +@opindex -f +@opindex --format +@cindex formatting of numbers in @command{seq} +Print all numbers using @var{format}. +@var{format} must contain exactly one of the @samp{printf}-style +floating point conversion specifications @samp{%a}, @samp{%e}, +@samp{%f}, @samp{%g}, @samp{%A}, @samp{%E}, @samp{%F}, @samp{%G}@. +The @samp{%} may be followed by zero or more flags taken from the set +@samp{-+#0 '}, then an optional width containing one or more digits, +then an optional precision consisting of a @samp{.} followed by zero +or more digits. @var{format} may also contain any number of @samp{%%} +conversion specifications. All conversion specifications have the +same meaning as with @samp{printf}. + +The default format is derived from @var{first}, @var{step}, and +@var{last}. If these all use a fixed point decimal representation, +the default format is @samp{%.@var{p}f}, where @var{p} is the minimum +precision that can represent the output numbers exactly. Otherwise, +the default format is @samp{%g}. + +@item -s @var{string} +@itemx --separator=@var{string} +@opindex -s +@opindex --separator +@cindex separator for numbers in @command{seq} +Separate numbers with @var{string}; default is a newline. +The output always terminates with a newline. + +@item -w +@itemx --equal-width +@opindex -w +@opindex --equal-width +Print all numbers with the same width, by padding with leading zeros. +@var{first}, @var{step}, and @var{last} should all use a fixed point +decimal representation. +(To have other kinds of padding, use @option{--format}). + +@end table + +You can get finer-grained control over output with @option{-f}: + +@example +$ seq -f '(%9.2E)' -9e5 1.1e6 1.3e6 +(-9.00E+05) +( 2.00E+05) +( 1.30E+06) +@end example + +If you want hexadecimal integer output, you can use @command{printf} +to perform the conversion: + +@example +$ printf '%x\n' $(seq 1048575 1024 1050623) +fffff +1003ff +1007ff +@end example + +For very long lists of numbers, use xargs to avoid +system limitations on the length of an argument list: + +@example +$ seq 1000000 | xargs printf '%x\n' | tail -n 3 +f423e +f423f +f4240 +@end example + +To generate octal output, use the printf @code{%o} format instead +of @code{%x}. + +On most systems, seq can produce whole-number output for values up to +at least @math{2^{53}}. Larger integers are approximated. The details +differ depending on your floating-point implementation. +@xref{Floating point}. A common +case is that @command{seq} works with integers through @math{2^{64}}, +and larger integers may not be numerically correct: + +@example +$ seq 50000000000000000000 2 50000000000000000004 +50000000000000000000 +50000000000000000000 +50000000000000000004 +@end example + +However, note that when limited to non-negative whole numbers, +an increment of less than 200, and no format-specifying option, +seq can print arbitrarily large numbers. +Therefore @command{seq inf} can be used to +generate an infinite sequence of numbers. + +Be careful when using @command{seq} with outlandish values: otherwise +you may see surprising results, as @command{seq} uses floating point +internally. For example, on the x86 platform, where the internal +representation uses a 64-bit fraction, the command: + +@example +seq 1 0.0000000000000000001 1.0000000000000000009 +@end example + +outputs 1.0000000000000000007 twice and skips 1.0000000000000000008. + +@exitstatus + + +@node File permissions +@chapter File permissions +@include perm.texi + + +@node File timestamps +@chapter File timestamps + +@cindex atime +@cindex birthtime +@cindex ctime +@cindex mtime +Standard POSIX files have three timestamps: the access timestamp +(atime) of the last read, the modification timestamp (mtime) of the +last write, and the status change timestamp (ctime) of the last change +to the file's meta-information. Some file systems support a +fourth time: the birth timestamp (birthtime) of when the file was +created; by definition, birthtime never changes. + +One common example of a ctime change is when the permissions of a file +change. Changing the permissions doesn't access the file, so atime +doesn't change, nor does it modify the file, so the mtime doesn't +change. Yet, something about the file itself has changed, and this +must be noted somewhere. This is the job of the ctime field. This is +necessary, so that, for example, a backup program can make a fresh +copy of the file, including the new permissions value. Another +operation that modifies a file's ctime without affecting the others is +renaming. + +Naively, a file's atime, mtime, and ctime are set to the current time +whenever you read, write, or change the attributes of the file +respectively, and searching a directory counts as reading it. A +file's atime and mtime can also be set directly, via the +@command{touch} command (@pxref{touch invocation}). In practice, +though, timestamps are not updated quite that way. + +For efficiency reasons, many systems are lazy about updating atimes: +when a program accesses a file, they may delay updating the file's +atime, or may not update the file's atime if the file has been +accessed recently, or may not update the atime at all. Similar +laziness, though typically not quite so extreme, applies to mtimes and +ctimes. + +Some systems emulate timestamps instead of supporting them directly, +and these emulations may disagree with the naive interpretation. For +example, a system may fake an atime or ctime by using the mtime. + +@cindex clock skew +The determination of what time is ``current'' depends on the +platform. Platforms with network file systems often use different +clocks for the operating system and for file systems; because +updates typically uses file systems' clocks by default, clock +skew can cause the resulting file timestamps to appear to be in a +program's ``future'' or ``past''. + +@cindex file timestamp resolution +When the system updates a file timestamp to a desired time @var{t} +(which is either the current time, or a time specified via the +@command{touch} command), there are several reasons the file's +timestamp may be set to a value that differs from @var{t}. First, +@var{t} may have a higher resolution than supported. Second, a file +system may use different resolutions for different types of times. +Third, file timestamps may use a different resolution than operating +system timestamps. Fourth, the operating system primitives used to +update timestamps may employ yet a different resolution. For example, +in theory a file system might use 10-microsecond resolution for access +timestamp and 100-nanosecond resolution for modification timestamp, and the +operating system might use nanosecond resolution for the current time +and microsecond resolution for the primitive that @command{touch} uses +to set a file's timestamp to an arbitrary value. + + +@include parse-datetime.texi + +@include sort-version.texi + +@c What's GNU? +@c Arnold Robbins +@node Opening the software toolbox +@chapter Opening the Software Toolbox + +An earlier version of this chapter appeared in +@uref{https://www.linuxjournal.com/article.php?sid=2762, the +@cite{What's GNU@?} column of the June 1994 @cite{Linux Journal}}. +It was written by Arnold Robbins. + +@menu +* Toolbox introduction:: Toolbox introduction +* I/O redirection:: I/O redirection +* The who command:: The @command{who} command +* The cut command:: The @command{cut} command +* The sort command:: The @command{sort} command +* The uniq command:: The @command{uniq} command +* Putting the tools together:: Putting the tools together +@end menu + + +@node Toolbox introduction +@unnumberedsec Toolbox Introduction + +This month's column is only peripherally related to the GNU Project, in +that it describes a number of the GNU tools on your GNU/Linux system +and how they +might be used. What it's really about is the ``Software Tools'' philosophy +of program development and usage. + +The software tools philosophy was an important and integral concept +in the initial design and development of Unix (of which GNU/Linux and GNU are +essentially clones). Unfortunately, in the modern day press of +Internetworking and flashy GUIs, it seems to have fallen by the +wayside. This is a shame, since it provides a powerful mental model +for solving many kinds of problems. + +Many people carry a Swiss Army knife around in their pants pockets (or +purse). A Swiss Army knife is a handy tool to have: it has several knife +blades, a screwdriver, tweezers, toothpick, nail file, corkscrew, and perhaps +a number of other things on it. For the everyday, small miscellaneous jobs +where you need a simple, general purpose tool, it's just the thing. + +On the other hand, an experienced carpenter doesn't build a house using +a Swiss Army knife. Instead, he has a toolbox chock full of specialized +tools -- a saw, a hammer, a screwdriver, a plane, and so on. And he knows +exactly when and where to use each tool; you won't catch him hammering nails +with the handle of his screwdriver. + +The Unix developers at Bell Labs were all professional programmers and trained +computer scientists. They had found that while a one-size-fits-all program +might appeal to a user because there's only one program to use, in practice +such programs are + +@enumerate a +@item +difficult to write, + +@item +difficult to maintain and +debug, and + +@item +difficult to extend to meet new situations. +@end enumerate + +Instead, they felt that programs should be specialized tools. In short, each +program ``should do one thing well.'' No more and no less. Such programs are +simpler to design, write, and get right -- they only do one thing. + +Furthermore, they found that with the right machinery for hooking programs +together, that the whole was greater than the sum of the parts. By combining +several special purpose programs, you could accomplish a specific task +that none of the programs was designed for, and accomplish it much more +quickly and easily than if you had to write a special purpose program. +We will see some (classic) examples of this further on in the column. +(An important additional point was that, if necessary, take a detour +and build any software tools you may need first, if you don't already +have something appropriate in the toolbox.) + +@node I/O redirection +@unnumberedsec I/O Redirection + +Hopefully, you are familiar with the basics of I/O redirection in the +shell, in particular the concepts of ``standard input,'' ``standard output,'' +and ``standard error''. Briefly, ``standard input'' is a data source, where +data comes from. A program should not need to either know or care if the +data source is a regular file, a keyboard, a magnetic tape, or even a punched +card reader. Similarly, ``standard output'' is a data sink, where data goes +to. The program should neither know nor care where this might be. +Programs that only read their standard input, do something to the data, +and then send it on, are called @dfn{filters}, by analogy to filters in a +water pipeline. + +With the Unix shell, it's very easy to set up data pipelines: + +@example +program_to_create_data | filter1 | ... | filterN > final.pretty.data +@end example + +We start out by creating the raw data; each filter applies some successive +transformation to the data, until by the time it comes out of the pipeline, +it is in the desired form. + +This is fine and good for standard input and standard output. Where does the +standard error come in to play? Well, think about @command{filter1} in +the pipeline above. What happens if it encounters an error in the data it +sees? If it writes an error message to standard output, it will just +disappear down the pipeline into @command{filter2}'s input, and the +user will probably never see it. So programs need a place where they can send +error messages so that the user will notice them. This is standard error, +and it is usually connected to your console or window, even if you have +redirected standard output of your program away from your screen. + +For filter programs to work together, the format of the data has to be +agreed upon. The most straightforward and easiest format to use is simply +lines of text. Unix data files are generally just streams of bytes, with +lines delimited by the ASCII LF (Line Feed) character, +conventionally called a ``newline'' in the Unix literature. (This is +@code{'\n'} if you're a C programmer.) This is the format used by all +the traditional filtering programs. (Many earlier operating systems +had elaborate facilities and special purpose programs for managing +binary data. Unix has always shied away from such things, under the +philosophy that it's easiest to simply be able to view and edit your +data with a text editor.) + +OK, enough introduction. Let's take a look at some of the tools, and then +we'll see how to hook them together in interesting ways. In the following +discussion, we will only present those command line options that interest +us. As you should always do, double check your system documentation +for the full story. + +@node The who command +@unnumberedsec The @command{who} Command + +The first program is the @command{who} command. By itself, it generates a +list of the users who are currently logged in. Although I'm writing +this on a single-user system, we'll pretend that several people are +logged in: + +@example +$ who +@print{} arnold console Jan 22 19:57 +@print{} miriam ttyp0 Jan 23 14:19(:0.0) +@print{} bill ttyp1 Jan 21 09:32(:0.0) +@print{} arnold ttyp2 Jan 23 20:48(:0.0) +@end example + +Here, the @samp{$} is the usual shell prompt, at which I typed @samp{who}. +There are three people logged in, and I am logged in twice. On traditional +Unix systems, user names are never more than eight characters long. This +little bit of trivia will be useful later. The output of @command{who} is nice, +but the data is not all that exciting. + +@node The cut command +@unnumberedsec The @command{cut} Command + +The next program we'll look at is the @command{cut} command. This program +cuts out columns or fields of input data. For example, we can tell it +to print just the login name and full name from the @file{/etc/passwd} +file. The @file{/etc/passwd} file has seven fields, separated by +colons: + +@example +arnold:xyzzy:2076:10:Arnold D. Robbins:/home/arnold:/bin/bash +@end example + +To get the first and fifth fields, we would use @command{cut} like this: + +@example +$ cut -d: -f1,5 /etc/passwd +@print{} root:Operator +@dots{} +@print{} arnold:Arnold D. Robbins +@print{} miriam:Miriam A. Robbins +@dots{} +@end example + +With the @option{-c} option, @command{cut} will cut out specific characters +(i.e., columns) in the input lines. This is useful for input data +that has fixed width fields, and does not have a field separator. For +example, list the Monday dates for the current month: + +@c Is using cal ok? Looked at gcal, but I don't like it. +@example +$ cal | cut -c 3-5 +@print{}Mo +@print{} +@print{} 6 +@print{} 13 +@print{} 20 +@print{} 27 +@end example + +@node The sort command +@unnumberedsec The @command{sort} Command + +Next we'll look at the @command{sort} command. This is one of the most +powerful commands on a Unix-style system; one that you will often find +yourself using when setting up fancy data plumbing. + +The @command{sort} +command reads and sorts each file named on the command line. It then +merges the sorted data and writes it to standard output. It will read +standard input if no files are given on the command line (thus +making it into a filter). The sort is based on the character collating +sequence or based on user-supplied ordering criteria. + + +@node The uniq command +@unnumberedsec The @command{uniq} Command + +Finally (at least for now), we'll look at the @command{uniq} program. When +sorting data, you will often end up with duplicate lines, lines that +are identical. Usually, all you need is one instance of each line. +This is where @command{uniq} comes in. The @command{uniq} program reads its +standard input. It prints only one +copy of each repeated line. It does have several options. Later on, +we'll use the @option{-c} option, which prints each unique line, preceded +by a count of the number of times that line occurred in the input. + + +@node Putting the tools together +@unnumberedsec Putting the Tools Together + +Now, let's suppose this is a large ISP server system with dozens of users +logged in. The management wants the system administrator to write a +program that will +generate a sorted list of logged in users. Furthermore, even if a user +is logged in multiple times, his or her name should only show up in the +output once. + +The administrator could sit down with the system documentation and write a C +program that did this. It would take perhaps a couple of hundred lines +of code and about two hours to write it, test it, and debug it. +However, knowing the software toolbox, the administrator can instead start out +by generating just a list of logged on users: + +@example +$ who | cut -c1-8 +@print{} arnold +@print{} miriam +@print{} bill +@print{} arnold +@end example + +Next, sort the list: + +@example +$ who | cut -c1-8 | sort +@print{} arnold +@print{} arnold +@print{} bill +@print{} miriam +@end example + +Finally, run the sorted list through @command{uniq}, to weed out duplicates: + +@example +$ who | cut -c1-8 | sort | uniq +@print{} arnold +@print{} bill +@print{} miriam +@end example + +The @command{sort} command actually has a @option{-u} option that does what +@command{uniq} does. However, @command{uniq} has other uses for which one +cannot substitute @samp{sort -u}. + +The administrator puts this pipeline into a shell script, and makes it +available for +all the users on the system (@samp{#} is the system administrator, +or @code{root}, prompt): + +@example +# cat > /usr/local/bin/listusers +who | cut -c1-8 | sort | uniq +^D +# chmod +x /usr/local/bin/listusers +@end example + +There are four major points to note here. First, with just four +programs, on one command line, the administrator was able to save about two +hours worth of work. Furthermore, the shell pipeline is just about as +efficient as the C program would be, and it is much more efficient in +terms of programmer time. People time is much more expensive than +computer time, and in our modern ``there's never enough time to do +everything'' society, saving two hours of programmer time is no mean +feat. + +Second, it is also important to emphasize that with the +@emph{combination} of the tools, it is possible to do a special +purpose job never imagined by the authors of the individual programs. + +Third, it is also valuable to build up your pipeline in stages, as we did here. +This allows you to view the data at each stage in the pipeline, which helps +you acquire the confidence that you are indeed using these tools correctly. + +Finally, by bundling the pipeline in a shell script, other users can use +your command, without having to remember the fancy plumbing you set up for +them. In terms of how you run them, shell scripts and compiled programs are +indistinguishable. + +After the previous warm-up exercise, we'll look at two additional, more +complicated pipelines. For them, we need to introduce two more tools. + +The first is the @command{tr} command, which stands for ``transliterate.'' +The @command{tr} command works on a character-by-character basis, changing +characters. Normally it is used for things like mapping upper case to +lower case: + +@example +$ echo ThIs ExAmPlE HaS MIXED case! | tr '[:upper:]' '[:lower:]' +@print{} this example has mixed case! +@end example + +There are several options of interest: + +@table @code +@item -c +work on the complement of the listed characters, i.e., +operations apply to characters not in the given set + +@item -d +delete characters in the first set from the output + +@item -s +squeeze repeated characters in the output into just one character. +@end table + +We will be using all three options in a moment. + +The other command we'll look at is @command{comm}. The @command{comm} +command takes two sorted input files as input data, and prints out the +files' lines in three columns. The output columns are the data lines +unique to the first file, the data lines unique to the second file, and +the data lines that are common to both. The @option{-1}, @option{-2}, and +@option{-3} command line options @emph{omit} the respective columns. (This is +non-intuitive and takes a little getting used to.) For example: + +@example +$ cat f1 +@print{} 11111 +@print{} 22222 +@print{} 33333 +@print{} 44444 +$ cat f2 +@print{} 00000 +@print{} 22222 +@print{} 33333 +@print{} 55555 +$ comm f1 f2 +@print{} 00000 +@print{} 11111 +@print{} 22222 +@print{} 33333 +@print{} 44444 +@print{} 55555 +@end example + +The file name @file{-} tells @command{comm} to read standard input +instead of a regular file. + +Now we're ready to build a fancy pipeline. The first application is a word +frequency counter. This helps an author determine if he or she is over-using +certain words. + +The first step is to change the case of all the letters in our input file +to one case. ``The'' and ``the'' are the same word when doing counting. + +@example +$ tr '[:upper:]' '[:lower:]' < whats.gnu | ... +@end example + +The next step is to get rid of punctuation. Quoted words and unquoted words +should be treated identically; it's easiest to just get the punctuation out of +the way. + +@example +$ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | ... +@end example + +The second @command{tr} command operates on the complement of the listed +characters, which are all the letters, the digits, the underscore, and +the blank. The @samp{\n} represents the newline character; it has to +be left alone. (The ASCII tab character should also be included for +good measure in a production script.) + +At this point, we have data consisting of words separated by blank space. +The words only contain alphanumeric characters (and the underscore). The +next step is break the data apart so that we have one word per line. This +makes the counting operation much easier, as we will see shortly. + +@example +$ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | +> tr -s ' ' '\n' | ... +@end example + +This command turns blanks into newlines. The @option{-s} option squeezes +multiple newline characters in the output into just one, removing +blank lines. (The @samp{>} is the shell's ``secondary prompt.'' +This is what the shell prints when it notices you haven't finished +typing in all of a command.) + +We now have data consisting of one word per line, no punctuation, all one +case. We're ready to count each word: + +@example +$ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | +> tr -s ' ' '\n' | sort | uniq -c | ... +@end example + +At this point, the data might look something like this: + +@example + 60 a + 2 able + 6 about + 1 above + 2 accomplish + 1 acquire + 1 actually + 2 additional +@end example + +The output is sorted by word, not by count! What we want is the most +frequently used words first. Fortunately, this is easy to accomplish, +with the help of two more @command{sort} options: + +@table @code +@item -n +do a numeric sort, not a textual one + +@item -r +reverse the order of the sort +@end table + +The final pipeline looks like this: + +@example +$ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | +> tr -s ' ' '\n' | sort | uniq -c | sort -n -r +@print{} 156 the +@print{} 60 a +@print{} 58 to +@print{} 51 of +@print{} 51 and +@dots{} +@end example + +Whew! That's a lot to digest. Yet, the same principles apply. With six +commands, on two lines (really one long one split for convenience), we've +created a program that does something interesting and useful, in much +less time than we could have written a C program to do the same thing. + +A minor modification to the above pipeline can give us a simple spelling +checker! To determine if you've spelled a word correctly, all you have to +do is look it up in a dictionary. If it is not there, then chances are +that your spelling is incorrect. So, we need a dictionary. +The conventional location for a dictionary is @file{/usr/share/dict/words}. + +Now, how to compare our file with the dictionary? As before, we generate +a sorted list of words, one per line: + +@example +$ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | +> tr -s ' ' '\n' | sort -u | ... +@end example + +Now, all we need is a list of words that are @emph{not} in the +dictionary. Here is where the @command{comm} command comes in. +Unfortunately @command{comm} operates on sorted input and +@file{/usr/share/dict/words} is not sorted the way that @command{sort} +and @command{comm} normally use, so we first create a properly-sorted +copy of the dictionary and then run a pipeline that uses the copy. + +@example +$ sort /usr/share/dict/words > sorted-words +$ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | +> tr -s ' ' '\n' | sort -u | +> comm -23 - sorted-words +@end example + +The @option{-2} and @option{-3} options eliminate lines that are only in the +dictionary (the second file), and lines that are in both files. Lines +only in the first file (standard input, our stream of words), are +words that are not in the dictionary. These are likely candidates for +spelling errors. This pipeline was the first cut at a production +spelling checker on Unix. + +There are some other tools that deserve brief mention. + +@table @command +@item grep +search files for text that matches a regular expression + +@item wc +count lines, words, characters + +@item tee +a T-fitting for data pipes, copies data to files and to standard output + +@item sed +the stream editor, an advanced tool + +@item awk +a data manipulation language, another advanced tool +@end table + +The software tools philosophy also espoused the following bit of +advice: ``Let someone else do the hard part.'' This means, take +something that gives you most of what you need, and then massage it the +rest of the way until it's in the form that you want. + +To summarize: + +@enumerate 1 +@item +Each program should do one thing well. No more, no less. + +@item +Combining programs with appropriate plumbing leads to results where +the whole is greater than the sum of the parts. It also leads to novel +uses of programs that the authors might never have imagined. + +@item +Programs should never print extraneous header or trailer data, since these +could get sent on down a pipeline. (A point we didn't mention earlier.) + +@item +Let someone else do the hard part. + +@item +Know your toolbox! Use each program appropriately. If you don't have an +appropriate tool, build one. +@end enumerate + +All the programs discussed are available as described in +@uref{https://www.gnu.org/software/coreutils/coreutils.html, +GNU core utilities}. + +None of what I have presented in this column is new. The Software Tools +philosophy was first introduced in the book @cite{Software Tools}, by +Brian Kernighan and P.J. Plauger (Addison-Wesley, ISBN 0-201-03669-X). +This book showed how to write and use software tools. It was written in +1976, using a preprocessor for FORTRAN named @command{ratfor} (RATional +FORtran). At the time, C was not as ubiquitous as it is now; FORTRAN +was. The last chapter presented a @command{ratfor} to FORTRAN +processor, written in @command{ratfor}. @command{ratfor} looks an awful +lot like C; if you know C, you won't have any problem following the +code. + +In 1981, the book was updated and made available as @cite{Software Tools +in Pascal} (Addison-Wesley, ISBN 0-201-10342-7). Both books are +still in print and are well worth +reading if you're a programmer. They certainly made a major change in +how I view programming. + +The programs in both books are available from +@uref{https://www.cs.princeton.edu/~bwk/, Brian Kernighan's home page}. +For a number of years, there was an active +Software Tools Users Group, whose members had ported the original +@command{ratfor} programs to essentially every computer system with a +FORTRAN compiler. The popularity of the group waned in the middle 1980s +as Unix began to spread beyond universities. + +With the current proliferation of GNU code and other clones of Unix programs, +these programs now receive little attention; modern C versions are +much more efficient and do more than these programs do. Nevertheless, as +exposition of good programming style, and evangelism for a still-valuable +philosophy, these books are unparalleled, and I recommend them highly. + +Acknowledgment: I would like to express my gratitude to Brian Kernighan +of Bell Labs, the original Software Toolsmith, for reviewing this column. + +@node GNU Free Documentation License +@appendix GNU Free Documentation License + +@include fdl.texi + +@node Concept index +@unnumbered Index + +@printindex cp + +@bye + +@c Local variables: +@c texinfo-column-for-description: 32 +@c End: diff --git a/doc/fdl.texi b/doc/fdl.texi new file mode 100644 index 0000000..eaf3da0 --- /dev/null +++ b/doc/fdl.texi @@ -0,0 +1,505 @@ +@c The GNU Free Documentation License. +@center Version 1.3, 3 November 2008 + +@c This file is intended to be included within another document, +@c hence no sectioning command or @node. + +@display +Copyright @copyright{} 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc. +@uref{https://fsf.org/} + +Everyone is permitted to copy and distribute verbatim copies +of this license document, but changing it is not allowed. +@end display + +@enumerate 0 +@item +PREAMBLE + +The purpose of this License is to make a manual, textbook, or other +functional and useful document @dfn{free} in the sense of freedom: to +assure everyone the effective freedom to copy and redistribute it, +with or without modifying it, either commercially or noncommercially. +Secondarily, this License preserves for the author and publisher a way +to get credit for their work, while not being considered responsible +for modifications made by others. + +This License is a kind of ``copyleft'', which means that derivative +works of the document must themselves be free in the same sense. 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See the +# GNU General Public License for more details. + +# You should have received a copy of the GNU General Public License +# along with this program. If not, see <https://www.gnu.org/licenses/>. + +info_TEXINFOS = doc/coreutils.texi + +doc_coreutils_TEXINFOS = \ + doc/perm.texi \ + doc/parse-datetime.texi \ + doc/constants.texi \ + doc/fdl.texi \ + doc/sort-version.texi + +# The customization variable CHECK_NORMAL_MENU_STRUCTURE is necessary with +# makeinfo versions ≥ 6.8. +MAKEINFO = @MAKEINFO@ -c CHECK_NORMAL_MENU_STRUCTURE=1 + +# The following is necessary if the package name is 8 characters or longer. +# If the info documentation would be split into 10 or more separate files, +# then this is necessary even if the package name is 7 characters long. +# +# Tell makeinfo to put everything in a single info file: <package>.info. +# Otherwise, it would also generate files with names like <package>.info-[123], +# and those names all map to one 14-byte name (<package>.info-) on some crufty +# old systems. +AM_MAKEINFOFLAGS = --no-split + +doc/constants.texi: $(top_srcdir)/src/tail.c $(top_srcdir)/src/shred.c + $(AM_V_GEN)LC_ALL=C; export LC_ALL; \ + $(MKDIR_P) doc && \ + { sed -n -e 's/^#define \(DEFAULT_MAX[_A-Z]*\) \(.*\)/@set \1 \2/p' \ + $(top_srcdir)/src/tail.c && \ + sed -n -e \ + 's/.*\(DEFAULT_PASSES\)[ =]* \([0-9]*\).*/@set SHRED_\1 \2/p'\ + $(top_srcdir)/src/shred.c; } > $@-t \ + && { cmp $@-t $@ >/dev/null 2>&1 || mv $@-t $@; rm -f $@-t; } + +MAINTAINERCLEANFILES += doc/constants.texi + +# Extended regular expressions to match word starts and ends. +_W = (^|[^A-Za-z0-9_]) +W_ = ([^A-Za-z0-9_]|$$) + +syntax_checks = \ + sc-avoid-builtin \ + sc-avoid-io \ + sc-avoid-non-zero \ + sc-avoid-path \ + sc-avoid-timezone \ + sc-avoid-zeroes \ + sc-exponent-grouping \ + sc-lower-case-var + +texi_files = $(srcdir)/doc/*.texi + +.PHONY: $(syntax_checks) check-texinfo + +# List words/regexps here that should not appear in the texinfo documentation. +check-texinfo: $(syntax_checks) + $(AM_V_GEN)fail=0; \ + grep '@url{' $(texi_files) && fail=1; \ + grep '\$$@"' $(texi_files) && fail=1; \ + grep -n '[^[:punct:]]@footnote' $(texi_files) && fail=1; \ + grep -n filename $(texi_files) \ + | $(EGREP) -v 'setfilename|[{]filename[}]' \ + && fail=1; \ + exit $$fail + +sc-avoid-builtin: + $(AM_V_GEN)$(EGREP) -i '$(_W)builtins?$(W_)' $(texi_files) \ + && exit 1 || : + +sc-avoid-path: + $(AM_V_GEN)fail=0; \ + $(EGREP) -i '$(_W)path(name)?s?$(W_)' $(texi_files) \ + | $(EGREP) -v \ + 'PATH=|path search|search path|@vindex PATH$$|@env[{]PATH[}]' \ + && fail=1; \ + exit $$fail + +# Use "time zone", not "timezone". +sc-avoid-timezone: + $(AM_V_GEN)$(EGREP) timezone $(texi_files) && exit 1 || : + +# Check for insufficient exponent grouping, e.g., +# @math{2^64} should be @math{2^{64}}. +sc-exponent-grouping: + $(AM_V_GEN)$(EGREP) '\{.*\^[0-9][0-9]' $(texi_files) && exit 1 || : + +# Say I/O, not IO. +sc-avoid-io: + $(AM_V_GEN)$(EGREP) '$(_W)IO$(W_)' $(texi_files) && exit 1 || : + +# I prefer nonzero over non-zero. +sc-avoid-non-zero: + $(AM_V_GEN)$(EGREP) non-zero $(texi_files) && exit 1 || : + +# Use "zeros", not "zeroes" (nothing wrong with "zeroes"; just be consistent). +sc-avoid-zeroes: + $(AM_V_GEN)$(EGREP) -i '$(_W)zeroes$(W_)' $(texi_files) \ + && exit 1 || : + +# The quantity inside @var{...} should not contain upper case letters. +# The leading backslash exemption is to permit in-macro uses like +# @var{\varName\} where the upper case letter is part of a parameter name. +find_upper_case_var = \ + '/\@var\{/ or next; \ + while (/\@var\{(.+?)}/g) \ + { \ + $$v = $$1; \ + $$v =~ /[A-Z]/ && $$v !~ /^\\/ and (print "$$ARGV:$$.:$$_"), $$m = 1 \ + } \ + END {$$m and (warn "$@: do not use upper case in \@var{...}\n"), exit 1}' +sc-lower-case-var: + $(AM_V_GEN)$(PERL) -e 1 || { echo $@: skipping test; exit 0; }; \ + $(PERL) -lne $(find_upper_case_var) $(texi_files) + +check-local: check-texinfo diff --git a/doc/parse-datetime.texi b/doc/parse-datetime.texi new file mode 100644 index 0000000..ec0160d --- /dev/null +++ b/doc/parse-datetime.texi @@ -0,0 +1,618 @@ +@c GNU date syntax documentation + +@c Copyright (C) 1994--2006, 2009--2023 Free Software Foundation, Inc. + +@c Permission is granted to copy, distribute and/or modify this document +@c under the terms of the GNU Free Documentation License, Version 1.3 or +@c any later version published by the Free Software Foundation; with no +@c Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A +@c copy of the license is at <https://www.gnu.org/licenses/fdl-1.3.en.html>. + +@node Date input formats +@chapter Date input formats + +@cindex date input formats +@findex parse_datetime + +First, a quote: + +@quotation +Our units of temporal measurement, from seconds on up to months, are so +complicated, asymmetrical and disjunctive so as to make coherent mental +reckoning in time all but impossible. Indeed, had some tyrannical god +contrived to enslave our minds to time, to make it all but impossible +for us to escape subjection to sodden routines and unpleasant surprises, +he could hardly have done better than handing down our present system. +It is like a set of trapezoidal building blocks, with no vertical or +horizontal surfaces, like a language in which the simplest thought +demands ornate constructions, useless particles and lengthy +circumlocutions. Unlike the more successful patterns of language and +science, which enable us to face experience boldly or at least +level-headedly, our system of temporal calculation silently and +persistently encourages our terror of time. + +@dots{} It is as though architects had to measure length in feet, width +in meters and height in ells; as though basic instruction manuals +demanded a knowledge of five different languages. It is no wonder then +that we often look into our own immediate past or future, last Tuesday +or a week from Sunday, with feelings of helpless confusion. @dots{} + +---Robert Grudin, @cite{Time and the Art of Living}. +@end quotation + +This section describes the textual date representations that GNU +programs accept. These are the strings you, as a user, can supply as +arguments to the various programs. The C interface (via the +@code{parse_datetime} function) is not described here. + +@menu +* General date syntax:: Common rules +* Calendar date items:: @samp{14 Nov 2022} +* Time of day items:: @samp{9:02pm} +* Time zone items:: @samp{UTC}, @samp{-0700}, @samp{+0900}, @dots{} +* Combined date and time of day items:: @samp{2022-11-14T21:02:42,000000-0500} +* Day of week items:: @samp{Monday} and others +* Relative items in date strings:: @samp{next tuesday, 2 years ago} +* Pure numbers in date strings:: @samp{20221114}, @samp{2102} +* Seconds since the Epoch:: @samp{@@1668477762} +* Specifying time zone rules:: @samp{TZ="America/New_York"}, @samp{TZ="UTC0"} +* Authors of parse_datetime:: Bellovin, Eggert, Salz, Berets, et al. +@end menu + + +@node General date syntax +@section General date syntax + +@cindex general date syntax + +@cindex items in date strings +A @dfn{date} is a string, possibly empty, containing many items +separated by whitespace. The whitespace may be omitted when no +ambiguity arises. The empty string means the beginning of today (i.e., +midnight). Order of the items is immaterial. A date string may contain +many flavors of items: + +@itemize @bullet +@item calendar date items +@item time of day items +@item time zone items +@item combined date and time of day items +@item day of the week items +@item relative items +@item pure numbers. +@end itemize + +@noindent We describe each of these item types in turn, below. + +@cindex numbers, written-out +@cindex ordinal numbers +@findex first @r{in date strings} +@findex next @r{in date strings} +@findex last @r{in date strings} +A few ordinal numbers may be written out in words in some contexts. This is +most useful for specifying day of the week items or relative items (see +below). Among the most commonly used ordinal numbers, the word +@samp{last} stands for @math{-1}, @samp{this} stands for 0, and +@samp{first} and @samp{next} both stand for 1. Because the word +@samp{second} stands for the unit of time there is no way to write the +ordinal number 2, but for convenience @samp{third} stands for 3, +@samp{fourth} for 4, @samp{fifth} for 5, +@samp{sixth} for 6, @samp{seventh} for 7, @samp{eighth} for 8, +@samp{ninth} for 9, @samp{tenth} for 10, @samp{eleventh} for 11 and +@samp{twelfth} for 12. + +@cindex months, written-out +When a month is written this way, it is still considered to be written +numerically, instead of being ``spelled in full''; this changes the +allowed strings. + +@cindex language, in dates +In the current implementation, only English is supported for words and +abbreviations like @samp{AM}, @samp{DST}, @samp{EST}, @samp{first}, +@samp{January}, @samp{Sunday}, @samp{tomorrow}, and @samp{year}. + +@cindex language, in dates +@cindex time zone item +The output of the @command{date} command +is not always acceptable as a date string, +not only because of the language problem, but also because there is no +standard meaning for time zone items like @samp{IST}@. When using +@command{date} to generate a date string intended to be parsed later, +specify a date format that is independent of language and that does not +use time zone items other than @samp{UTC} and @samp{Z}@. Here are some +ways to do this: + +@example +$ LC_ALL=C TZ=UTC0 date +Tue Nov 15 02:02:42 UTC 2022 +$ TZ=UTC0 date +'%Y-%m-%d %H:%M:%SZ' +2022-11-15 02:02:42Z +$ date --rfc-3339=ns # --rfc-3339 is a GNU extension. +2022-11-14 21:02:42.000000000-05:00 +$ date --rfc-email # a GNU extension +Mon, 14 Nov 2022 21:02:42 -0500 +$ date +'%Y-%m-%d %H:%M:%S %z' # %z is a GNU extension. +2022-11-14 21:02:42 -0500 +$ date +'@@%s.%N' # %s and %N are GNU extensions. +@@1668477762.692722128 +@end example + +@cindex case, ignored in dates +@cindex comments, in dates +Alphabetic case is completely ignored in dates. Comments may be introduced +between round parentheses, as long as included parentheses are properly +nested. Hyphens not followed by a digit are currently ignored. Leading +zeros on numbers are ignored. + +@cindex leap seconds +Invalid dates like @samp{2022-02-29} or times like @samp{24:00} are +rejected. In the typical case of a host that does not support leap +seconds, a time like @samp{23:59:60} is rejected even if it +corresponds to a valid leap second. + + +@node Calendar date items +@section Calendar date items + +@cindex calendar date item + +A @dfn{calendar date item} specifies a day of the year. It is +specified differently, depending on whether the month is specified +numerically or literally. All these strings specify the same calendar date: + +@example +2022-11-14 # ISO 8601. +22-11-14 # Assume 19xx for 69 through 99, + # 20xx for 00 through 68 (not recommended). +11/14/2022 # Common U.S. writing. +14 November 2022 +14 Nov 2022 # Three-letter abbreviations always allowed. +November 14, 2022 +14-nov-2022 +14nov2022 +@end example + +The year can also be omitted. In this case, the last specified year is +used, or the current year if none. For example: + +@example +11/14 +nov 14 +@end example + +Here are the rules. + +@cindex ISO 8601 date format +@cindex date format, ISO 8601 +For numeric months, the ISO 8601 format +@samp{@var{year}-@var{month}-@var{day}} is allowed, where @var{year} is +any positive number, @var{month} is a number between 01 and 12, and +@var{day} is a number between 01 and 31. A leading zero must be present +if a number is less than ten. If @var{year} is 68 or smaller, then 2000 +is added to it; otherwise, if @var{year} is less than 100, +then 1900 is added to it. The construct +@samp{@var{month}/@var{day}/@var{year}}, popular in the United States, +is accepted. Also @samp{@var{month}/@var{day}}, omitting the year. + +@cindex month names in date strings +@cindex abbreviations for months +Literal months may be spelled out in full: @samp{January}, +@samp{February}, @samp{March}, @samp{April}, @samp{May}, @samp{June}, +@samp{July}, @samp{August}, @samp{September}, @samp{October}, +@samp{November} or @samp{December}. Literal months may be abbreviated +to their first three letters, possibly followed by an abbreviating dot. +It is also permitted to write @samp{Sept} instead of @samp{September}. + +When months are written literally, the calendar date may be given as any +of the following: + +@example +@var{day} @var{month} @var{year} +@var{day} @var{month} +@var{month} @var{day} @var{year} +@var{day}-@var{month}-@var{year} +@end example + +Or, omitting the year: + +@example +@var{month} @var{day} +@end example + + +@node Time of day items +@section Time of day items + +@cindex time of day item + +A @dfn{time of day item} in date strings specifies the time on a given +day. Here are some examples, all of which represent the same time: + +@example +20:02:00.000000 +20:02 +8:02pm +20:02-0500 # In EST (U.S. Eastern Standard Time). +@end example + +@cindex leap seconds +More generally, the time of day may be given as +@samp{@var{hour}:@var{minute}:@var{second}}, where @var{hour} is +a number between 0 and 23, @var{minute} is a number between 0 and +59, and @var{second} is a number between 0 and 59 possibly followed by +@samp{.} or @samp{,} and a fraction containing one or more digits. +Alternatively, +@samp{:@var{second}} can be omitted, in which case it is taken to +be zero. On the rare hosts that support leap seconds, @var{second} +may be 60. + +@findex am @r{in date strings} +@findex pm @r{in date strings} +@findex midnight @r{in date strings} +@findex noon @r{in date strings} +If the time is followed by @samp{am} or @samp{pm} (or @samp{a.m.} +or @samp{p.m.}), @var{hour} is restricted to run from 1 to 12, and +@samp{:@var{minute}} may be omitted (taken to be zero). @samp{am} +indicates the first half of the day, @samp{pm} indicates the second +half of the day. In this notation, 12 is the predecessor of 1: +midnight is @samp{12am} while noon is @samp{12pm}. +(This is the zero-oriented interpretation of @samp{12am} and @samp{12pm}, +as opposed to the old tradition derived from Latin +which uses @samp{12m} for noon and @samp{12pm} for midnight.) + +@cindex time zone correction +@cindex minutes, time zone correction by +The time may alternatively be followed by a time zone correction, +expressed as @samp{@var{s}@var{hh}@var{mm}}, where @var{s} is @samp{+} +or @samp{-}, @var{hh} is a number of zone hours and @var{mm} is a number +of zone minutes. +The zone minutes term, @var{mm}, may be omitted, in which case +the one- or two-digit correction is interpreted as a number of hours. +You can also separate @var{hh} from @var{mm} with a colon. +When a time zone correction is given this way, it +forces interpretation of the time relative to +Coordinated Universal Time (UTC), overriding any previous +specification for the time zone or the local time zone. For example, +@samp{+0530} and @samp{+05:30} both stand for the time zone 5.5 hours +ahead of UTC (e.g., India). +This is the best way to +specify a time zone correction by fractional parts of an hour. +The maximum zone correction is 24 hours. + +Either @samp{am}/@samp{pm} or a time zone correction may be specified, +but not both. + + +@node Time zone items +@section Time zone items + +@cindex time zone item + +A @dfn{time zone item} specifies an international time zone, indicated +by a small set of letters, e.g., @samp{UTC} or @samp{Z} +for Coordinated Universal +Time. Any included periods are ignored. By following a +non-daylight-saving time zone by the string @samp{DST} in a separate +word (that is, separated by some white space), the corresponding +daylight saving time zone may be specified. +Alternatively, a non-daylight-saving time zone can be followed by a +time zone correction, to add the two values. This is normally done +only for @samp{UTC}; for example, @samp{UTC+05:30} is equivalent to +@samp{+05:30}. + +Time zone items other than @samp{UTC} and @samp{Z} +are obsolescent and are not recommended, because they +are ambiguous; for example, @samp{EST} has a different meaning in +Australia than in the United States, and @samp{A} has different +meaning as a military time zone than as an obsolete +RFC 822 time zone. Instead, it's better to use +unambiguous numeric time zone corrections like @samp{-0500}, as +described in the previous section. + +If neither a time zone item nor a time zone correction is supplied, +timestamps are interpreted using the rules of the default time zone +(@pxref{Specifying time zone rules}). + + +@node Combined date and time of day items +@section Combined date and time of day items + +@cindex combined date and time of day item +@cindex ISO 8601 date and time of day format +@cindex date and time of day format, ISO 8601 + +The ISO 8601 date and time of day extended format consists of an ISO +8601 date, a @samp{T} character separator, and an ISO 8601 time of +day. This format is also recognized if the @samp{T} is replaced by a +space. + +In this format, the time of day should use 24-hour notation. +Fractional seconds are allowed, with either comma or period preceding +the fraction. ISO 8601 fractional minutes and hours are not +supported. Typically, hosts support nanosecond timestamp resolution; +excess precision is silently discarded. + +Here are some examples: + +@example +2022-09-24T20:02:00.052-05:00 +2022-12-31T23:59:59,999999999+11:00 +1970-01-01 00:00Z +@end example + +@node Day of week items +@section Day of week items + +@cindex day of week item + +The explicit mention of a day of the week will forward the date +(only if necessary) to reach that day of the week in the future. + +Days of the week may be spelled out in full: @samp{Sunday}, +@samp{Monday}, @samp{Tuesday}, @samp{Wednesday}, @samp{Thursday}, +@samp{Friday} or @samp{Saturday}. Days may be abbreviated to their +first three letters, optionally followed by a period. The special +abbreviations @samp{Tues} for @samp{Tuesday}, @samp{Wednes} for +@samp{Wednesday} and @samp{Thur} or @samp{Thurs} for @samp{Thursday} are +also allowed. + +@findex next @var{day} +@findex last @var{day} +A number may precede a day of the week item to move forward +supplementary weeks. It is best used in expression like @samp{third +monday}. In this context, @samp{last @var{day}} or @samp{next +@var{day}} is also acceptable; they move one week before or after +the day that @var{day} by itself would represent. + +A comma following a day of the week item is ignored. + + +@node Relative items in date strings +@section Relative items in date strings + +@cindex relative items in date strings +@cindex displacement of dates + +@dfn{Relative items} adjust a date (or the current date if none) forward +or backward. The effects of relative items accumulate. Here are some +examples: + +@example +1 year +1 year ago +3 years +2 days +@end example + +@findex year @r{in date strings} +@findex month @r{in date strings} +@findex fortnight @r{in date strings} +@findex week @r{in date strings} +@findex day @r{in date strings} +@findex hour @r{in date strings} +@findex minute @r{in date strings} +The unit of time displacement may be selected by the string @samp{year} +or @samp{month} for moving by whole years or months. These are fuzzy +units, as years and months are not all of equal duration. More precise +units are @samp{fortnight} which is worth 14 days, @samp{week} worth 7 +days, @samp{day} worth 24 hours, @samp{hour} worth 60 minutes, +@samp{minute} or @samp{min} worth 60 seconds, and @samp{second} or +@samp{sec} worth one second. An @samp{s} suffix on these units is +accepted and ignored. + +@findex ago @r{in date strings} +The unit of time may be preceded by a multiplier, given as an optionally +signed number. Unsigned numbers are taken as positively signed. No +number at all implies 1 for a multiplier. Following a relative item by +the string @samp{ago} is equivalent to preceding the unit by a +multiplier with value @math{-1}. + +@findex day @r{in date strings} +@findex tomorrow @r{in date strings} +@findex yesterday @r{in date strings} +The string @samp{tomorrow} is worth one day in the future (equivalent +to @samp{day}), the string @samp{yesterday} is worth +one day in the past (equivalent to @samp{day ago}). + +@findex now @r{in date strings} +@findex today @r{in date strings} +@findex this @r{in date strings} +The strings @samp{now} or @samp{today} are relative items corresponding +to zero-valued time displacement, these strings come from the fact +a zero-valued time displacement represents the current time when not +otherwise changed by previous items. They may be used to stress other +items, like in @samp{12:00 today}. The string @samp{this} also has +the meaning of a zero-valued time displacement, but is preferred in +date strings like @samp{this thursday}. + +When a relative item causes the resulting date to cross a boundary +where the clocks were adjusted, typically for daylight saving time, +the resulting date and time are adjusted accordingly. + +The fuzz in units can cause problems with relative items. For +example, @samp{2022-12-31 -1 month} might evaluate to 2022-12-01, +because 2022-11-31 is an invalid date. To determine the previous +month more reliably, you can ask for the month before the 15th of the +current month. For example: + +@example +$ date -R +Thu, 31 Dec 2022 13:02:39 -0400 +$ date --date='-1 month' +'Last month was %B?' +Last month was December? +$ date --date="$(date +%Y-%m-15) -1 month" +'Last month was %B!' +Last month was November! +@end example + +Also, take care when manipulating dates around clock changes such as +daylight saving leaps. In a few cases these have added or subtracted +as much as 24 hours from the clock, so it is often wise to adopt +universal time by setting the @env{TZ} environment variable to +@samp{UTC0} before embarking on calendrical calculations. + +@node Pure numbers in date strings +@section Pure numbers in date strings + +@cindex pure numbers in date strings + +The precise interpretation of a pure decimal number depends +on the context in the date string. + +If the decimal number is of the form @var{yyyy}@var{mm}@var{dd} and no +other calendar date item (@pxref{Calendar date items}) appears before it +in the date string, then @var{yyyy} is read as the year, @var{mm} as the +month number and @var{dd} as the day of the month, for the specified +calendar date. + +If the decimal number is of the form @var{hh}@var{mm} and no other time +of day item appears before it in the date string, then @var{hh} is read +as the hour of the day and @var{mm} as the minute of the hour, for the +specified time of day. @var{mm} can also be omitted. + +If both a calendar date and a time of day appear to the left of a number +in the date string, but no relative item, then the number overrides the +year. + + +@node Seconds since the Epoch +@section Seconds since the Epoch + +If you precede a number with @samp{@@}, it represents an internal +timestamp as a count of seconds. The number can contain an internal +decimal point (either @samp{.} or @samp{,}); any excess precision not +supported by the internal representation is truncated toward minus +infinity. Such a number cannot be combined with any other date +item, as it specifies a complete timestamp. + +@cindex beginning of time, for POSIX +@cindex Epoch, for POSIX +Internally, computer times are represented as a count of seconds since +an Epoch---a well-defined point of time. On GNU and +POSIX systems, the Epoch is 1970-01-01 00:00:00 UTC, so +@samp{@@0} represents this time, @samp{@@1} represents 1970-01-01 +00:00:01 UTC, and so forth. GNU and most other +POSIX-compliant systems support such times as an extension +to POSIX, using negative counts, so that @samp{@@-1} +represents 1969-12-31 23:59:59 UTC. + +Most modern systems count seconds with 64-bit two's-complement integers +of seconds with nanosecond subcounts, which is a range that includes +the known lifetime of the universe with nanosecond resolution. +Some obsolescent systems count seconds with 32-bit two's-complement +integers and can represent times from 1901-12-13 20:45:52 through +2038-01-19 03:14:07 UTC@. A few systems sport other time ranges. + +@cindex leap seconds +On most hosts, these counts ignore the presence of leap seconds. +For example, on most hosts @samp{@@1483228799} represents 2016-12-31 +23:59:59 UTC, @samp{@@1483228800} represents 2017-01-01 00:00:00 +UTC, and there is no way to represent the intervening leap second +2016-12-31 23:59:60 UTC. + +@node Specifying time zone rules +@section Specifying time zone rules + +@vindex TZ +Normally, dates are interpreted using the rules of the current time +zone, which in turn are specified by the @env{TZ} environment +variable, or by a system default if @env{TZ} is not set. To specify a +different set of default time zone rules that apply just to one date, +start the date with a string of the form @samp{TZ="@var{rule}"}. The +two quote characters (@samp{"}) must be present in the date, and any +quotes or backslashes within @var{rule} must be escaped by a +backslash. + +For example, with the GNU @command{date} command you can +answer the question ``What time is it in New York when a Paris clock +shows 6:30am on October 31, 2022?'' by using a date beginning with +@samp{TZ="Europe/Paris"} as shown in the following shell transcript: + +@example +$ export TZ="America/New_York" +$ date --date='TZ="Europe/Paris" 2022-10-31 06:30' +Mon Oct 31 01:30:00 EDT 2022 +@end example + +In this example, the @option{--date} operand begins with its own +@env{TZ} setting, so the rest of that operand is processed according +to @samp{Europe/Paris} rules, treating the string @samp{2022-11-14 +06:30} as if it were in Paris. However, since the output of the +@command{date} command is processed according to the overall time zone +rules, it uses New York time. (Paris was normally six hours ahead of +New York in 2022, but this example refers to a brief Halloween period +when the gap was five hours.) + +A @env{TZ} value is a rule that typically names a location in the +@uref{https://www.iana.org/time-zones, @samp{tz} database}. +A recent catalog of location names appears in the +@uref{https://twiki.org/cgi-bin/xtra/tzdatepick.html, TWiki Date and Time +Gateway}. A few non-GNU hosts require a colon before a +location name in a @env{TZ} setting, e.g., +@samp{TZ=":America/New_York"}. + +The @samp{tz} database includes a wide variety of locations ranging +from @samp{Africa/Abidjan} to @samp{Pacific/Tongatapu}, but +if you are at sea and have your own private time zone, or if you are +using a non-GNU host that does not support the @samp{tz} +database, you may need to use a POSIX rule instead. +The previously-mentioned POSIX rule @samp{UTC0} says that the time zone +abbreviation is @samp{UTC}, the zone is zero hours away from +Greenwich, and there is no daylight saving time. +POSIX rules can also specify nonzero Greenwich offsets. +For example, the following shell transcript answers the question +``What time is it five and a half hours east of Greenwich when a clock +seven hours west of Greenwich shows 9:50pm on July 12, 2022?'' + +@example +$ TZ="<+0530>-5:30" date --date='TZ="<-07>+7" 2022-07-12 21:50' +Wed Jul 13 10:20:00 +0530 2022 +@end example + +@noindent +This example uses the somewhat-confusing POSIX convention for rules. +@samp{TZ="<-07>+7"} says that the time zone abbreviation is @samp{-07} +and the time zone is 7 hours west of Greenwich, and +@samp{TZ="<+0530>-5:30"} says that the time zone abbreviation is @samp{+0530} +and the time zone is 5 hours 30 minutes east of Greenwich. +(One should never use a setting like @samp{TZ="UTC-5"}, since +this would incorrectly imply that local time is five hours east of +Greenwich and the time zone is called ``UTC''.) +Although trickier POSIX @env{TZ} settings like +@samp{TZ="<-05>+5<-04>,M3.2.0/2,M11.1.0/2"} can specify some daylight +saving regimes, location-based settings like +@samp{TZ="America/New_York"} are typically simpler and more accurate +historically. @xref{TZ Variable,, Specifying the Time Zone with @code{TZ}, +libc, The GNU C Library}. + +@node Authors of parse_datetime +@section Authors of @code{parse_datetime} +@c the anchor keeps the old node name, to try to avoid breaking links +@anchor{Authors of get_date} + +@cindex authors of @code{parse_datetime} + +@cindex Bellovin, Steven M. +@cindex Salz, Rich +@cindex Berets, Jim +@cindex MacKenzie, David +@cindex Meyering, Jim +@cindex Eggert, Paul +@code{parse_datetime} started life as @code{getdate}, as originally +implemented by Steven M. Bellovin +(@email{smb@@research.att.com}) while at the University of North Carolina +at Chapel Hill. The code was later tweaked by a couple of people on +Usenet, then completely overhauled by Rich $alz (@email{rsalz@@bbn.com}) +and Jim Berets (@email{jberets@@bbn.com}) in August, 1990. Various +revisions for the GNU system were made by David MacKenzie, Jim Meyering, +Paul Eggert and others, including renaming it to @code{get_date} to +avoid a conflict with the alternative Posix function @code{getdate}, +and a later rename to @code{parse_datetime}. The Posix function +@code{getdate} can parse more locale-specific dates using +@code{strptime}, but relies on an environment variable and external +file, and lacks the thread-safety of @code{parse_datetime}. + +@cindex Pinard, F. +@cindex Berry, K. +This chapter was originally produced by Fran@,{c}ois Pinard +(@email{pinard@@iro.umontreal.ca}) from the @file{parse_datetime.y} source code, +and then edited by K. Berry (@email{kb@@cs.umb.edu}). diff --git a/doc/perm.texi b/doc/perm.texi new file mode 100644 index 0000000..45ff1d4 --- /dev/null +++ b/doc/perm.texi @@ -0,0 +1,641 @@ +@c File mode bits + +@c Copyright (C) 1994--2023 Free Software Foundation, Inc. + +@c Permission is granted to copy, distribute and/or modify this document +@c under the terms of the GNU Free Documentation License, Version 1.3 or +@c any later version published by the Free Software Foundation; with no +@c Invariant Sections, with no Front-Cover Texts, and with no Back-Cover +@c Texts. A copy of the license is included in the ``GNU Free +@c Documentation License'' file as part of this distribution. + +Each file has a set of @dfn{file mode bits} that control the kinds of +access that users have to that file. They can be represented either in +symbolic form or as an octal number. + +@menu +* Mode Structure:: Structure of file mode bits. +* Symbolic Modes:: Mnemonic representation of file mode bits. +* Numeric Modes:: File mode bits as octal numbers. +* Operator Numeric Modes:: ANDing, ORing, and setting modes octally. +* Directory Setuid and Setgid:: Set-user-ID and set-group-ID on directories. +@end menu + +@node Mode Structure +@section Structure of File Mode Bits + +The file mode bits have two parts: the @dfn{file permission bits}, +which control ordinary access to the file, and @dfn{special mode +bits}, which affect only some files. + +There are three kinds of permissions that a user can have for a file: + +@enumerate +@item +@cindex read permission +permission to read the file. For directories, this means permission to +list the contents of the directory. +@item +@cindex write permission +permission to write to (change) the file. For directories, this means +permission to create and remove files in the directory. +@item +@cindex execute/search permission +permission to execute the file (run it as a program). For directories, +this means permission to access files in the directory. +@end enumerate + +There are three categories of users who may have different permissions +to perform any of the above operations on a file: + +@enumerate +@item +the file's owner; +@item +other users who are in the file's group; +@item +everyone else. +@end enumerate + +@cindex owner, default +@cindex group owner, default +Files are given an owner and group when they are created. Usually the +owner is the current user and the group is the group of the directory +the file is in, but this varies with the operating system, the +file system the file is created on, and the way the file is created. You +can change the owner and group of a file by using the @command{chown} and +@command{chgrp} commands. + +In addition to the three sets of three permissions listed above, the +file mode bits have three special components, which affect only +executable files (programs) and, on most systems, directories: + +@table @asis +@item The @dfn{set-user-ID bit} (@dfn{setuid bit}). +@cindex set-user-ID +@cindex setuid +On execution, set the process's effective user ID to that of the file. +For directories on a few systems, give files created in the directory +the same owner as the directory, no matter who creates them, and set +the set-user-ID bit of newly-created subdirectories. + +@item The @dfn{set-group-ID bit} (@dfn{setgid bit}). +@cindex set-group-ID +@cindex setgid +On execution, set the process's effective group ID to that of the file. +For directories on most systems, give files created in the directory +the same group as the directory, no matter what group the user who +creates them is in, and set the set-group-ID bit of newly-created +subdirectories. + +@item The @dfn{restricted deletion flag} or @dfn{sticky bit}. +@cindex sticky +@cindex swap space, saving text image in +@cindex text image, saving in swap space +@cindex restricted deletion flag +Prevent unprivileged users from removing or renaming a file in a directory +unless they own the file or the directory; this is commonly +found on world-writable directories like @file{/tmp}. +For regular files on some older systems, save the program's text image on the +swap device so it will load more quickly when run, so that the image +is ``sticky''. +@end table + +In addition to the file mode bits listed above, there may be file attributes +specific to the file system, e.g., access control lists (ACLs), whether a +file is compressed, whether a file can be modified (immutability), and whether +a file can be dumped. These are usually set using programs +specific to the file system. For example: +@c should probably say a lot more about ACLs... someday + +@table @asis +@item ext2 +On GNU and GNU/Linux the file attributes specific to +the ext2 file system are set using @command{chattr}. + +@item FFS +On FreeBSD the file flags specific to the FFS +file system are set using @command{chflags}. +@end table + +Even if a file's mode bits allow an operation on that file, +that operation may still fail, because: + +@itemize +@item +the file-system-specific attributes or flags do not permit it; or + +@item +the file system is mounted as read-only. +@end itemize + +For example, if the immutable attribute is set on a file, +it cannot be modified, regardless of the fact that you +may have just run @code{chmod a+w FILE}. + +@node Symbolic Modes +@section Symbolic Modes + +@cindex symbolic modes +@dfn{Symbolic modes} represent changes to files' mode bits as +operations on single-character symbols. They allow you to modify either +all or selected parts of files' mode bits, optionally based on +their previous values, and perhaps on the current @code{umask} as well +(@pxref{Umask and Protection}). + +The format of symbolic modes is: + +@example +@r{[}ugoa@dots{}@r{][}-+=@r{]}@var{perms}@dots{}@r{[},@dots{}@r{]} +@end example + +@noindent +where @var{perms} is either zero or more letters from the set +@samp{rwxXst}, or a single letter from the set @samp{ugo}. + +The following sections describe the operators and other details of +symbolic modes. + +@menu +* Setting Permissions:: Basic operations on permissions. +* Copying Permissions:: Copying existing permissions. +* Changing Special Mode Bits:: Special mode bits. +* Conditional Executability:: Conditionally affecting executability. +* Multiple Changes:: Making multiple changes. +* Umask and Protection:: The effect of the umask. +@end menu + +@node Setting Permissions +@subsection Setting Permissions + +The basic symbolic operations on a file's permissions are adding, +removing, and setting the permission that certain users have to read, +write, and execute or search the file. These operations have the following +format: + +@example +@var{users} @var{operation} @var{permissions} +@end example + +@noindent +The spaces between the three parts above are shown for readability only; +symbolic modes cannot contain spaces. + +The @var{users} part tells which users' access to the file is changed. +It consists of one or more of the following letters (or it can be empty; +@pxref{Umask and Protection}, for a description of what happens then). When +more than one of these letters is given, the order that they are in does +not matter. + +@table @code +@item u +@cindex owner of file, permissions for +the user who owns the file; +@item g +@cindex group, permissions for +other users who are in the file's group; +@item o +@cindex other permissions +all other users; +@item a +all users; the same as @samp{ugo}. +@end table + +The @var{operation} part tells how to change the affected users' access +to the file, and is one of the following symbols: + +@table @code +@item + +@cindex adding permissions +to add the @var{permissions} to whatever permissions the @var{users} +already have for the file; +@item - +@cindex removing permissions +@cindex subtracting permissions +to remove the @var{permissions} from whatever permissions the +@var{users} already have for the file; +@item = +@cindex setting permissions +to make the @var{permissions} the only permissions that the @var{users} +have for the file. +@end table + +The @var{permissions} part tells what kind of access to the file should +be changed; it is normally zero or more of the following letters. As with the +@var{users} part, the order does not matter when more than one letter is +given. Omitting the @var{permissions} part is useful only with the +@samp{=} operation, where it gives the specified @var{users} no access +at all to the file. + +@table @code +@item r +@cindex read permission, symbolic +the permission the @var{users} have to read the file; +@item w +@cindex write permission, symbolic +the permission the @var{users} have to write to the file; +@item x +@cindex execute/search permission, symbolic +the permission the @var{users} have to execute the file, +or search it if it is a directory. +@end table + +For example, to give everyone permission to read and write a regular file, +but not to execute it, use: + +@example +a=rw +@end example + +To remove write permission for all users other than the file's +owner, use: + +@example +go-w +@end example + +@noindent +The above command does not affect the access that the owner of +the file has to it, nor does it affect whether other users can +read or execute the file. + +To give everyone except a file's owner no permission to do anything with +that file, use the mode below. Other users could still remove the file, +if they have write permission on the directory it is in. + +@example +go= +@end example + +@noindent +Another way to specify the same thing is: + +@example +og-rwx +@end example + +@node Copying Permissions +@subsection Copying Existing Permissions + +@cindex copying existing permissions +@cindex permissions, copying existing +You can base a file's permissions on its existing permissions. To do +this, instead of using a series of @samp{r}, @samp{w}, or @samp{x} +letters after the +operator, you use the letter @samp{u}, @samp{g}, or @samp{o}. For +example, the mode + +@example +o+g +@end example + +@noindent +adds the permissions for users who are in a file's group to the +permissions that other users have for the file. Thus, if the file +started out as mode 664 (@samp{rw-rw-r--}), the above mode would change +it to mode 666 (@samp{rw-rw-rw-}). If the file had started out as mode +741 (@samp{rwxr----x}), the above mode would change it to mode 745 +(@samp{rwxr--r-x}). The @samp{-} and @samp{=} operations work +analogously. + +@node Changing Special Mode Bits +@subsection Changing Special Mode Bits + +@cindex changing special mode bits +In addition to changing a file's read, write, and execute/search permissions, +you can change its special mode bits. @xref{Mode Structure}, for a +summary of these special mode bits. + +To change the file mode bits to set the user ID on execution, use +@samp{u} in the @var{users} part of the symbolic mode and +@samp{s} in the @var{permissions} part. + +To change the file mode bits to set the group ID on execution, use +@samp{g} in the @var{users} part of the symbolic mode and +@samp{s} in the @var{permissions} part. + +To set both user and group ID on execution, omit the @var{users} part +of the symbolic mode (or use @samp{a}) and use @samp{s} in the +@var{permissions} part. + +To change the file mode bits to set the restricted deletion flag or sticky bit, +omit the @var{users} part of the symbolic mode (or use @samp{a}) and use +@samp{t} in the @var{permissions} part. + +For example, to set the set-user-ID mode bit of a program, +you can use the mode: + +@example +u+s +@end example + +To remove both set-user-ID and set-group-ID mode bits from +it, you can use the mode: + +@example +a-s +@end example + +To set the restricted deletion flag or sticky bit, you can use +the mode: + +@example ++t +@end example + +The combination @samp{o+s} has no effect. On GNU systems +the combinations @samp{u+t} and @samp{g+t} have no effect, and +@samp{o+t} acts like plain @samp{+t}. + +The @samp{=} operator is not very useful with special mode bits. +For example, the mode: + +@example +o=t +@end example + +@noindent +does set the restricted deletion flag or sticky bit, but it also +removes all read, write, and execute/search permissions that users not in the +file's group might have had for it. + +@xref{Directory Setuid and Setgid}, for additional rules concerning +set-user-ID and set-group-ID bits and directories. + +@node Conditional Executability +@subsection Conditional Executability + +@cindex conditional executability +There is one more special type of symbolic permission: if you use +@samp{X} instead of @samp{x}, execute/search permission is affected only if the +file is a directory or already had execute permission. + +For example, this mode: + +@example +a+X +@end example + +@noindent +gives all users permission to search directories, or to execute files if +anyone could execute them before. + +@node Multiple Changes +@subsection Making Multiple Changes + +@cindex multiple changes to permissions +The format of symbolic modes is actually more complex than described +above (@pxref{Setting Permissions}). It provides two ways to make +multiple changes to files' mode bits. + +The first way is to specify multiple @var{operation} and +@var{permissions} parts after a @var{users} part in the symbolic mode. + +For example, the mode: + +@example +og+rX-w +@end example + +@noindent +gives users other than the owner of the file read permission and, if +it is a directory or if someone already had execute permission +to it, gives them execute/search permission; and it also denies them write +permission to the file. It does not affect the permission that the +owner of the file has for it. The above mode is equivalent to +the two modes: + +@example +og+rX +og-w +@end example + +The second way to make multiple changes is to specify more than one +simple symbolic mode, separated by commas. For example, the mode: + +@example +a+r,go-w +@end example + +@noindent +gives everyone permission to read the file and removes write +permission on it for all users except its owner. Another example: + +@example +u=rwx,g=rx,o= +@end example + +@noindent +sets all of the permission bits for the file explicitly. (It +gives users who are not in the file's group no permission at all for +it.) + +The two methods can be combined. The mode: + +@example +a+r,g+x-w +@end example + +@noindent +gives all users permission to read the file, and gives users who are in +the file's group permission to execute/search it as well, but not permission +to write to it. The above mode could be written in several different +ways; another is: + +@example +u+r,g+rx,o+r,g-w +@end example + +@node Umask and Protection +@subsection The Umask and Protection + +@cindex umask and modes +@cindex modes and umask +If the @var{users} part of a symbolic mode is omitted, it defaults to +@samp{a} (affect all users), except that any permissions that are +@emph{set} in the system variable @code{umask} are @emph{not affected}. +The value of @code{umask} can be set using the +@code{umask} command. Its default value varies from system to system. + +@cindex giving away permissions +Omitting the @var{users} part of a symbolic mode is generally not useful +with operations other than @samp{+}. It is useful with @samp{+} because +it allows you to use @code{umask} as an easily customizable protection +against giving away more permission to files than you intended to. + +As an example, if @code{umask} has the value 2, which removes write +permission for users who are not in the file's group, then the mode: + +@example ++w +@end example + +@noindent +adds permission to write to the file to its owner and to other users who +are in the file's group, but @emph{not} to other users. In contrast, +the mode: + +@example +a+w +@end example + +@noindent +ignores @code{umask}, and @emph{does} give write permission for +the file to all users. + +@node Numeric Modes +@section Numeric Modes + +@cindex numeric modes +@cindex file mode bits, numeric +@cindex octal numbers for file modes +As an +alternative to giving a symbolic mode, you can give an octal (base 8) +number that represents the mode. + +The permissions granted to the user, +to other users in the file's group, +and to other users not in the file's group each require three +bits: one bit for read, one for write, and one for execute/search permission. +These three bits are represented as one octal digit; +for example, if all three are present, the resulting 111 (in binary) +is represented as the digit 7 (in octal). The three special +mode bits also require one bit each, and they are as a group +represented as another octal digit. Here is how the bits are arranged, +starting with the highest valued bit: + +@example +Value in Corresponding +Mode Mode Bit + + Special mode bits: +4000 Set user ID +2000 Set group ID +1000 Restricted deletion flag or sticky bit + + The file's owner: + 400 Read + 200 Write + 100 Execute/search + + Other users in the file's group: + 40 Read + 20 Write + 10 Execute/search + + Other users not in the file's group: + 4 Read + 2 Write + 1 Execute/search +@end example + +For example, numeric mode @samp{4751} corresponds to symbolic mode +@samp{u=srwx,g=rx,o=x}, and numeric mode @samp{664} corresponds to symbolic mode +@samp{ug=rw,o=r}. Numeric mode @samp{0} corresponds to symbolic mode +@samp{a=}. + +A numeric mode is usually shorter than the corresponding symbolic +mode, but it is limited in that normally it cannot take into account the +previous file mode bits; it can only set them absolutely. +The set-user-ID and set-group-ID bits of directories are an exception +to this general limitation. @xref{Directory Setuid and Setgid}. +Also, operator numeric modes can take previous file mode bits into +account. @xref{Operator Numeric Modes}. + +Numeric modes are always interpreted in octal; you do not have to add a +leading @samp{0}, as you do in C@. Mode @samp{0055} is the same as +mode @samp{55}. However, modes of five digits or more, such as +@samp{00055}, are sometimes special (@pxref{Directory Setuid and Setgid}). + +@node Operator Numeric Modes +@section Operator Numeric Modes + +An operator numeric mode is a numeric mode that is prefixed by a +@samp{-}, @samp{+}, or @samp{=} operator, which has the same +interpretation as in symbolic modes. For example, @samp{+440} enables +read permission for the file's owner and group, @samp{-1} disables +execute permission for other users, and @samp{=600} clears all +permissions except for enabling read-write permissions for the file's +owner. Operator numeric modes can be combined with symbolic modes by +separating them with a comma; for example, @samp{=0,u+r} clears all +permissions except for enabling read permission for the file's owner. + +The commands @samp{chmod =755 @var{dir}} and @samp{chmod 755 +@var{dir}} differ in that the former clears the directory @var{dir}'s +setuid and setgid bits, whereas the latter preserves them. +@xref{Directory Setuid and Setgid}. + +Operator numeric modes are a GNU extension. + +@node Directory Setuid and Setgid +@section Directories and the Set-User-ID and Set-Group-ID Bits + +On most systems, if a directory's set-group-ID bit is set, newly +created subfiles inherit the same group as the directory, and newly +created subdirectories inherit the set-group-ID bit of the parent +directory. On a few systems, a directory's set-user-ID bit has a +similar effect on the ownership of new subfiles and the set-user-ID +bits of new subdirectories. These mechanisms let users share files +more easily, by lessening the need to use @command{chmod} or +@command{chown} to share new files. + +These convenience mechanisms rely on the set-user-ID and set-group-ID +bits of directories. If commands like @command{chmod} and +@command{mkdir} routinely cleared these bits on directories, the +mechanisms would be less convenient and it would be harder to share +files. Therefore, a command like @command{chmod} does not affect the +set-user-ID or set-group-ID bits of a directory unless the user +specifically mentions them in a symbolic mode, or uses an operator +numeric mode such as @samp{=755}, or sets them in a numeric mode, or +clears them in a numeric mode that has five or more octal digits. +For example, on systems that support +set-group-ID inheritance: + +@example +# These commands leave the set-user-ID and +# set-group-ID bits of the subdirectories alone, +# so that they retain their default values. +mkdir A B C +chmod 755 A +chmod 0755 B +chmod u=rwx,go=rx C +mkdir -m 755 D +mkdir -m 0755 E +mkdir -m u=rwx,go=rx F +@end example + +If you want to try to set these bits, you must mention them +explicitly in the symbolic or numeric modes, e.g.: + +@example +# These commands try to set the set-user-ID +# and set-group-ID bits of the subdirectories. +mkdir G +chmod 6755 G +chmod +6000 G +chmod u=rwx,go=rx,a+s G +mkdir -m 6755 H +mkdir -m +6000 I +mkdir -m u=rwx,go=rx,a+s J +@end example + +If you want to try to clear these bits, you must mention them +explicitly in a symbolic mode, or use an operator numeric mode, or +specify a numeric mode with five or more octal digits, e.g.: + +@example +# These commands try to clear the set-user-ID +# and set-group-ID bits of the directory D. +chmod a-s D +chmod -6000 D +chmod =755 D +chmod 00755 D +@end example + +This behavior is a GNU extension. Portable scripts should +not rely on requests to set or clear these bits on directories, as +POSIX allows implementations to ignore these requests. +The GNU behavior with numeric modes of four or fewer digits +is intended for scripts portable to systems that preserve these bits; +the behavior with numeric modes of five or more digits is for scripts +portable to systems that do not preserve the bits. diff --git a/doc/sort-version.texi b/doc/sort-version.texi new file mode 100644 index 0000000..de2ddb5 --- /dev/null +++ b/doc/sort-version.texi @@ -0,0 +1,909 @@ +@c GNU Version-sort ordering documentation + +@c Copyright (C) 2019--2023 Free Software Foundation, Inc. + +@c Permission is granted to copy, distribute and/or modify this document +@c under the terms of the GNU Free Documentation License, Version 1.3 or +@c any later version published by the Free Software Foundation; with no +@c Invariant Sections, no Front-Cover Texts, and no Back-Cover +@c Texts. A copy of the license is included in the ``GNU Free +@c Documentation License'' file as part of this distribution. + +@c Written by Assaf Gordon + +@node Version sort ordering +@chapter Version sort ordering + + + +@node Version sort overview +@section Version sort overview + +@dfn{Version sort} puts items such as file names and lines of +text in an order that feels natural to people, when the text +contains a mixture of letters and digits. + +Lexicographic sorting usually does not produce the order that one expects +because comparisons are made on a character-by-character basis. + +Compare the sorting of the following items: + +@example +Lexicographic sort: Version Sort: + +a1 a1 +a120 a2 +a13 a13 +a2 a120 +@end example + +Version sort functionality in GNU Coreutils is available in the @samp{ls -v}, +@samp{ls --sort=version}, @samp{sort -V}, and +@samp{sort --version-sort} commands. + + + +@node Using version sort in GNU Coreutils +@subsection Using version sort in GNU Coreutils + +Two GNU Coreutils programs use version sort: @command{ls} and @command{sort}. + +To list files in version sort order, use @command{ls} +with the @option{-v} or @option{--sort=version} option: + +@example +default sort: version sort: + +$ ls -1 $ ls -1 -v +a1 a1 +a100 a1.4 +a1.13 a1.13 +a1.4 a1.40 +a1.40 a2 +a2 a100 +@end example + +To sort text files in version sort order, use @command{sort} with +the @option{-V} or @option{--version-sort} option: + +@example +$ cat input +b3 +b11 +b1 +b20 + + +lexicographic order: version sort order: + +$ sort input $ sort -V input +b1 b1 +b11 b3 +b20 b11 +b3 b20 +@end example + +To sort a specific field in a file, use @option{-k/--key} with +@samp{V} type sorting, which is often combined with @samp{b} to +ignore leading blanks in the field: + +@example +$ cat input2 +100 b3 apples +2000 b11 oranges +3000 b1 potatoes +4000 b20 bananas +$ sort -k 2bV,2 input2 +3000 b1 potatoes +100 b3 apples +2000 b11 oranges +4000 b20 bananas +@end example + +@node Version sort and natural sort +@subsection Version sort and natural sort + +In GNU Coreutils, the name @dfn{version sort} was chosen because it is based +on Debian GNU/Linux's algorithm of sorting packages' versions. + +Its goal is to answer questions like +``Which package is newer, @file{firefox-60.7.2} or @file{firefox-60.12.3}?'' + +In Coreutils this algorithm was slightly modified to work on more +general input such as textual strings and file names +(see @ref{Differences from Debian version sort}). + +In other contexts, such as other programs and other programming +languages, a similar sorting functionality is called +@uref{https://en.wikipedia.org/wiki/Natural_sort_order,natural sort}. + + +@node Variations in version sort order +@subsection Variations in version sort order + +Currently there is no standard for version sort. + +That is: there is no one correct way or universally agreed-upon way to +order items. Each program and each programming language can decide its +own ordering algorithm and call it ``version sort'', ``natural sort'', +or other names. + +See @ref{Other version/natural sort implementations} for many examples of +differing sorting possibilities, each with its own rules and variations. + +If you find a bug in the Coreutils implementation of version-sort, please +report it. @xref{Reporting version sort bugs}. + + +@node Version sort implementation +@section Version sort implementation + +GNU Coreutils version sort is based on the ``upstream version'' +part of +@uref{https://www.debian.org/doc/debian-policy/ch-controlfields.html#version, +Debian's versioning scheme}. + +This section describes the GNU Coreutils sort ordering rules. + +The next section (@ref{Differences from Debian version +sort}) describes some differences between GNU Coreutils +and Debian version sort. + + +@node Version-sort ordering rules +@subsection Version-sort ordering rules + +The version sort ordering rules are: + +@enumerate +@item +The strings are compared from left to right. + +@item +First the initial part of each string consisting entirely of non-digit +bytes is determined. + +@enumerate A +@item +These two parts (either of which may be empty) are compared lexically. +If a difference is found it is returned. + +@item +The lexical comparison is a lexicographic comparison of byte strings, +except that: + +@enumerate a +@item +ASCII letters sort before other bytes. +@item +A tilde sorts before anything, even an empty string. +@end enumerate +@end enumerate + +@item +Then the initial part of the remainder of each string that contains +all the leading digits is determined. The numerical values represented by +these two parts are compared, and any difference found is returned as +the result of the comparison. + +@enumerate A +@item +For these purposes an empty string (which can only occur at the end of +one or both version strings being compared) counts as zero. + +@item +Because the numerical value is used, non-identical strings can compare +equal. For example, @samp{123} compares equal to @samp{00123}, and +the empty string compares equal to @samp{0}. +@end enumerate + +@item +These two steps (comparing and removing initial non-digit strings and +initial digit strings) are repeated until a difference is found or +both strings are exhausted. +@end enumerate + +Consider the version-sort comparison of two file names: +@file{foo07.7z} and @file{foo7a.7z}. The two strings will be broken +down to the following parts, and the parts compared respectively from +each string: + +@example +foo @r{vs} foo @r{(rule 2, non-digits)} +07 @r{vs} 7 @r{(rule 3, digits)} +. @r{vs} a. @r{(rule 2)} +7 @r{vs} 7 @r{(rule 3)} +z @r{vs} z @r{(rule 2)} +@end example + +Comparison flow based on above algorithm: + +@enumerate +@item +The first parts (@samp{foo}) are identical. + +@item +The second parts (@samp{07} and @samp{7}) are compared numerically, +and compare equal. + +@item +The third parts (@samp{.} vs @samp{a.}) are compared +lexically by ASCII value (rule 2.B). + +@item +The first byte of the first string (@samp{.}) is compared +to the first byte of the second string (@samp{a}). + +@item +Rule 2.B.a says letters sorts before non-letters. +Hence, @samp{a} comes before @samp{.}. + +@item +The returned result is that @file{foo7a.7z} comes before @file{foo07.7z}. +@end enumerate + +Result when using sort: + +@example +$ cat input3 +foo07.7z +foo7a.7z +$ sort -V input3 +foo7a.7z +foo07.7z +@end example + +See @ref{Differences from Debian version sort} for +additional rules that extend the Debian algorithm in Coreutils. + + +@node Version sort is not the same as numeric sort +@subsection Version sort is not the same as numeric sort + +Consider the following text file: + +@example +$ cat input4 +8.10 +8.5 +8.1 +8.01 +8.010 +8.100 +8.49 + +Numerical Sort: Version Sort: + +$ sort -n input4 $ sort -V input4 +8.01 8.01 +8.010 8.1 +8.1 8.5 +8.10 8.010 +8.100 8.10 +8.49 8.49 +8.5 8.100 +@end example + +Numeric sort (@samp{sort -n}) treats the entire string as a single numeric +value, and compares it to other values. For example, @samp{8.1}, @samp{8.10} and +@samp{8.100} are numerically equivalent, and are ordered together. Similarly, +@samp{8.49} is numerically less than @samp{8.5}, and appears before first. + +Version sort (@samp{sort -V}) first breaks down the string into digit and +non-digit parts, and only then compares each part (see annotated +example in @ref{Version-sort ordering rules}). + +Comparing the string @samp{8.1} to @samp{8.01}, first the +@samp{8}s are compared (and are identical), then the +dots (@samp{.}) are compared and are identical, and lastly the +remaining digits are compared numerically (@samp{1} and @samp{01}) -- +which are numerically equal. Hence, @samp{8.01} and @samp{8.1} +are grouped together. + +Similarly, comparing @samp{8.5} to @samp{8.49} -- the @samp{8} +and @samp{.} parts are identical, then the numeric values @samp{5} and +@samp{49} are compared. The resulting @samp{5} appears before @samp{49}. + +This sorting order (where @samp{8.5} comes before @samp{8.49}) is common when +assigning versions to computer programs (while perhaps not intuitive +or ``natural'' for people). + +@node Version sort punctuation +@subsection Version sort punctuation + +Punctuation is sorted by ASCII order (rule 2.B). + +@example +$ touch 1.0.5_src.tar.gz 1.0_src.tar.gz +$ ls -v -1 +1.0.5_src.tar.gz +1.0_src.tar.gz +@end example + +Why is @file{1.0.5_src.tar.gz} listed before @file{1.0_src.tar.gz}? + +Based on the version-sort ordering rules, the strings are broken down +into the following parts: + +@example + 1 @r{vs} 1 @r{(rule 3, all digits)} + . @r{vs} . @r{(rule 2, all non-digits)} + 0 @r{vs} 0 @r{(rule 3)} + . @r{vs} _src.tar.gz @r{(rule 2)} + 5 @r{vs} empty string @r{(no more bytes in the file name)} +_src.tar.gz @r{vs} empty string +@end example + +The fourth parts (@samp{.} and @samp{_src.tar.gz}) are compared +lexically by ASCII order. The @samp{.} (ASCII value 46) is +less than @samp{_} (ASCII value 95) -- and should be listed before it. + +Hence, @file{1.0.5_src.tar.gz} is listed first. + +If a different byte appears instead of the underscore (for +example, percent sign @samp{%} ASCII value 37, which is less +than dot's ASCII value of 46), that file will be listed first: + +@example +$ touch 1.0.5_src.tar.gz 1.0%zzzzz.gz +1.0%zzzzz.gz +1.0.5_src.tar.gz +@end example + +The same reasoning applies to the following example, as @samp{.} with +ASCII value 46 is less than @samp{/} with ASCII value 47: + +@example +$ cat input5 +3.0/ +3.0.5 +$ sort -V input5 +3.0.5 +3.0/ +@end example + + +@node Punctuation vs letters +@subsection Punctuation vs letters + +Rule 2.B.a says letters sort before non-letters +(after breaking down a string to digit and non-digit parts). + +@example +$ cat input6 +a% +az +$ sort -V input6 +az +a% +@end example + +The input strings consist entirely of non-digits, and based on the +above algorithm have only one part, all non-digits +(@samp{a%} vs @samp{az}). + +Each part is then compared lexically, +byte-by-byte; @samp{a} compares identically in both +strings. + +Rule 2.B.a says a letter like @samp{z} sorts before +a non-letter like @samp{%} -- hence @samp{az} appears first (despite +@samp{z} having ASCII value of 122, much larger than @samp{%} +with ASCII value 37). + +@node The tilde @samp{~} +@subsection The tilde @samp{~} + +Rule 2.B.b says the tilde @samp{~} (ASCII 126) sorts +before other bytes, and before an empty string. + +@example +$ cat input7 +1 +1% +1.2 +1~ +~ +$ sort -V input7 +~ +1~ +1 +1% +1.2 +@end example + +The sorting algorithm starts by breaking down the string into +non-digit (rule 2) and digit parts (rule 3). + +In the above input file, only the last line in the input file starts +with a non-digit (@samp{~}). This is the first part. All other lines +in the input file start with a digit -- their first non-digit part is +empty. + +Based on rule 2.B.b, tilde @samp{~} sorts before other bytes +and before the empty string -- hence it comes before all other strings, +and is listed first in the sorted output. + +The remaining lines (@samp{1}, @samp{1%}, @samp{1.2}, @samp{1~}) +follow similar logic: The digit part is extracted (1 for all strings) +and compares equal. The following extracted parts for the remaining +input lines are: empty part, @samp{%}, @samp{.}, @samp{~}. + +Tilde sorts before all others, hence the line @samp{1~} appears next. + +The remaining lines (@samp{1}, @samp{1%}, @samp{1.2}) are sorted based +on previously explained rules. + +@node Version sort ignores locale +@subsection Version sort ignores locale + +In version sort, Unicode characters are compared byte-by-byte according +to their binary representation, ignoring their Unicode value or the +current locale. + +Most commonly, Unicode characters are encoded as UTF-8 bytes; for +example, GREEK SMALL LETTER ALPHA (U+03B1, @samp{α}) is encoded as the +UTF-8 sequence @samp{0xCE 0xB1}). The encoding is compared +byte-by-byte, e.g., first @samp{0xCE} (decimal value 206) then +@samp{0xB1} (decimal value 177). + +@example +$ touch aa az "a%" "aα" +$ ls -1 -v +aa +az +a% +aα +@end example + +Ignoring the first letter (@samp{a}) which is identical in all +strings, the compared values are: + +@samp{a} and @samp{z} are letters, and sort before +all other non-digits. + +Then, percent sign @samp{%} (ASCII value 37) is compared to the +first byte of the UTF-8 sequence of @samp{α}, which is 0xCE or 206). The +value 37 is smaller, hence @samp{a%} is listed before @samp{aα}. + +@node Differences from Debian version sort +@section Differences from Debian version sort + +GNU Coreutils version sort differs slightly from the +official Debian algorithm, in order to accommodate more general usage +and file name listing. + + +@node Hyphen-minus and colon +@subsection Hyphen-minus @samp{-} and colon @samp{:} + +In Debian's version string syntax the version consists of three parts: +@example +[epoch:]upstream_version[-debian_revision] +@end example +The @samp{epoch} and @samp{debian_revision} parts are optional. + +Example of such version strings: + +@example +60.7.2esr-1~deb9u1 +52.9.0esr-1~deb9u1 +1:2.3.4-1+b2 +327-2 +1:1.0.13-3 +2:1.19.2-1+deb9u5 +@end example + +If the @samp{debian_revision part} is not present, +hyphens @samp{-} are not allowed. +If epoch is not present, colons @samp{:} are not allowed. + +If these parts are present, hyphen and/or colons can appear only once +in valid Debian version strings. + +In GNU Coreutils, such restrictions are not reasonable (a file name can +have many hyphens, a line of text can have many colons). + +As a result, in GNU Coreutils hyphens and colons are treated exactly +like all other punctuation, i.e., they are sorted after +letters. @xref{Version sort punctuation}. + +In Debian, these characters are treated differently than in Coreutils: +a version string with hyphen will sort before similar strings without +hyphens. + +Compare: + +@example +$ touch 1ab-cd 1abb +$ ls -v -1 +1abb +1ab-cd +$ if dpkg --compare-versions 1abb lt 1ab-cd +> then echo sorted +> else echo out of order +> fi +out of order +@end example + +For further details, see @ref{Comparing two strings using Debian's +algorithm} and @uref{https://bugs.gnu.org/35939,GNU Bug 35939}. + +@node Special priority in GNU Coreutils version sort +@subsection Special priority in GNU Coreutils version sort + +In GNU Coreutils version sort, the following items have +special priority and sort before all other strings (listed in order): + +@enumerate +@item The empty string + +@item The string @samp{.} (a single dot, ASCII 46) + +@item The string @samp{..} (two dots) + +@item Strings starting with dot (@samp{.}) sort before +strings starting with any other byte. +@end enumerate + +Example: + +@example +$ printf '%s\n' a "" b "." c ".." ".d20" ".d3" | sort -V +. +.. +.d3 +.d20 +a +b +c +@end example + +These priorities make perfect sense for @samp{ls -v}: The special +files dot @samp{.} and dot-dot @samp{..} will be listed +first, followed by any hidden files (files starting with a dot), +followed by non-hidden files. + +For @samp{sort -V} these priorities might seem arbitrary. However, +because the sorting code is shared between the @command{ls} and @command{sort} +program, the ordering rules are the same. + +@node Special handling of file extensions +@subsection Special handling of file extensions + +GNU Coreutils version sort implements specialized handling +of strings that look like file names with extensions. +This enables slightly more natural ordering of file +names. + +The following additional rules apply when comparing two strings where +both begin with non-@samp{.}. They also apply when comparing two +strings where both begin with @samp{.} but neither is @samp{.} or @samp{..}. + +@enumerate +@item +A suffix (i.e., a file extension) is defined as: a dot, followed by an +ASCII letter or tilde, followed by zero or more ASCII letters, digits, +or tildes; all repeated zero or more times, and ending at string end. +This is equivalent to matching the extended regular expression +@code{(\.[A-Za-z~][A-Za-z0-9~]*)*$} in the C locale. +The longest such match is used, except that a suffix is not +allowed to match an entire nonempty string. + +@item +The suffixes are temporarily removed, and the strings are compared +without them, using version sort (see @ref{Version-sort ordering +rules}) without special priority (see @ref{Special priority in GNU +Coreutils version sort}). + +@item +If the suffix-less strings do not compare equal, this comparison +result is used and the suffixes are effectively ignored. + +@item +If the suffix-less strings compare equal, the suffixes are restored +and the entire strings are compared using version sort. +@end enumerate + +Examples for rule 1: + +@itemize +@item +@samp{hello-8.txt}: the suffix is @samp{.txt} + +@item +@samp{hello-8.2.txt}: the suffix is @samp{.txt} +(@samp{.2} is not included because the dot is not followed by a letter) + +@item +@samp{hello-8.0.12.tar.gz}: the suffix is @samp{.tar.gz} (@samp{.0.12} +is not included) + +@item +@samp{hello-8.2}: no suffix (suffix is an empty string) + +@item +@samp{hello.foobar65}: the suffix is @samp{.foobar65} + +@item +@samp{gcc-c++-10.8.12-0.7rc2.fc9.tar.bz2}: the suffix is +@samp{.fc9.tar.bz2} (@samp{.7rc2} is not included as it begins with a digit) + +@item +@samp{.autom4te.cfg}: the suffix is the entire string. +@end itemize + +Examples for rule 2: + +@itemize +@item +Comparing @samp{hello-8.txt} to @samp{hello-8.2.12.txt}, the +@samp{.txt} suffix is temporarily removed from both strings. + +@item +Comparing @samp{foo-10.3.tar.gz} to @samp{foo-10.tar.xz}, the suffixes +@samp{.tar.gz} and @samp{.tar.xz} are temporarily removed from the +strings. +@end itemize + +Example for rule 3: + +@itemize +@item +Comparing @samp{hello.foobar65} to @samp{hello.foobar4}, the suffixes +(@samp{.foobar65} and @samp{.foobar4}) are temporarily removed. The +remaining strings are identical (@samp{hello}). The suffixes are then +restored, and the entire strings are compared (@samp{hello.foobar4} comes +first). +@end itemize + +Examples for rule 4: + +@itemize +@item +When comparing the strings @samp{hello-8.2.txt} and @samp{hello-8.10.txt}, the +suffixes (@samp{.txt}) are temporarily removed. The remaining strings +(@samp{hello-8.2} and @samp{hello-8.10}) are compared as previously described +(@samp{hello-8.2} comes first). +@slanted{(In this case the suffix removal algorithm +does not have a noticeable effect on the resulting order.)} +@end itemize + +@b{How does the suffix-removal algorithm effect ordering results?} + +Consider the comparison of hello-8.txt and hello-8.2.txt. + +Without the suffix-removal algorithm, the strings will be broken down +to the following parts: + +@example +hello- @r{vs} hello- @r{(rule 2, all non-digits)} +8 @r{vs} 8 @r{(rule 3, all digits)} +.txt @r{vs} . @r{(rule 2)} +empty @r{vs} 2 +empty @r{vs} .txt +@end example + +The comparison of the third parts (@samp{.} vs +@samp{.txt}) will determine that the shorter string comes first -- +resulting in @file{hello-8.2.txt} appearing first. + +Indeed this is the order in which Debian's @command{dpkg} compares the strings. + +A more natural result is that @file{hello-8.txt} should come before +@file{hello-8.2.txt}, and this is where the suffix-removal comes into play: + +The suffixes (@samp{.txt}) are removed, and the remaining strings are +broken down into the following parts: + +@example +hello- @r{vs} hello- @r{(rule 2, all non-digits)} +8 @r{vs} 8 @r{(rule 3, all digits)} +empty @r{vs} . @r{(rule 2)} +empty @r{vs} 2 +@end example + +As empty strings sort before non-empty strings, the result is @samp{hello-8} +being first. + +A real-world example would be listing files such as: +@file{gcc_10.fc9.tar.gz} +and @file{gcc_10.8.12.7rc2.fc9.tar.bz2}: Debian's algorithm would list +@file{gcc_10.8.12.7rc2.fc9.tar.bz2} first, while @samp{ls -v} will list +@file{gcc_10.fc9.tar.gz} first. + +These priorities make sense for @samp{ls -v}: +Versioned files will be listed in a more natural order. + +For @samp{sort -V} these priorities might seem arbitrary. However, +because the sorting code is shared between the @command{ls} and @command{sort} +program, the ordering rules are the same. + + +@node Comparing two strings using Debian's algorithm +@subsection Comparing two strings using Debian's algorithm + +The Debian program @command{dpkg} (available on all Debian and Ubuntu +installations) can compare two strings using the @option{--compare-versions} +option. + +To use it, create a helper shell function (simply copy & paste the +following snippet to your shell command-prompt): + +@example +compver() @{ + if dpkg --compare-versions "$1" lt "$2" + then printf '%s\n' "$1" "$2" + else printf '%s\n' "$2" "$1" + fi +@} +@end example + +Then compare two strings by calling @command{compver}: + +@example +$ compver 8.49 8.5 +8.5 +8.49 +@end example + +Note that @command{dpkg} will warn if the strings have invalid syntax: + +@example +$ compver "foo07.7z" "foo7a.7z" +dpkg: warning: version 'foo07.7z' has bad syntax: + version number does not start with digit +dpkg: warning: version 'foo7a.7z' has bad syntax: + version number does not start with digit +foo7a.7z +foo07.7z +$ compver "3.0/" "3.0.5" +dpkg: warning: version '3.0/' has bad syntax: + invalid character in version number +3.0.5 +3.0/ +@end example + +To illustrate the different handling of hyphens between Debian and +Coreutils algorithms (see +@ref{Hyphen-minus and colon}): + +@example +$ compver abb ab-cd 2>/dev/null $ printf 'abb\nab-cd\n' | sort -V +ab-cd abb +abb ab-cd +@end example + +To illustrate the different handling of file extension: (see @ref{Special +handling of file extensions}): + +@example +$ compver hello-8.txt hello-8.2.txt 2>/dev/null +hello-8.2.txt +hello-8.txt +$ printf '%s\n' hello-8.txt hello-8.2.txt | sort -V +hello-8.txt +hello-8.2.txt +@end example + + +@node Advanced version sort topics +@section Advanced Topics + + +@node Reporting version sort bugs +@subsection Reporting version sort bugs + +If you suspect a bug in GNU Coreutils version sort (i.e., in the +output of @samp{ls -v} or @samp{sort -V}), please first check the following: + +@enumerate +@item +Is the result consistent with Debian's own ordering (using @command{dpkg}, see +@ref{Comparing two strings using Debian's algorithm})? If it is, then this +is not a bug -- please do not report it. + +@item +If the result differs from Debian's, is it explained by one of the +sections in @ref{Differences from Debian version sort}? If it is, +then this is not a bug -- please do not report it. + +@item +If you have a question about specific ordering which is not explained +here, please write to @email{coreutils@@gnu.org}, and provide a +concise example that will help us diagnose the issue. + +@item +If you still suspect a bug which is not explained by the above, please +write to @email{bug-coreutils@@gnu.org} with a concrete example of the +suspected incorrect output, with details on why you think it is +incorrect. + +@end enumerate + +@node Other version/natural sort implementations +@subsection Other version/natural sort implementations + +As previously mentioned, there are multiple variations on +version/natural sort, each with its own rules. Some examples are: + +@itemize + +@item +Natural Sorting variants in +@uref{https://rosettacode.org/wiki/Natural_sorting,Rosetta Code}. + +@item +Python's @uref{https://pypi.org/project/natsort/,natsort package} +(includes detailed description of their sorting rules: +@uref{https://natsort.readthedocs.io/en/master/howitworks.html, +natsort -- how it works}). + +@item +Ruby's @uref{https://github.com/github/version_sorter,version_sorter}. + +@item +Perl has multiple packages for natural and version sorts +(each likely with its own rules and nuances): +@uref{https://metacpan.org/pod/Sort::Naturally,Sort::Naturally}, +@uref{https://metacpan.org/pod/Sort::Versions,Sort::Versions}, +@uref{https://metacpan.org/pod/CPAN::Version,CPAN::Version}. + +@item +PHP has a built-in function +@uref{https://www.php.net/manual/en/function.natsort.php,natsort}. + +@item +NodeJS's @uref{https://www.npmjs.com/package/natural-sort,natural-sort package}. + +@item +In zsh, the +@uref{http://zsh.sourceforge.net/Doc/Release/Expansion.html#Glob-Qualifiers, +glob modifier} @samp{*(n)} will expand to files in natural sort order. + +@item +When writing C programs, the GNU libc library (@samp{glibc}) +provides the +@uref{https://man7.org/linux/man-pages/man3/strverscmp.3.html, +strverscmp(3)} function to compare two strings, and +@uref{https://man7.org/linux/man-pages/man3/versionsort.3.html,versionsort(3)} +function to compare two directory entries (despite the names, they are +not identical to GNU Coreutils version sort ordering). + +@item +Using Debian's sorting algorithm in: + +@itemize +@item +python: @uref{https://stackoverflow.com/a/4957741, +Stack Overflow Example #4957741}. + +@item +NodeJS: @uref{https://www.npmjs.com/package/deb-version-compare, +deb-version-compare}. +@end itemize + +@end itemize + + +@node Related source code +@subsection Related source code + +@itemize + +@item +Debian's code which splits a version string into +@code{epoch/upstream_version/debian_revision} parts: +@uref{https://git.dpkg.org/cgit/dpkg/dpkg.git/tree/lib/dpkg/parsehelp.c#n191, +parsehelp.c:parseversion()}. + +@item +Debian's code which performs the @code{upstream_version} comparison: +@uref{https://git.dpkg.org/cgit/dpkg/dpkg.git/tree/lib/dpkg/version.c#n140, +version.c}. + +@item +Gnulib code (used by GNU Coreutils) which performs the version comparison: +@uref{https://git.savannah.gnu.org/cgit/gnulib.git/tree/lib/filevercmp.c, +filevercmp.c}. +@end itemize diff --git a/doc/stamp-vti b/doc/stamp-vti new file mode 100644 index 0000000..a4ec8d7 --- /dev/null +++ b/doc/stamp-vti @@ -0,0 +1,4 @@ +@set UPDATED 29 August 2023 +@set UPDATED-MONTH August 2023 +@set EDITION 9.4 +@set VERSION 9.4 diff --git a/doc/version.texi b/doc/version.texi new file mode 100644 index 0000000..a4ec8d7 --- /dev/null +++ b/doc/version.texi @@ -0,0 +1,4 @@ +@set UPDATED 29 August 2023 +@set UPDATED-MONTH August 2023 +@set EDITION 9.4 +@set VERSION 9.4 |