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+This is bash.info, produced by makeinfo version 6.8 from bashref.texi.
+
+This text is a brief description of the features that are present in the
+Bash shell (version 5.2, 19 September 2022).
+
+ This is Edition 5.2, last updated 19 September 2022, of 'The GNU Bash
+Reference Manual', for 'Bash', Version 5.2.
+
+ Copyright (C) 1988-2022 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, no Front-Cover Texts, and
+ 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
+* Bash: (bash). The GNU Bourne-Again SHell.
+END-INFO-DIR-ENTRY
+
+
+File: bash.info, Node: Top, Next: Introduction, Prev: (dir), Up: (dir)
+
+Bash Features
+*************
+
+This text is a brief description of the features that are present in the
+Bash shell (version 5.2, 19 September 2022). The Bash home page is
+<http://www.gnu.org/software/bash/>.
+
+ This is Edition 5.2, last updated 19 September 2022, of 'The GNU Bash
+Reference Manual', for 'Bash', Version 5.2.
+
+ Bash contains features that appear in other popular shells, and some
+features that only appear in Bash. Some of the shells that Bash has
+borrowed concepts from are the Bourne Shell ('sh'), the Korn Shell
+('ksh'), and the C-shell ('csh' and its successor, 'tcsh'). The
+following menu breaks the features up into categories, noting which
+features were inspired by other shells and which are specific to Bash.
+
+ This manual is meant as a brief introduction to features found in
+Bash. The Bash manual page should be used as the definitive reference
+on shell behavior.
+
+* Menu:
+
+* Introduction:: An introduction to the shell.
+* Definitions:: Some definitions used in the rest of this
+ manual.
+* Basic Shell Features:: The shell "building blocks".
+* Shell Builtin Commands:: Commands that are a part of the shell.
+* Shell Variables:: Variables used or set by Bash.
+* Bash Features:: Features found only in Bash.
+* Job Control:: What job control is and how Bash allows you
+ to use it.
+* Command Line Editing:: Chapter describing the command line
+ editing features.
+* Using History Interactively:: Command History Expansion
+* Installing Bash:: How to build and install Bash on your system.
+* Reporting Bugs:: How to report bugs in Bash.
+* Major Differences From The Bourne Shell:: A terse list of the differences
+ between Bash and historical
+ versions of /bin/sh.
+* GNU Free Documentation License:: Copying and sharing this documentation.
+* Indexes:: Various indexes for this manual.
+
+
+File: bash.info, Node: Introduction, Next: Definitions, Up: Top
+
+1 Introduction
+**************
+
+* Menu:
+
+* What is Bash?:: A short description of Bash.
+* What is a shell?:: A brief introduction to shells.
+
+
+File: bash.info, Node: What is Bash?, Next: What is a shell?, Up: Introduction
+
+1.1 What is Bash?
+=================
+
+Bash is the shell, or command language interpreter, for the GNU
+operating system. The name is an acronym for the 'Bourne-Again SHell',
+a pun on Stephen Bourne, the author of the direct ancestor of the
+current Unix shell 'sh', which appeared in the Seventh Edition Bell Labs
+Research version of Unix.
+
+ Bash is largely compatible with 'sh' and incorporates useful features
+from the Korn shell 'ksh' and the C shell 'csh'. It is intended to be a
+conformant implementation of the IEEE POSIX Shell and Tools portion of
+the IEEE POSIX specification (IEEE Standard 1003.1). It offers
+functional improvements over 'sh' for both interactive and programming
+use.
+
+ While the GNU operating system provides other shells, including a
+version of 'csh', Bash is the default shell. Like other GNU software,
+Bash is quite portable. It currently runs on nearly every version of
+Unix and a few other operating systems - independently-supported ports
+exist for MS-DOS, OS/2, and Windows platforms.
+
+
+File: bash.info, Node: What is a shell?, Prev: What is Bash?, Up: Introduction
+
+1.2 What is a shell?
+====================
+
+At its base, a shell is simply a macro processor that executes commands.
+The term macro processor means functionality where text and symbols are
+expanded to create larger expressions.
+
+ A Unix shell is both a command interpreter and a programming
+language. As a command interpreter, the shell provides the user
+interface to the rich set of GNU utilities. The programming language
+features allow these utilities to be combined. Files containing
+commands can be created, and become commands themselves. These new
+commands have the same status as system commands in directories such as
+'/bin', allowing users or groups to establish custom environments to
+automate their common tasks.
+
+ Shells may be used interactively or non-interactively. In
+interactive mode, they accept input typed from the keyboard. When
+executing non-interactively, shells execute commands read from a file.
+
+ A shell allows execution of GNU commands, both synchronously and
+asynchronously. The shell waits for synchronous commands to complete
+before accepting more input; asynchronous commands continue to execute
+in parallel with the shell while it reads and executes additional
+commands. The "redirection" constructs permit fine-grained control of
+the input and output of those commands. Moreover, the shell allows
+control over the contents of commands' environments.
+
+ Shells also provide a small set of built-in commands ("builtins")
+implementing functionality impossible or inconvenient to obtain via
+separate utilities. For example, 'cd', 'break', 'continue', and 'exec'
+cannot be implemented outside of the shell because they directly
+manipulate the shell itself. The 'history', 'getopts', 'kill', or 'pwd'
+builtins, among others, could be implemented in separate utilities, but
+they are more convenient to use as builtin commands. All of the shell
+builtins are described in subsequent sections.
+
+ While executing commands is essential, most of the power (and
+complexity) of shells is due to their embedded programming languages.
+Like any high-level language, the shell provides variables, flow control
+constructs, quoting, and functions.
+
+ Shells offer features geared specifically for interactive use rather
+than to augment the programming language. These interactive features
+include job control, command line editing, command history and aliases.
+Each of these features is described in this manual.
+
+
+File: bash.info, Node: Definitions, Next: Basic Shell Features, Prev: Introduction, Up: Top
+
+2 Definitions
+*************
+
+These definitions are used throughout the remainder of this manual.
+
+'POSIX'
+ A family of open system standards based on Unix. Bash is primarily
+ concerned with the Shell and Utilities portion of the POSIX 1003.1
+ standard.
+
+'blank'
+ A space or tab character.
+
+'builtin'
+ A command that is implemented internally by the shell itself,
+ rather than by an executable program somewhere in the file system.
+
+'control operator'
+ A 'token' that performs a control function. It is a 'newline' or
+ one of the following: '||', '&&', '&', ';', ';;', ';&', ';;&', '|',
+ '|&', '(', or ')'.
+
+'exit status'
+ The value returned by a command to its caller. The value is
+ restricted to eight bits, so the maximum value is 255.
+
+'field'
+ A unit of text that is the result of one of the shell expansions.
+ After expansion, when executing a command, the resulting fields are
+ used as the command name and arguments.
+
+'filename'
+ A string of characters used to identify a file.
+
+'job'
+ A set of processes comprising a pipeline, and any processes
+ descended from it, that are all in the same process group.
+
+'job control'
+ A mechanism by which users can selectively stop (suspend) and
+ restart (resume) execution of processes.
+
+'metacharacter'
+ A character that, when unquoted, separates words. A metacharacter
+ is a 'space', 'tab', 'newline', or one of the following characters:
+ '|', '&', ';', '(', ')', '<', or '>'.
+
+'name'
+ A 'word' consisting solely of letters, numbers, and underscores,
+ and beginning with a letter or underscore. 'Name's are used as
+ shell variable and function names. Also referred to as an
+ 'identifier'.
+
+'operator'
+ A 'control operator' or a 'redirection operator'. *Note
+ Redirections::, for a list of redirection operators. Operators
+ contain at least one unquoted 'metacharacter'.
+
+'process group'
+ A collection of related processes each having the same process
+ group ID.
+
+'process group ID'
+ A unique identifier that represents a 'process group' during its
+ lifetime.
+
+'reserved word'
+ A 'word' that has a special meaning to the shell. Most reserved
+ words introduce shell flow control constructs, such as 'for' and
+ 'while'.
+
+'return status'
+ A synonym for 'exit status'.
+
+'signal'
+ A mechanism by which a process may be notified by the kernel of an
+ event occurring in the system.
+
+'special builtin'
+ A shell builtin command that has been classified as special by the
+ POSIX standard.
+
+'token'
+ A sequence of characters considered a single unit by the shell. It
+ is either a 'word' or an 'operator'.
+
+'word'
+ A sequence of characters treated as a unit by the shell. Words may
+ not include unquoted 'metacharacters'.
+
+
+File: bash.info, Node: Basic Shell Features, Next: Shell Builtin Commands, Prev: Definitions, Up: Top
+
+3 Basic Shell Features
+**********************
+
+Bash is an acronym for 'Bourne-Again SHell'. The Bourne shell is the
+traditional Unix shell originally written by Stephen Bourne. All of the
+Bourne shell builtin commands are available in Bash, The rules for
+evaluation and quoting are taken from the POSIX specification for the
+'standard' Unix shell.
+
+ This chapter briefly summarizes the shell's 'building blocks':
+commands, control structures, shell functions, shell parameters, shell
+expansions, redirections, which are a way to direct input and output
+from and to named files, and how the shell executes commands.
+
+* Menu:
+
+* Shell Syntax:: What your input means to the shell.
+* Shell Commands:: The types of commands you can use.
+* Shell Functions:: Grouping commands by name.
+* Shell Parameters:: How the shell stores values.
+* Shell Expansions:: How Bash expands parameters and the various
+ expansions available.
+* Redirections:: A way to control where input and output go.
+* Executing Commands:: What happens when you run a command.
+* Shell Scripts:: Executing files of shell commands.
+
+
+File: bash.info, Node: Shell Syntax, Next: Shell Commands, Up: Basic Shell Features
+
+3.1 Shell Syntax
+================
+
+* Menu:
+
+* Shell Operation:: The basic operation of the shell.
+* Quoting:: How to remove the special meaning from characters.
+* Comments:: How to specify comments.
+
+When the shell reads input, it proceeds through a sequence of
+operations. If the input indicates the beginning of a comment, the
+shell ignores the comment symbol ('#'), and the rest of that line.
+
+ Otherwise, roughly speaking, the shell reads its input and divides
+the input into words and operators, employing the quoting rules to
+select which meanings to assign various words and characters.
+
+ The shell then parses these tokens into commands and other
+constructs, removes the special meaning of certain words or characters,
+expands others, redirects input and output as needed, executes the
+specified command, waits for the command's exit status, and makes that
+exit status available for further inspection or processing.
+
+
+File: bash.info, Node: Shell Operation, Next: Quoting, Up: Shell Syntax
+
+3.1.1 Shell Operation
+---------------------
+
+The following is a brief description of the shell's operation when it
+reads and executes a command. Basically, the shell does the following:
+
+ 1. Reads its input from a file (*note Shell Scripts::), from a string
+ supplied as an argument to the '-c' invocation option (*note
+ Invoking Bash::), or from the user's terminal.
+
+ 2. Breaks the input into words and operators, obeying the quoting
+ rules described in *note Quoting::. These tokens are separated by
+ 'metacharacters'. Alias expansion is performed by this step (*note
+ Aliases::).
+
+ 3. Parses the tokens into simple and compound commands (*note Shell
+ Commands::).
+
+ 4. Performs the various shell expansions (*note Shell Expansions::),
+ breaking the expanded tokens into lists of filenames (*note
+ Filename Expansion::) and commands and arguments.
+
+ 5. Performs any necessary redirections (*note Redirections::) and
+ removes the redirection operators and their operands from the
+ argument list.
+
+ 6. Executes the command (*note Executing Commands::).
+
+ 7. Optionally waits for the command to complete and collects its exit
+ status (*note Exit Status::).
+
+
+File: bash.info, Node: Quoting, Next: Comments, Prev: Shell Operation, Up: Shell Syntax
+
+3.1.2 Quoting
+-------------
+
+* Menu:
+
+* Escape Character:: How to remove the special meaning from a single
+ character.
+* Single Quotes:: How to inhibit all interpretation of a sequence
+ of characters.
+* Double Quotes:: How to suppress most of the interpretation of a
+ sequence of characters.
+* ANSI-C Quoting:: How to expand ANSI-C sequences in quoted strings.
+* Locale Translation:: How to translate strings into different languages.
+
+Quoting is used to remove the special meaning of certain characters or
+words to the shell. Quoting can be used to disable special treatment
+for special characters, to prevent reserved words from being recognized
+as such, and to prevent parameter expansion.
+
+ Each of the shell metacharacters (*note Definitions::) has special
+meaning to the shell and must be quoted if it is to represent itself.
+When the command history expansion facilities are being used (*note
+History Interaction::), the "history expansion" character, usually '!',
+must be quoted to prevent history expansion. *Note Bash History
+Facilities::, for more details concerning history expansion.
+
+ There are three quoting mechanisms: the "escape character", single
+quotes, and double quotes.
+
+
+File: bash.info, Node: Escape Character, Next: Single Quotes, Up: Quoting
+
+3.1.2.1 Escape Character
+........................
+
+A non-quoted backslash '\' is the Bash escape character. It preserves
+the literal value of the next character that follows, with the exception
+of 'newline'. If a '\newline' pair appears, and the backslash itself is
+not quoted, the '\newline' is treated as a line continuation (that is,
+it is removed from the input stream and effectively ignored).
+
+
+File: bash.info, Node: Single Quotes, Next: Double Quotes, Prev: Escape Character, Up: Quoting
+
+3.1.2.2 Single Quotes
+.....................
+
+Enclosing characters in single quotes (''') preserves the literal value
+of each character within the quotes. A single quote may not occur
+between single quotes, even when preceded by a backslash.
+
+
+File: bash.info, Node: Double Quotes, Next: ANSI-C Quoting, Prev: Single Quotes, Up: Quoting
+
+3.1.2.3 Double Quotes
+.....................
+
+Enclosing characters in double quotes ('"') preserves the literal value
+of all characters within the quotes, with the exception of '$', '`',
+'\', and, when history expansion is enabled, '!'. When the shell is in
+POSIX mode (*note Bash POSIX Mode::), the '!' has no special meaning
+within double quotes, even when history expansion is enabled. The
+characters '$' and '`' retain their special meaning within double quotes
+(*note Shell Expansions::). The backslash retains its special meaning
+only when followed by one of the following characters: '$', '`', '"',
+'\', or 'newline'. Within double quotes, backslashes that are followed
+by one of these characters are removed. Backslashes preceding
+characters without a special meaning are left unmodified. A double
+quote may be quoted within double quotes by preceding it with a
+backslash. If enabled, history expansion will be performed unless an
+'!' appearing in double quotes is escaped using a backslash. The
+backslash preceding the '!' is not removed.
+
+ The special parameters '*' and '@' have special meaning when in
+double quotes (*note Shell Parameter Expansion::).
+
+
+File: bash.info, Node: ANSI-C Quoting, Next: Locale Translation, Prev: Double Quotes, Up: Quoting
+
+3.1.2.4 ANSI-C Quoting
+......................
+
+Character sequences of the form $'STRING' are treated as a special kind
+of single quotes. The sequence expands to STRING, with
+backslash-escaped characters in STRING replaced as specified by the ANSI
+C standard. Backslash escape sequences, if present, are decoded as
+follows:
+
+'\a'
+ alert (bell)
+'\b'
+ backspace
+'\e'
+'\E'
+ an escape character (not ANSI C)
+'\f'
+ form feed
+'\n'
+ newline
+'\r'
+ carriage return
+'\t'
+ horizontal tab
+'\v'
+ vertical tab
+'\\'
+ backslash
+'\''
+ single quote
+'\"'
+ double quote
+'\?'
+ question mark
+'\NNN'
+ the eight-bit character whose value is the octal value NNN (one to
+ three octal digits)
+'\xHH'
+ the eight-bit character whose value is the hexadecimal value HH
+ (one or two hex digits)
+'\uHHHH'
+ the Unicode (ISO/IEC 10646) character whose value is the
+ hexadecimal value HHHH (one to four hex digits)
+'\UHHHHHHHH'
+ the Unicode (ISO/IEC 10646) character whose value is the
+ hexadecimal value HHHHHHHH (one to eight hex digits)
+'\cX'
+ a control-X character
+
+The expanded result is single-quoted, as if the dollar sign had not been
+present.
+
+
+File: bash.info, Node: Locale Translation, Prev: ANSI-C Quoting, Up: Quoting
+
+3.1.2.5 Locale-Specific Translation
+...................................
+
+* Menu:
+
+* Creating Internationalized Scripts:: How to use translations and different
+ languages in your scripts.
+
+Prefixing a double-quoted string with a dollar sign ('$'), such as
+$"hello, world", will cause the string to be translated according to the
+current locale. The 'gettext' infrastructure performs the lookup and
+translation, using the 'LC_MESSAGES', 'TEXTDOMAINDIR', and 'TEXTDOMAIN'
+shell variables, as explained below. See the gettext documentation for
+additional details not covered here. If the current locale is 'C' or
+'POSIX', if there are no translations available, of if the string is not
+translated, the dollar sign is ignored. Since this is a form of double
+quoting, the string remains double-quoted by default, whether or not it
+is translated and replaced. If the 'noexpand_translation' option is
+enabled using the 'shopt' builtin (*note The Shopt Builtin::),
+translated strings are single-quoted instead of double-quoted.
+
+ The rest of this section is a brief overview of how you use gettext
+to create translations for strings in a shell script named SCRIPTNAME.
+There are more details in the gettext documentation.
+
+
+File: bash.info, Node: Creating Internationalized Scripts, Up: Locale Translation
+
+Once you've marked the strings in your script that you want to translate
+using $"...", you create a gettext "template" file using the command
+
+ bash --dump-po-strings SCRIPTNAME > DOMAIN.pot
+
+The DOMAIN is your "message domain". It's just an arbitrary string
+that's used to identify the files gettext needs, like a package or
+script name. It needs to be unique among all the message domains on
+systems where you install the translations, so gettext knows which
+translations correspond to your script. You'll use the template file to
+create translations for each target language. The template file
+conventionally has the suffix '.pot'.
+
+ You copy this template file to a separate file for each target
+language you want to support (called "PO" files, which use the suffix
+'.po'). PO files use various naming conventions, but when you are
+working to translate a template file into a particular language, you
+first copy the template file to a file whose name is the language you
+want to target, with the '.po' suffix. For instance, the Spanish
+translations of your strings would be in a file named 'es.po', and to
+get started using a message domain named "example," you would run
+
+ cp example.pot es.po
+
+Ultimately, PO files are often named DOMAIN.po and installed in
+directories that contain multiple translation files for a particular
+language.
+
+ Whichever naming convention you choose, you will need to translate
+the strings in the PO files into the appropriate languages. This has to
+be done manually.
+
+ When you have the translations and PO files complete, you'll use the
+gettext tools to produce what are called "MO" files, which are compiled
+versions of the PO files the gettext tools use to look up translations
+efficiently. MO files are also called "message catalog" files. You use
+the 'msgfmt' program to do this. For instance, if you had a file with
+Spanish translations, you could run
+
+ msgfmt -o es.mo es.po
+
+to produce the corresponding MO file.
+
+ Once you have the MO files, you decide where to install them and use
+the 'TEXTDOMAINDIR' shell variable to tell the gettext tools where they
+are. Make sure to use the same message domain to name the MO files as
+you did for the PO files when you install them.
+
+ Your users will use the 'LANG' or 'LC_MESSAGES' shell variables to
+select the desired language.
+
+ You set the 'TEXTDOMAIN' variable to the script's message domain. As
+above, you use the message domain to name your translation files.
+
+ You, or possibly your users, set the 'TEXTDOMAINDIR' variable to the
+name of a directory where the message catalog files are stored. If you
+install the message files into the system's standard message catalog
+directory, you don't need to worry about this variable.
+
+ The directory where the message catalog files are stored varies
+between systems. Some use the message catalog selected by the
+'LC_MESSAGES' shell variable. Others create the name of the message
+catalog from the value of the 'TEXTDOMAIN' shell variable, possibly
+adding the '.mo' suffix. If you use the 'TEXTDOMAIN' variable, you may
+need to set the 'TEXTDOMAINDIR' variable to the location of the message
+catalog files, as above. It's common to use both variables in this
+fashion: '$TEXTDOMAINDIR'/'$LC_MESSAGES'/LC_MESSAGES/'$TEXTDOMAIN'.mo.
+
+ If you used that last convention, and you wanted to store the message
+catalog files with Spanish (es) and Esperanto (eo) translations into a
+local directory you use for custom translation files, you could run
+
+ TEXTDOMAIN=example
+ TEXTDOMAINDIR=/usr/local/share/locale
+
+ cp es.mo ${TEXTDOMAINDIR}/es/LC_MESSAGES/${TEXTDOMAIN}.mo
+ cp eo.mo ${TEXTDOMAINDIR}/eo/LC_MESSAGES/${TEXTDOMAIN}.mo
+
+ When all of this is done, and the message catalog files containing
+the compiled translations are installed in the correct location, your
+users will be able to see translated strings in any of the supported
+languages by setting the 'LANG' or 'LC_MESSAGES' environment variables
+before running your script.
+
+
+File: bash.info, Node: Comments, Prev: Quoting, Up: Shell Syntax
+
+3.1.3 Comments
+--------------
+
+In a non-interactive shell, or an interactive shell in which the
+'interactive_comments' option to the 'shopt' builtin is enabled (*note
+The Shopt Builtin::), a word beginning with '#' causes that word and all
+remaining characters on that line to be ignored. An interactive shell
+without the 'interactive_comments' option enabled does not allow
+comments. The 'interactive_comments' option is on by default in
+interactive shells. *Note Interactive Shells::, for a description of
+what makes a shell interactive.
+
+
+File: bash.info, Node: Shell Commands, Next: Shell Functions, Prev: Shell Syntax, Up: Basic Shell Features
+
+3.2 Shell Commands
+==================
+
+A simple shell command such as 'echo a b c' consists of the command
+itself followed by arguments, separated by spaces.
+
+ More complex shell commands are composed of simple commands arranged
+together in a variety of ways: in a pipeline in which the output of one
+command becomes the input of a second, in a loop or conditional
+construct, or in some other grouping.
+
+* Menu:
+
+* Reserved Words:: Words that have special meaning to the shell.
+* Simple Commands:: The most common type of command.
+* Pipelines:: Connecting the input and output of several
+ commands.
+* Lists:: How to execute commands sequentially.
+* Compound Commands:: Shell commands for control flow.
+* Coprocesses:: Two-way communication between commands.
+* GNU Parallel:: Running commands in parallel.
+
+
+File: bash.info, Node: Reserved Words, Next: Simple Commands, Up: Shell Commands
+
+3.2.1 Reserved Words
+--------------------
+
+Reserved words are words that have special meaning to the shell. They
+are used to begin and end the shell's compound commands.
+
+ The following words are recognized as reserved when unquoted and the
+first word of a command (see below for exceptions):
+
+'if' 'then' 'elif' 'else' 'fi' 'time'
+'for' 'in' 'until' 'while' 'do' 'done'
+'case' 'esac' 'coproc''select''function'
+'{' '}' '[[' ']]' '!'
+
+'in' is recognized as a reserved word if it is the third word of a
+'case' or 'select' command. 'in' and 'do' are recognized as reserved
+words if they are the third word in a 'for' command.
+
+
+File: bash.info, Node: Simple Commands, Next: Pipelines, Prev: Reserved Words, Up: Shell Commands
+
+3.2.2 Simple Commands
+---------------------
+
+A simple command is the kind of command encountered most often. It's
+just a sequence of words separated by 'blank's, terminated by one of the
+shell's control operators (*note Definitions::). The first word
+generally specifies a command to be executed, with the rest of the words
+being that command's arguments.
+
+ The return status (*note Exit Status::) of a simple command is its
+exit status as provided by the POSIX 1003.1 'waitpid' function, or 128+N
+if the command was terminated by signal N.
+
+
+File: bash.info, Node: Pipelines, Next: Lists, Prev: Simple Commands, Up: Shell Commands
+
+3.2.3 Pipelines
+---------------
+
+A 'pipeline' is a sequence of one or more commands separated by one of
+the control operators '|' or '|&'.
+
+ The format for a pipeline is
+ [time [-p]] [!] COMMAND1 [ | or |& COMMAND2 ] ...
+
+The output of each command in the pipeline is connected via a pipe to
+the input of the next command. That is, each command reads the previous
+command's output. This connection is performed before any redirections
+specified by COMMAND1.
+
+ If '|&' is used, COMMAND1's standard error, in addition to its
+standard output, is connected to COMMAND2's standard input through the
+pipe; it is shorthand for '2>&1 |'. This implicit redirection of the
+standard error to the standard output is performed after any
+redirections specified by COMMAND1.
+
+ The reserved word 'time' causes timing statistics to be printed for
+the pipeline once it finishes. The statistics currently consist of
+elapsed (wall-clock) time and user and system time consumed by the
+command's execution. The '-p' option changes the output format to that
+specified by POSIX. When the shell is in POSIX mode (*note Bash POSIX
+Mode::), it does not recognize 'time' as a reserved word if the next
+token begins with a '-'. The 'TIMEFORMAT' variable may be set to a
+format string that specifies how the timing information should be
+displayed. *Note Bash Variables::, for a description of the available
+formats. The use of 'time' as a reserved word permits the timing of
+shell builtins, shell functions, and pipelines. An external 'time'
+command cannot time these easily.
+
+ When the shell is in POSIX mode (*note Bash POSIX Mode::), 'time' may
+be followed by a newline. In this case, the shell displays the total
+user and system time consumed by the shell and its children. The
+'TIMEFORMAT' variable may be used to specify the format of the time
+information.
+
+ If the pipeline is not executed asynchronously (*note Lists::), the
+shell waits for all commands in the pipeline to complete.
+
+ Each command in a multi-command pipeline, where pipes are created, is
+executed in its own "subshell", which is a separate process (*note
+Command Execution Environment::). If the 'lastpipe' option is enabled
+using the 'shopt' builtin (*note The Shopt Builtin::), the last element
+of a pipeline may be run by the shell process when job control is not
+active.
+
+ The exit status of a pipeline is the exit status of the last command
+in the pipeline, unless the 'pipefail' option is enabled (*note The Set
+Builtin::). If 'pipefail' is enabled, the pipeline's return status is
+the value of the last (rightmost) command to exit with a non-zero
+status, or zero if all commands exit successfully. If the reserved word
+'!' precedes the pipeline, the exit status is the logical negation of
+the exit status as described above. The shell waits for all commands in
+the pipeline to terminate before returning a value.
+
+
+File: bash.info, Node: Lists, Next: Compound Commands, Prev: Pipelines, Up: Shell Commands
+
+3.2.4 Lists of Commands
+-----------------------
+
+A 'list' is a sequence of one or more pipelines separated by one of the
+operators ';', '&', '&&', or '||', and optionally terminated by one of
+';', '&', or a 'newline'.
+
+ Of these list operators, '&&' and '||' have equal precedence,
+followed by ';' and '&', which have equal precedence.
+
+ A sequence of one or more newlines may appear in a 'list' to delimit
+commands, equivalent to a semicolon.
+
+ If a command is terminated by the control operator '&', the shell
+executes the command asynchronously in a subshell. This is known as
+executing the command in the "background", and these are referred to as
+"asynchronous" commands. The shell does not wait for the command to
+finish, and the return status is 0 (true). When job control is not
+active (*note Job Control::), the standard input for asynchronous
+commands, in the absence of any explicit redirections, is redirected
+from '/dev/null'.
+
+ Commands separated by a ';' are executed sequentially; the shell
+waits for each command to terminate in turn. The return status is the
+exit status of the last command executed.
+
+ AND and OR lists are sequences of one or more pipelines separated by
+the control operators '&&' and '||', respectively. AND and OR lists are
+executed with left associativity.
+
+ An AND list has the form
+ COMMAND1 && COMMAND2
+
+COMMAND2 is executed if, and only if, COMMAND1 returns an exit status of
+zero (success).
+
+ An OR list has the form
+ COMMAND1 || COMMAND2
+
+COMMAND2 is executed if, and only if, COMMAND1 returns a non-zero exit
+status.
+
+ The return status of AND and OR lists is the exit status of the last
+command executed in the list.
+
+
+File: bash.info, Node: Compound Commands, Next: Coprocesses, Prev: Lists, Up: Shell Commands
+
+3.2.5 Compound Commands
+-----------------------
+
+* Menu:
+
+* Looping Constructs:: Shell commands for iterative action.
+* Conditional Constructs:: Shell commands for conditional execution.
+* Command Grouping:: Ways to group commands.
+
+Compound commands are the shell programming language constructs. Each
+construct begins with a reserved word or control operator and is
+terminated by a corresponding reserved word or operator. Any
+redirections (*note Redirections::) associated with a compound command
+apply to all commands within that compound command unless explicitly
+overridden.
+
+ In most cases a list of commands in a compound command's description
+may be separated from the rest of the command by one or more newlines,
+and may be followed by a newline in place of a semicolon.
+
+ Bash provides looping constructs, conditional commands, and
+mechanisms to group commands and execute them as a unit.
+
+
+File: bash.info, Node: Looping Constructs, Next: Conditional Constructs, Up: Compound Commands
+
+3.2.5.1 Looping Constructs
+..........................
+
+Bash supports the following looping constructs.
+
+ Note that wherever a ';' appears in the description of a command's
+syntax, it may be replaced with one or more newlines.
+
+'until'
+ The syntax of the 'until' command is:
+
+ until TEST-COMMANDS; do CONSEQUENT-COMMANDS; done
+
+ Execute CONSEQUENT-COMMANDS as long as TEST-COMMANDS has an exit
+ status which is not zero. The return status is the exit status of
+ the last command executed in CONSEQUENT-COMMANDS, or zero if none
+ was executed.
+
+'while'
+ The syntax of the 'while' command is:
+
+ while TEST-COMMANDS; do CONSEQUENT-COMMANDS; done
+
+ Execute CONSEQUENT-COMMANDS as long as TEST-COMMANDS has an exit
+ status of zero. The return status is the exit status of the last
+ command executed in CONSEQUENT-COMMANDS, or zero if none was
+ executed.
+
+'for'
+ The syntax of the 'for' command is:
+
+ for NAME [ [in [WORDS ...] ] ; ] do COMMANDS; done
+
+ Expand WORDS (*note Shell Expansions::), and execute COMMANDS once
+ for each member in the resultant list, with NAME bound to the
+ current member. If 'in WORDS' is not present, the 'for' command
+ executes the COMMANDS once for each positional parameter that is
+ set, as if 'in "$@"' had been specified (*note Special
+ Parameters::).
+
+ The return status is the exit status of the last command that
+ executes. If there are no items in the expansion of WORDS, no
+ commands are executed, and the return status is zero.
+
+ An alternate form of the 'for' command is also supported:
+
+ for (( EXPR1 ; EXPR2 ; EXPR3 )) ; do COMMANDS ; done
+
+ First, the arithmetic expression EXPR1 is evaluated according to
+ the rules described below (*note Shell Arithmetic::). The
+ arithmetic expression EXPR2 is then evaluated repeatedly until it
+ evaluates to zero. Each time EXPR2 evaluates to a non-zero value,
+ COMMANDS are executed and the arithmetic expression EXPR3 is
+ evaluated. If any expression is omitted, it behaves as if it
+ evaluates to 1. The return value is the exit status of the last
+ command in COMMANDS that is executed, or false if any of the
+ expressions is invalid.
+
+ The 'break' and 'continue' builtins (*note Bourne Shell Builtins::)
+may be used to control loop execution.
+
+
+File: bash.info, Node: Conditional Constructs, Next: Command Grouping, Prev: Looping Constructs, Up: Compound Commands
+
+3.2.5.2 Conditional Constructs
+..............................
+
+'if'
+ The syntax of the 'if' command is:
+
+ if TEST-COMMANDS; then
+ CONSEQUENT-COMMANDS;
+ [elif MORE-TEST-COMMANDS; then
+ MORE-CONSEQUENTS;]
+ [else ALTERNATE-CONSEQUENTS;]
+ fi
+
+ The TEST-COMMANDS list is executed, and if its return status is
+ zero, the CONSEQUENT-COMMANDS list is executed. If TEST-COMMANDS
+ returns a non-zero status, each 'elif' list is executed in turn,
+ and if its exit status is zero, the corresponding MORE-CONSEQUENTS
+ is executed and the command completes. If 'else
+ ALTERNATE-CONSEQUENTS' is present, and the final command in the
+ final 'if' or 'elif' clause has a non-zero exit status, then
+ ALTERNATE-CONSEQUENTS is executed. The return status is the exit
+ status of the last command executed, or zero if no condition tested
+ true.
+
+'case'
+ The syntax of the 'case' command is:
+
+ case WORD in
+ [ [(] PATTERN [| PATTERN]...) COMMAND-LIST ;;]...
+ esac
+
+ 'case' will selectively execute the COMMAND-LIST corresponding to
+ the first PATTERN that matches WORD. The match is performed
+ according to the rules described below in *note Pattern Matching::.
+ If the 'nocasematch' shell option (see the description of 'shopt'
+ in *note The Shopt Builtin::) is enabled, the match is performed
+ without regard to the case of alphabetic characters. The '|' is
+ used to separate multiple patterns, and the ')' operator terminates
+ a pattern list. A list of patterns and an associated command-list
+ is known as a CLAUSE.
+
+ Each clause must be terminated with ';;', ';&', or ';;&'. The WORD
+ undergoes tilde expansion, parameter expansion, command
+ substitution, arithmetic expansion, and quote removal (*note Shell
+ Parameter Expansion::) before matching is attempted. Each PATTERN
+ undergoes tilde expansion, parameter expansion, command
+ substitution, arithmetic expansion, process substitution, and quote
+ removal.
+
+ There may be an arbitrary number of 'case' clauses, each terminated
+ by a ';;', ';&', or ';;&'. The first pattern that matches
+ determines the command-list that is executed. It's a common idiom
+ to use '*' as the final pattern to define the default case, since
+ that pattern will always match.
+
+ Here is an example using 'case' in a script that could be used to
+ describe one interesting feature of an animal:
+
+ echo -n "Enter the name of an animal: "
+ read ANIMAL
+ echo -n "The $ANIMAL has "
+ case $ANIMAL in
+ horse | dog | cat) echo -n "four";;
+ man | kangaroo ) echo -n "two";;
+ *) echo -n "an unknown number of";;
+ esac
+ echo " legs."
+
+
+ If the ';;' operator is used, no subsequent matches are attempted
+ after the first pattern match. Using ';&' in place of ';;' causes
+ execution to continue with the COMMAND-LIST associated with the
+ next clause, if any. Using ';;&' in place of ';;' causes the shell
+ to test the patterns in the next clause, if any, and execute any
+ associated COMMAND-LIST on a successful match, continuing the case
+ statement execution as if the pattern list had not matched.
+
+ The return status is zero if no PATTERN is matched. Otherwise, the
+ return status is the exit status of the COMMAND-LIST executed.
+
+'select'
+
+ The 'select' construct allows the easy generation of menus. It has
+ almost the same syntax as the 'for' command:
+
+ select NAME [in WORDS ...]; do COMMANDS; done
+
+ The list of words following 'in' is expanded, generating a list of
+ items, and the set of expanded words is printed on the standard
+ error output stream, each preceded by a number. If the 'in WORDS'
+ is omitted, the positional parameters are printed, as if 'in "$@"'
+ had been specified. 'select' then displays the 'PS3' prompt and
+ reads a line from the standard input. If the line consists of a
+ number corresponding to one of the displayed words, then the value
+ of NAME is set to that word. If the line is empty, the words and
+ prompt are displayed again. If 'EOF' is read, the 'select' command
+ completes and returns 1. Any other value read causes NAME to be
+ set to null. The line read is saved in the variable 'REPLY'.
+
+ The COMMANDS are executed after each selection until a 'break'
+ command is executed, at which point the 'select' command completes.
+
+ Here is an example that allows the user to pick a filename from the
+ current directory, and displays the name and index of the file
+ selected.
+
+ select fname in *;
+ do
+ echo you picked $fname \($REPLY\)
+ break;
+ done
+
+'((...))'
+ (( EXPRESSION ))
+
+ The arithmetic EXPRESSION is evaluated according to the rules
+ described below (*note Shell Arithmetic::). The EXPRESSION
+ undergoes the same expansions as if it were within double quotes,
+ but double quote characters in EXPRESSION are not treated specially
+ are removed. If the value of the expression is non-zero, the
+ return status is 0; otherwise the return status is 1.
+
+'[[...]]'
+ [[ EXPRESSION ]]
+
+ Return a status of 0 or 1 depending on the evaluation of the
+ conditional expression EXPRESSION. Expressions are composed of the
+ primaries described below in *note Bash Conditional Expressions::.
+ The words between the '[[' and ']]' do not undergo word splitting
+ and filename expansion. The shell performs tilde expansion,
+ parameter and variable expansion, arithmetic expansion, command
+ substitution, process substitution, and quote removal on those
+ words (the expansions that would occur if the words were enclosed
+ in double quotes). Conditional operators such as '-f' must be
+ unquoted to be recognized as primaries.
+
+ When used with '[[', the '<' and '>' operators sort
+ lexicographically using the current locale.
+
+ When the '==' and '!=' operators are used, the string to the right
+ of the operator is considered a pattern and matched according to
+ the rules described below in *note Pattern Matching::, as if the
+ 'extglob' shell option were enabled. The '=' operator is identical
+ to '=='. If the 'nocasematch' shell option (see the description of
+ 'shopt' in *note The Shopt Builtin::) is enabled, the match is
+ performed without regard to the case of alphabetic characters. The
+ return value is 0 if the string matches ('==') or does not match
+ ('!=') the pattern, and 1 otherwise.
+
+ If you quote any part of the pattern, using any of the shell's
+ quoting mechanisms, the quoted portion is matched literally. This
+ means every character in the quoted portion matches itself, instead
+ of having any special pattern matching meaning.
+
+ An additional binary operator, '=~', is available, with the same
+ precedence as '==' and '!='. When you use '=~', the string to the
+ right of the operator is considered a POSIX extended regular
+ expression pattern and matched accordingly (using the POSIX
+ 'regcomp' and 'regexec' interfaces usually described in regex(3)).
+ The return value is 0 if the string matches the pattern, and 1 if
+ it does not. If the regular expression is syntactically incorrect,
+ the conditional expression returns 2. If the 'nocasematch' shell
+ option (see the description of 'shopt' in *note The Shopt
+ Builtin::) is enabled, the match is performed without regard to the
+ case of alphabetic characters.
+
+ You can quote any part of the pattern to force the quoted portion
+ to be matched literally instead of as a regular expression (see
+ above). If the pattern is stored in a shell variable, quoting the
+ variable expansion forces the entire pattern to be matched
+ literally.
+
+ The pattern will match if it matches any part of the string. If
+ you want to force the pattern to match the entire string, anchor
+ the pattern using the '^' and '$' regular expression operators.
+
+ For example, the following will match a line (stored in the shell
+ variable 'line') if there is a sequence of characters anywhere in
+ the value consisting of any number, including zero, of characters
+ in the 'space' character class, immediately followed by zero or one
+ instances of 'a', then a 'b':
+
+ [[ $line =~ [[:space:]]*(a)?b ]]
+
+ That means values for 'line' like 'aab', ' aaaaaab', 'xaby', and '
+ ab' will all match, as will a line containing a 'b' anywhere in its
+ value.
+
+ If you want to match a character that's special to the regular
+ expression grammar ('^$|[]()\.*+?'), it has to be quoted to remove
+ its special meaning. This means that in the pattern 'xxx.txt', the
+ '.' matches any character in the string (its usual regular
+ expression meaning), but in the pattern '"xxx.txt"', it can only
+ match a literal '.'.
+
+ Likewise, if you want to include a character in your pattern that
+ has a special meaning to the regular expression grammar, you must
+ make sure it's not quoted. If you want to anchor a pattern at the
+ beginning or end of the string, for instance, you cannot quote the
+ '^' or '$' characters using any form of shell quoting.
+
+ If you want to match 'initial string' at the start of a line, the
+ following will work:
+ [[ $line =~ ^"initial string" ]]
+ but this will not:
+ [[ $line =~ "^initial string" ]]
+ because in the second example the '^' is quoted and doesn't have
+ its usual special meaning.
+
+ It is sometimes difficult to specify a regular expression properly
+ without using quotes, or to keep track of the quoting used by
+ regular expressions while paying attention to shell quoting and the
+ shell's quote removal. Storing the regular expression in a shell
+ variable is often a useful way to avoid problems with quoting
+ characters that are special to the shell. For example, the
+ following is equivalent to the pattern used above:
+
+ pattern='[[:space:]]*(a)?b'
+ [[ $line =~ $pattern ]]
+
+ Shell programmers should take special care with backslashes, since
+ backslashes are used by both the shell and regular expressions to
+ remove the special meaning from the following character. This
+ means that after the shell's word expansions complete (*note Shell
+ Expansions::), any backslashes remaining in parts of the pattern
+ that were originally not quoted can remove the special meaning of
+ pattern characters. If any part of the pattern is quoted, the
+ shell does its best to ensure that the regular expression treats
+ those remaining backslashes as literal, if they appeared in a
+ quoted portion.
+
+ The following two sets of commands are _not_ equivalent:
+
+ pattern='\.'
+
+ [[ . =~ $pattern ]]
+ [[ . =~ \. ]]
+
+ [[ . =~ "$pattern" ]]
+ [[ . =~ '\.' ]]
+
+ The first two matches will succeed, but the second two will not,
+ because in the second two the backslash will be part of the pattern
+ to be matched. In the first two examples, the pattern passed to
+ the regular expression parser is '\.'. The backslash removes the
+ special meaning from '.', so the literal '.' matches. In the
+ second two examples, the pattern passed to the regular expression
+ parser has the backslash quoted (e.g., '\\\.'), which will not
+ match the string, since it does not contain a backslash. If the
+ string in the first examples were anything other than '.', say 'a',
+ the pattern would not match, because the quoted '.' in the pattern
+ loses its special meaning of matching any single character.
+
+ Bracket expressions in regular expressions can be sources of errors
+ as well, since characters that are normally special in regular
+ expressions lose their special meanings between brackets. However,
+ you can use bracket expressions to match special pattern characters
+ without quoting them, so they are sometimes useful for this
+ purpose.
+
+ Though it might seem like a strange way to write it, the following
+ pattern will match a '.' in the string:
+
+ [[ . =~ [.] ]]
+
+ The shell performs any word expansions before passing the pattern
+ to the regular expression functions, so you can assume that the
+ shell's quoting takes precedence. As noted above, the regular
+ expression parser will interpret any unquoted backslashes remaining
+ in the pattern after shell expansion according to its own rules.
+ The intention is to avoid making shell programmers quote things
+ twice as much as possible, so shell quoting should be sufficient to
+ quote special pattern characters where that's necessary.
+
+ The array variable 'BASH_REMATCH' records which parts of the string
+ matched the pattern. The element of 'BASH_REMATCH' with index 0
+ contains the portion of the string matching the entire regular
+ expression. Substrings matched by parenthesized subexpressions
+ within the regular expression are saved in the remaining
+ 'BASH_REMATCH' indices. The element of 'BASH_REMATCH' with index N
+ is the portion of the string matching the Nth parenthesized
+ subexpression.
+
+ Bash sets 'BASH_REMATCH' in the global scope; declaring it as a
+ local variable will lead to unexpected results.
+
+ Expressions may be combined using the following operators, listed
+ in decreasing order of precedence:
+
+ '( EXPRESSION )'
+ Returns the value of EXPRESSION. This may be used to override
+ the normal precedence of operators.
+
+ '! EXPRESSION'
+ True if EXPRESSION is false.
+
+ 'EXPRESSION1 && EXPRESSION2'
+ True if both EXPRESSION1 and EXPRESSION2 are true.
+
+ 'EXPRESSION1 || EXPRESSION2'
+ True if either EXPRESSION1 or EXPRESSION2 is true.
+
+ The '&&' and '||' operators do not evaluate EXPRESSION2 if the
+ value of EXPRESSION1 is sufficient to determine the return value of
+ the entire conditional expression.
+
+
+File: bash.info, Node: Command Grouping, Prev: Conditional Constructs, Up: Compound Commands
+
+3.2.5.3 Grouping Commands
+.........................
+
+Bash provides two ways to group a list of commands to be executed as a
+unit. When commands are grouped, redirections may be applied to the
+entire command list. For example, the output of all the commands in the
+list may be redirected to a single stream.
+
+'()'
+ ( LIST )
+
+ Placing a list of commands between parentheses forces the shell to
+ create a subshell (*note Command Execution Environment::), and each
+ of the commands in LIST is executed in that subshell environment.
+ Since the LIST is executed in a subshell, variable assignments do
+ not remain in effect after the subshell completes.
+
+'{}'
+ { LIST; }
+
+ Placing a list of commands between curly braces causes the list to
+ be executed in the current shell context. No subshell is created.
+ The semicolon (or newline) following LIST is required.
+
+ In addition to the creation of a subshell, there is a subtle
+difference between these two constructs due to historical reasons. The
+braces are reserved words, so they must be separated from the LIST by
+'blank's or other shell metacharacters. The parentheses are operators,
+and are recognized as separate tokens by the shell even if they are not
+separated from the LIST by whitespace.
+
+ The exit status of both of these constructs is the exit status of
+LIST.
+
+
+File: bash.info, Node: Coprocesses, Next: GNU Parallel, Prev: Compound Commands, Up: Shell Commands
+
+3.2.6 Coprocesses
+-----------------
+
+A 'coprocess' is a shell command preceded by the 'coproc' reserved word.
+A coprocess is executed asynchronously in a subshell, as if the command
+had been terminated with the '&' control operator, with a two-way pipe
+established between the executing shell and the coprocess.
+
+ The syntax for a coprocess is:
+
+ coproc [NAME] COMMAND [REDIRECTIONS]
+
+This creates a coprocess named NAME. COMMAND may be either a simple
+command (*note Simple Commands::) or a compound command (*note Compound
+Commands::). NAME is a shell variable name. If NAME is not supplied,
+the default name is 'COPROC'.
+
+ The recommended form to use for a coprocess is
+
+ coproc NAME { COMMAND; }
+
+This form is recommended because simple commands result in the coprocess
+always being named 'COPROC', and it is simpler to use and more complete
+than the other compound commands.
+
+ There are other forms of coprocesses:
+
+ coproc NAME COMPOUND-COMMAND
+ coproc COMPOUND-COMMAND
+ coproc SIMPLE-COMMAND
+
+If COMMAND is a compound command, NAME is optional. The word following
+'coproc' determines whether that word is interpreted as a variable name:
+it is interpreted as NAME if it is not a reserved word that introduces a
+compound command. If COMMAND is a simple command, NAME is not allowed;
+this is to avoid confusion between NAME and the first word of the simple
+command.
+
+ When the coprocess is executed, the shell creates an array variable
+(*note Arrays::) named NAME in the context of the executing shell. The
+standard output of COMMAND is connected via a pipe to a file descriptor
+in the executing shell, and that file descriptor is assigned to NAME[0].
+The standard input of COMMAND is connected via a pipe to a file
+descriptor in the executing shell, and that file descriptor is assigned
+to NAME[1]. This pipe is established before any redirections specified
+by the command (*note Redirections::). The file descriptors can be
+utilized as arguments to shell commands and redirections using standard
+word expansions. Other than those created to execute command and
+process substitutions, the file descriptors are not available in
+subshells.
+
+ The process ID of the shell spawned to execute the coprocess is
+available as the value of the variable 'NAME_PID'. The 'wait' builtin
+command may be used to wait for the coprocess to terminate.
+
+ Since the coprocess is created as an asynchronous command, the
+'coproc' command always returns success. The return status of a
+coprocess is the exit status of COMMAND.
+
+
+File: bash.info, Node: GNU Parallel, Prev: Coprocesses, Up: Shell Commands
+
+3.2.7 GNU Parallel
+------------------
+
+There are ways to run commands in parallel that are not built into Bash.
+GNU Parallel is a tool to do just that.
+
+ GNU Parallel, as its name suggests, can be used to build and run
+commands in parallel. You may run the same command with different
+arguments, whether they are filenames, usernames, hostnames, or lines
+read from files. GNU Parallel provides shorthand references to many of
+the most common operations (input lines, various portions of the input
+line, different ways to specify the input source, and so on). Parallel
+can replace 'xargs' or feed commands from its input sources to several
+different instances of Bash.
+
+ For a complete description, refer to the GNU Parallel documentation,
+which is available at
+<https://www.gnu.org/software/parallel/parallel_tutorial.html>.
+
+
+File: bash.info, Node: Shell Functions, Next: Shell Parameters, Prev: Shell Commands, Up: Basic Shell Features
+
+3.3 Shell Functions
+===================
+
+Shell functions are a way to group commands for later execution using a
+single name for the group. They are executed just like a "regular"
+command. When the name of a shell function is used as a simple command
+name, the list of commands associated with that function name is
+executed. Shell functions are executed in the current shell context; no
+new process is created to interpret them.
+
+ Functions are declared using this syntax:
+ FNAME () COMPOUND-COMMAND [ REDIRECTIONS ]
+
+ or
+
+ function FNAME [()] COMPOUND-COMMAND [ REDIRECTIONS ]
+
+ This defines a shell function named FNAME. The reserved word
+'function' is optional. If the 'function' reserved word is supplied,
+the parentheses are optional. The "body" of the function is the
+compound command COMPOUND-COMMAND (*note Compound Commands::). That
+command is usually a LIST enclosed between { and }, but may be any
+compound command listed above. If the 'function' reserved word is used,
+but the parentheses are not supplied, the braces are recommended.
+COMPOUND-COMMAND is executed whenever FNAME is specified as the name of
+a simple command. When the shell is in POSIX mode (*note Bash POSIX
+Mode::), FNAME must be a valid shell name and may not be the same as one
+of the special builtins (*note Special Builtins::). In default mode, a
+function name can be any unquoted shell word that does not contain '$'.
+Any redirections (*note Redirections::) associated with the shell
+function are performed when the function is executed. A function
+definition may be deleted using the '-f' option to the 'unset' builtin
+(*note Bourne Shell Builtins::).
+
+ The exit status of a function definition is zero unless a syntax
+error occurs or a readonly function with the same name already exists.
+When executed, the exit status of a function is the exit status of the
+last command executed in the body.
+
+ Note that for historical reasons, in the most common usage the curly
+braces that surround the body of the function must be separated from the
+body by 'blank's or newlines. This is because the braces are reserved
+words and are only recognized as such when they are separated from the
+command list by whitespace or another shell metacharacter. Also, when
+using the braces, the LIST must be terminated by a semicolon, a '&', or
+a newline.
+
+ When a function is executed, the arguments to the function become the
+positional parameters during its execution (*note Positional
+Parameters::). The special parameter '#' that expands to the number of
+positional parameters is updated to reflect the change. Special
+parameter '0' is unchanged. The first element of the 'FUNCNAME'
+variable is set to the name of the function while the function is
+executing.
+
+ All other aspects of the shell execution environment are identical
+between a function and its caller with these exceptions: the 'DEBUG' and
+'RETURN' traps are not inherited unless the function has been given the
+'trace' attribute using the 'declare' builtin or the '-o functrace'
+option has been enabled with the 'set' builtin, (in which case all
+functions inherit the 'DEBUG' and 'RETURN' traps), and the 'ERR' trap is
+not inherited unless the '-o errtrace' shell option has been enabled.
+*Note Bourne Shell Builtins::, for the description of the 'trap'
+builtin.
+
+ The 'FUNCNEST' variable, if set to a numeric value greater than 0,
+defines a maximum function nesting level. Function invocations that
+exceed the limit cause the entire command to abort.
+
+ If the builtin command 'return' is executed in a function, the
+function completes and execution resumes with the next command after the
+function call. Any command associated with the 'RETURN' trap is
+executed before execution resumes. When a function completes, the
+values of the positional parameters and the special parameter '#' are
+restored to the values they had prior to the function's execution. If a
+numeric argument is given to 'return', that is the function's return
+status; otherwise the function's return status is the exit status of the
+last command executed before the 'return'.
+
+ Variables local to the function may be declared with the 'local'
+builtin ("local variables"). Ordinarily, variables and their values are
+shared between a function and its caller. These variables are visible
+only to the function and the commands it invokes. This is particularly
+important when a shell function calls other functions.
+
+ In the following description, the "current scope" is a currently-
+executing function. Previous scopes consist of that function's caller
+and so on, back to the "global" scope, where the shell is not executing
+any shell function. Consequently, a local variable at the current local
+scope is a variable declared using the 'local' or 'declare' builtins in
+the function that is currently executing.
+
+ Local variables "shadow" variables with the same name declared at
+previous scopes. For instance, a local variable declared in a function
+hides a global variable of the same name: references and assignments
+refer to the local variable, leaving the global variable unmodified.
+When the function returns, the global variable is once again visible.
+
+ The shell uses "dynamic scoping" to control a variable's visibility
+within functions. With dynamic scoping, visible variables and their
+values are a result of the sequence of function calls that caused
+execution to reach the current function. The value of a variable that a
+function sees depends on its value within its caller, if any, whether
+that caller is the "global" scope or another shell function. This is
+also the value that a local variable declaration "shadows", and the
+value that is restored when the function returns.
+
+ For example, if a variable 'var' is declared as local in function
+'func1', and 'func1' calls another function 'func2', references to 'var'
+made from within 'func2' will resolve to the local variable 'var' from
+'func1', shadowing any global variable named 'var'.
+
+ The following script demonstrates this behavior. When executed, the
+script displays
+
+ In func2, var = func1 local
+
+ func1()
+ {
+ local var='func1 local'
+ func2
+ }
+
+ func2()
+ {
+ echo "In func2, var = $var"
+ }
+
+ var=global
+ func1
+
+ The 'unset' builtin also acts using the same dynamic scope: if a
+variable is local to the current scope, 'unset' will unset it; otherwise
+the unset will refer to the variable found in any calling scope as
+described above. If a variable at the current local scope is unset, it
+will remain so (appearing as unset) until it is reset in that scope or
+until the function returns. Once the function returns, any instance of
+the variable at a previous scope will become visible. If the unset acts
+on a variable at a previous scope, any instance of a variable with that
+name that had been shadowed will become visible (see below how
+'localvar_unset'shell option changes this behavior).
+
+ Function names and definitions may be listed with the '-f' option to
+the 'declare' ('typeset') builtin command (*note Bash Builtins::). The
+'-F' option to 'declare' or 'typeset' will list the function names only
+(and optionally the source file and line number, if the 'extdebug' shell
+option is enabled). Functions may be exported so that child shell
+processes (those created when executing a separate shell invocation)
+automatically have them defined with the '-f' option to the 'export'
+builtin (*note Bourne Shell Builtins::).
+
+ Functions may be recursive. The 'FUNCNEST' variable may be used to
+limit the depth of the function call stack and restrict the number of
+function invocations. By default, no limit is placed on the number of
+recursive calls.
+
+
+File: bash.info, Node: Shell Parameters, Next: Shell Expansions, Prev: Shell Functions, Up: Basic Shell Features
+
+3.4 Shell Parameters
+====================
+
+* Menu:
+
+* Positional Parameters:: The shell's command-line arguments.
+* Special Parameters:: Parameters denoted by special characters.
+
+A "parameter" is an entity that stores values. It can be a 'name', a
+number, or one of the special characters listed below. A "variable" is
+a parameter denoted by a 'name'. A variable has a 'value' and zero or
+more 'attributes'. Attributes are assigned using the 'declare' builtin
+command (see the description of the 'declare' builtin in *note Bash
+Builtins::).
+
+ A parameter is set if it has been assigned a value. The null string
+is a valid value. Once a variable is set, it may be unset only by using
+the 'unset' builtin command.
+
+ A variable may be assigned to by a statement of the form
+ NAME=[VALUE]
+If VALUE is not given, the variable is assigned the null string. All
+VALUEs undergo tilde expansion, parameter and variable expansion,
+command substitution, arithmetic expansion, and quote removal (*note
+Shell Parameter Expansion::). If the variable has its 'integer'
+attribute set, then VALUE is evaluated as an arithmetic expression even
+if the '$((...))' expansion is not used (*note Arithmetic Expansion::).
+Word splitting and filename expansion are not performed. Assignment
+statements may also appear as arguments to the 'alias', 'declare',
+'typeset', 'export', 'readonly', and 'local' builtin commands
+("declaration" commands). When in POSIX mode (*note Bash POSIX Mode::),
+these builtins may appear in a command after one or more instances of
+the 'command' builtin and retain these assignment statement properties.
+
+ In the context where an assignment statement is assigning a value to
+a shell variable or array index (*note Arrays::), the '+=' operator can
+be used to append to or add to the variable's previous value. This
+includes arguments to builtin commands such as 'declare' that accept
+assignment statements (declaration commands). When '+=' is applied to a
+variable for which the 'integer' attribute has been set, VALUE is
+evaluated as an arithmetic expression and added to the variable's
+current value, which is also evaluated. When '+=' is applied to an
+array variable using compound assignment (*note Arrays::), the
+variable's value is not unset (as it is when using '='), and new values
+are appended to the array beginning at one greater than the array's
+maximum index (for indexed arrays), or added as additional key-value
+pairs in an associative array. When applied to a string-valued
+variable, VALUE is expanded and appended to the variable's value.
+
+ A variable can be assigned the 'nameref' attribute using the '-n'
+option to the 'declare' or 'local' builtin commands (*note Bash
+Builtins::) to create a "nameref", or a reference to another variable.
+This allows variables to be manipulated indirectly. Whenever the
+nameref variable is referenced, assigned to, unset, or has its
+attributes modified (other than using or changing the nameref attribute
+itself), the operation is actually performed on the variable specified
+by the nameref variable's value. A nameref is commonly used within
+shell functions to refer to a variable whose name is passed as an
+argument to the function. For instance, if a variable name is passed to
+a shell function as its first argument, running
+ declare -n ref=$1
+inside the function creates a nameref variable 'ref' whose value is the
+variable name passed as the first argument. References and assignments
+to 'ref', and changes to its attributes, are treated as references,
+assignments, and attribute modifications to the variable whose name was
+passed as '$1'.
+
+ If the control variable in a 'for' loop has the nameref attribute,
+the list of words can be a list of shell variables, and a name reference
+will be established for each word in the list, in turn, when the loop is
+executed. Array variables cannot be given the nameref attribute.
+However, nameref variables can reference array variables and subscripted
+array variables. Namerefs can be unset using the '-n' option to the
+'unset' builtin (*note Bourne Shell Builtins::). Otherwise, if 'unset'
+is executed with the name of a nameref variable as an argument, the
+variable referenced by the nameref variable will be unset.
+
+
+File: bash.info, Node: Positional Parameters, Next: Special Parameters, Up: Shell Parameters
+
+3.4.1 Positional Parameters
+---------------------------
+
+A "positional parameter" is a parameter denoted by one or more digits,
+other than the single digit '0'. Positional parameters are assigned
+from the shell's arguments when it is invoked, and may be reassigned
+using the 'set' builtin command. Positional parameter 'N' may be
+referenced as '${N}', or as '$N' when 'N' consists of a single digit.
+Positional parameters may not be assigned to with assignment statements.
+The 'set' and 'shift' builtins are used to set and unset them (*note
+Shell Builtin Commands::). The positional parameters are temporarily
+replaced when a shell function is executed (*note Shell Functions::).
+
+ When a positional parameter consisting of more than a single digit is
+expanded, it must be enclosed in braces.
+
+
+File: bash.info, Node: Special Parameters, Prev: Positional Parameters, Up: Shell Parameters
+
+3.4.2 Special Parameters
+------------------------
+
+The shell treats several parameters specially. These parameters may
+only be referenced; assignment to them is not allowed.
+
+'*'
+ ($*) Expands to the positional parameters, starting from one. When
+ the expansion is not within double quotes, each positional
+ parameter expands to a separate word. In contexts where it is
+ performed, those words are subject to further word splitting and
+ filename expansion. When the expansion occurs within double
+ quotes, it expands to a single word with the value of each
+ parameter separated by the first character of the 'IFS' special
+ variable. That is, '"$*"' is equivalent to '"$1C$2C..."', where C
+ is the first character of the value of the 'IFS' variable. If
+ 'IFS' is unset, the parameters are separated by spaces. If 'IFS'
+ is null, the parameters are joined without intervening separators.
+
+'@'
+ ($@) Expands to the positional parameters, starting from one. In
+ contexts where word splitting is performed, this expands each
+ positional parameter to a separate word; if not within double
+ quotes, these words are subject to word splitting. In contexts
+ where word splitting is not performed, this expands to a single
+ word with each positional parameter separated by a space. When the
+ expansion occurs within double quotes, and word splitting is
+ performed, each parameter expands to a separate word. That is,
+ '"$@"' is equivalent to '"$1" "$2" ...'. If the double-quoted
+ expansion occurs within a word, the expansion of the first
+ parameter is joined with the beginning part of the original word,
+ and the expansion of the last parameter is joined with the last
+ part of the original word. When there are no positional
+ parameters, '"$@"' and '$@' expand to nothing (i.e., they are
+ removed).
+
+'#'
+ ($#) Expands to the number of positional parameters in decimal.
+
+'?'
+ ($?) Expands to the exit status of the most recently executed
+ foreground pipeline.
+
+'-'
+ ($-, a hyphen.) Expands to the current option flags as specified
+ upon invocation, by the 'set' builtin command, or those set by the
+ shell itself (such as the '-i' option).
+
+'$'
+ ($$) Expands to the process ID of the shell. In a subshell, it
+ expands to the process ID of the invoking shell, not the subshell.
+
+'!'
+ ($!) Expands to the process ID of the job most recently placed
+ into the background, whether executed as an asynchronous command or
+ using the 'bg' builtin (*note Job Control Builtins::).
+
+'0'
+ ($0) Expands to the name of the shell or shell script. This is set
+ at shell initialization. If Bash is invoked with a file of
+ commands (*note Shell Scripts::), '$0' is set to the name of that
+ file. If Bash is started with the '-c' option (*note Invoking
+ Bash::), then '$0' is set to the first argument after the string to
+ be executed, if one is present. Otherwise, it is set to the
+ filename used to invoke Bash, as given by argument zero.
+
+
+File: bash.info, Node: Shell Expansions, Next: Redirections, Prev: Shell Parameters, Up: Basic Shell Features
+
+3.5 Shell Expansions
+====================
+
+Expansion is performed on the command line after it has been split into
+'token's. There are seven kinds of expansion performed:
+
+ * brace expansion
+ * tilde expansion
+ * parameter and variable expansion
+ * command substitution
+ * arithmetic expansion
+ * word splitting
+ * filename expansion
+
+* Menu:
+
+* Brace Expansion:: Expansion of expressions within braces.
+* Tilde Expansion:: Expansion of the ~ character.
+* Shell Parameter Expansion:: How Bash expands variables to their values.
+* Command Substitution:: Using the output of a command as an argument.
+* Arithmetic Expansion:: How to use arithmetic in shell expansions.
+* Process Substitution:: A way to write and read to and from a
+ command.
+* Word Splitting:: How the results of expansion are split into separate
+ arguments.
+* Filename Expansion:: A shorthand for specifying filenames matching patterns.
+* Quote Removal:: How and when quote characters are removed from
+ words.
+
+ The order of expansions is: brace expansion; tilde expansion,
+parameter and variable expansion, arithmetic expansion, and command
+substitution (done in a left-to-right fashion); word splitting; and
+filename expansion.
+
+ On systems that can support it, there is an additional expansion
+available: "process substitution". This is performed at the same time
+as tilde, parameter, variable, and arithmetic expansion and command
+substitution.
+
+ After these expansions are performed, quote characters present in the
+original word are removed unless they have been quoted themselves
+("quote removal").
+
+ Only brace expansion, word splitting, and filename expansion can
+increase the number of words of the expansion; other expansions expand a
+single word to a single word. The only exceptions to this are the
+expansions of '"$@"' and '$*' (*note Special Parameters::), and
+'"${NAME[@]}"' and '${NAME[*]}' (*note Arrays::).
+
+ After all expansions, 'quote removal' (*note Quote Removal::) is
+performed.
+
+
+File: bash.info, Node: Brace Expansion, Next: Tilde Expansion, Up: Shell Expansions
+
+3.5.1 Brace Expansion
+---------------------
+
+Brace expansion is a mechanism by which arbitrary strings may be
+generated. This mechanism is similar to "filename expansion" (*note
+Filename Expansion::), but the filenames generated need not exist.
+Patterns to be brace expanded take the form of an optional PREAMBLE,
+followed by either a series of comma-separated strings or a sequence
+expression between a pair of braces, followed by an optional POSTSCRIPT.
+The preamble is prefixed to each string contained within the braces, and
+the postscript is then appended to each resulting string, expanding left
+to right.
+
+ Brace expansions may be nested. The results of each expanded string
+are not sorted; left to right order is preserved. For example,
+ bash$ echo a{d,c,b}e
+ ade ace abe
+
+ A sequence expression takes the form '{X..Y[..INCR]}', where X and Y
+are either integers or letters, and INCR, an optional increment, is an
+integer. When integers are supplied, the expression expands to each
+number between X and Y, inclusive. Supplied integers may be prefixed
+with '0' to force each term to have the same width. When either X or Y
+begins with a zero, the shell attempts to force all generated terms to
+contain the same number of digits, zero-padding where necessary. When
+letters are supplied, the expression expands to each character
+lexicographically between X and Y, inclusive, using the default C
+locale. Note that both X and Y must be of the same type (integer or
+letter). When the increment is supplied, it is used as the difference
+between each term. The default increment is 1 or -1 as appropriate.
+
+ Brace expansion is performed before any other expansions, and any
+characters special to other expansions are preserved in the result. It
+is strictly textual. Bash does not apply any syntactic interpretation
+to the context of the expansion or the text between the braces.
+
+ A correctly-formed brace expansion must contain unquoted opening and
+closing braces, and at least one unquoted comma or a valid sequence
+expression. Any incorrectly formed brace expansion is left unchanged.
+
+ A { or ',' may be quoted with a backslash to prevent its being
+considered part of a brace expression. To avoid conflicts with
+parameter expansion, the string '${' is not considered eligible for
+brace expansion, and inhibits brace expansion until the closing '}'.
+
+ This construct is typically used as shorthand when the common prefix
+of the strings to be generated is longer than in the above example:
+ mkdir /usr/local/src/bash/{old,new,dist,bugs}
+ or
+ chown root /usr/{ucb/{ex,edit},lib/{ex?.?*,how_ex}}
+
+
+File: bash.info, Node: Tilde Expansion, Next: Shell Parameter Expansion, Prev: Brace Expansion, Up: Shell Expansions
+
+3.5.2 Tilde Expansion
+---------------------
+
+If a word begins with an unquoted tilde character ('~'), all of the
+characters up to the first unquoted slash (or all characters, if there
+is no unquoted slash) are considered a "tilde-prefix". If none of the
+characters in the tilde-prefix are quoted, the characters in the
+tilde-prefix following the tilde are treated as a possible "login name".
+If this login name is the null string, the tilde is replaced with the
+value of the 'HOME' shell variable. If 'HOME' is unset, the home
+directory of the user executing the shell is substituted instead.
+Otherwise, the tilde-prefix is replaced with the home directory
+associated with the specified login name.
+
+ If the tilde-prefix is '~+', the value of the shell variable 'PWD'
+replaces the tilde-prefix. If the tilde-prefix is '~-', the value of
+the shell variable 'OLDPWD', if it is set, is substituted.
+
+ If the characters following the tilde in the tilde-prefix consist of
+a number N, optionally prefixed by a '+' or a '-', the tilde-prefix is
+replaced with the corresponding element from the directory stack, as it
+would be displayed by the 'dirs' builtin invoked with the characters
+following tilde in the tilde-prefix as an argument (*note The Directory
+Stack::). If the tilde-prefix, sans the tilde, consists of a number
+without a leading '+' or '-', '+' is assumed.
+
+ If the login name is invalid, or the tilde expansion fails, the word
+is left unchanged.
+
+ Each variable assignment is checked for unquoted tilde-prefixes
+immediately following a ':' or the first '='. In these cases, tilde
+expansion is also performed. Consequently, one may use filenames with
+tildes in assignments to 'PATH', 'MAILPATH', and 'CDPATH', and the shell
+assigns the expanded value.
+
+ The following table shows how Bash treats unquoted tilde-prefixes:
+
+'~'
+ The value of '$HOME'
+'~/foo'
+ '$HOME/foo'
+
+'~fred/foo'
+ The subdirectory 'foo' of the home directory of the user 'fred'
+
+'~+/foo'
+ '$PWD/foo'
+
+'~-/foo'
+ '${OLDPWD-'~-'}/foo'
+
+'~N'
+ The string that would be displayed by 'dirs +N'
+
+'~+N'
+ The string that would be displayed by 'dirs +N'
+
+'~-N'
+ The string that would be displayed by 'dirs -N'
+
+ Bash also performs tilde expansion on words satisfying the conditions
+of variable assignments (*note Shell Parameters::) when they appear as
+arguments to simple commands. Bash does not do this, except for the
+declaration commands listed above, when in POSIX mode.
+
+
+File: bash.info, Node: Shell Parameter Expansion, Next: Command Substitution, Prev: Tilde Expansion, Up: Shell Expansions
+
+3.5.3 Shell Parameter Expansion
+-------------------------------
+
+The '$' character introduces parameter expansion, command substitution,
+or arithmetic expansion. The parameter name or symbol to be expanded
+may be enclosed in braces, which are optional but serve to protect the
+variable to be expanded from characters immediately following it which
+could be interpreted as part of the name.
+
+ When braces are used, the matching ending brace is the first '}' not
+escaped by a backslash or within a quoted string, and not within an
+embedded arithmetic expansion, command substitution, or parameter
+expansion.
+
+ The basic form of parameter expansion is ${PARAMETER}. The value of
+PARAMETER is substituted. The PARAMETER is a shell parameter as
+described above (*note Shell Parameters::) or an array reference (*note
+Arrays::). The braces are required when PARAMETER is a positional
+parameter with more than one digit, or when PARAMETER is followed by a
+character that is not to be interpreted as part of its name.
+
+ If the first character of PARAMETER is an exclamation point (!), and
+PARAMETER is not a nameref, it introduces a level of indirection. Bash
+uses the value formed by expanding the rest of PARAMETER as the new
+PARAMETER; this is then expanded and that value is used in the rest of
+the expansion, rather than the expansion of the original PARAMETER.
+This is known as 'indirect expansion'. The value is subject to tilde
+expansion, parameter expansion, command substitution, and arithmetic
+expansion. If PARAMETER is a nameref, this expands to the name of the
+variable referenced by PARAMETER instead of performing the complete
+indirect expansion. The exceptions to this are the expansions of
+${!PREFIX*} and ${!NAME[@]} described below. The exclamation point must
+immediately follow the left brace in order to introduce indirection.
+
+ In each of the cases below, WORD is subject to tilde expansion,
+parameter expansion, command substitution, and arithmetic expansion.
+
+ When not performing substring expansion, using the form described
+below (e.g., ':-'), Bash tests for a parameter that is unset or null.
+Omitting the colon results in a test only for a parameter that is unset.
+Put another way, if the colon is included, the operator tests for both
+PARAMETER's existence and that its value is not null; if the colon is
+omitted, the operator tests only for existence.
+
+'${PARAMETER:-WORD}'
+ If PARAMETER is unset or null, the expansion of WORD is
+ substituted. Otherwise, the value of PARAMETER is substituted.
+
+ $ v=123
+ $ echo ${v-unset}
+ 123
+
+'${PARAMETER:=WORD}'
+ If PARAMETER is unset or null, the expansion of WORD is assigned to
+ PARAMETER. The value of PARAMETER is then substituted. Positional
+ parameters and special parameters may not be assigned to in this
+ way.
+
+ $ var=
+ $ : ${var:=DEFAULT}
+ $ echo $var
+ DEFAULT
+
+'${PARAMETER:?WORD}'
+ If PARAMETER is null or unset, the expansion of WORD (or a message
+ to that effect if WORD is not present) is written to the standard
+ error and the shell, if it is not interactive, exits. Otherwise,
+ the value of PARAMETER is substituted.
+
+ $ var=
+ $ : ${var:?var is unset or null}
+ bash: var: var is unset or null
+
+'${PARAMETER:+WORD}'
+ If PARAMETER is null or unset, nothing is substituted, otherwise
+ the expansion of WORD is substituted.
+
+ $ var=123
+ $ echo ${var:+var is set and not null}
+ var is set and not null
+
+'${PARAMETER:OFFSET}'
+'${PARAMETER:OFFSET:LENGTH}'
+ This is referred to as Substring Expansion. It expands to up to
+ LENGTH characters of the value of PARAMETER starting at the
+ character specified by OFFSET. If PARAMETER is '@' or '*', an
+ indexed array subscripted by '@' or '*', or an associative array
+ name, the results differ as described below. If LENGTH is omitted,
+ it expands to the substring of the value of PARAMETER starting at
+ the character specified by OFFSET and extending to the end of the
+ value. LENGTH and OFFSET are arithmetic expressions (*note Shell
+ Arithmetic::).
+
+ If OFFSET evaluates to a number less than zero, the value is used
+ as an offset in characters from the end of the value of PARAMETER.
+ If LENGTH evaluates to a number less than zero, it is interpreted
+ as an offset in characters from the end of the value of PARAMETER
+ rather than a number of characters, and the expansion is the
+ characters between OFFSET and that result. Note that a negative
+ offset must be separated from the colon by at least one space to
+ avoid being confused with the ':-' expansion.
+
+ Here are some examples illustrating substring expansion on
+ parameters and subscripted arrays:
+
+ $ string=01234567890abcdefgh
+ $ echo ${string:7}
+ 7890abcdefgh
+ $ echo ${string:7:0}
+
+ $ echo ${string:7:2}
+ 78
+ $ echo ${string:7:-2}
+ 7890abcdef
+ $ echo ${string: -7}
+ bcdefgh
+ $ echo ${string: -7:0}
+
+ $ echo ${string: -7:2}
+ bc
+ $ echo ${string: -7:-2}
+ bcdef
+ $ set -- 01234567890abcdefgh
+ $ echo ${1:7}
+ 7890abcdefgh
+ $ echo ${1:7:0}
+
+ $ echo ${1:7:2}
+ 78
+ $ echo ${1:7:-2}
+ 7890abcdef
+ $ echo ${1: -7}
+ bcdefgh
+ $ echo ${1: -7:0}
+
+ $ echo ${1: -7:2}
+ bc
+ $ echo ${1: -7:-2}
+ bcdef
+ $ array[0]=01234567890abcdefgh
+ $ echo ${array[0]:7}
+ 7890abcdefgh
+ $ echo ${array[0]:7:0}
+
+ $ echo ${array[0]:7:2}
+ 78
+ $ echo ${array[0]:7:-2}
+ 7890abcdef
+ $ echo ${array[0]: -7}
+ bcdefgh
+ $ echo ${array[0]: -7:0}
+
+ $ echo ${array[0]: -7:2}
+ bc
+ $ echo ${array[0]: -7:-2}
+ bcdef
+
+ If PARAMETER is '@' or '*', the result is LENGTH positional
+ parameters beginning at OFFSET. A negative OFFSET is taken
+ relative to one greater than the greatest positional parameter, so
+ an offset of -1 evaluates to the last positional parameter. It is
+ an expansion error if LENGTH evaluates to a number less than zero.
+
+ The following examples illustrate substring expansion using
+ positional parameters:
+
+ $ set -- 1 2 3 4 5 6 7 8 9 0 a b c d e f g h
+ $ echo ${@:7}
+ 7 8 9 0 a b c d e f g h
+ $ echo ${@:7:0}
+
+ $ echo ${@:7:2}
+ 7 8
+ $ echo ${@:7:-2}
+ bash: -2: substring expression < 0
+ $ echo ${@: -7:2}
+ b c
+ $ echo ${@:0}
+ ./bash 1 2 3 4 5 6 7 8 9 0 a b c d e f g h
+ $ echo ${@:0:2}
+ ./bash 1
+ $ echo ${@: -7:0}
+
+
+ If PARAMETER is an indexed array name subscripted by '@' or '*',
+ the result is the LENGTH members of the array beginning with
+ '${PARAMETER[OFFSET]}'. A negative OFFSET is taken relative to one
+ greater than the maximum index of the specified array. It is an
+ expansion error if LENGTH evaluates to a number less than zero.
+
+ These examples show how you can use substring expansion with
+ indexed arrays:
+
+ $ array=(0 1 2 3 4 5 6 7 8 9 0 a b c d e f g h)
+ $ echo ${array[@]:7}
+ 7 8 9 0 a b c d e f g h
+ $ echo ${array[@]:7:2}
+ 7 8
+ $ echo ${array[@]: -7:2}
+ b c
+ $ echo ${array[@]: -7:-2}
+ bash: -2: substring expression < 0
+ $ echo ${array[@]:0}
+ 0 1 2 3 4 5 6 7 8 9 0 a b c d e f g h
+ $ echo ${array[@]:0:2}
+ 0 1
+ $ echo ${array[@]: -7:0}
+
+
+ Substring expansion applied to an associative array produces
+ undefined results.
+
+ Substring indexing is zero-based unless the positional parameters
+ are used, in which case the indexing starts at 1 by default. If
+ OFFSET is 0, and the positional parameters are used, '$0' is
+ prefixed to the list.
+
+'${!PREFIX*}'
+'${!PREFIX@}'
+ Expands to the names of variables whose names begin with PREFIX,
+ separated by the first character of the 'IFS' special variable.
+ When '@' is used and the expansion appears within double quotes,
+ each variable name expands to a separate word.
+
+'${!NAME[@]}'
+'${!NAME[*]}'
+ If NAME is an array variable, expands to the list of array indices
+ (keys) assigned in NAME. If NAME is not an array, expands to 0 if
+ NAME is set and null otherwise. When '@' is used and the expansion
+ appears within double quotes, each key expands to a separate word.
+
+'${#PARAMETER}'
+ The length in characters of the expanded value of PARAMETER is
+ substituted. If PARAMETER is '*' or '@', the value substituted is
+ the number of positional parameters. If PARAMETER is an array name
+ subscripted by '*' or '@', the value substituted is the number of
+ elements in the array. If PARAMETER is an indexed array name
+ subscripted by a negative number, that number is interpreted as
+ relative to one greater than the maximum index of PARAMETER, so
+ negative indices count back from the end of the array, and an index
+ of -1 references the last element.
+
+'${PARAMETER#WORD}'
+'${PARAMETER##WORD}'
+ The WORD is expanded to produce a pattern and matched according to
+ the rules described below (*note Pattern Matching::). If the
+ pattern matches the beginning of the expanded value of PARAMETER,
+ then the result of the expansion is the expanded value of PARAMETER
+ with the shortest matching pattern (the '#' case) or the longest
+ matching pattern (the '##' case) deleted. If PARAMETER is '@' or
+ '*', the pattern removal operation is applied to each positional
+ parameter in turn, and the expansion is the resultant list. If
+ PARAMETER is an array variable subscripted with '@' or '*', the
+ pattern removal operation is applied to each member of the array in
+ turn, and the expansion is the resultant list.
+
+'${PARAMETER%WORD}'
+'${PARAMETER%%WORD}'
+ The WORD is expanded to produce a pattern and matched according to
+ the rules described below (*note Pattern Matching::). If the
+ pattern matches a trailing portion of the expanded value of
+ PARAMETER, then the result of the expansion is the value of
+ PARAMETER with the shortest matching pattern (the '%' case) or the
+ longest matching pattern (the '%%' case) deleted. If PARAMETER is
+ '@' or '*', the pattern removal operation is applied to each
+ positional parameter in turn, and the expansion is the resultant
+ list. If PARAMETER is an array variable subscripted with '@' or
+ '*', the pattern removal operation is applied to each member of the
+ array in turn, and the expansion is the resultant list.
+
+'${PARAMETER/PATTERN/STRING}'
+'${PARAMETER//PATTERN/STRING}'
+'${PARAMETER/#PATTERN/STRING}'
+'${PARAMETER/%PATTERN/STRING}'
+ The PATTERN is expanded to produce a pattern just as in filename
+ expansion. PARAMETER is expanded and the longest match of PATTERN
+ against its value is replaced with STRING. STRING undergoes tilde
+ expansion, parameter and variable expansion, arithmetic expansion,
+ command and process substitution, and quote removal. The match is
+ performed according to the rules described below (*note Pattern
+ Matching::).
+
+ In the first form above, only the first match is replaced. If
+ there are two slashes separating PARAMETER and PATTERN (the second
+ form above), all matches of PATTERN are replaced with STRING. If
+ PATTERN is preceded by '#' (the third form above), it must match at
+ the beginning of the expanded value of PARAMETER. If PATTERN is
+ preceded by '%' (the fourth form above), it must match at the end
+ of the expanded value of PARAMETER. If the expansion of STRING is
+ null, matches of PATTERN are deleted. If STRING is null, matches
+ of PATTERN are deleted and the '/' following PATTERN may be
+ omitted.
+
+ If the 'patsub_replacement' shell option is enabled using 'shopt',
+ any unquoted instances of '&' in STRING are replaced with the
+ matching portion of PATTERN. This is intended to duplicate a
+ common 'sed' idiom.
+
+ Quoting any part of STRING inhibits replacement in the expansion of
+ the quoted portion, including replacement strings stored in shell
+ variables. Backslash will escape '&' in STRING; the backslash is
+ removed in order to permit a literal '&' in the replacement string.
+ Users should take care if STRING is double-quoted to avoid unwanted
+ interactions between the backslash and double-quoting, since
+ backslash has special meaning within double quotes. Pattern
+ substitution performs the check for unquoted '&' after expanding
+ STRING, so users should ensure to properly quote any occurrences of
+ '&' they want to be taken literally in the replacement and ensure
+ any instances of '&' they want to be replaced are unquoted.
+
+ For instance,
+
+ var=abcdef
+ rep='& '
+ echo ${var/abc/& }
+ echo "${var/abc/& }"
+ echo ${var/abc/$rep}
+ echo "${var/abc/$rep}"
+
+ will display four lines of "abc def", while
+
+ var=abcdef
+ rep='& '
+ echo ${var/abc/\& }
+ echo "${var/abc/\& }"
+ echo ${var/abc/"& "}
+ echo ${var/abc/"$rep"}
+
+ will display four lines of "& def". Like the pattern removal
+ operators, double quotes surrounding the replacement string quote
+ the expanded characters, while double quotes enclosing the entire
+ parameter substitution do not, since the expansion is performed in
+ a context that doesn't take any enclosing double quotes into
+ account.
+
+ Since backslash can escape '&', it can also escape a backslash in
+ the replacement string. This means that '\\' will insert a literal
+ backslash into the replacement, so these two 'echo' commands
+
+ var=abcdef
+ rep='\\&xyz'
+ echo ${var/abc/\\&xyz}
+ echo ${var/abc/$rep}
+
+ will both output '\abcxyzdef'.
+
+ It should rarely be necessary to enclose only STRING in double
+ quotes.
+
+ If the 'nocasematch' shell option (see the description of 'shopt'
+ in *note The Shopt Builtin::) is enabled, the match is performed
+ without regard to the case of alphabetic characters. If PARAMETER
+ is '@' or '*', the substitution operation is applied to each
+ positional parameter in turn, and the expansion is the resultant
+ list. If PARAMETER is an array variable subscripted with '@' or
+ '*', the substitution operation is applied to each member of the
+ array in turn, and the expansion is the resultant list.
+
+'${PARAMETER^PATTERN}'
+'${PARAMETER^^PATTERN}'
+'${PARAMETER,PATTERN}'
+'${PARAMETER,,PATTERN}'
+ This expansion modifies the case of alphabetic characters in
+ PARAMETER. The PATTERN is expanded to produce a pattern just as in
+ filename expansion. Each character in the expanded value of
+ PARAMETER is tested against PATTERN, and, if it matches the
+ pattern, its case is converted. The pattern should not attempt to
+ match more than one character.
+
+ The '^' operator converts lowercase letters matching PATTERN to
+ uppercase; the ',' operator converts matching uppercase letters to
+ lowercase. The '^^' and ',,' expansions convert each matched
+ character in the expanded value; the '^' and ',' expansions match
+ and convert only the first character in the expanded value. If
+ PATTERN is omitted, it is treated like a '?', which matches every
+ character.
+
+ If PARAMETER is '@' or '*', the case modification operation is
+ applied to each positional parameter in turn, and the expansion is
+ the resultant list. If PARAMETER is an array variable subscripted
+ with '@' or '*', the case modification operation is applied to each
+ member of the array in turn, and the expansion is the resultant
+ list.
+
+'${PARAMETER@OPERATOR}'
+ The expansion is either a transformation of the value of PARAMETER
+ or information about PARAMETER itself, depending on the value of
+ OPERATOR. Each OPERATOR is a single letter:
+
+ 'U'
+ The expansion is a string that is the value of PARAMETER with
+ lowercase alphabetic characters converted to uppercase.
+ 'u'
+ The expansion is a string that is the value of PARAMETER with
+ the first character converted to uppercase, if it is
+ alphabetic.
+ 'L'
+ The expansion is a string that is the value of PARAMETER with
+ uppercase alphabetic characters converted to lowercase.
+ 'Q'
+ The expansion is a string that is the value of PARAMETER
+ quoted in a format that can be reused as input.
+ 'E'
+ The expansion is a string that is the value of PARAMETER with
+ backslash escape sequences expanded as with the '$'...''
+ quoting mechanism.
+ 'P'
+ The expansion is a string that is the result of expanding the
+ value of PARAMETER as if it were a prompt string (*note
+ Controlling the Prompt::).
+ 'A'
+ The expansion is a string in the form of an assignment
+ statement or 'declare' command that, if evaluated, will
+ recreate PARAMETER with its attributes and value.
+ 'K'
+ Produces a possibly-quoted version of the value of PARAMETER,
+ except that it prints the values of indexed and associative
+ arrays as a sequence of quoted key-value pairs (*note
+ Arrays::).
+ 'a'
+ The expansion is a string consisting of flag values
+ representing PARAMETER's attributes.
+ 'k'
+ Like the 'K' transformation, but expands the keys and values
+ of indexed and associative arrays to separate words after word
+ splitting.
+
+ If PARAMETER is '@' or '*', the operation is applied to each
+ positional parameter in turn, and the expansion is the resultant
+ list. If PARAMETER is an array variable subscripted with '@' or
+ '*', the operation is applied to each member of the array in turn,
+ and the expansion is the resultant list.
+
+ The result of the expansion is subject to word splitting and
+ filename expansion as described below.
+
+
+File: bash.info, Node: Command Substitution, Next: Arithmetic Expansion, Prev: Shell Parameter Expansion, Up: Shell Expansions
+
+3.5.4 Command Substitution
+--------------------------
+
+Command substitution allows the output of a command to replace the
+command itself. Command substitution occurs when a command is enclosed
+as follows:
+ $(COMMAND)
+or
+ `COMMAND`
+
+Bash performs the expansion by executing COMMAND in a subshell
+environment and replacing the command substitution with the standard
+output of the command, with any trailing newlines deleted. Embedded
+newlines are not deleted, but they may be removed during word splitting.
+The command substitution '$(cat FILE)' can be replaced by the equivalent
+but faster '$(< FILE)'.
+
+ When the old-style backquote form of substitution is used, backslash
+retains its literal meaning except when followed by '$', '`', or '\'.
+The first backquote not preceded by a backslash terminates the command
+substitution. When using the '$(COMMAND)' form, all characters between
+the parentheses make up the command; none are treated specially.
+
+ Command substitutions may be nested. To nest when using the
+backquoted form, escape the inner backquotes with backslashes.
+
+ If the substitution appears within double quotes, word splitting and
+filename expansion are not performed on the results.
+
+
+File: bash.info, Node: Arithmetic Expansion, Next: Process Substitution, Prev: Command Substitution, Up: Shell Expansions
+
+3.5.5 Arithmetic Expansion
+--------------------------
+
+Arithmetic expansion allows the evaluation of an arithmetic expression
+and the substitution of the result. The format for arithmetic expansion
+is:
+
+ $(( EXPRESSION ))
+
+ The EXPRESSION undergoes the same expansions as if it were within
+double quotes, but double quote characters in EXPRESSION are not treated
+specially and are removed. All tokens in the expression undergo
+parameter and variable expansion, command substitution, and quote
+removal. The result is treated as the arithmetic expression to be
+evaluated. Arithmetic expansions may be nested.
+
+ The evaluation is performed according to the rules listed below
+(*note Shell Arithmetic::). If the expression is invalid, Bash prints a
+message indicating failure to the standard error and no substitution
+occurs.
+
+
+File: bash.info, Node: Process Substitution, Next: Word Splitting, Prev: Arithmetic Expansion, Up: Shell Expansions
+
+3.5.6 Process Substitution
+--------------------------
+
+Process substitution allows a process's input or output to be referred
+to using a filename. It takes the form of
+ <(LIST)
+or
+ >(LIST)
+The process LIST is run asynchronously, and its input or output appears
+as a filename. This filename is passed as an argument to the current
+command as the result of the expansion. If the '>(LIST)' form is used,
+writing to the file will provide input for LIST. If the '<(LIST)' form
+is used, the file passed as an argument should be read to obtain the
+output of LIST. Note that no space may appear between the '<' or '>'
+and the left parenthesis, otherwise the construct would be interpreted
+as a redirection. Process substitution is supported on systems that
+support named pipes (FIFOs) or the '/dev/fd' method of naming open
+files.
+
+ When available, process substitution is performed simultaneously with
+parameter and variable expansion, command substitution, and arithmetic
+expansion.
+
+
+File: bash.info, Node: Word Splitting, Next: Filename Expansion, Prev: Process Substitution, Up: Shell Expansions
+
+3.5.7 Word Splitting
+--------------------
+
+The shell scans the results of parameter expansion, command
+substitution, and arithmetic expansion that did not occur within double
+quotes for word splitting.
+
+ The shell treats each character of '$IFS' as a delimiter, and splits
+the results of the other expansions into words using these characters as
+field terminators. If 'IFS' is unset, or its value is exactly
+'<space><tab><newline>', the default, then sequences of ' <space>',
+'<tab>', and '<newline>' at the beginning and end of the results of the
+previous expansions are ignored, and any sequence of 'IFS' characters
+not at the beginning or end serves to delimit words. If 'IFS' has a
+value other than the default, then sequences of the whitespace
+characters 'space', 'tab', and 'newline' are ignored at the beginning
+and end of the word, as long as the whitespace character is in the value
+of 'IFS' (an 'IFS' whitespace character). Any character in 'IFS' that
+is not 'IFS' whitespace, along with any adjacent 'IFS' whitespace
+characters, delimits a field. A sequence of 'IFS' whitespace characters
+is also treated as a delimiter. If the value of 'IFS' is null, no word
+splitting occurs.
+
+ Explicit null arguments ('""' or '''') are retained and passed to
+commands as empty strings. Unquoted implicit null arguments, resulting
+from the expansion of parameters that have no values, are removed. If a
+parameter with no value is expanded within double quotes, a null
+argument results and is retained and passed to a command as an empty
+string. When a quoted null argument appears as part of a word whose
+expansion is non-null, the null argument is removed. That is, the word
+'-d''' becomes '-d' after word splitting and null argument removal.
+
+ Note that if no expansion occurs, no splitting is performed.
+
+
+File: bash.info, Node: Filename Expansion, Next: Quote Removal, Prev: Word Splitting, Up: Shell Expansions
+
+3.5.8 Filename Expansion
+------------------------
+
+* Menu:
+
+* Pattern Matching:: How the shell matches patterns.
+
+After word splitting, unless the '-f' option has been set (*note The Set
+Builtin::), Bash scans each word for the characters '*', '?', and '['.
+If one of these characters appears, and is not quoted, then the word is
+regarded as a PATTERN, and replaced with an alphabetically sorted list
+of filenames matching the pattern (*note Pattern Matching::). If no
+matching filenames are found, and the shell option 'nullglob' is
+disabled, the word is left unchanged. If the 'nullglob' option is set,
+and no matches are found, the word is removed. If the 'failglob' shell
+option is set, and no matches are found, an error message is printed and
+the command is not executed. If the shell option 'nocaseglob' is
+enabled, the match is performed without regard to the case of alphabetic
+characters.
+
+ When a pattern is used for filename expansion, the character '.' at
+the start of a filename or immediately following a slash must be matched
+explicitly, unless the shell option 'dotglob' is set. In order to match
+the filenames '.' and '..', the pattern must begin with '.' (for
+example, '.?'), even if 'dotglob' is set. If the 'globskipdots' shell
+option is enabled, the filenames '.' and '..' are never matched, even if
+the pattern begins with a '.'. When not matching filenames, the '.'
+character is not treated specially.
+
+ When matching a filename, the slash character must always be matched
+explicitly by a slash in the pattern, but in other matching contexts it
+can be matched by a special pattern character as described below (*note
+Pattern Matching::).
+
+ See the description of 'shopt' in *note The Shopt Builtin::, for a
+description of the 'nocaseglob', 'nullglob', 'globskipdots', 'failglob',
+and 'dotglob' options.
+
+ The 'GLOBIGNORE' shell variable may be used to restrict the set of
+file names matching a pattern. If 'GLOBIGNORE' is set, each matching
+file name that also matches one of the patterns in 'GLOBIGNORE' is
+removed from the list of matches. If the 'nocaseglob' option is set,
+the matching against the patterns in 'GLOBIGNORE' is performed without
+regard to case. The filenames '.' and '..' are always ignored when
+'GLOBIGNORE' is set and not null. However, setting 'GLOBIGNORE' to a
+non-null value has the effect of enabling the 'dotglob' shell option, so
+all other filenames beginning with a '.' will match. To get the old
+behavior of ignoring filenames beginning with a '.', make '.*' one of
+the patterns in 'GLOBIGNORE'. The 'dotglob' option is disabled when
+'GLOBIGNORE' is unset.
+
+
+File: bash.info, Node: Pattern Matching, Up: Filename Expansion
+
+3.5.8.1 Pattern Matching
+........................
+
+Any character that appears in a pattern, other than the special pattern
+characters described below, matches itself. The NUL character may not
+occur in a pattern. A backslash escapes the following character; the
+escaping backslash is discarded when matching. The special pattern
+characters must be quoted if they are to be matched literally.
+
+ The special pattern characters have the following meanings:
+'*'
+ Matches any string, including the null string. When the 'globstar'
+ shell option is enabled, and '*' is used in a filename expansion
+ context, two adjacent '*'s used as a single pattern will match all
+ files and zero or more directories and subdirectories. If followed
+ by a '/', two adjacent '*'s will match only directories and
+ subdirectories.
+'?'
+ Matches any single character.
+'[...]'
+ Matches any one of the enclosed characters. A pair of characters
+ separated by a hyphen denotes a RANGE EXPRESSION; any character
+ that falls between those two characters, inclusive, using the
+ current locale's collating sequence and character set, is matched.
+ If the first character following the '[' is a '!' or a '^' then any
+ character not enclosed is matched. A '-' may be matched by
+ including it as the first or last character in the set. A ']' may
+ be matched by including it as the first character in the set. The
+ sorting order of characters in range expressions, and the
+ characters included in the range, are determined by the current
+ locale and the values of the 'LC_COLLATE' and 'LC_ALL' shell
+ variables, if set.
+
+ For example, in the default C locale, '[a-dx-z]' is equivalent to
+ '[abcdxyz]'. Many locales sort characters in dictionary order, and
+ in these locales '[a-dx-z]' is typically not equivalent to
+ '[abcdxyz]'; it might be equivalent to '[aBbCcDdxYyZz]', for
+ example. To obtain the traditional interpretation of ranges in
+ bracket expressions, you can force the use of the C locale by
+ setting the 'LC_COLLATE' or 'LC_ALL' environment variable to the
+ value 'C', or enable the 'globasciiranges' shell option.
+
+ Within '[' and ']', "character classes" can be specified using the
+ syntax '[:'CLASS':]', where CLASS is one of the following classes
+ defined in the POSIX standard:
+ alnum alpha ascii blank cntrl digit graph lower
+ print punct space upper word xdigit
+ A character class matches any character belonging to that class.
+ The 'word' character class matches letters, digits, and the
+ character '_'.
+
+ Within '[' and ']', an "equivalence class" can be specified using
+ the syntax '[='C'=]', which matches all characters with the same
+ collation weight (as defined by the current locale) as the
+ character C.
+
+ Within '[' and ']', the syntax '[.'SYMBOL'.]' matches the collating
+ symbol SYMBOL.
+
+ If the 'extglob' shell option is enabled using the 'shopt' builtin,
+the shell recognizes several extended pattern matching operators. In
+the following description, a PATTERN-LIST is a list of one or more
+patterns separated by a '|'. When matching filenames, the 'dotglob'
+shell option determines the set of filenames that are tested, as
+described above. Composite patterns may be formed using one or more of
+the following sub-patterns:
+
+'?(PATTERN-LIST)'
+ Matches zero or one occurrence of the given patterns.
+
+'*(PATTERN-LIST)'
+ Matches zero or more occurrences of the given patterns.
+
+'+(PATTERN-LIST)'
+ Matches one or more occurrences of the given patterns.
+
+'@(PATTERN-LIST)'
+ Matches one of the given patterns.
+
+'!(PATTERN-LIST)'
+ Matches anything except one of the given patterns.
+
+ The 'extglob' option changes the behavior of the parser, since the
+parentheses are normally treated as operators with syntactic meaning.
+To ensure that extended matching patterns are parsed correctly, make
+sure that 'extglob' is enabled before parsing constructs containing the
+patterns, including shell functions and command substitutions.
+
+ When matching filenames, the 'dotglob' shell option determines the
+set of filenames that are tested: when 'dotglob' is enabled, the set of
+filenames includes all files beginning with '.', but the filenames '.'
+and '..' must be matched by a pattern or sub-pattern that begins with a
+dot; when it is disabled, the set does not include any filenames
+beginning with "." unless the pattern or sub-pattern begins with a '.'.
+As above, '.' only has a special meaning when matching filenames.
+
+ Complicated extended pattern matching against long strings is slow,
+especially when the patterns contain alternations and the strings
+contain multiple matches. Using separate matches against shorter
+strings, or using arrays of strings instead of a single long string, may
+be faster.
+
+
+File: bash.info, Node: Quote Removal, Prev: Filename Expansion, Up: Shell Expansions
+
+3.5.9 Quote Removal
+-------------------
+
+After the preceding expansions, all unquoted occurrences of the
+characters '\', ''', and '"' that did not result from one of the above
+expansions are removed.
+
+
+File: bash.info, Node: Redirections, Next: Executing Commands, Prev: Shell Expansions, Up: Basic Shell Features
+
+3.6 Redirections
+================
+
+Before a command is executed, its input and output may be "redirected"
+using a special notation interpreted by the shell. "Redirection" allows
+commands' file handles to be duplicated, opened, closed, made to refer
+to different files, and can change the files the command reads from and
+writes to. Redirection may also be used to modify file handles in the
+current shell execution environment. The following redirection
+operators may precede or appear anywhere within a simple command or may
+follow a command. Redirections are processed in the order they appear,
+from left to right.
+
+ Each redirection that may be preceded by a file descriptor number may
+instead be preceded by a word of the form {VARNAME}. In this case, for
+each redirection operator except >&- and <&-, the shell will allocate a
+file descriptor greater than 10 and assign it to {VARNAME}. If >&- or
+<&- is preceded by {VARNAME}, the value of VARNAME defines the file
+descriptor to close. If {VARNAME} is supplied, the redirection persists
+beyond the scope of the command, allowing the shell programmer to manage
+the file descriptor's lifetime manually. The 'varredir_close' shell
+option manages this behavior (*note The Shopt Builtin::).
+
+ In the following descriptions, if the file descriptor number is
+omitted, and the first character of the redirection operator is '<', the
+redirection refers to the standard input (file descriptor 0). If the
+first character of the redirection operator is '>', the redirection
+refers to the standard output (file descriptor 1).
+
+ The word following the redirection operator in the following
+descriptions, unless otherwise noted, is subjected to brace expansion,
+tilde expansion, parameter expansion, command substitution, arithmetic
+expansion, quote removal, filename expansion, and word splitting. If it
+expands to more than one word, Bash reports an error.
+
+ Note that the order of redirections is significant. For example, the
+command
+ ls > DIRLIST 2>&1
+directs both standard output (file descriptor 1) and standard error
+(file descriptor 2) to the file DIRLIST, while the command
+ ls 2>&1 > DIRLIST
+directs only the standard output to file DIRLIST, because the standard
+error was made a copy of the standard output before the standard output
+was redirected to DIRLIST.
+
+ Bash handles several filenames specially when they are used in
+redirections, as described in the following table. If the operating
+system on which Bash is running provides these special files, bash will
+use them; otherwise it will emulate them internally with the behavior
+described below.
+
+'/dev/fd/FD'
+ If FD is a valid integer, file descriptor FD is duplicated.
+
+'/dev/stdin'
+ File descriptor 0 is duplicated.
+
+'/dev/stdout'
+ File descriptor 1 is duplicated.
+
+'/dev/stderr'
+ File descriptor 2 is duplicated.
+
+'/dev/tcp/HOST/PORT'
+ If HOST is a valid hostname or Internet address, and PORT is an
+ integer port number or service name, Bash attempts to open the
+ corresponding TCP socket.
+
+'/dev/udp/HOST/PORT'
+ If HOST is a valid hostname or Internet address, and PORT is an
+ integer port number or service name, Bash attempts to open the
+ corresponding UDP socket.
+
+ A failure to open or create a file causes the redirection to fail.
+
+ Redirections using file descriptors greater than 9 should be used
+with care, as they may conflict with file descriptors the shell uses
+internally.
+
+3.6.1 Redirecting Input
+-----------------------
+
+Redirection of input causes the file whose name results from the
+expansion of WORD to be opened for reading on file descriptor 'n', or
+the standard input (file descriptor 0) if 'n' is not specified.
+
+ The general format for redirecting input is:
+ [N]<WORD
+
+3.6.2 Redirecting Output
+------------------------
+
+Redirection of output causes the file whose name results from the
+expansion of WORD to be opened for writing on file descriptor N, or the
+standard output (file descriptor 1) if N is not specified. If the file
+does not exist it is created; if it does exist it is truncated to zero
+size.
+
+ The general format for redirecting output is:
+ [N]>[|]WORD
+
+ If the redirection operator is '>', and the 'noclobber' option to the
+'set' builtin has been enabled, the redirection will fail if the file
+whose name results from the expansion of WORD exists and is a regular
+file. If the redirection operator is '>|', or the redirection operator
+is '>' and the 'noclobber' option is not enabled, the redirection is
+attempted even if the file named by WORD exists.
+
+3.6.3 Appending Redirected Output
+---------------------------------
+
+Redirection of output in this fashion causes the file whose name results
+from the expansion of WORD to be opened for appending on file descriptor
+N, or the standard output (file descriptor 1) if N is not specified. If
+the file does not exist it is created.
+
+ The general format for appending output is:
+ [N]>>WORD
+
+3.6.4 Redirecting Standard Output and Standard Error
+----------------------------------------------------
+
+This construct allows both the standard output (file descriptor 1) and
+the standard error output (file descriptor 2) to be redirected to the
+file whose name is the expansion of WORD.
+
+ There are two formats for redirecting standard output and standard
+error:
+ &>WORD
+and
+ >&WORD
+Of the two forms, the first is preferred. This is semantically
+equivalent to
+ >WORD 2>&1
+ When using the second form, WORD may not expand to a number or '-'.
+If it does, other redirection operators apply (see Duplicating File
+Descriptors below) for compatibility reasons.
+
+3.6.5 Appending Standard Output and Standard Error
+--------------------------------------------------
+
+This construct allows both the standard output (file descriptor 1) and
+the standard error output (file descriptor 2) to be appended to the file
+whose name is the expansion of WORD.
+
+ The format for appending standard output and standard error is:
+ &>>WORD
+This is semantically equivalent to
+ >>WORD 2>&1
+ (see Duplicating File Descriptors below).
+
+3.6.6 Here Documents
+--------------------
+
+This type of redirection instructs the shell to read input from the
+current source until a line containing only WORD (with no trailing
+blanks) is seen. All of the lines read up to that point are then used
+as the standard input (or file descriptor N if N is specified) for a
+command.
+
+ The format of here-documents is:
+ [N]<<[-]WORD
+ HERE-DOCUMENT
+ DELIMITER
+
+ No parameter and variable expansion, command substitution, arithmetic
+expansion, or filename expansion is performed on WORD. If any part of
+WORD is quoted, the DELIMITER is the result of quote removal on WORD,
+and the lines in the here-document are not expanded. If WORD is
+unquoted, all lines of the here-document are subjected to parameter
+expansion, command substitution, and arithmetic expansion, the character
+sequence '\newline' is ignored, and '\' must be used to quote the
+characters '\', '$', and '`'.
+
+ If the redirection operator is '<<-', then all leading tab characters
+are stripped from input lines and the line containing DELIMITER. This
+allows here-documents within shell scripts to be indented in a natural
+fashion.
+
+3.6.7 Here Strings
+------------------
+
+A variant of here documents, the format is:
+ [N]<<< WORD
+
+ The WORD undergoes tilde expansion, parameter and variable expansion,
+command substitution, arithmetic expansion, and quote removal. Filename
+expansion and word splitting are not performed. The result is supplied
+as a single string, with a newline appended, to the command on its
+standard input (or file descriptor N if N is specified).
+
+3.6.8 Duplicating File Descriptors
+----------------------------------
+
+The redirection operator
+ [N]<&WORD
+is used to duplicate input file descriptors. If WORD expands to one or
+more digits, the file descriptor denoted by N is made to be a copy of
+that file descriptor. If the digits in WORD do not specify a file
+descriptor open for input, a redirection error occurs. If WORD
+evaluates to '-', file descriptor N is closed. If N is not specified,
+the standard input (file descriptor 0) is used.
+
+ The operator
+ [N]>&WORD
+is used similarly to duplicate output file descriptors. If N is not
+specified, the standard output (file descriptor 1) is used. If the
+digits in WORD do not specify a file descriptor open for output, a
+redirection error occurs. If WORD evaluates to '-', file descriptor N
+is closed. As a special case, if N is omitted, and WORD does not expand
+to one or more digits or '-', the standard output and standard error are
+redirected as described previously.
+
+3.6.9 Moving File Descriptors
+-----------------------------
+
+The redirection operator
+ [N]<&DIGIT-
+moves the file descriptor DIGIT to file descriptor N, or the standard
+input (file descriptor 0) if N is not specified. DIGIT is closed after
+being duplicated to N.
+
+ Similarly, the redirection operator
+ [N]>&DIGIT-
+moves the file descriptor DIGIT to file descriptor N, or the standard
+output (file descriptor 1) if N is not specified.
+
+3.6.10 Opening File Descriptors for Reading and Writing
+-------------------------------------------------------
+
+The redirection operator
+ [N]<>WORD
+causes the file whose name is the expansion of WORD to be opened for
+both reading and writing on file descriptor N, or on file descriptor 0
+if N is not specified. If the file does not exist, it is created.
+
+
+File: bash.info, Node: Executing Commands, Next: Shell Scripts, Prev: Redirections, Up: Basic Shell Features
+
+3.7 Executing Commands
+======================
+
+* Menu:
+
+* Simple Command Expansion:: How Bash expands simple commands before
+ executing them.
+* Command Search and Execution:: How Bash finds commands and runs them.
+* Command Execution Environment:: The environment in which Bash
+ executes commands that are not
+ shell builtins.
+* Environment:: The environment given to a command.
+* Exit Status:: The status returned by commands and how Bash
+ interprets it.
+* Signals:: What happens when Bash or a command it runs
+ receives a signal.
+
+
+File: bash.info, Node: Simple Command Expansion, Next: Command Search and Execution, Up: Executing Commands
+
+3.7.1 Simple Command Expansion
+------------------------------
+
+When a simple command is executed, the shell performs the following
+expansions, assignments, and redirections, from left to right, in the
+following order.
+
+ 1. The words that the parser has marked as variable assignments (those
+ preceding the command name) and redirections are saved for later
+ processing.
+
+ 2. The words that are not variable assignments or redirections are
+ expanded (*note Shell Expansions::). If any words remain after
+ expansion, the first word is taken to be the name of the command
+ and the remaining words are the arguments.
+
+ 3. Redirections are performed as described above (*note
+ Redirections::).
+
+ 4. The text after the '=' in each variable assignment undergoes tilde
+ expansion, parameter expansion, command substitution, arithmetic
+ expansion, and quote removal before being assigned to the variable.
+
+ If no command name results, the variable assignments affect the
+current shell environment. In the case of such a command (one that
+consists only of assignment statements and redirections), assignment
+statements are performed before redirections. Otherwise, the variables
+are added to the environment of the executed command and do not affect
+the current shell environment. If any of the assignments attempts to
+assign a value to a readonly variable, an error occurs, and the command
+exits with a non-zero status.
+
+ If no command name results, redirections are performed, but do not
+affect the current shell environment. A redirection error causes the
+command to exit with a non-zero status.
+
+ If there is a command name left after expansion, execution proceeds
+as described below. Otherwise, the command exits. If one of the
+expansions contained a command substitution, the exit status of the
+command is the exit status of the last command substitution performed.
+If there were no command substitutions, the command exits with a status
+of zero.
+
+
+File: bash.info, Node: Command Search and Execution, Next: Command Execution Environment, Prev: Simple Command Expansion, Up: Executing Commands
+
+3.7.2 Command Search and Execution
+----------------------------------
+
+After a command has been split into words, if it results in a simple
+command and an optional list of arguments, the following actions are
+taken.
+
+ 1. If the command name contains no slashes, the shell attempts to
+ locate it. If there exists a shell function by that name, that
+ function is invoked as described in *note Shell Functions::.
+
+ 2. If the name does not match a function, the shell searches for it in
+ the list of shell builtins. If a match is found, that builtin is
+ invoked.
+
+ 3. If the name is neither a shell function nor a builtin, and contains
+ no slashes, Bash searches each element of '$PATH' for a directory
+ containing an executable file by that name. Bash uses a hash table
+ to remember the full pathnames of executable files to avoid
+ multiple 'PATH' searches (see the description of 'hash' in *note
+ Bourne Shell Builtins::). A full search of the directories in
+ '$PATH' is performed only if the command is not found in the hash
+ table. If the search is unsuccessful, the shell searches for a
+ defined shell function named 'command_not_found_handle'. If that
+ function exists, it is invoked in a separate execution environment
+ with the original command and the original command's arguments as
+ its arguments, and the function's exit status becomes the exit
+ status of that subshell. If that function is not defined, the
+ shell prints an error message and returns an exit status of 127.
+
+ 4. If the search is successful, or if the command name contains one or
+ more slashes, the shell executes the named program in a separate
+ execution environment. Argument 0 is set to the name given, and
+ the remaining arguments to the command are set to the arguments
+ supplied, if any.
+
+ 5. If this execution fails because the file is not in executable
+ format, and the file is not a directory, it is assumed to be a
+ "shell script" and the shell executes it as described in *note
+ Shell Scripts::.
+
+ 6. If the command was not begun asynchronously, the shell waits for
+ the command to complete and collects its exit status.
+
+
+File: bash.info, Node: Command Execution Environment, Next: Environment, Prev: Command Search and Execution, Up: Executing Commands
+
+3.7.3 Command Execution Environment
+-----------------------------------
+
+The shell has an "execution environment", which consists of the
+following:
+
+ * open files inherited by the shell at invocation, as modified by
+ redirections supplied to the 'exec' builtin
+
+ * the current working directory as set by 'cd', 'pushd', or 'popd',
+ or inherited by the shell at invocation
+
+ * the file creation mode mask as set by 'umask' or inherited from the
+ shell's parent
+
+ * current traps set by 'trap'
+
+ * shell parameters that are set by variable assignment or with 'set'
+ or inherited from the shell's parent in the environment
+
+ * shell functions defined during execution or inherited from the
+ shell's parent in the environment
+
+ * options enabled at invocation (either by default or with
+ command-line arguments) or by 'set'
+
+ * options enabled by 'shopt' (*note The Shopt Builtin::)
+
+ * shell aliases defined with 'alias' (*note Aliases::)
+
+ * various process IDs, including those of background jobs (*note
+ Lists::), the value of '$$', and the value of '$PPID'
+
+ When a simple command other than a builtin or shell function is to be
+executed, it is invoked in a separate execution environment that
+consists of the following. Unless otherwise noted, the values are
+inherited from the shell.
+
+ * the shell's open files, plus any modifications and additions
+ specified by redirections to the command
+
+ * the current working directory
+
+ * the file creation mode mask
+
+ * shell variables and functions marked for export, along with
+ variables exported for the command, passed in the environment
+ (*note Environment::)
+
+ * traps caught by the shell are reset to the values inherited from
+ the shell's parent, and traps ignored by the shell are ignored
+
+ A command invoked in this separate environment cannot affect the
+shell's execution environment.
+
+ A "subshell" is a copy of the shell process.
+
+ Command substitution, commands grouped with parentheses, and
+asynchronous commands are invoked in a subshell environment that is a
+duplicate of the shell environment, except that traps caught by the
+shell are reset to the values that the shell inherited from its parent
+at invocation. Builtin commands that are invoked as part of a pipeline
+are also executed in a subshell environment. Changes made to the
+subshell environment cannot affect the shell's execution environment.
+
+ Subshells spawned to execute command substitutions inherit the value
+of the '-e' option from the parent shell. When not in POSIX mode, Bash
+clears the '-e' option in such subshells.
+
+ If a command is followed by a '&' and job control is not active, the
+default standard input for the command is the empty file '/dev/null'.
+Otherwise, the invoked command inherits the file descriptors of the
+calling shell as modified by redirections.
+
+
+File: bash.info, Node: Environment, Next: Exit Status, Prev: Command Execution Environment, Up: Executing Commands
+
+3.7.4 Environment
+-----------------
+
+When a program is invoked it is given an array of strings called the
+"environment". This is a list of name-value pairs, of the form
+'name=value'.
+
+ Bash provides several ways to manipulate the environment. On
+invocation, the shell scans its own environment and creates a parameter
+for each name found, automatically marking it for 'export' to child
+processes. Executed commands inherit the environment. The 'export' and
+'declare -x' commands allow parameters and functions to be added to and
+deleted from the environment. If the value of a parameter in the
+environment is modified, the new value becomes part of the environment,
+replacing the old. The environment inherited by any executed command
+consists of the shell's initial environment, whose values may be
+modified in the shell, less any pairs removed by the 'unset' and 'export
+-n' commands, plus any additions via the 'export' and 'declare -x'
+commands.
+
+ The environment for any simple command or function may be augmented
+temporarily by prefixing it with parameter assignments, as described in
+*note Shell Parameters::. These assignment statements affect only the
+environment seen by that command.
+
+ If the '-k' option is set (*note The Set Builtin::), then all
+parameter assignments are placed in the environment for a command, not
+just those that precede the command name.
+
+ When Bash invokes an external command, the variable '$_' is set to
+the full pathname of the command and passed to that command in its
+environment.
+
+
+File: bash.info, Node: Exit Status, Next: Signals, Prev: Environment, Up: Executing Commands
+
+3.7.5 Exit Status
+-----------------
+
+The exit status of an executed command is the value returned by the
+'waitpid' system call or equivalent function. Exit statuses fall
+between 0 and 255, though, as explained below, the shell may use values
+above 125 specially. Exit statuses from shell builtins and compound
+commands are also limited to this range. Under certain circumstances,
+the shell will use special values to indicate specific failure modes.
+
+ For the shell's purposes, a command which exits with a zero exit
+status has succeeded. A non-zero exit status indicates failure. This
+seemingly counter-intuitive scheme is used so there is one well-defined
+way to indicate success and a variety of ways to indicate various
+failure modes. When a command terminates on a fatal signal whose number
+is N, Bash uses the value 128+N as the exit status.
+
+ If a command is not found, the child process created to execute it
+returns a status of 127. If a command is found but is not executable,
+the return status is 126.
+
+ If a command fails because of an error during expansion or
+redirection, the exit status is greater than zero.
+
+ The exit status is used by the Bash conditional commands (*note
+Conditional Constructs::) and some of the list constructs (*note
+Lists::).
+
+ All of the Bash builtins return an exit status of zero if they
+succeed and a non-zero status on failure, so they may be used by the
+conditional and list constructs. All builtins return an exit status of
+2 to indicate incorrect usage, generally invalid options or missing
+arguments.
+
+ The exit status of the last command is available in the special
+parameter $? (*note Special Parameters::).
+
+
+File: bash.info, Node: Signals, Prev: Exit Status, Up: Executing Commands
+
+3.7.6 Signals
+-------------
+
+When Bash is interactive, in the absence of any traps, it ignores
+'SIGTERM' (so that 'kill 0' does not kill an interactive shell), and
+'SIGINT' is caught and handled (so that the 'wait' builtin is
+interruptible). When Bash receives a 'SIGINT', it breaks out of any
+executing loops. In all cases, Bash ignores 'SIGQUIT'. If job control
+is in effect (*note Job Control::), Bash ignores 'SIGTTIN', 'SIGTTOU',
+and 'SIGTSTP'.
+
+ Non-builtin commands started by Bash have signal handlers set to the
+values inherited by the shell from its parent. When job control is not
+in effect, asynchronous commands ignore 'SIGINT' and 'SIGQUIT' in
+addition to these inherited handlers. Commands run as a result of
+command substitution ignore the keyboard-generated job control signals
+'SIGTTIN', 'SIGTTOU', and 'SIGTSTP'.
+
+ The shell exits by default upon receipt of a 'SIGHUP'. Before
+exiting, an interactive shell resends the 'SIGHUP' to all jobs, running
+or stopped. Stopped jobs are sent 'SIGCONT' to ensure that they receive
+the 'SIGHUP'. To prevent the shell from sending the 'SIGHUP' signal to
+a particular job, it should be removed from the jobs table with the
+'disown' builtin (*note Job Control Builtins::) or marked to not receive
+'SIGHUP' using 'disown -h'.
+
+ If the 'huponexit' shell option has been set with 'shopt' (*note The
+Shopt Builtin::), Bash sends a 'SIGHUP' to all jobs when an interactive
+login shell exits.
+
+ If Bash is waiting for a command to complete and receives a signal
+for which a trap has been set, the trap will not be executed until the
+command completes. When Bash is waiting for an asynchronous command via
+the 'wait' builtin, the reception of a signal for which a trap has been
+set will cause the 'wait' builtin to return immediately with an exit
+status greater than 128, immediately after which the trap is executed.
+
+ When job control is not enabled, and Bash is waiting for a foreground
+command to complete, the shell receives keyboard-generated signals such
+as 'SIGINT' (usually generated by '^C') that users commonly intend to
+send to that command. This happens because the shell and the command
+are in the same process group as the terminal, and '^C' sends 'SIGINT'
+to all processes in that process group. See *note Job Control::, for a
+more in-depth discussion of process groups.
+
+ When Bash is running without job control enabled and receives
+'SIGINT' while waiting for a foreground command, it waits until that
+foreground command terminates and then decides what to do about the
+'SIGINT':
+
+ 1. If the command terminates due to the 'SIGINT', Bash concludes that
+ the user meant to end the entire script, and acts on the 'SIGINT'
+ (e.g., by running a 'SIGINT' trap or exiting itself);
+
+ 2. If the pipeline does not terminate due to 'SIGINT', the program
+ handled the 'SIGINT' itself and did not treat it as a fatal signal.
+ In that case, Bash does not treat 'SIGINT' as a fatal signal,
+ either, instead assuming that the 'SIGINT' was used as part of the
+ program's normal operation (e.g., 'emacs' uses it to abort editing
+ commands) or deliberately discarded. However, Bash will run any
+ trap set on 'SIGINT', as it does with any other trapped signal it
+ receives while it is waiting for the foreground command to
+ complete, for compatibility.
+
+
+File: bash.info, Node: Shell Scripts, Prev: Executing Commands, Up: Basic Shell Features
+
+3.8 Shell Scripts
+=================
+
+A shell script is a text file containing shell commands. When such a
+file is used as the first non-option argument when invoking Bash, and
+neither the '-c' nor '-s' option is supplied (*note Invoking Bash::),
+Bash reads and executes commands from the file, then exits. This mode
+of operation creates a non-interactive shell. The shell first searches
+for the file in the current directory, and looks in the directories in
+'$PATH' if not found there.
+
+ When Bash runs a shell script, it sets the special parameter '0' to
+the name of the file, rather than the name of the shell, and the
+positional parameters are set to the remaining arguments, if any are
+given. If no additional arguments are supplied, the positional
+parameters are unset.
+
+ A shell script may be made executable by using the 'chmod' command to
+turn on the execute bit. When Bash finds such a file while searching
+the '$PATH' for a command, it creates a new instance of itself to
+execute it. In other words, executing
+ filename ARGUMENTS
+is equivalent to executing
+ bash filename ARGUMENTS
+
+if 'filename' is an executable shell script. This subshell
+reinitializes itself, so that the effect is as if a new shell had been
+invoked to interpret the script, with the exception that the locations
+of commands remembered by the parent (see the description of 'hash' in
+*note Bourne Shell Builtins::) are retained by the child.
+
+ Most versions of Unix make this a part of the operating system's
+command execution mechanism. If the first line of a script begins with
+the two characters '#!', the remainder of the line specifies an
+interpreter for the program and, depending on the operating system, one
+or more optional arguments for that interpreter. Thus, you can specify
+Bash, 'awk', Perl, or some other interpreter and write the rest of the
+script file in that language.
+
+ The arguments to the interpreter consist of one or more optional
+arguments following the interpreter name on the first line of the script
+file, followed by the name of the script file, followed by the rest of
+the arguments supplied to the script. The details of how the
+interpreter line is split into an interpreter name and a set of
+arguments vary across systems. Bash will perform this action on
+operating systems that do not handle it themselves. Note that some
+older versions of Unix limit the interpreter name and a single argument
+to a maximum of 32 characters, so it's not portable to assume that using
+more than one argument will work.
+
+ Bash scripts often begin with '#! /bin/bash' (assuming that Bash has
+been installed in '/bin'), since this ensures that Bash will be used to
+interpret the script, even if it is executed under another shell. It's
+a common idiom to use 'env' to find 'bash' even if it's been installed
+in another directory: '#!/usr/bin/env bash' will find the first
+occurrence of 'bash' in '$PATH'.
+
+
+File: bash.info, Node: Shell Builtin Commands, Next: Shell Variables, Prev: Basic Shell Features, Up: Top
+
+4 Shell Builtin Commands
+************************
+
+* Menu:
+
+* Bourne Shell Builtins:: Builtin commands inherited from the Bourne
+ Shell.
+* Bash Builtins:: Table of builtins specific to Bash.
+* Modifying Shell Behavior:: Builtins to modify shell attributes and
+ optional behavior.
+* Special Builtins:: Builtin commands classified specially by
+ POSIX.
+
+Builtin commands are contained within the shell itself. When the name
+of a builtin command is used as the first word of a simple command
+(*note Simple Commands::), the shell executes the command directly,
+without invoking another program. Builtin commands are necessary to
+implement functionality impossible or inconvenient to obtain with
+separate utilities.
+
+ This section briefly describes the builtins which Bash inherits from
+the Bourne Shell, as well as the builtin commands which are unique to or
+have been extended in Bash.
+
+ Several builtin commands are described in other chapters: builtin
+commands which provide the Bash interface to the job control facilities
+(*note Job Control Builtins::), the directory stack (*note Directory
+Stack Builtins::), the command history (*note Bash History Builtins::),
+and the programmable completion facilities (*note Programmable
+Completion Builtins::).
+
+ Many of the builtins have been extended by POSIX or Bash.
+
+ Unless otherwise noted, each builtin command documented as accepting
+options preceded by '-' accepts '--' to signify the end of the options.
+The ':', 'true', 'false', and 'test'/'[' builtins do not accept options
+and do not treat '--' specially. The 'exit', 'logout', 'return',
+'break', 'continue', 'let', and 'shift' builtins accept and process
+arguments beginning with '-' without requiring '--'. Other builtins
+that accept arguments but are not specified as accepting options
+interpret arguments beginning with '-' as invalid options and require
+'--' to prevent this interpretation.
+
+
+File: bash.info, Node: Bourne Shell Builtins, Next: Bash Builtins, Up: Shell Builtin Commands
+
+4.1 Bourne Shell Builtins
+=========================
+
+The following shell builtin commands are inherited from the Bourne
+Shell. These commands are implemented as specified by the POSIX
+standard.
+
+': (a colon)'
+ : [ARGUMENTS]
+
+ Do nothing beyond expanding ARGUMENTS and performing redirections.
+ The return status is zero.
+
+'. (a period)'
+ . FILENAME [ARGUMENTS]
+
+ Read and execute commands from the FILENAME argument in the current
+ shell context. If FILENAME does not contain a slash, the 'PATH'
+ variable is used to find FILENAME, but FILENAME does not need to be
+ executable. When Bash is not in POSIX mode, it searches the
+ current directory if FILENAME is not found in '$PATH'. If any
+ ARGUMENTS are supplied, they become the positional parameters when
+ FILENAME is executed. Otherwise the positional parameters are
+ unchanged. If the '-T' option is enabled, '.' inherits any trap on
+ 'DEBUG'; if it is not, any 'DEBUG' trap string is saved and
+ restored around the call to '.', and '.' unsets the 'DEBUG' trap
+ while it executes. If '-T' is not set, and the sourced file
+ changes the 'DEBUG' trap, the new value is retained when '.'
+ completes. The return status is the exit status of the last
+ command executed, or zero if no commands are executed. If FILENAME
+ is not found, or cannot be read, the return status is non-zero.
+ This builtin is equivalent to 'source'.
+
+'break'
+ break [N]
+
+ Exit from a 'for', 'while', 'until', or 'select' loop. If N is
+ supplied, the Nth enclosing loop is exited. N must be greater than
+ or equal to 1. The return status is zero unless N is not greater
+ than or equal to 1.
+
+'cd'
+ cd [-L|[-P [-e]] [-@] [DIRECTORY]
+
+ Change the current working directory to DIRECTORY. If DIRECTORY is
+ not supplied, the value of the 'HOME' shell variable is used. If
+ the shell variable 'CDPATH' exists, it is used as a search path:
+ each directory name in 'CDPATH' is searched for DIRECTORY, with
+ alternative directory names in 'CDPATH' separated by a colon (':').
+ If DIRECTORY begins with a slash, 'CDPATH' is not used.
+
+ The '-P' option means to not follow symbolic links: symbolic links
+ are resolved while 'cd' is traversing DIRECTORY and before
+ processing an instance of '..' in DIRECTORY.
+
+ By default, or when the '-L' option is supplied, symbolic links in
+ DIRECTORY are resolved after 'cd' processes an instance of '..' in
+ DIRECTORY.
+
+ If '..' appears in DIRECTORY, it is processed by removing the
+ immediately preceding pathname component, back to a slash or the
+ beginning of DIRECTORY.
+
+ If the '-e' option is supplied with '-P' and the current working
+ directory cannot be successfully determined after a successful
+ directory change, 'cd' will return an unsuccessful status.
+
+ On systems that support it, the '-@' option presents the extended
+ attributes associated with a file as a directory.
+
+ If DIRECTORY is '-', it is converted to '$OLDPWD' before the
+ directory change is attempted.
+
+ If a non-empty directory name from 'CDPATH' is used, or if '-' is
+ the first argument, and the directory change is successful, the
+ absolute pathname of the new working directory is written to the
+ standard output.
+
+ If the directory change is successful, 'cd' sets the value of the
+ 'PWD' environment variable to the new directory name, and sets the
+ 'OLDPWD' environment variable to the value of the current working
+ directory before the change.
+
+ The return status is zero if the directory is successfully changed,
+ non-zero otherwise.
+
+'continue'
+ continue [N]
+
+ Resume the next iteration of an enclosing 'for', 'while', 'until',
+ or 'select' loop. If N is supplied, the execution of the Nth
+ enclosing loop is resumed. N must be greater than or equal to 1.
+ The return status is zero unless N is not greater than or equal to
+ 1.
+
+'eval'
+ eval [ARGUMENTS]
+
+ The arguments are concatenated together into a single command,
+ which is then read and executed, and its exit status returned as
+ the exit status of 'eval'. If there are no arguments or only empty
+ arguments, the return status is zero.
+
+'exec'
+ exec [-cl] [-a NAME] [COMMAND [ARGUMENTS]]
+
+ If COMMAND is supplied, it replaces the shell without creating a
+ new process. If the '-l' option is supplied, the shell places a
+ dash at the beginning of the zeroth argument passed to COMMAND.
+ This is what the 'login' program does. The '-c' option causes
+ COMMAND to be executed with an empty environment. If '-a' is
+ supplied, the shell passes NAME as the zeroth argument to COMMAND.
+ If COMMAND cannot be executed for some reason, a non-interactive
+ shell exits, unless the 'execfail' shell option is enabled. In
+ that case, it returns failure. An interactive shell returns
+ failure if the file cannot be executed. A subshell exits
+ unconditionally if 'exec' fails. If no COMMAND is specified,
+ redirections may be used to affect the current shell environment.
+ If there are no redirection errors, the return status is zero;
+ otherwise the return status is non-zero.
+
+'exit'
+ exit [N]
+
+ Exit the shell, returning a status of N to the shell's parent. If
+ N is omitted, the exit status is that of the last command executed.
+ Any trap on 'EXIT' is executed before the shell terminates.
+
+'export'
+ export [-fn] [-p] [NAME[=VALUE]]
+
+ Mark each NAME to be passed to child processes in the environment.
+ If the '-f' option is supplied, the NAMEs refer to shell functions;
+ otherwise the names refer to shell variables. The '-n' option
+ means to no longer mark each NAME for export. If no NAMEs are
+ supplied, or if the '-p' option is given, a list of names of all
+ exported variables is displayed. The '-p' option displays output
+ in a form that may be reused as input. If a variable name is
+ followed by =VALUE, the value of the variable is set to VALUE.
+
+ The return status is zero unless an invalid option is supplied, one
+ of the names is not a valid shell variable name, or '-f' is
+ supplied with a name that is not a shell function.
+
+'getopts'
+ getopts OPTSTRING NAME [ARG ...]
+
+ 'getopts' is used by shell scripts to parse positional parameters.
+ OPTSTRING contains the option characters to be recognized; if a
+ character is followed by a colon, the option is expected to have an
+ argument, which should be separated from it by whitespace. The
+ colon (':') and question mark ('?') may not be used as option
+ characters. Each time it is invoked, 'getopts' places the next
+ option in the shell variable NAME, initializing NAME if it does not
+ exist, and the index of the next argument to be processed into the
+ variable 'OPTIND'. 'OPTIND' is initialized to 1 each time the
+ shell or a shell script is invoked. When an option requires an
+ argument, 'getopts' places that argument into the variable
+ 'OPTARG'. The shell does not reset 'OPTIND' automatically; it must
+ be manually reset between multiple calls to 'getopts' within the
+ same shell invocation if a new set of parameters is to be used.
+
+ When the end of options is encountered, 'getopts' exits with a
+ return value greater than zero. 'OPTIND' is set to the index of
+ the first non-option argument, and NAME is set to '?'.
+
+ 'getopts' normally parses the positional parameters, but if more
+ arguments are supplied as ARG values, 'getopts' parses those
+ instead.
+
+ 'getopts' can report errors in two ways. If the first character of
+ OPTSTRING is a colon, SILENT error reporting is used. In normal
+ operation, diagnostic messages are printed when invalid options or
+ missing option arguments are encountered. If the variable 'OPTERR'
+ is set to 0, no error messages will be displayed, even if the first
+ character of 'optstring' is not a colon.
+
+ If an invalid option is seen, 'getopts' places '?' into NAME and,
+ if not silent, prints an error message and unsets 'OPTARG'. If
+ 'getopts' is silent, the option character found is placed in
+ 'OPTARG' and no diagnostic message is printed.
+
+ If a required argument is not found, and 'getopts' is not silent, a
+ question mark ('?') is placed in NAME, 'OPTARG' is unset, and a
+ diagnostic message is printed. If 'getopts' is silent, then a
+ colon (':') is placed in NAME and 'OPTARG' is set to the option
+ character found.
+
+'hash'
+ hash [-r] [-p FILENAME] [-dt] [NAME]
+
+ Each time 'hash' is invoked, it remembers the full pathnames of the
+ commands specified as NAME arguments, so they need not be searched
+ for on subsequent invocations. The commands are found by searching
+ through the directories listed in '$PATH'. Any
+ previously-remembered pathname is discarded. The '-p' option
+ inhibits the path search, and FILENAME is used as the location of
+ NAME. The '-r' option causes the shell to forget all remembered
+ locations. The '-d' option causes the shell to forget the
+ remembered location of each NAME. If the '-t' option is supplied,
+ the full pathname to which each NAME corresponds is printed. If
+ multiple NAME arguments are supplied with '-t', the NAME is printed
+ before the hashed full pathname. The '-l' option causes output to
+ be displayed in a format that may be reused as input. If no
+ arguments are given, or if only '-l' is supplied, information about
+ remembered commands is printed. The return status is zero unless a
+ NAME is not found or an invalid option is supplied.
+
+'pwd'
+ pwd [-LP]
+
+ Print the absolute pathname of the current working directory. If
+ the '-P' option is supplied, the pathname printed will not contain
+ symbolic links. If the '-L' option is supplied, the pathname
+ printed may contain symbolic links. The return status is zero
+ unless an error is encountered while determining the name of the
+ current directory or an invalid option is supplied.
+
+'readonly'
+ readonly [-aAf] [-p] [NAME[=VALUE]] ...
+
+ Mark each NAME as readonly. The values of these names may not be
+ changed by subsequent assignment. If the '-f' option is supplied,
+ each NAME refers to a shell function. The '-a' option means each
+ NAME refers to an indexed array variable; the '-A' option means
+ each NAME refers to an associative array variable. If both options
+ are supplied, '-A' takes precedence. If no NAME arguments are
+ given, or if the '-p' option is supplied, a list of all readonly
+ names is printed. The other options may be used to restrict the
+ output to a subset of the set of readonly names. The '-p' option
+ causes output to be displayed in a format that may be reused as
+ input. If a variable name is followed by =VALUE, the value of the
+ variable is set to VALUE. The return status is zero unless an
+ invalid option is supplied, one of the NAME arguments is not a
+ valid shell variable or function name, or the '-f' option is
+ supplied with a name that is not a shell function.
+
+'return'
+ return [N]
+
+ Cause a shell function to stop executing and return the value N to
+ its caller. If N is not supplied, the return value is the exit
+ status of the last command executed in the function. If 'return'
+ is executed by a trap handler, the last command used to determine
+ the status is the last command executed before the trap handler.
+ If 'return' is executed during a 'DEBUG' trap, the last command
+ used to determine the status is the last command executed by the
+ trap handler before 'return' was invoked. 'return' may also be
+ used to terminate execution of a script being executed with the '.'
+ ('source') builtin, returning either N or the exit status of the
+ last command executed within the script as the exit status of the
+ script. If N is supplied, the return value is its least
+ significant 8 bits. Any command associated with the 'RETURN' trap
+ is executed before execution resumes after the function or script.
+ The return status is non-zero if 'return' is supplied a non-numeric
+ argument or is used outside a function and not during the execution
+ of a script by '.' or 'source'.
+
+'shift'
+ shift [N]
+
+ Shift the positional parameters to the left by N. The positional
+ parameters from N+1 ... '$#' are renamed to '$1' ... '$#'-N.
+ Parameters represented by the numbers '$#' down to '$#'-N+1 are
+ unset. N must be a non-negative number less than or equal to '$#'.
+ If N is zero or greater than '$#', the positional parameters are
+ not changed. If N is not supplied, it is assumed to be 1. The
+ return status is zero unless N is greater than '$#' or less than
+ zero, non-zero otherwise.
+
+'test'
+'['
+ test EXPR
+
+ Evaluate a conditional expression EXPR and return a status of 0
+ (true) or 1 (false). Each operator and operand must be a separate
+ argument. Expressions are composed of the primaries described
+ below in *note Bash Conditional Expressions::. 'test' does not
+ accept any options, nor does it accept and ignore an argument of
+ '--' as signifying the end of options.
+
+ When the '[' form is used, the last argument to the command must be
+ a ']'.
+
+ Expressions may be combined using the following operators, listed
+ in decreasing order of precedence. The evaluation depends on the
+ number of arguments; see below. Operator precedence is used when
+ there are five or more arguments.
+
+ '! EXPR'
+ True if EXPR is false.
+
+ '( EXPR )'
+ Returns the value of EXPR. This may be used to override the
+ normal precedence of operators.
+
+ 'EXPR1 -a EXPR2'
+ True if both EXPR1 and EXPR2 are true.
+
+ 'EXPR1 -o EXPR2'
+ True if either EXPR1 or EXPR2 is true.
+
+ The 'test' and '[' builtins evaluate conditional expressions using
+ a set of rules based on the number of arguments.
+
+ 0 arguments
+ The expression is false.
+
+ 1 argument
+ The expression is true if, and only if, the argument is not
+ null.
+
+ 2 arguments
+ If the first argument is '!', the expression is true if and
+ only if the second argument is null. If the first argument is
+ one of the unary conditional operators (*note Bash Conditional
+ Expressions::), the expression is true if the unary test is
+ true. If the first argument is not a valid unary operator,
+ the expression is false.
+
+ 3 arguments
+ The following conditions are applied in the order listed.
+
+ 1. If the second argument is one of the binary conditional
+ operators (*note Bash Conditional Expressions::), the
+ result of the expression is the result of the binary test
+ using the first and third arguments as operands. The
+ '-a' and '-o' operators are considered binary operators
+ when there are three arguments.
+ 2. If the first argument is '!', the value is the negation
+ of the two-argument test using the second and third
+ arguments.
+ 3. If the first argument is exactly '(' and the third
+ argument is exactly ')', the result is the one-argument
+ test of the second argument.
+ 4. Otherwise, the expression is false.
+
+ 4 arguments
+ The following conditions are applied in the order listed.
+
+ 1. If the first argument is '!', the result is the negation
+ of the three-argument expression composed of the
+ remaining arguments.
+ 2. If the first argument is exactly '(' and the fourth
+ argument is exactly ')', the result is the two-argument
+ test of the second and third arguments.
+ 3. Otherwise, the expression is parsed and evaluated
+ according to precedence using the rules listed above.
+
+ 5 or more arguments
+ The expression is parsed and evaluated according to precedence
+ using the rules listed above.
+
+ When used with 'test' or '[', the '<' and '>' operators sort
+ lexicographically using ASCII ordering.
+
+'times'
+ times
+
+ Print out the user and system times used by the shell and its
+ children. The return status is zero.
+
+'trap'
+ trap [-lp] [ARG] [SIGSPEC ...]
+
+ The commands in ARG are to be read and executed when the shell
+ receives signal SIGSPEC. If ARG is absent (and there is a single
+ SIGSPEC) or equal to '-', each specified signal's disposition is
+ reset to the value it had when the shell was started. If ARG is
+ the null string, then the signal specified by each SIGSPEC is
+ ignored by the shell and commands it invokes. If ARG is not
+ present and '-p' has been supplied, the shell displays the trap
+ commands associated with each SIGSPEC. If no arguments are
+ supplied, or only '-p' is given, 'trap' prints the list of commands
+ associated with each signal number in a form that may be reused as
+ shell input. The '-l' option causes the shell to print a list of
+ signal names and their corresponding numbers. Each SIGSPEC is
+ either a signal name or a signal number. Signal names are case
+ insensitive and the 'SIG' prefix is optional.
+
+ If a SIGSPEC is '0' or 'EXIT', ARG is executed when the shell
+ exits. If a SIGSPEC is 'DEBUG', the command ARG is executed before
+ every simple command, 'for' command, 'case' command, 'select'
+ command, every arithmetic 'for' command, and before the first
+ command executes in a shell function. Refer to the description of
+ the 'extdebug' option to the 'shopt' builtin (*note The Shopt
+ Builtin::) for details of its effect on the 'DEBUG' trap. If a
+ SIGSPEC is 'RETURN', the command ARG is executed each time a shell
+ function or a script executed with the '.' or 'source' builtins
+ finishes executing.
+
+ If a SIGSPEC is 'ERR', the command ARG is executed whenever a
+ pipeline (which may consist of a single simple command), a list, or
+ a compound command returns a non-zero exit status, subject to the
+ following conditions. The 'ERR' trap is not executed if the failed
+ command is part of the command list immediately following an
+ 'until' or 'while' keyword, part of the test following the 'if' or
+ 'elif' reserved words, part of a command executed in a '&&' or '||'
+ list except the command following the final '&&' or '||', any
+ command in a pipeline but the last, or if the command's return
+ status is being inverted using '!'. These are the same conditions
+ obeyed by the 'errexit' ('-e') option.
+
+ Signals ignored upon entry to the shell cannot be trapped or reset.
+ Trapped signals that are not being ignored are reset to their
+ original values in a subshell or subshell environment when one is
+ created.
+
+ The return status is zero unless a SIGSPEC does not specify a valid
+ signal.
+
+'umask'
+ umask [-p] [-S] [MODE]
+
+ Set the shell process's file creation mask to MODE. If MODE begins
+ with a digit, it is interpreted as an octal number; if not, it is
+ interpreted as a symbolic mode mask similar to that accepted by the
+ 'chmod' command. If MODE is omitted, the current value of the mask
+ is printed. If the '-S' option is supplied without a MODE
+ argument, the mask is printed in a symbolic format. If the '-p'
+ option is supplied, and MODE is omitted, the output is in a form
+ that may be reused as input. The return status is zero if the mode
+ is successfully changed or if no MODE argument is supplied, and
+ non-zero otherwise.
+
+ Note that when the mode is interpreted as an octal number, each
+ number of the umask is subtracted from '7'. Thus, a umask of '022'
+ results in permissions of '755'.
+
+'unset'
+ unset [-fnv] [NAME]
+
+ Remove each variable or function NAME. If the '-v' option is
+ given, each NAME refers to a shell variable and that variable is
+ removed. If the '-f' option is given, the NAMEs refer to shell
+ functions, and the function definition is removed. If the '-n'
+ option is supplied, and NAME is a variable with the 'nameref'
+ attribute, NAME will be unset rather than the variable it
+ references. '-n' has no effect if the '-f' option is supplied. If
+ no options are supplied, each NAME refers to a variable; if there
+ is no variable by that name, a function with that name, if any, is
+ unset. Readonly variables and functions may not be unset. Some
+ shell variables lose their special behavior if they are unset; such
+ behavior is noted in the description of the individual variables.
+ The return status is zero unless a NAME is readonly or may not be
+ unset.
+
+
+File: bash.info, Node: Bash Builtins, Next: Modifying Shell Behavior, Prev: Bourne Shell Builtins, Up: Shell Builtin Commands
+
+4.2 Bash Builtin Commands
+=========================
+
+This section describes builtin commands which are unique to or have been
+extended in Bash. Some of these commands are specified in the POSIX
+standard.
+
+'alias'
+ alias [-p] [NAME[=VALUE] ...]
+
+ Without arguments or with the '-p' option, 'alias' prints the list
+ of aliases on the standard output in a form that allows them to be
+ reused as input. If arguments are supplied, an alias is defined
+ for each NAME whose VALUE is given. If no VALUE is given, the name
+ and value of the alias is printed. Aliases are described in *note
+ Aliases::.
+
+'bind'
+ bind [-m KEYMAP] [-lpsvPSVX]
+ bind [-m KEYMAP] [-q FUNCTION] [-u FUNCTION] [-r KEYSEQ]
+ bind [-m KEYMAP] -f FILENAME
+ bind [-m KEYMAP] -x KEYSEQ:SHELL-COMMAND
+ bind [-m KEYMAP] KEYSEQ:FUNCTION-NAME
+ bind [-m KEYMAP] KEYSEQ:READLINE-COMMAND
+ bind READLINE-COMMAND-LINE
+
+ Display current Readline (*note Command Line Editing::) key and
+ function bindings, bind a key sequence to a Readline function or
+ macro, or set a Readline variable. Each non-option argument is a
+ command as it would appear in a Readline initialization file (*note
+ Readline Init File::), but each binding or command must be passed
+ as a separate argument; e.g., '"\C-x\C-r":re-read-init-file'.
+
+ Options, if supplied, have the following meanings:
+
+ '-m KEYMAP'
+ Use KEYMAP as the keymap to be affected by the subsequent
+ bindings. Acceptable KEYMAP names are 'emacs',
+ 'emacs-standard', 'emacs-meta', 'emacs-ctlx', 'vi', 'vi-move',
+ 'vi-command', and 'vi-insert'. 'vi' is equivalent to
+ 'vi-command' ('vi-move' is also a synonym); 'emacs' is
+ equivalent to 'emacs-standard'.
+
+ '-l'
+ List the names of all Readline functions.
+
+ '-p'
+ Display Readline function names and bindings in such a way
+ that they can be used as input or in a Readline initialization
+ file.
+
+ '-P'
+ List current Readline function names and bindings.
+
+ '-v'
+ Display Readline variable names and values in such a way that
+ they can be used as input or in a Readline initialization
+ file.
+
+ '-V'
+ List current Readline variable names and values.
+
+ '-s'
+ Display Readline key sequences bound to macros and the strings
+ they output in such a way that they can be used as input or in
+ a Readline initialization file.
+
+ '-S'
+ Display Readline key sequences bound to macros and the strings
+ they output.
+
+ '-f FILENAME'
+ Read key bindings from FILENAME.
+
+ '-q FUNCTION'
+ Query about which keys invoke the named FUNCTION.
+
+ '-u FUNCTION'
+ Unbind all keys bound to the named FUNCTION.
+
+ '-r KEYSEQ'
+ Remove any current binding for KEYSEQ.
+
+ '-x KEYSEQ:SHELL-COMMAND'
+ Cause SHELL-COMMAND to be executed whenever KEYSEQ is entered.
+ When SHELL-COMMAND is executed, the shell sets the
+ 'READLINE_LINE' variable to the contents of the Readline line
+ buffer and the 'READLINE_POINT' and 'READLINE_MARK' variables
+ to the current location of the insertion point and the saved
+ insertion point (the MARK), respectively. The shell assigns
+ any numeric argument the user supplied to the
+ 'READLINE_ARGUMENT' variable. If there was no argument, that
+ variable is not set. If the executed command changes the
+ value of any of 'READLINE_LINE', 'READLINE_POINT', or
+ 'READLINE_MARK', those new values will be reflected in the
+ editing state.
+
+ '-X'
+ List all key sequences bound to shell commands and the
+ associated commands in a format that can be reused as input.
+
+ The return status is zero unless an invalid option is supplied or
+ an error occurs.
+
+'builtin'
+ builtin [SHELL-BUILTIN [ARGS]]
+
+ Run a shell builtin, passing it ARGS, and return its exit status.
+ This is useful when defining a shell function with the same name as
+ a shell builtin, retaining the functionality of the builtin within
+ the function. The return status is non-zero if SHELL-BUILTIN is
+ not a shell builtin command.
+
+'caller'
+ caller [EXPR]
+
+ Returns the context of any active subroutine call (a shell function
+ or a script executed with the '.' or 'source' builtins).
+
+ Without EXPR, 'caller' displays the line number and source filename
+ of the current subroutine call. If a non-negative integer is
+ supplied as EXPR, 'caller' displays the line number, subroutine
+ name, and source file corresponding to that position in the current
+ execution call stack. This extra information may be used, for
+ example, to print a stack trace. The current frame is frame 0.
+
+ The return value is 0 unless the shell is not executing a
+ subroutine call or EXPR does not correspond to a valid position in
+ the call stack.
+
+'command'
+ command [-pVv] COMMAND [ARGUMENTS ...]
+
+ Runs COMMAND with ARGUMENTS ignoring any shell function named
+ COMMAND. Only shell builtin commands or commands found by
+ searching the 'PATH' are executed. If there is a shell function
+ named 'ls', running 'command ls' within the function will execute
+ the external command 'ls' instead of calling the function
+ recursively. The '-p' option means to use a default value for
+ 'PATH' that is guaranteed to find all of the standard utilities.
+ The return status in this case is 127 if COMMAND cannot be found or
+ an error occurred, and the exit status of COMMAND otherwise.
+
+ If either the '-V' or '-v' option is supplied, a description of
+ COMMAND is printed. The '-v' option causes a single word
+ indicating the command or file name used to invoke COMMAND to be
+ displayed; the '-V' option produces a more verbose description. In
+ this case, the return status is zero if COMMAND is found, and
+ non-zero if not.
+
+'declare'
+ declare [-aAfFgiIlnrtux] [-p] [NAME[=VALUE] ...]
+
+ Declare variables and give them attributes. If no NAMEs are given,
+ then display the values of variables instead.
+
+ The '-p' option will display the attributes and values of each
+ NAME. When '-p' is used with NAME arguments, additional options,
+ other than '-f' and '-F', are ignored.
+
+ When '-p' is supplied without NAME arguments, 'declare' will
+ display the attributes and values of all variables having the
+ attributes specified by the additional options. If no other
+ options are supplied with '-p', 'declare' will display the
+ attributes and values of all shell variables. The '-f' option will
+ restrict the display to shell functions.
+
+ The '-F' option inhibits the display of function definitions; only
+ the function name and attributes are printed. If the 'extdebug'
+ shell option is enabled using 'shopt' (*note The Shopt Builtin::),
+ the source file name and line number where each NAME is defined are
+ displayed as well. '-F' implies '-f'.
+
+ The '-g' option forces variables to be created or modified at the
+ global scope, even when 'declare' is executed in a shell function.
+ It is ignored in all other cases.
+
+ The '-I' option causes local variables to inherit the attributes
+ (except the 'nameref' attribute) and value of any existing variable
+ with the same NAME at a surrounding scope. If there is no existing
+ variable, the local variable is initially unset.
+
+ The following options can be used to restrict output to variables
+ with the specified attributes or to give variables attributes:
+
+ '-a'
+ Each NAME is an indexed array variable (*note Arrays::).
+
+ '-A'
+ Each NAME is an associative array variable (*note Arrays::).
+
+ '-f'
+ Use function names only.
+
+ '-i'
+ The variable is to be treated as an integer; arithmetic
+ evaluation (*note Shell Arithmetic::) is performed when the
+ variable is assigned a value.
+
+ '-l'
+ When the variable is assigned a value, all upper-case
+ characters are converted to lower-case. The upper-case
+ attribute is disabled.
+
+ '-n'
+ Give each NAME the 'nameref' attribute, making it a name
+ reference to another variable. That other variable is defined
+ by the value of NAME. All references, assignments, and
+ attribute modifications to NAME, except for those using or
+ changing the '-n' attribute itself, are performed on the
+ variable referenced by NAME's value. The nameref attribute
+ cannot be applied to array variables.
+
+ '-r'
+ Make NAMEs readonly. These names cannot then be assigned
+ values by subsequent assignment statements or unset.
+
+ '-t'
+ Give each NAME the 'trace' attribute. Traced functions
+ inherit the 'DEBUG' and 'RETURN' traps from the calling shell.
+ The trace attribute has no special meaning for variables.
+
+ '-u'
+ When the variable is assigned a value, all lower-case
+ characters are converted to upper-case. The lower-case
+ attribute is disabled.
+
+ '-x'
+ Mark each NAME for export to subsequent commands via the
+ environment.
+
+ Using '+' instead of '-' turns off the attribute instead, with the
+ exceptions that '+a' and '+A' may not be used to destroy array
+ variables and '+r' will not remove the readonly attribute. When
+ used in a function, 'declare' makes each NAME local, as with the
+ 'local' command, unless the '-g' option is used. If a variable
+ name is followed by =VALUE, the value of the variable is set to
+ VALUE.
+
+ When using '-a' or '-A' and the compound assignment syntax to
+ create array variables, additional attributes do not take effect
+ until subsequent assignments.
+
+ The return status is zero unless an invalid option is encountered,
+ an attempt is made to define a function using '-f foo=bar', an
+ attempt is made to assign a value to a readonly variable, an
+ attempt is made to assign a value to an array variable without
+ using the compound assignment syntax (*note Arrays::), one of the
+ NAMEs is not a valid shell variable name, an attempt is made to
+ turn off readonly status for a readonly variable, an attempt is
+ made to turn off array status for an array variable, or an attempt
+ is made to display a non-existent function with '-f'.
+
+'echo'
+ echo [-neE] [ARG ...]
+
+ Output the ARGs, separated by spaces, terminated with a newline.
+ The return status is 0 unless a write error occurs. If '-n' is
+ specified, the trailing newline is suppressed. If the '-e' option
+ is given, interpretation of the following backslash-escaped
+ characters is enabled. The '-E' option disables the interpretation
+ of these escape characters, even on systems where they are
+ interpreted by default. The 'xpg_echo' shell option may be used to
+ dynamically determine whether or not 'echo' expands these escape
+ characters by default. 'echo' does not interpret '--' to mean the
+ end of options.
+
+ 'echo' interprets the following escape sequences:
+ '\a'
+ alert (bell)
+ '\b'
+ backspace
+ '\c'
+ suppress further output
+ '\e'
+ '\E'
+ escape
+ '\f'
+ form feed
+ '\n'
+ new line
+ '\r'
+ carriage return
+ '\t'
+ horizontal tab
+ '\v'
+ vertical tab
+ '\\'
+ backslash
+ '\0NNN'
+ the eight-bit character whose value is the octal value NNN
+ (zero to three octal digits)
+ '\xHH'
+ the eight-bit character whose value is the hexadecimal value
+ HH (one or two hex digits)
+ '\uHHHH'
+ the Unicode (ISO/IEC 10646) character whose value is the
+ hexadecimal value HHHH (one to four hex digits)
+ '\UHHHHHHHH'
+ the Unicode (ISO/IEC 10646) character whose value is the
+ hexadecimal value HHHHHHHH (one to eight hex digits)
+
+'enable'
+ enable [-a] [-dnps] [-f FILENAME] [NAME ...]
+
+ Enable and disable builtin shell commands. Disabling a builtin
+ allows a disk command which has the same name as a shell builtin to
+ be executed without specifying a full pathname, even though the
+ shell normally searches for builtins before disk commands. If '-n'
+ is used, the NAMEs become disabled. Otherwise NAMEs are enabled.
+ For example, to use the 'test' binary found via '$PATH' instead of
+ the shell builtin version, type 'enable -n test'.
+
+ If the '-p' option is supplied, or no NAME arguments appear, a list
+ of shell builtins is printed. With no other arguments, the list
+ consists of all enabled shell builtins. The '-a' option means to
+ list each builtin with an indication of whether or not it is
+ enabled.
+
+ The '-f' option means to load the new builtin command NAME from
+ shared object FILENAME, on systems that support dynamic loading.
+ Bash will use the value of the 'BASH_LOADABLES_PATH' variable as a
+ colon-separated list of directories in which to search for
+ FILENAME. The default is system-dependent. The '-d' option will
+ delete a builtin loaded with '-f'.
+
+ If there are no options, a list of the shell builtins is displayed.
+ The '-s' option restricts 'enable' to the POSIX special builtins.
+ If '-s' is used with '-f', the new builtin becomes a special
+ builtin (*note Special Builtins::).
+
+ If no options are supplied and a NAME is not a shell builtin,
+ 'enable' will attempt to load NAME from a shared object named NAME,
+ as if the command were 'enable -f NAME NAME'.
+
+ The return status is zero unless a NAME is not a shell builtin or
+ there is an error loading a new builtin from a shared object.
+
+'help'
+ help [-dms] [PATTERN]
+
+ Display helpful information about builtin commands. If PATTERN is
+ specified, 'help' gives detailed help on all commands matching
+ PATTERN, otherwise a list of the builtins is printed.
+
+ Options, if supplied, have the following meanings:
+
+ '-d'
+ Display a short description of each PATTERN
+ '-m'
+ Display the description of each PATTERN in a manpage-like
+ format
+ '-s'
+ Display only a short usage synopsis for each PATTERN
+
+ The return status is zero unless no command matches PATTERN.
+
+'let'
+ let EXPRESSION [EXPRESSION ...]
+
+ The 'let' builtin allows arithmetic to be performed on shell
+ variables. Each EXPRESSION is evaluated according to the rules
+ given below in *note Shell Arithmetic::. If the last EXPRESSION
+ evaluates to 0, 'let' returns 1; otherwise 0 is returned.
+
+'local'
+ local [OPTION] NAME[=VALUE] ...
+
+ For each argument, a local variable named NAME is created, and
+ assigned VALUE. The OPTION can be any of the options accepted by
+ 'declare'. 'local' can only be used within a function; it makes
+ the variable NAME have a visible scope restricted to that function
+ and its children. If NAME is '-', the set of shell options is made
+ local to the function in which 'local' is invoked: shell options
+ changed using the 'set' builtin inside the function are restored to
+ their original values when the function returns. The restore is
+ effected as if a series of 'set' commands were executed to restore
+ the values that were in place before the function. The return
+ status is zero unless 'local' is used outside a function, an
+ invalid NAME is supplied, or NAME is a readonly variable.
+
+'logout'
+ logout [N]
+
+ Exit a login shell, returning a status of N to the shell's parent.
+
+'mapfile'
+ mapfile [-d DELIM] [-n COUNT] [-O ORIGIN] [-s COUNT]
+ [-t] [-u FD] [-C CALLBACK] [-c QUANTUM] [ARRAY]
+
+ Read lines from the standard input into the indexed array variable
+ ARRAY, or from file descriptor FD if the '-u' option is supplied.
+ The variable 'MAPFILE' is the default ARRAY. Options, if supplied,
+ have the following meanings:
+
+ '-d'
+ The first character of DELIM is used to terminate each input
+ line, rather than newline. If DELIM is the empty string,
+ 'mapfile' will terminate a line when it reads a NUL character.
+ '-n'
+ Copy at most COUNT lines. If COUNT is 0, all lines are
+ copied.
+ '-O'
+ Begin assigning to ARRAY at index ORIGIN. The default index
+ is 0.
+ '-s'
+ Discard the first COUNT lines read.
+ '-t'
+ Remove a trailing DELIM (default newline) from each line read.
+ '-u'
+ Read lines from file descriptor FD instead of the standard
+ input.
+ '-C'
+ Evaluate CALLBACK each time QUANTUM lines are read. The '-c'
+ option specifies QUANTUM.
+ '-c'
+ Specify the number of lines read between each call to
+ CALLBACK.
+
+ If '-C' is specified without '-c', the default quantum is 5000.
+ When CALLBACK is evaluated, it is supplied the index of the next
+ array element to be assigned and the line to be assigned to that
+ element as additional arguments. CALLBACK is evaluated after the
+ line is read but before the array element is assigned.
+
+ If not supplied with an explicit origin, 'mapfile' will clear ARRAY
+ before assigning to it.
+
+ 'mapfile' returns successfully unless an invalid option or option
+ argument is supplied, ARRAY is invalid or unassignable, or ARRAY is
+ not an indexed array.
+
+'printf'
+ printf [-v VAR] FORMAT [ARGUMENTS]
+
+ Write the formatted ARGUMENTS to the standard output under the
+ control of the FORMAT. The '-v' option causes the output to be
+ assigned to the variable VAR rather than being printed to the
+ standard output.
+
+ The FORMAT is a character string which contains three types of
+ objects: plain characters, which are simply copied to standard
+ output, character escape sequences, which are converted and copied
+ to the standard output, and format specifications, each of which
+ causes printing of the next successive ARGUMENT. In addition to
+ the standard 'printf(1)' formats, 'printf' interprets the following
+ extensions:
+
+ '%b'
+ Causes 'printf' to expand backslash escape sequences in the
+ corresponding ARGUMENT in the same way as 'echo -e' (*note
+ Bash Builtins::).
+ '%q'
+ Causes 'printf' to output the corresponding ARGUMENT in a
+ format that can be reused as shell input.
+ '%Q'
+ like '%q', but applies any supplied precision to the ARGUMENT
+ before quoting it.
+ '%(DATEFMT)T'
+ Causes 'printf' to output the date-time string resulting from
+ using DATEFMT as a format string for 'strftime'(3). The
+ corresponding ARGUMENT is an integer representing the number
+ of seconds since the epoch. Two special argument values may
+ be used: -1 represents the current time, and -2 represents the
+ time the shell was invoked. If no argument is specified,
+ conversion behaves as if -1 had been given. This is an
+ exception to the usual 'printf' behavior.
+
+ The %b, %q, and %T directives all use the field width and precision
+ arguments from the format specification and write that many bytes
+ from (or use that wide a field for) the expanded argument, which
+ usually contains more characters than the original.
+
+ Arguments to non-string format specifiers are treated as C language
+ constants, except that a leading plus or minus sign is allowed, and
+ if the leading character is a single or double quote, the value is
+ the ASCII value of the following character.
+
+ The FORMAT is reused as necessary to consume all of the ARGUMENTS.
+ If the FORMAT requires more ARGUMENTS than are supplied, the extra
+ format specifications behave as if a zero value or null string, as
+ appropriate, had been supplied. The return value is zero on
+ success, non-zero on failure.
+
+'read'
+ read [-ers] [-a ANAME] [-d DELIM] [-i TEXT] [-n NCHARS]
+ [-N NCHARS] [-p PROMPT] [-t TIMEOUT] [-u FD] [NAME ...]
+
+ One line is read from the standard input, or from the file
+ descriptor FD supplied as an argument to the '-u' option, split
+ into words as described above in *note Word Splitting::, and the
+ first word is assigned to the first NAME, the second word to the
+ second NAME, and so on. If there are more words than names, the
+ remaining words and their intervening delimiters are assigned to
+ the last NAME. If there are fewer words read from the input stream
+ than names, the remaining names are assigned empty values. The
+ characters in the value of the 'IFS' variable are used to split the
+ line into words using the same rules the shell uses for expansion
+ (described above in *note Word Splitting::). The backslash
+ character '\' may be used to remove any special meaning for the
+ next character read and for line continuation.
+
+ Options, if supplied, have the following meanings:
+
+ '-a ANAME'
+ The words are assigned to sequential indices of the array
+ variable ANAME, starting at 0. All elements are removed from
+ ANAME before the assignment. Other NAME arguments are
+ ignored.
+
+ '-d DELIM'
+ The first character of DELIM is used to terminate the input
+ line, rather than newline. If DELIM is the empty string,
+ 'read' will terminate a line when it reads a NUL character.
+
+ '-e'
+ Readline (*note Command Line Editing::) is used to obtain the
+ line. Readline uses the current (or default, if line editing
+ was not previously active) editing settings, but uses
+ Readline's default filename completion.
+
+ '-i TEXT'
+ If Readline is being used to read the line, TEXT is placed
+ into the editing buffer before editing begins.
+
+ '-n NCHARS'
+ 'read' returns after reading NCHARS characters rather than
+ waiting for a complete line of input, but honors a delimiter
+ if fewer than NCHARS characters are read before the delimiter.
+
+ '-N NCHARS'
+ 'read' returns after reading exactly NCHARS characters rather
+ than waiting for a complete line of input, unless EOF is
+ encountered or 'read' times out. Delimiter characters
+ encountered in the input are not treated specially and do not
+ cause 'read' to return until NCHARS characters are read. The
+ result is not split on the characters in 'IFS'; the intent is
+ that the variable is assigned exactly the characters read
+ (with the exception of backslash; see the '-r' option below).
+
+ '-p PROMPT'
+ Display PROMPT, without a trailing newline, before attempting
+ to read any input. The prompt is displayed only if input is
+ coming from a terminal.
+
+ '-r'
+ If this option is given, backslash does not act as an escape
+ character. The backslash is considered to be part of the
+ line. In particular, a backslash-newline pair may not then be
+ used as a line continuation.
+
+ '-s'
+ Silent mode. If input is coming from a terminal, characters
+ are not echoed.
+
+ '-t TIMEOUT'
+ Cause 'read' to time out and return failure if a complete line
+ of input (or a specified number of characters) is not read
+ within TIMEOUT seconds. TIMEOUT may be a decimal number with
+ a fractional portion following the decimal point. This option
+ is only effective if 'read' is reading input from a terminal,
+ pipe, or other special file; it has no effect when reading
+ from regular files. If 'read' times out, 'read' saves any
+ partial input read into the specified variable NAME. If
+ TIMEOUT is 0, 'read' returns immediately, without trying to
+ read any data. The exit status is 0 if input is available on
+ the specified file descriptor, or the read will return EOF,
+ non-zero otherwise. The exit status is greater than 128 if
+ the timeout is exceeded.
+
+ '-u FD'
+ Read input from file descriptor FD.
+
+ If no NAMEs are supplied, the line read, without the ending
+ delimiter but otherwise unmodified, is assigned to the variable
+ 'REPLY'. The exit status is zero, unless end-of-file is
+ encountered, 'read' times out (in which case the status is greater
+ than 128), a variable assignment error (such as assigning to a
+ readonly variable) occurs, or an invalid file descriptor is
+ supplied as the argument to '-u'.
+
+'readarray'
+ readarray [-d DELIM] [-n COUNT] [-O ORIGIN] [-s COUNT]
+ [-t] [-u FD] [-C CALLBACK] [-c QUANTUM] [ARRAY]
+
+ Read lines from the standard input into the indexed array variable
+ ARRAY, or from file descriptor FD if the '-u' option is supplied.
+
+ A synonym for 'mapfile'.
+
+'source'
+ source FILENAME
+
+ A synonym for '.' (*note Bourne Shell Builtins::).
+
+'type'
+ type [-afptP] [NAME ...]
+
+ For each NAME, indicate how it would be interpreted if used as a
+ command name.
+
+ If the '-t' option is used, 'type' prints a single word which is
+ one of 'alias', 'function', 'builtin', 'file' or 'keyword', if NAME
+ is an alias, shell function, shell builtin, disk file, or shell
+ reserved word, respectively. If the NAME is not found, then
+ nothing is printed, and 'type' returns a failure status.
+
+ If the '-p' option is used, 'type' either returns the name of the
+ disk file that would be executed, or nothing if '-t' would not
+ return 'file'.
+
+ The '-P' option forces a path search for each NAME, even if '-t'
+ would not return 'file'.
+
+ If a command is hashed, '-p' and '-P' print the hashed value, which
+ is not necessarily the file that appears first in '$PATH'.
+
+ If the '-a' option is used, 'type' returns all of the places that
+ contain an executable named FILE. This includes aliases and
+ functions, if and only if the '-p' option is not also used.
+
+ If the '-f' option is used, 'type' does not attempt to find shell
+ functions, as with the 'command' builtin.
+
+ The return status is zero if all of the NAMEs are found, non-zero
+ if any are not found.
+
+'typeset'
+ typeset [-afFgrxilnrtux] [-p] [NAME[=VALUE] ...]
+
+ The 'typeset' command is supplied for compatibility with the Korn
+ shell. It is a synonym for the 'declare' builtin command.
+
+'ulimit'
+ ulimit [-HS] -a
+ ulimit [-HS] [-bcdefiklmnpqrstuvxPRT] [LIMIT]
+
+ 'ulimit' provides control over the resources available to processes
+ started by the shell, on systems that allow such control. If an
+ option is given, it is interpreted as follows:
+
+ '-S'
+ Change and report the soft limit associated with a resource.
+
+ '-H'
+ Change and report the hard limit associated with a resource.
+
+ '-a'
+ All current limits are reported; no limits are set.
+
+ '-b'
+ The maximum socket buffer size.
+
+ '-c'
+ The maximum size of core files created.
+
+ '-d'
+ The maximum size of a process's data segment.
+
+ '-e'
+ The maximum scheduling priority ("nice").
+
+ '-f'
+ The maximum size of files written by the shell and its
+ children.
+
+ '-i'
+ The maximum number of pending signals.
+
+ '-k'
+ The maximum number of kqueues that may be allocated.
+
+ '-l'
+ The maximum size that may be locked into memory.
+
+ '-m'
+ The maximum resident set size (many systems do not honor this
+ limit).
+
+ '-n'
+ The maximum number of open file descriptors (most systems do
+ not allow this value to be set).
+
+ '-p'
+ The pipe buffer size.
+
+ '-q'
+ The maximum number of bytes in POSIX message queues.
+
+ '-r'
+ The maximum real-time scheduling priority.
+
+ '-s'
+ The maximum stack size.
+
+ '-t'
+ The maximum amount of cpu time in seconds.
+
+ '-u'
+ The maximum number of processes available to a single user.
+
+ '-v'
+ The maximum amount of virtual memory available to the shell,
+ and, on some systems, to its children.
+
+ '-x'
+ The maximum number of file locks.
+
+ '-P'
+ The maximum number of pseudoterminals.
+
+ '-R'
+ The maximum time a real-time process can run before blocking,
+ in microseconds.
+
+ '-T'
+ The maximum number of threads.
+
+ If LIMIT is given, and the '-a' option is not used, LIMIT is the
+ new value of the specified resource. The special LIMIT values
+ 'hard', 'soft', and 'unlimited' stand for the current hard limit,
+ the current soft limit, and no limit, respectively. A hard limit
+ cannot be increased by a non-root user once it is set; a soft limit
+ may be increased up to the value of the hard limit. Otherwise, the
+ current value of the soft limit for the specified resource is
+ printed, unless the '-H' option is supplied. When more than one
+ resource is specified, the limit name and unit, if appropriate, are
+ printed before the value. When setting new limits, if neither '-H'
+ nor '-S' is supplied, both the hard and soft limits are set. If no
+ option is given, then '-f' is assumed. Values are in 1024-byte
+ increments, except for '-t', which is in seconds; '-R', which is in
+ microseconds; '-p', which is in units of 512-byte blocks; '-P',
+ '-T', '-b', '-k', '-n' and '-u', which are unscaled values; and,
+ when in POSIX Mode (*note Bash POSIX Mode::), '-c' and '-f', which
+ are in 512-byte increments.
+
+ The return status is zero unless an invalid option or argument is
+ supplied, or an error occurs while setting a new limit.
+
+'unalias'
+ unalias [-a] [NAME ... ]
+
+ Remove each NAME from the list of aliases. If '-a' is supplied,
+ all aliases are removed. Aliases are described in *note Aliases::.
+
+
+File: bash.info, Node: Modifying Shell Behavior, Next: Special Builtins, Prev: Bash Builtins, Up: Shell Builtin Commands
+
+4.3 Modifying Shell Behavior
+============================
+
+* Menu:
+
+* The Set Builtin:: Change the values of shell attributes and
+ positional parameters.
+* The Shopt Builtin:: Modify shell optional behavior.
+
+
+File: bash.info, Node: The Set Builtin, Next: The Shopt Builtin, Up: Modifying Shell Behavior
+
+4.3.1 The Set Builtin
+---------------------
+
+This builtin is so complicated that it deserves its own section. 'set'
+allows you to change the values of shell options and set the positional
+parameters, or to display the names and values of shell variables.
+
+'set'
+ set [-abefhkmnptuvxBCEHPT] [-o OPTION-NAME] [--] [-] [ARGUMENT ...]
+ set [+abefhkmnptuvxBCEHPT] [+o OPTION-NAME] [--] [-] [ARGUMENT ...]
+
+ If no options or arguments are supplied, 'set' displays the names
+ and values of all shell variables and functions, sorted according
+ to the current locale, in a format that may be reused as input for
+ setting or resetting the currently-set variables. Read-only
+ variables cannot be reset. In POSIX mode, only shell variables are
+ listed.
+
+ When options are supplied, they set or unset shell attributes.
+ Options, if specified, have the following meanings:
+
+ '-a'
+ Each variable or function that is created or modified is given
+ the export attribute and marked for export to the environment
+ of subsequent commands.
+
+ '-b'
+ Cause the status of terminated background jobs to be reported
+ immediately, rather than before printing the next primary
+ prompt.
+
+ '-e'
+ Exit immediately if a pipeline (*note Pipelines::), which may
+ consist of a single simple command (*note Simple Commands::),
+ a list (*note Lists::), or a compound command (*note Compound
+ Commands::) returns a non-zero status. The shell does not
+ exit if the command that fails is part of the command list
+ immediately following a 'while' or 'until' keyword, part of
+ the test in an 'if' statement, part of any command executed in
+ a '&&' or '||' list except the command following the final
+ '&&' or '||', any command in a pipeline but the last, or if
+ the command's return status is being inverted with '!'. If a
+ compound command other than a subshell returns a non-zero
+ status because a command failed while '-e' was being ignored,
+ the shell does not exit. A trap on 'ERR', if set, is executed
+ before the shell exits.
+
+ This option applies to the shell environment and each subshell
+ environment separately (*note Command Execution
+ Environment::), and may cause subshells to exit before
+ executing all the commands in the subshell.
+
+ If a compound command or shell function executes in a context
+ where '-e' is being ignored, none of the commands executed
+ within the compound command or function body will be affected
+ by the '-e' setting, even if '-e' is set and a command returns
+ a failure status. If a compound command or shell function
+ sets '-e' while executing in a context where '-e' is ignored,
+ that setting will not have any effect until the compound
+ command or the command containing the function call completes.
+
+ '-f'
+ Disable filename expansion (globbing).
+
+ '-h'
+ Locate and remember (hash) commands as they are looked up for
+ execution. This option is enabled by default.
+
+ '-k'
+ All arguments in the form of assignment statements are placed
+ in the environment for a command, not just those that precede
+ the command name.
+
+ '-m'
+ Job control is enabled (*note Job Control::). All processes
+ run in a separate process group. When a background job
+ completes, the shell prints a line containing its exit status.
+
+ '-n'
+ Read commands but do not execute them. This may be used to
+ check a script for syntax errors. This option is ignored by
+ interactive shells.
+
+ '-o OPTION-NAME'
+
+ Set the option corresponding to OPTION-NAME:
+
+ 'allexport'
+ Same as '-a'.
+
+ 'braceexpand'
+ Same as '-B'.
+
+ 'emacs'
+ Use an 'emacs'-style line editing interface (*note
+ Command Line Editing::). This also affects the editing
+ interface used for 'read -e'.
+
+ 'errexit'
+ Same as '-e'.
+
+ 'errtrace'
+ Same as '-E'.
+
+ 'functrace'
+ Same as '-T'.
+
+ 'hashall'
+ Same as '-h'.
+
+ 'histexpand'
+ Same as '-H'.
+
+ 'history'
+ Enable command history, as described in *note Bash
+ History Facilities::. This option is on by default in
+ interactive shells.
+
+ 'ignoreeof'
+ An interactive shell will not exit upon reading EOF.
+
+ 'keyword'
+ Same as '-k'.
+
+ 'monitor'
+ Same as '-m'.
+
+ 'noclobber'
+ Same as '-C'.
+
+ 'noexec'
+ Same as '-n'.
+
+ 'noglob'
+ Same as '-f'.
+
+ 'nolog'
+ Currently ignored.
+
+ 'notify'
+ Same as '-b'.
+
+ 'nounset'
+ Same as '-u'.
+
+ 'onecmd'
+ Same as '-t'.
+
+ 'physical'
+ Same as '-P'.
+
+ 'pipefail'
+ If set, the return value of a pipeline is the value of
+ the last (rightmost) command to exit with a non-zero
+ status, or zero if all commands in the pipeline exit
+ successfully. This option is disabled by default.
+
+ 'posix'
+ Change the behavior of Bash where the default operation
+ differs from the POSIX standard to match the standard
+ (*note Bash POSIX Mode::). This is intended to make Bash
+ behave as a strict superset of that standard.
+
+ 'privileged'
+ Same as '-p'.
+
+ 'verbose'
+ Same as '-v'.
+
+ 'vi'
+ Use a 'vi'-style line editing interface. This also
+ affects the editing interface used for 'read -e'.
+
+ 'xtrace'
+ Same as '-x'.
+
+ '-p'
+ Turn on privileged mode. In this mode, the '$BASH_ENV' and
+ '$ENV' files are not processed, shell functions are not
+ inherited from the environment, and the 'SHELLOPTS',
+ 'BASHOPTS', 'CDPATH' and 'GLOBIGNORE' variables, if they
+ appear in the environment, are ignored. If the shell is
+ started with the effective user (group) id not equal to the
+ real user (group) id, and the '-p' option is not supplied,
+ these actions are taken and the effective user id is set to
+ the real user id. If the '-p' option is supplied at startup,
+ the effective user id is not reset. Turning this option off
+ causes the effective user and group ids to be set to the real
+ user and group ids.
+
+ '-r'
+ Enable restricted shell mode. This option cannot be unset
+ once it has been set.
+
+ '-t'
+ Exit after reading and executing one command.
+
+ '-u'
+ Treat unset variables and parameters other than the special
+ parameters '@' or '*', or array variables subscripted with '@'
+ or '*', as an error when performing parameter expansion. An
+ error message will be written to the standard error, and a
+ non-interactive shell will exit.
+
+ '-v'
+ Print shell input lines as they are read.
+
+ '-x'
+ Print a trace of simple commands, 'for' commands, 'case'
+ commands, 'select' commands, and arithmetic 'for' commands and
+ their arguments or associated word lists after they are
+ expanded and before they are executed. The value of the 'PS4'
+ variable is expanded and the resultant value is printed before
+ the command and its expanded arguments.
+
+ '-B'
+ The shell will perform brace expansion (*note Brace
+ Expansion::). This option is on by default.
+
+ '-C'
+ Prevent output redirection using '>', '>&', and '<>' from
+ overwriting existing files.
+
+ '-E'
+ If set, any trap on 'ERR' is inherited by shell functions,
+ command substitutions, and commands executed in a subshell
+ environment. The 'ERR' trap is normally not inherited in such
+ cases.
+
+ '-H'
+ Enable '!' style history substitution (*note History
+ Interaction::). This option is on by default for interactive
+ shells.
+
+ '-P'
+ If set, do not resolve symbolic links when performing commands
+ such as 'cd' which change the current directory. The physical
+ directory is used instead. By default, Bash follows the
+ logical chain of directories when performing commands which
+ change the current directory.
+
+ For example, if '/usr/sys' is a symbolic link to
+ '/usr/local/sys' then:
+ $ cd /usr/sys; echo $PWD
+ /usr/sys
+ $ cd ..; pwd
+ /usr
+
+ If 'set -P' is on, then:
+ $ cd /usr/sys; echo $PWD
+ /usr/local/sys
+ $ cd ..; pwd
+ /usr/local
+
+ '-T'
+ If set, any trap on 'DEBUG' and 'RETURN' are inherited by
+ shell functions, command substitutions, and commands executed
+ in a subshell environment. The 'DEBUG' and 'RETURN' traps are
+ normally not inherited in such cases.
+
+ '--'
+ If no arguments follow this option, then the positional
+ parameters are unset. Otherwise, the positional parameters
+ are set to the ARGUMENTS, even if some of them begin with a
+ '-'.
+
+ '-'
+ Signal the end of options, cause all remaining ARGUMENTS to be
+ assigned to the positional parameters. The '-x' and '-v'
+ options are turned off. If there are no arguments, the
+ positional parameters remain unchanged.
+
+ Using '+' rather than '-' causes these options to be turned off.
+ The options can also be used upon invocation of the shell. The
+ current set of options may be found in '$-'.
+
+ The remaining N ARGUMENTS are positional parameters and are
+ assigned, in order, to '$1', '$2', ... '$N'. The special parameter
+ '#' is set to N.
+
+ The return status is always zero unless an invalid option is
+ supplied.
+
+
+File: bash.info, Node: The Shopt Builtin, Prev: The Set Builtin, Up: Modifying Shell Behavior
+
+4.3.2 The Shopt Builtin
+-----------------------
+
+This builtin allows you to change additional shell optional behavior.
+
+'shopt'
+ shopt [-pqsu] [-o] [OPTNAME ...]
+
+ Toggle the values of settings controlling optional shell behavior.
+ The settings can be either those listed below, or, if the '-o'
+ option is used, those available with the '-o' option to the 'set'
+ builtin command (*note The Set Builtin::). With no options, or
+ with the '-p' option, a list of all settable options is displayed,
+ with an indication of whether or not each is set; if OPTNAMEs are
+ supplied, the output is restricted to those options. The '-p'
+ option causes output to be displayed in a form that may be reused
+ as input. Other options have the following meanings:
+
+ '-s'
+ Enable (set) each OPTNAME.
+
+ '-u'
+ Disable (unset) each OPTNAME.
+
+ '-q'
+ Suppresses normal output; the return status indicates whether
+ the OPTNAME is set or unset. If multiple OPTNAME arguments
+ are given with '-q', the return status is zero if all OPTNAMEs
+ are enabled; non-zero otherwise.
+
+ '-o'
+ Restricts the values of OPTNAME to be those defined for the
+ '-o' option to the 'set' builtin (*note The Set Builtin::).
+
+ If either '-s' or '-u' is used with no OPTNAME arguments, 'shopt'
+ shows only those options which are set or unset, respectively.
+
+ Unless otherwise noted, the 'shopt' options are disabled (off) by
+ default.
+
+ The return status when listing options is zero if all OPTNAMEs are
+ enabled, non-zero otherwise. When setting or unsetting options,
+ the return status is zero unless an OPTNAME is not a valid shell
+ option.
+
+ The list of 'shopt' options is:
+
+ 'assoc_expand_once'
+ If set, the shell suppresses multiple evaluation of
+ associative array subscripts during arithmetic expression
+ evaluation, while executing builtins that can perform variable
+ assignments, and while executing builtins that perform array
+ dereferencing.
+
+ 'autocd'
+ If set, a command name that is the name of a directory is
+ executed as if it were the argument to the 'cd' command. This
+ option is only used by interactive shells.
+
+ 'cdable_vars'
+ If this is set, an argument to the 'cd' builtin command that
+ is not a directory is assumed to be the name of a variable
+ whose value is the directory to change to.
+
+ 'cdspell'
+ If set, minor errors in the spelling of a directory component
+ in a 'cd' command will be corrected. The errors checked for
+ are transposed characters, a missing character, and a
+ character too many. If a correction is found, the corrected
+ path is printed, and the command proceeds. This option is
+ only used by interactive shells.
+
+ 'checkhash'
+ If this is set, Bash checks that a command found in the hash
+ table exists before trying to execute it. If a hashed command
+ no longer exists, a normal path search is performed.
+
+ 'checkjobs'
+ If set, Bash lists the status of any stopped and running jobs
+ before exiting an interactive shell. If any jobs are running,
+ this causes the exit to be deferred until a second exit is
+ attempted without an intervening command (*note Job
+ Control::). The shell always postpones exiting if any jobs
+ are stopped.
+
+ 'checkwinsize'
+ If set, Bash checks the window size after each external
+ (non-builtin) command and, if necessary, updates the values of
+ 'LINES' and 'COLUMNS'. This option is enabled by default.
+
+ 'cmdhist'
+ If set, Bash attempts to save all lines of a multiple-line
+ command in the same history entry. This allows easy
+ re-editing of multi-line commands. This option is enabled by
+ default, but only has an effect if command history is enabled
+ (*note Bash History Facilities::).
+
+ 'compat31'
+ 'compat32'
+ 'compat40'
+ 'compat41'
+ 'compat42'
+ 'compat43'
+ 'compat44'
+ These control aspects of the shell's compatibility mode (*note
+ Shell Compatibility Mode::).
+
+ 'complete_fullquote'
+ If set, Bash quotes all shell metacharacters in filenames and
+ directory names when performing completion. If not set, Bash
+ removes metacharacters such as the dollar sign from the set of
+ characters that will be quoted in completed filenames when
+ these metacharacters appear in shell variable references in
+ words to be completed. This means that dollar signs in
+ variable names that expand to directories will not be quoted;
+ however, any dollar signs appearing in filenames will not be
+ quoted, either. This is active only when bash is using
+ backslashes to quote completed filenames. This variable is
+ set by default, which is the default Bash behavior in versions
+ through 4.2.
+
+ 'direxpand'
+ If set, Bash replaces directory names with the results of word
+ expansion when performing filename completion. This changes
+ the contents of the Readline editing buffer. If not set, Bash
+ attempts to preserve what the user typed.
+
+ 'dirspell'
+ If set, Bash attempts spelling correction on directory names
+ during word completion if the directory name initially
+ supplied does not exist.
+
+ 'dotglob'
+ If set, Bash includes filenames beginning with a '.' in the
+ results of filename expansion. The filenames '.' and '..'
+ must always be matched explicitly, even if 'dotglob' is set.
+
+ 'execfail'
+ If this is set, a non-interactive shell will not exit if it
+ cannot execute the file specified as an argument to the 'exec'
+ builtin command. An interactive shell does not exit if 'exec'
+ fails.
+
+ 'expand_aliases'
+ If set, aliases are expanded as described below under Aliases,
+ *note Aliases::. This option is enabled by default for
+ interactive shells.
+
+ 'extdebug'
+ If set at shell invocation, or in a shell startup file,
+ arrange to execute the debugger profile before the shell
+ starts, identical to the '--debugger' option. If set after
+ invocation, behavior intended for use by debuggers is enabled:
+
+ 1. The '-F' option to the 'declare' builtin (*note Bash
+ Builtins::) displays the source file name and line number
+ corresponding to each function name supplied as an
+ argument.
+
+ 2. If the command run by the 'DEBUG' trap returns a non-zero
+ value, the next command is skipped and not executed.
+
+ 3. If the command run by the 'DEBUG' trap returns a value of
+ 2, and the shell is executing in a subroutine (a shell
+ function or a shell script executed by the '.' or
+ 'source' builtins), the shell simulates a call to
+ 'return'.
+
+ 4. 'BASH_ARGC' and 'BASH_ARGV' are updated as described in
+ their descriptions (*note Bash Variables::).
+
+ 5. Function tracing is enabled: command substitution, shell
+ functions, and subshells invoked with '( COMMAND )'
+ inherit the 'DEBUG' and 'RETURN' traps.
+
+ 6. Error tracing is enabled: command substitution, shell
+ functions, and subshells invoked with '( COMMAND )'
+ inherit the 'ERR' trap.
+
+ 'extglob'
+ If set, the extended pattern matching features described above
+ (*note Pattern Matching::) are enabled.
+
+ 'extquote'
+ If set, '$'STRING'' and '$"STRING"' quoting is performed
+ within '${PARAMETER}' expansions enclosed in double quotes.
+ This option is enabled by default.
+
+ 'failglob'
+ If set, patterns which fail to match filenames during filename
+ expansion result in an expansion error.
+
+ 'force_fignore'
+ If set, the suffixes specified by the 'FIGNORE' shell variable
+ cause words to be ignored when performing word completion even
+ if the ignored words are the only possible completions. *Note
+ Bash Variables::, for a description of 'FIGNORE'. This option
+ is enabled by default.
+
+ 'globasciiranges'
+ If set, range expressions used in pattern matching bracket
+ expressions (*note Pattern Matching::) behave as if in the
+ traditional C locale when performing comparisons. That is,
+ the current locale's collating sequence is not taken into
+ account, so 'b' will not collate between 'A' and 'B', and
+ upper-case and lower-case ASCII characters will collate
+ together.
+
+ 'globskipdots'
+ If set, filename expansion will never match the filenames '.'
+ and '..', even if the pattern begins with a '.'. This option
+ is enabled by default.
+
+ 'globstar'
+ If set, the pattern '**' used in a filename expansion context
+ will match all files and zero or more directories and
+ subdirectories. If the pattern is followed by a '/', only
+ directories and subdirectories match.
+
+ 'gnu_errfmt'
+ If set, shell error messages are written in the standard GNU
+ error message format.
+
+ 'histappend'
+ If set, the history list is appended to the file named by the
+ value of the 'HISTFILE' variable when the shell exits, rather
+ than overwriting the file.
+
+ 'histreedit'
+ If set, and Readline is being used, a user is given the
+ opportunity to re-edit a failed history substitution.
+
+ 'histverify'
+ If set, and Readline is being used, the results of history
+ substitution are not immediately passed to the shell parser.
+ Instead, the resulting line is loaded into the Readline
+ editing buffer, allowing further modification.
+
+ 'hostcomplete'
+ If set, and Readline is being used, Bash will attempt to
+ perform hostname completion when a word containing a '@' is
+ being completed (*note Commands For Completion::). This
+ option is enabled by default.
+
+ 'huponexit'
+ If set, Bash will send 'SIGHUP' to all jobs when an
+ interactive login shell exits (*note Signals::).
+
+ 'inherit_errexit'
+ If set, command substitution inherits the value of the
+ 'errexit' option, instead of unsetting it in the subshell
+ environment. This option is enabled when POSIX mode is
+ enabled.
+
+ 'interactive_comments'
+ Allow a word beginning with '#' to cause that word and all
+ remaining characters on that line to be ignored in an
+ interactive shell. This option is enabled by default.
+
+ 'lastpipe'
+ If set, and job control is not active, the shell runs the last
+ command of a pipeline not executed in the background in the
+ current shell environment.
+
+ 'lithist'
+ If enabled, and the 'cmdhist' option is enabled, multi-line
+ commands are saved to the history with embedded newlines
+ rather than using semicolon separators where possible.
+
+ 'localvar_inherit'
+ If set, local variables inherit the value and attributes of a
+ variable of the same name that exists at a previous scope
+ before any new value is assigned. The 'nameref' attribute is
+ not inherited.
+
+ 'localvar_unset'
+ If set, calling 'unset' on local variables in previous
+ function scopes marks them so subsequent lookups find them
+ unset until that function returns. This is identical to the
+ behavior of unsetting local variables at the current function
+ scope.
+
+ 'login_shell'
+ The shell sets this option if it is started as a login shell
+ (*note Invoking Bash::). The value may not be changed.
+
+ 'mailwarn'
+ If set, and a file that Bash is checking for mail has been
+ accessed since the last time it was checked, the message '"The
+ mail in MAILFILE has been read"' is displayed.
+
+ 'no_empty_cmd_completion'
+ If set, and Readline is being used, Bash will not attempt to
+ search the 'PATH' for possible completions when completion is
+ attempted on an empty line.
+
+ 'nocaseglob'
+ If set, Bash matches filenames in a case-insensitive fashion
+ when performing filename expansion.
+
+ 'nocasematch'
+ If set, Bash matches patterns in a case-insensitive fashion
+ when performing matching while executing 'case' or '[['
+ conditional commands (*note Conditional Constructs::, when
+ performing pattern substitution word expansions, or when
+ filtering possible completions as part of programmable
+ completion.
+
+ 'noexpand_translation'
+ If set, Bash encloses the translated results of $"..."
+ quoting in single quotes instead of double quotes. If the
+ string is not translated, this has no effect.
+
+ 'nullglob'
+ If set, Bash allows filename patterns which match no files to
+ expand to a null string, rather than themselves.
+
+ 'patsub_replacement'
+ If set, Bash expands occurrences of '&' in the replacement
+ string of pattern substitution to the text matched by the
+ pattern, as described above (*note Shell Parameter
+ Expansion::). This option is enabled by default.
+
+ 'progcomp'
+ If set, the programmable completion facilities (*note
+ Programmable Completion::) are enabled. This option is
+ enabled by default.
+
+ 'progcomp_alias'
+ If set, and programmable completion is enabled, Bash treats a
+ command name that doesn't have any completions as a possible
+ alias and attempts alias expansion. If it has an alias, Bash
+ attempts programmable completion using the command word
+ resulting from the expanded alias.
+
+ 'promptvars'
+ If set, prompt strings undergo parameter expansion, command
+ substitution, arithmetic expansion, and quote removal after
+ being expanded as described below (*note Controlling the
+ Prompt::). This option is enabled by default.
+
+ 'restricted_shell'
+ The shell sets this option if it is started in restricted mode
+ (*note The Restricted Shell::). The value may not be changed.
+ This is not reset when the startup files are executed,
+ allowing the startup files to discover whether or not a shell
+ is restricted.
+
+ 'shift_verbose'
+ If this is set, the 'shift' builtin prints an error message
+ when the shift count exceeds the number of positional
+ parameters.
+
+ 'sourcepath'
+ If set, the '.' ('source') builtin uses the value of 'PATH' to
+ find the directory containing the file supplied as an
+ argument. This option is enabled by default.
+
+ 'varredir_close'
+ If set, the shell automatically closes file descriptors
+ assigned using the '{varname}' redirection syntax (*note
+ Redirections::) instead of leaving them open when the command
+ completes.
+
+ 'xpg_echo'
+ If set, the 'echo' builtin expands backslash-escape sequences
+ by default.
+
+
+File: bash.info, Node: Special Builtins, Prev: Modifying Shell Behavior, Up: Shell Builtin Commands
+
+4.4 Special Builtins
+====================
+
+For historical reasons, the POSIX standard has classified several
+builtin commands as _special_. When Bash is executing in POSIX mode,
+the special builtins differ from other builtin commands in three
+respects:
+
+ 1. Special builtins are found before shell functions during command
+ lookup.
+
+ 2. If a special builtin returns an error status, a non-interactive
+ shell exits.
+
+ 3. Assignment statements preceding the command stay in effect in the
+ shell environment after the command completes.
+
+ When Bash is not executing in POSIX mode, these builtins behave no
+differently than the rest of the Bash builtin commands. The Bash POSIX
+mode is described in *note Bash POSIX Mode::.
+
+ These are the POSIX special builtins:
+ break : . continue eval exec exit export readonly return set
+ shift trap unset
+
+
+File: bash.info, Node: Shell Variables, Next: Bash Features, Prev: Shell Builtin Commands, Up: Top
+
+5 Shell Variables
+*****************
+
+* Menu:
+
+* Bourne Shell Variables:: Variables which Bash uses in the same way
+ as the Bourne Shell.
+* Bash Variables:: List of variables that exist in Bash.
+
+This chapter describes the shell variables that Bash uses. Bash
+automatically assigns default values to a number of variables.
+
+
+File: bash.info, Node: Bourne Shell Variables, Next: Bash Variables, Up: Shell Variables
+
+5.1 Bourne Shell Variables
+==========================
+
+Bash uses certain shell variables in the same way as the Bourne shell.
+In some cases, Bash assigns a default value to the variable.
+
+'CDPATH'
+ A colon-separated list of directories used as a search path for the
+ 'cd' builtin command.
+
+'HOME'
+ The current user's home directory; the default for the 'cd' builtin
+ command. The value of this variable is also used by tilde
+ expansion (*note Tilde Expansion::).
+
+'IFS'
+ A list of characters that separate fields; used when the shell
+ splits words as part of expansion.
+
+'MAIL'
+ If this parameter is set to a filename or directory name and the
+ 'MAILPATH' variable is not set, Bash informs the user of the
+ arrival of mail in the specified file or Maildir-format directory.
+
+'MAILPATH'
+ A colon-separated list of filenames which the shell periodically
+ checks for new mail. Each list entry can specify the message that
+ is printed when new mail arrives in the mail file by separating the
+ filename from the message with a '?'. When used in the text of the
+ message, '$_' expands to the name of the current mail file.
+
+'OPTARG'
+ The value of the last option argument processed by the 'getopts'
+ builtin.
+
+'OPTIND'
+ The index of the last option argument processed by the 'getopts'
+ builtin.
+
+'PATH'
+ A colon-separated list of directories in which the shell looks for
+ commands. A zero-length (null) directory name in the value of
+ 'PATH' indicates the current directory. A null directory name may
+ appear as two adjacent colons, or as an initial or trailing colon.
+
+'PS1'
+ The primary prompt string. The default value is '\s-\v\$ '. *Note
+ Controlling the Prompt::, for the complete list of escape sequences
+ that are expanded before 'PS1' is displayed.
+
+'PS2'
+ The secondary prompt string. The default value is '> '. 'PS2' is
+ expanded in the same way as 'PS1' before being displayed.
+
+
+File: bash.info, Node: Bash Variables, Prev: Bourne Shell Variables, Up: Shell Variables
+
+5.2 Bash Variables
+==================
+
+These variables are set or used by Bash, but other shells do not
+normally treat them specially.
+
+ A few variables used by Bash are described in different chapters:
+variables for controlling the job control facilities (*note Job Control
+Variables::).
+
+'_'
+ ($_, an underscore.) At shell startup, set to the pathname used to
+ invoke the shell or shell script being executed as passed in the
+ environment or argument list. Subsequently, expands to the last
+ argument to the previous simple command executed in the foreground,
+ after expansion. Also set to the full pathname used to invoke each
+ command executed and placed in the environment exported to that
+ command. When checking mail, this parameter holds the name of the
+ mail file.
+
+'BASH'
+ The full pathname used to execute the current instance of Bash.
+
+'BASHOPTS'
+ A colon-separated list of enabled shell options. Each word in the
+ list is a valid argument for the '-s' option to the 'shopt' builtin
+ command (*note The Shopt Builtin::). The options appearing in
+ 'BASHOPTS' are those reported as 'on' by 'shopt'. If this variable
+ is in the environment when Bash starts up, each shell option in the
+ list will be enabled before reading any startup files. This
+ variable is readonly.
+
+'BASHPID'
+ Expands to the process ID of the current Bash process. This
+ differs from '$$' under certain circumstances, such as subshells
+ that do not require Bash to be re-initialized. Assignments to
+ 'BASHPID' have no effect. If 'BASHPID' is unset, it loses its
+ special properties, even if it is subsequently reset.
+
+'BASH_ALIASES'
+ An associative array variable whose members correspond to the
+ internal list of aliases as maintained by the 'alias' builtin.
+ (*note Bourne Shell Builtins::). Elements added to this array
+ appear in the alias list; however, unsetting array elements
+ currently does not cause aliases to be removed from the alias list.
+ If 'BASH_ALIASES' is unset, it loses its special properties, even
+ if it is subsequently reset.
+
+'BASH_ARGC'
+ An array variable whose values are the number of parameters in each
+ frame of the current bash execution call stack. The number of
+ parameters to the current subroutine (shell function or script
+ executed with '.' or 'source') is at the top of the stack. When a
+ subroutine is executed, the number of parameters passed is pushed
+ onto 'BASH_ARGC'. The shell sets 'BASH_ARGC' only when in extended
+ debugging mode (see *note The Shopt Builtin:: for a description of
+ the 'extdebug' option to the 'shopt' builtin). Setting 'extdebug'
+ after the shell has started to execute a script, or referencing
+ this variable when 'extdebug' is not set, may result in
+ inconsistent values.
+
+'BASH_ARGV'
+ An array variable containing all of the parameters in the current
+ bash execution call stack. The final parameter of the last
+ subroutine call is at the top of the stack; the first parameter of
+ the initial call is at the bottom. When a subroutine is executed,
+ the parameters supplied are pushed onto 'BASH_ARGV'. The shell
+ sets 'BASH_ARGV' only when in extended debugging mode (see *note
+ The Shopt Builtin:: for a description of the 'extdebug' option to
+ the 'shopt' builtin). Setting 'extdebug' after the shell has
+ started to execute a script, or referencing this variable when
+ 'extdebug' is not set, may result in inconsistent values.
+
+'BASH_ARGV0'
+ When referenced, this variable expands to the name of the shell or
+ shell script (identical to '$0'; *Note Special Parameters::, for
+ the description of special parameter 0). Assignment to
+ 'BASH_ARGV0' causes the value assigned to also be assigned to '$0'.
+ If 'BASH_ARGV0' is unset, it loses its special properties, even if
+ it is subsequently reset.
+
+'BASH_CMDS'
+ An associative array variable whose members correspond to the
+ internal hash table of commands as maintained by the 'hash' builtin
+ (*note Bourne Shell Builtins::). Elements added to this array
+ appear in the hash table; however, unsetting array elements
+ currently does not cause command names to be removed from the hash
+ table. If 'BASH_CMDS' is unset, it loses its special properties,
+ even if it is subsequently reset.
+
+'BASH_COMMAND'
+ The command currently being executed or about to be executed,
+ unless the shell is executing a command as the result of a trap, in
+ which case it is the command executing at the time of the trap. If
+ 'BASH_COMMAND' is unset, it loses its special properties, even if
+ it is subsequently reset.
+
+'BASH_COMPAT'
+ The value is used to set the shell's compatibility level. *Note
+ Shell Compatibility Mode::, for a description of the various
+ compatibility levels and their effects. The value may be a decimal
+ number (e.g., 4.2) or an integer (e.g., 42) corresponding to the
+ desired compatibility level. If 'BASH_COMPAT' is unset or set to
+ the empty string, the compatibility level is set to the default for
+ the current version. If 'BASH_COMPAT' is set to a value that is
+ not one of the valid compatibility levels, the shell prints an
+ error message and sets the compatibility level to the default for
+ the current version. The valid values correspond to the
+ compatibility levels described below (*note Shell Compatibility
+ Mode::). For example, 4.2 and 42 are valid values that correspond
+ to the 'compat42' 'shopt' option and set the compatibility level to
+ 42. The current version is also a valid value.
+
+'BASH_ENV'
+ If this variable is set when Bash is invoked to execute a shell
+ script, its value is expanded and used as the name of a startup
+ file to read before executing the script. *Note Bash Startup
+ Files::.
+
+'BASH_EXECUTION_STRING'
+ The command argument to the '-c' invocation option.
+
+'BASH_LINENO'
+ An array variable whose members are the line numbers in source
+ files where each corresponding member of 'FUNCNAME' was invoked.
+ '${BASH_LINENO[$i]}' is the line number in the source file
+ ('${BASH_SOURCE[$i+1]}') where '${FUNCNAME[$i]}' was called (or
+ '${BASH_LINENO[$i-1]}' if referenced within another shell
+ function). Use 'LINENO' to obtain the current line number.
+
+'BASH_LOADABLES_PATH'
+ A colon-separated list of directories in which the shell looks for
+ dynamically loadable builtins specified by the 'enable' command.
+
+'BASH_REMATCH'
+ An array variable whose members are assigned by the '=~' binary
+ operator to the '[[' conditional command (*note Conditional
+ Constructs::). The element with index 0 is the portion of the
+ string matching the entire regular expression. The element with
+ index N is the portion of the string matching the Nth parenthesized
+ subexpression.
+
+'BASH_SOURCE'
+ An array variable whose members are the source filenames where the
+ corresponding shell function names in the 'FUNCNAME' array variable
+ are defined. The shell function '${FUNCNAME[$i]}' is defined in
+ the file '${BASH_SOURCE[$i]}' and called from
+ '${BASH_SOURCE[$i+1]}'
+
+'BASH_SUBSHELL'
+ Incremented by one within each subshell or subshell environment
+ when the shell begins executing in that environment. The initial
+ value is 0. If 'BASH_SUBSHELL' is unset, it loses its special
+ properties, even if it is subsequently reset.
+
+'BASH_VERSINFO'
+ A readonly array variable (*note Arrays::) whose members hold
+ version information for this instance of Bash. The values assigned
+ to the array members are as follows:
+
+ 'BASH_VERSINFO[0]'
+ The major version number (the "release").
+
+ 'BASH_VERSINFO[1]'
+ The minor version number (the "version").
+
+ 'BASH_VERSINFO[2]'
+ The patch level.
+
+ 'BASH_VERSINFO[3]'
+ The build version.
+
+ 'BASH_VERSINFO[4]'
+ The release status (e.g., 'beta1').
+
+ 'BASH_VERSINFO[5]'
+ The value of 'MACHTYPE'.
+
+'BASH_VERSION'
+ The version number of the current instance of Bash.
+
+'BASH_XTRACEFD'
+ If set to an integer corresponding to a valid file descriptor, Bash
+ will write the trace output generated when 'set -x' is enabled to
+ that file descriptor. This allows tracing output to be separated
+ from diagnostic and error messages. The file descriptor is closed
+ when 'BASH_XTRACEFD' is unset or assigned a new value. Unsetting
+ 'BASH_XTRACEFD' or assigning it the empty string causes the trace
+ output to be sent to the standard error. Note that setting
+ 'BASH_XTRACEFD' to 2 (the standard error file descriptor) and then
+ unsetting it will result in the standard error being closed.
+
+'CHILD_MAX'
+ Set the number of exited child status values for the shell to
+ remember. Bash will not allow this value to be decreased below a
+ POSIX-mandated minimum, and there is a maximum value (currently
+ 8192) that this may not exceed. The minimum value is
+ system-dependent.
+
+'COLUMNS'
+ Used by the 'select' command to determine the terminal width when
+ printing selection lists. Automatically set if the 'checkwinsize'
+ option is enabled (*note The Shopt Builtin::), or in an interactive
+ shell upon receipt of a 'SIGWINCH'.
+
+'COMP_CWORD'
+ An index into '${COMP_WORDS}' of the word containing the current
+ cursor position. This variable is available only in shell
+ functions invoked by the programmable completion facilities (*note
+ Programmable Completion::).
+
+'COMP_LINE'
+ The current command line. This variable is available only in shell
+ functions and external commands invoked by the programmable
+ completion facilities (*note Programmable Completion::).
+
+'COMP_POINT'
+ The index of the current cursor position relative to the beginning
+ of the current command. If the current cursor position is at the
+ end of the current command, the value of this variable is equal to
+ '${#COMP_LINE}'. This variable is available only in shell
+ functions and external commands invoked by the programmable
+ completion facilities (*note Programmable Completion::).
+
+'COMP_TYPE'
+ Set to an integer value corresponding to the type of completion
+ attempted that caused a completion function to be called: <TAB>,
+ for normal completion, '?', for listing completions after
+ successive tabs, '!', for listing alternatives on partial word
+ completion, '@', to list completions if the word is not unmodified,
+ or '%', for menu completion. This variable is available only in
+ shell functions and external commands invoked by the programmable
+ completion facilities (*note Programmable Completion::).
+
+'COMP_KEY'
+ The key (or final key of a key sequence) used to invoke the current
+ completion function.
+
+'COMP_WORDBREAKS'
+ The set of characters that the Readline library treats as word
+ separators when performing word completion. If 'COMP_WORDBREAKS'
+ is unset, it loses its special properties, even if it is
+ subsequently reset.
+
+'COMP_WORDS'
+ An array variable consisting of the individual words in the current
+ command line. The line is split into words as Readline would split
+ it, using 'COMP_WORDBREAKS' as described above. This variable is
+ available only in shell functions invoked by the programmable
+ completion facilities (*note Programmable Completion::).
+
+'COMPREPLY'
+ An array variable from which Bash reads the possible completions
+ generated by a shell function invoked by the programmable
+ completion facility (*note Programmable Completion::). Each array
+ element contains one possible completion.
+
+'COPROC'
+ An array variable created to hold the file descriptors for output
+ from and input to an unnamed coprocess (*note Coprocesses::).
+
+'DIRSTACK'
+ An array variable containing the current contents of the directory
+ stack. Directories appear in the stack in the order they are
+ displayed by the 'dirs' builtin. Assigning to members of this
+ array variable may be used to modify directories already in the
+ stack, but the 'pushd' and 'popd' builtins must be used to add and
+ remove directories. Assignment to this variable will not change
+ the current directory. If 'DIRSTACK' is unset, it loses its
+ special properties, even if it is subsequently reset.
+
+'EMACS'
+ If Bash finds this variable in the environment when the shell
+ starts with value 't', it assumes that the shell is running in an
+ Emacs shell buffer and disables line editing.
+
+'ENV'
+ Expanded and executed similarly to 'BASH_ENV' (*note Bash Startup
+ Files::) when an interactive shell is invoked in POSIX Mode (*note
+ Bash POSIX Mode::).
+
+'EPOCHREALTIME'
+ Each time this parameter is referenced, it expands to the number of
+ seconds since the Unix Epoch as a floating point value with
+ micro-second granularity (see the documentation for the C library
+ function 'time' for the definition of Epoch). Assignments to
+ 'EPOCHREALTIME' are ignored. If 'EPOCHREALTIME' is unset, it loses
+ its special properties, even if it is subsequently reset.
+
+'EPOCHSECONDS'
+ Each time this parameter is referenced, it expands to the number of
+ seconds since the Unix Epoch (see the documentation for the C
+ library function 'time' for the definition of Epoch). Assignments
+ to 'EPOCHSECONDS' are ignored. If 'EPOCHSECONDS' is unset, it
+ loses its special properties, even if it is subsequently reset.
+
+'EUID'
+ The numeric effective user id of the current user. This variable
+ is readonly.
+
+'EXECIGNORE'
+ A colon-separated list of shell patterns (*note Pattern Matching::)
+ defining the list of filenames to be ignored by command search
+ using 'PATH'. Files whose full pathnames match one of these
+ patterns are not considered executable files for the purposes of
+ completion and command execution via 'PATH' lookup. This does not
+ affect the behavior of the '[', 'test', and '[[' commands. Full
+ pathnames in the command hash table are not subject to
+ 'EXECIGNORE'. Use this variable to ignore shared library files
+ that have the executable bit set, but are not executable files.
+ The pattern matching honors the setting of the 'extglob' shell
+ option.
+
+'FCEDIT'
+ The editor used as a default by the '-e' option to the 'fc' builtin
+ command.
+
+'FIGNORE'
+ A colon-separated list of suffixes to ignore when performing
+ filename completion. A filename whose suffix matches one of the
+ entries in 'FIGNORE' is excluded from the list of matched
+ filenames. A sample value is '.o:~'
+
+'FUNCNAME'
+ An array variable containing the names of all shell functions
+ currently in the execution call stack. The element with index 0 is
+ the name of any currently-executing shell function. The
+ bottom-most element (the one with the highest index) is '"main"'.
+ This variable exists only when a shell function is executing.
+ Assignments to 'FUNCNAME' have no effect. If 'FUNCNAME' is unset,
+ it loses its special properties, even if it is subsequently reset.
+
+ This variable can be used with 'BASH_LINENO' and 'BASH_SOURCE'.
+ Each element of 'FUNCNAME' has corresponding elements in
+ 'BASH_LINENO' and 'BASH_SOURCE' to describe the call stack. For
+ instance, '${FUNCNAME[$i]}' was called from the file
+ '${BASH_SOURCE[$i+1]}' at line number '${BASH_LINENO[$i]}'. The
+ 'caller' builtin displays the current call stack using this
+ information.
+
+'FUNCNEST'
+ If set to a numeric value greater than 0, defines a maximum
+ function nesting level. Function invocations that exceed this
+ nesting level will cause the current command to abort.
+
+'GLOBIGNORE'
+ A colon-separated list of patterns defining the set of file names
+ to be ignored by filename expansion. If a file name matched by a
+ filename expansion pattern also matches one of the patterns in
+ 'GLOBIGNORE', it is removed from the list of matches. The pattern
+ matching honors the setting of the 'extglob' shell option.
+
+'GROUPS'
+ An array variable containing the list of groups of which the
+ current user is a member. Assignments to 'GROUPS' have no effect.
+ If 'GROUPS' is unset, it loses its special properties, even if it
+ is subsequently reset.
+
+'histchars'
+ Up to three characters which control history expansion, quick
+ substitution, and tokenization (*note History Interaction::). The
+ first character is the "history expansion" character, that is, the
+ character which signifies the start of a history expansion,
+ normally '!'. The second character is the character which
+ signifies 'quick substitution' when seen as the first character on
+ a line, normally '^'. The optional third character is the
+ character which indicates that the remainder of the line is a
+ comment when found as the first character of a word, usually '#'.
+ The history comment character causes history substitution to be
+ skipped for the remaining words on the line. It does not
+ necessarily cause the shell parser to treat the rest of the line as
+ a comment.
+
+'HISTCMD'
+ The history number, or index in the history list, of the current
+ command. Assignments to 'HISTCMD' are ignored. If 'HISTCMD' is
+ unset, it loses its special properties, even if it is subsequently
+ reset.
+
+'HISTCONTROL'
+ A colon-separated list of values controlling how commands are saved
+ on the history list. If the list of values includes 'ignorespace',
+ lines which begin with a space character are not saved in the
+ history list. A value of 'ignoredups' causes lines which match the
+ previous history entry to not be saved. A value of 'ignoreboth' is
+ shorthand for 'ignorespace' and 'ignoredups'. A value of
+ 'erasedups' causes all previous lines matching the current line to
+ be removed from the history list before that line is saved. Any
+ value not in the above list is ignored. If 'HISTCONTROL' is unset,
+ or does not include a valid value, all lines read by the shell
+ parser are saved on the history list, subject to the value of
+ 'HISTIGNORE'. The second and subsequent lines of a multi-line
+ compound command are not tested, and are added to the history
+ regardless of the value of 'HISTCONTROL'.
+
+'HISTFILE'
+ The name of the file to which the command history is saved. The
+ default value is '~/.bash_history'.
+
+'HISTFILESIZE'
+ The maximum number of lines contained in the history file. When
+ this variable is assigned a value, the history file is truncated,
+ if necessary, to contain no more than that number of lines by
+ removing the oldest entries. The history file is also truncated to
+ this size after writing it when a shell exits. If the value is 0,
+ the history file is truncated to zero size. Non-numeric values and
+ numeric values less than zero inhibit truncation. The shell sets
+ the default value to the value of 'HISTSIZE' after reading any
+ startup files.
+
+'HISTIGNORE'
+ A colon-separated list of patterns used to decide which command
+ lines should be saved on the history list. Each pattern is
+ anchored at the beginning of the line and must match the complete
+ line (no implicit '*' is appended). Each pattern is tested against
+ the line after the checks specified by 'HISTCONTROL' are applied.
+ In addition to the normal shell pattern matching characters, '&'
+ matches the previous history line. '&' may be escaped using a
+ backslash; the backslash is removed before attempting a match. The
+ second and subsequent lines of a multi-line compound command are
+ not tested, and are added to the history regardless of the value of
+ 'HISTIGNORE'. The pattern matching honors the setting of the
+ 'extglob' shell option.
+
+ 'HISTIGNORE' subsumes the function of 'HISTCONTROL'. A pattern of
+ '&' is identical to 'ignoredups', and a pattern of '[ ]*' is
+ identical to 'ignorespace'. Combining these two patterns,
+ separating them with a colon, provides the functionality of
+ 'ignoreboth'.
+
+'HISTSIZE'
+ The maximum number of commands to remember on the history list. If
+ the value is 0, commands are not saved in the history list.
+ Numeric values less than zero result in every command being saved
+ on the history list (there is no limit). The shell sets the
+ default value to 500 after reading any startup files.
+
+'HISTTIMEFORMAT'
+ If this variable is set and not null, its value is used as a format
+ string for 'strftime' to print the time stamp associated with each
+ history entry displayed by the 'history' builtin. If this variable
+ is set, time stamps are written to the history file so they may be
+ preserved across shell sessions. This uses the history comment
+ character to distinguish timestamps from other history lines.
+
+'HOSTFILE'
+ Contains the name of a file in the same format as '/etc/hosts' that
+ should be read when the shell needs to complete a hostname. The
+ list of possible hostname completions may be changed while the
+ shell is running; the next time hostname completion is attempted
+ after the value is changed, Bash adds the contents of the new file
+ to the existing list. If 'HOSTFILE' is set, but has no value, or
+ does not name a readable file, Bash attempts to read '/etc/hosts'
+ to obtain the list of possible hostname completions. When
+ 'HOSTFILE' is unset, the hostname list is cleared.
+
+'HOSTNAME'
+ The name of the current host.
+
+'HOSTTYPE'
+ A string describing the machine Bash is running on.
+
+'IGNOREEOF'
+ Controls the action of the shell on receipt of an 'EOF' character
+ as the sole input. If set, the value denotes the number of
+ consecutive 'EOF' characters that can be read as the first
+ character on an input line before the shell will exit. If the
+ variable exists but does not have a numeric value, or has no value,
+ then the default is 10. If the variable does not exist, then 'EOF'
+ signifies the end of input to the shell. This is only in effect
+ for interactive shells.
+
+'INPUTRC'
+ The name of the Readline initialization file, overriding the
+ default of '~/.inputrc'.
+
+'INSIDE_EMACS'
+ If Bash finds this variable in the environment when the shell
+ starts, it assumes that the shell is running in an Emacs shell
+ buffer and may disable line editing depending on the value of
+ 'TERM'.
+
+'LANG'
+ Used to determine the locale category for any category not
+ specifically selected with a variable starting with 'LC_'.
+
+'LC_ALL'
+ This variable overrides the value of 'LANG' and any other 'LC_'
+ variable specifying a locale category.
+
+'LC_COLLATE'
+ This variable determines the collation order used when sorting the
+ results of filename expansion, and determines the behavior of range
+ expressions, equivalence classes, and collating sequences within
+ filename expansion and pattern matching (*note Filename
+ Expansion::).
+
+'LC_CTYPE'
+ This variable determines the interpretation of characters and the
+ behavior of character classes within filename expansion and pattern
+ matching (*note Filename Expansion::).
+
+'LC_MESSAGES'
+ This variable determines the locale used to translate double-quoted
+ strings preceded by a '$' (*note Locale Translation::).
+
+'LC_NUMERIC'
+ This variable determines the locale category used for number
+ formatting.
+
+'LC_TIME'
+ This variable determines the locale category used for data and time
+ formatting.
+
+'LINENO'
+ The line number in the script or shell function currently
+ executing. If 'LINENO' is unset, it loses its special properties,
+ even if it is subsequently reset.
+
+'LINES'
+ Used by the 'select' command to determine the column length for
+ printing selection lists. Automatically set if the 'checkwinsize'
+ option is enabled (*note The Shopt Builtin::), or in an interactive
+ shell upon receipt of a 'SIGWINCH'.
+
+'MACHTYPE'
+ A string that fully describes the system type on which Bash is
+ executing, in the standard GNU CPU-COMPANY-SYSTEM format.
+
+'MAILCHECK'
+ How often (in seconds) that the shell should check for mail in the
+ files specified in the 'MAILPATH' or 'MAIL' variables. The default
+ is 60 seconds. When it is time to check for mail, the shell does
+ so before displaying the primary prompt. If this variable is
+ unset, or set to a value that is not a number greater than or equal
+ to zero, the shell disables mail checking.
+
+'MAPFILE'
+ An array variable created to hold the text read by the 'mapfile'
+ builtin when no variable name is supplied.
+
+'OLDPWD'
+ The previous working directory as set by the 'cd' builtin.
+
+'OPTERR'
+ If set to the value 1, Bash displays error messages generated by
+ the 'getopts' builtin command.
+
+'OSTYPE'
+ A string describing the operating system Bash is running on.
+
+'PIPESTATUS'
+ An array variable (*note Arrays::) containing a list of exit status
+ values from the processes in the most-recently-executed foreground
+ pipeline (which may contain only a single command).
+
+'POSIXLY_CORRECT'
+ If this variable is in the environment when Bash starts, the shell
+ enters POSIX mode (*note Bash POSIX Mode::) before reading the
+ startup files, as if the '--posix' invocation option had been
+ supplied. If it is set while the shell is running, Bash enables
+ POSIX mode, as if the command
+ set -o posix
+ had been executed. When the shell enters POSIX mode, it sets this
+ variable if it was not already set.
+
+'PPID'
+ The process ID of the shell's parent process. This variable is
+ readonly.
+
+'PROMPT_COMMAND'
+ If this variable is set, and is an array, the value of each set
+ element is interpreted as a command to execute before printing the
+ primary prompt ('$PS1'). If this is set but not an array variable,
+ its value is used as a command to execute instead.
+
+'PROMPT_DIRTRIM'
+ If set to a number greater than zero, the value is used as the
+ number of trailing directory components to retain when expanding
+ the '\w' and '\W' prompt string escapes (*note Controlling the
+ Prompt::). Characters removed are replaced with an ellipsis.
+
+'PS0'
+ The value of this parameter is expanded like 'PS1' and displayed by
+ interactive shells after reading a command and before the command
+ is executed.
+
+'PS3'
+ The value of this variable is used as the prompt for the 'select'
+ command. If this variable is not set, the 'select' command prompts
+ with '#? '
+
+'PS4'
+ The value of this parameter is expanded like 'PS1' and the expanded
+ value is the prompt printed before the command line is echoed when
+ the '-x' option is set (*note The Set Builtin::). The first
+ character of the expanded value is replicated multiple times, as
+ necessary, to indicate multiple levels of indirection. The default
+ is '+ '.
+
+'PWD'
+ The current working directory as set by the 'cd' builtin.
+
+'RANDOM'
+ Each time this parameter is referenced, it expands to a random
+ integer between 0 and 32767. Assigning a value to this variable
+ seeds the random number generator. If 'RANDOM' is unset, it loses
+ its special properties, even if it is subsequently reset.
+
+'READLINE_ARGUMENT'
+ Any numeric argument given to a Readline command that was defined
+ using 'bind -x' (*note Bash Builtins:: when it was invoked.
+
+'READLINE_LINE'
+ The contents of the Readline line buffer, for use with 'bind -x'
+ (*note Bash Builtins::).
+
+'READLINE_MARK'
+ The position of the "mark" (saved insertion point) in the Readline
+ line buffer, for use with 'bind -x' (*note Bash Builtins::). The
+ characters between the insertion point and the mark are often
+ called the "region".
+
+'READLINE_POINT'
+ The position of the insertion point in the Readline line buffer,
+ for use with 'bind -x' (*note Bash Builtins::).
+
+'REPLY'
+ The default variable for the 'read' builtin.
+
+'SECONDS'
+ This variable expands to the number of seconds since the shell was
+ started. Assignment to this variable resets the count to the value
+ assigned, and the expanded value becomes the value assigned plus
+ the number of seconds since the assignment. The number of seconds
+ at shell invocation and the current time are always determined by
+ querying the system clock. If 'SECONDS' is unset, it loses its
+ special properties, even if it is subsequently reset.
+
+'SHELL'
+ This environment variable expands to the full pathname to the
+ shell. If it is not set when the shell starts, Bash assigns to it
+ the full pathname of the current user's login shell.
+
+'SHELLOPTS'
+ A colon-separated list of enabled shell options. Each word in the
+ list is a valid argument for the '-o' option to the 'set' builtin
+ command (*note The Set Builtin::). The options appearing in
+ 'SHELLOPTS' are those reported as 'on' by 'set -o'. If this
+ variable is in the environment when Bash starts up, each shell
+ option in the list will be enabled before reading any startup
+ files. This variable is readonly.
+
+'SHLVL'
+ Incremented by one each time a new instance of Bash is started.
+ This is intended to be a count of how deeply your Bash shells are
+ nested.
+
+'SRANDOM'
+ This variable expands to a 32-bit pseudo-random number each time it
+ is referenced. The random number generator is not linear on
+ systems that support '/dev/urandom' or 'arc4random', so each
+ returned number has no relationship to the numbers preceding it.
+ The random number generator cannot be seeded, so assignments to
+ this variable have no effect. If 'SRANDOM' is unset, it loses its
+ special properties, even if it is subsequently reset.
+
+'TIMEFORMAT'
+ The value of this parameter is used as a format string specifying
+ how the timing information for pipelines prefixed with the 'time'
+ reserved word should be displayed. The '%' character introduces an
+ escape sequence that is expanded to a time value or other
+ information. The escape sequences and their meanings are as
+ follows; the braces denote optional portions.
+
+ '%%'
+ A literal '%'.
+
+ '%[P][l]R'
+ The elapsed time in seconds.
+
+ '%[P][l]U'
+ The number of CPU seconds spent in user mode.
+
+ '%[P][l]S'
+ The number of CPU seconds spent in system mode.
+
+ '%P'
+ The CPU percentage, computed as (%U + %S) / %R.
+
+ The optional P is a digit specifying the precision, the number of
+ fractional digits after a decimal point. A value of 0 causes no
+ decimal point or fraction to be output. At most three places after
+ the decimal point may be specified; values of P greater than 3 are
+ changed to 3. If P is not specified, the value 3 is used.
+
+ The optional 'l' specifies a longer format, including minutes, of
+ the form MMmSS.FFs. The value of P determines whether or not the
+ fraction is included.
+
+ If this variable is not set, Bash acts as if it had the value
+ $'\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS'
+ If the value is null, no timing information is displayed. A
+ trailing newline is added when the format string is displayed.
+
+'TMOUT'
+ If set to a value greater than zero, 'TMOUT' is treated as the
+ default timeout for the 'read' builtin (*note Bash Builtins::).
+ The 'select' command (*note Conditional Constructs::) terminates if
+ input does not arrive after 'TMOUT' seconds when input is coming
+ from a terminal.
+
+ In an interactive shell, the value is interpreted as the number of
+ seconds to wait for a line of input after issuing the primary
+ prompt. Bash terminates after waiting for that number of seconds
+ if a complete line of input does not arrive.
+
+'TMPDIR'
+ If set, Bash uses its value as the name of a directory in which
+ Bash creates temporary files for the shell's use.
+
+'UID'
+ The numeric real user id of the current user. This variable is
+ readonly.
+
+
+File: bash.info, Node: Bash Features, Next: Job Control, Prev: Shell Variables, Up: Top
+
+6 Bash Features
+***************
+
+This chapter describes features unique to Bash.
+
+* Menu:
+
+* Invoking Bash:: Command line options that you can give
+ to Bash.
+* Bash Startup Files:: When and how Bash executes scripts.
+* Interactive Shells:: What an interactive shell is.
+* Bash Conditional Expressions:: Primitives used in composing expressions for
+ the 'test' builtin.
+* Shell Arithmetic:: Arithmetic on shell variables.
+* Aliases:: Substituting one command for another.
+* Arrays:: Array Variables.
+* The Directory Stack:: History of visited directories.
+* Controlling the Prompt:: Customizing the various prompt strings.
+* The Restricted Shell:: A more controlled mode of shell execution.
+* Bash POSIX Mode:: Making Bash behave more closely to what
+ the POSIX standard specifies.
+* Shell Compatibility Mode:: How Bash supports behavior that was present
+ in earlier versions and has changed.
+
+
+File: bash.info, Node: Invoking Bash, Next: Bash Startup Files, Up: Bash Features
+
+6.1 Invoking Bash
+=================
+
+ bash [long-opt] [-ir] [-abefhkmnptuvxdBCDHP] [-o OPTION]
+ [-O SHOPT_OPTION] [ARGUMENT ...]
+ bash [long-opt] [-abefhkmnptuvxdBCDHP] [-o OPTION]
+ [-O SHOPT_OPTION] -c STRING [ARGUMENT ...]
+ bash [long-opt] -s [-abefhkmnptuvxdBCDHP] [-o OPTION]
+ [-O SHOPT_OPTION] [ARGUMENT ...]
+
+ All of the single-character options used with the 'set' builtin
+(*note The Set Builtin::) can be used as options when the shell is
+invoked. In addition, there are several multi-character options that
+you can use. These options must appear on the command line before the
+single-character options to be recognized.
+
+'--debugger'
+ Arrange for the debugger profile to be executed before the shell
+ starts. Turns on extended debugging mode (see *note The Shopt
+ Builtin:: for a description of the 'extdebug' option to the 'shopt'
+ builtin).
+
+'--dump-po-strings'
+ A list of all double-quoted strings preceded by '$' is printed on
+ the standard output in the GNU 'gettext' PO (portable object) file
+ format. Equivalent to '-D' except for the output format.
+
+'--dump-strings'
+ Equivalent to '-D'.
+
+'--help'
+ Display a usage message on standard output and exit successfully.
+
+'--init-file FILENAME'
+'--rcfile FILENAME'
+ Execute commands from FILENAME (instead of '~/.bashrc') in an
+ interactive shell.
+
+'--login'
+ Equivalent to '-l'.
+
+'--noediting'
+ Do not use the GNU Readline library (*note Command Line Editing::)
+ to read command lines when the shell is interactive.
+
+'--noprofile'
+ Don't load the system-wide startup file '/etc/profile' or any of
+ the personal initialization files '~/.bash_profile',
+ '~/.bash_login', or '~/.profile' when Bash is invoked as a login
+ shell.
+
+'--norc'
+ Don't read the '~/.bashrc' initialization file in an interactive
+ shell. This is on by default if the shell is invoked as 'sh'.
+
+'--posix'
+ Change the behavior of Bash where the default operation differs
+ from the POSIX standard to match the standard. This is intended to
+ make Bash behave as a strict superset of that standard. *Note Bash
+ POSIX Mode::, for a description of the Bash POSIX mode.
+
+'--restricted'
+ Make the shell a restricted shell (*note The Restricted Shell::).
+
+'--verbose'
+ Equivalent to '-v'. Print shell input lines as they're read.
+
+'--version'
+ Show version information for this instance of Bash on the standard
+ output and exit successfully.
+
+ There are several single-character options that may be supplied at
+invocation which are not available with the 'set' builtin.
+
+'-c'
+ Read and execute commands from the first non-option argument
+ COMMAND_STRING, then exit. If there are arguments after the
+ COMMAND_STRING, the first argument is assigned to '$0' and any
+ remaining arguments are assigned to the positional parameters. The
+ assignment to '$0' sets the name of the shell, which is used in
+ warning and error messages.
+
+'-i'
+ Force the shell to run interactively. Interactive shells are
+ described in *note Interactive Shells::.
+
+'-l'
+ Make this shell act as if it had been directly invoked by login.
+ When the shell is interactive, this is equivalent to starting a
+ login shell with 'exec -l bash'. When the shell is not
+ interactive, the login shell startup files will be executed. 'exec
+ bash -l' or 'exec bash --login' will replace the current shell with
+ a Bash login shell. *Note Bash Startup Files::, for a description
+ of the special behavior of a login shell.
+
+'-r'
+ Make the shell a restricted shell (*note The Restricted Shell::).
+
+'-s'
+ If this option is present, or if no arguments remain after option
+ processing, then commands are read from the standard input. This
+ option allows the positional parameters to be set when invoking an
+ interactive shell or when reading input through a pipe.
+
+'-D'
+ A list of all double-quoted strings preceded by '$' is printed on
+ the standard output. These are the strings that are subject to
+ language translation when the current locale is not 'C' or 'POSIX'
+ (*note Locale Translation::). This implies the '-n' option; no
+ commands will be executed.
+
+'[-+]O [SHOPT_OPTION]'
+ SHOPT_OPTION is one of the shell options accepted by the 'shopt'
+ builtin (*note The Shopt Builtin::). If SHOPT_OPTION is present,
+ '-O' sets the value of that option; '+O' unsets it. If
+ SHOPT_OPTION is not supplied, the names and values of the shell
+ options accepted by 'shopt' are printed on the standard output. If
+ the invocation option is '+O', the output is displayed in a format
+ that may be reused as input.
+
+'--'
+ A '--' signals the end of options and disables further option
+ processing. Any arguments after the '--' are treated as filenames
+ and arguments.
+
+ A _login_ shell is one whose first character of argument zero is '-',
+or one invoked with the '--login' option.
+
+ An _interactive_ shell is one started without non-option arguments,
+unless '-s' is specified, without specifying the '-c' option, and whose
+input and output are both connected to terminals (as determined by
+'isatty(3)'), or one started with the '-i' option. *Note Interactive
+Shells::, for more information.
+
+ If arguments remain after option processing, and neither the '-c' nor
+the '-s' option has been supplied, the first argument is assumed to be
+the name of a file containing shell commands (*note Shell Scripts::).
+When Bash is invoked in this fashion, '$0' is set to the name of the
+file, and the positional parameters are set to the remaining arguments.
+Bash reads and executes commands from this file, then exits. Bash's
+exit status is the exit status of the last command executed in the
+script. If no commands are executed, the exit status is 0.
+
+
+File: bash.info, Node: Bash Startup Files, Next: Interactive Shells, Prev: Invoking Bash, Up: Bash Features
+
+6.2 Bash Startup Files
+======================
+
+This section describes how Bash executes its startup files. If any of
+the files exist but cannot be read, Bash reports an error. Tildes are
+expanded in filenames as described above under Tilde Expansion (*note
+Tilde Expansion::).
+
+ Interactive shells are described in *note Interactive Shells::.
+
+Invoked as an interactive login shell, or with '--login'
+........................................................
+
+When Bash is invoked as an interactive login shell, or as a
+non-interactive shell with the '--login' option, it first reads and
+executes commands from the file '/etc/profile', if that file exists.
+After reading that file, it looks for '~/.bash_profile',
+'~/.bash_login', and '~/.profile', in that order, and reads and executes
+commands from the first one that exists and is readable. The
+'--noprofile' option may be used when the shell is started to inhibit
+this behavior.
+
+ When an interactive login shell exits, or a non-interactive login
+shell executes the 'exit' builtin command, Bash reads and executes
+commands from the file '~/.bash_logout', if it exists.
+
+Invoked as an interactive non-login shell
+.........................................
+
+When an interactive shell that is not a login shell is started, Bash
+reads and executes commands from '~/.bashrc', if that file exists. This
+may be inhibited by using the '--norc' option. The '--rcfile FILE'
+option will force Bash to read and execute commands from FILE instead of
+'~/.bashrc'.
+
+ So, typically, your '~/.bash_profile' contains the line
+ if [ -f ~/.bashrc ]; then . ~/.bashrc; fi
+after (or before) any login-specific initializations.
+
+Invoked non-interactively
+.........................
+
+When Bash is started non-interactively, to run a shell script, for
+example, it looks for the variable 'BASH_ENV' in the environment,
+expands its value if it appears there, and uses the expanded value as
+the name of a file to read and execute. Bash behaves as if the
+following command were executed:
+ if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi
+but the value of the 'PATH' variable is not used to search for the
+filename.
+
+ As noted above, if a non-interactive shell is invoked with the
+'--login' option, Bash attempts to read and execute commands from the
+login shell startup files.
+
+Invoked with name 'sh'
+......................
+
+If Bash is invoked with the name 'sh', it tries to mimic the startup
+behavior of historical versions of 'sh' as closely as possible, while
+conforming to the POSIX standard as well.
+
+ When invoked as an interactive login shell, or as a non-interactive
+shell with the '--login' option, it first attempts to read and execute
+commands from '/etc/profile' and '~/.profile', in that order. The
+'--noprofile' option may be used to inhibit this behavior. When invoked
+as an interactive shell with the name 'sh', Bash looks for the variable
+'ENV', expands its value if it is defined, and uses the expanded value
+as the name of a file to read and execute. Since a shell invoked as
+'sh' does not attempt to read and execute commands from any other
+startup files, the '--rcfile' option has no effect. A non-interactive
+shell invoked with the name 'sh' does not attempt to read any other
+startup files.
+
+ When invoked as 'sh', Bash enters POSIX mode after the startup files
+are read.
+
+Invoked in POSIX mode
+.....................
+
+When Bash is started in POSIX mode, as with the '--posix' command line
+option, it follows the POSIX standard for startup files. In this mode,
+interactive shells expand the 'ENV' variable and commands are read and
+executed from the file whose name is the expanded value. No other
+startup files are read.
+
+Invoked by remote shell daemon
+..............................
+
+Bash attempts to determine when it is being run with its standard input
+connected to a network connection, as when executed by the historical
+remote shell daemon, usually 'rshd', or the secure shell daemon 'sshd'.
+If Bash determines it is being run non-interactively in this fashion, it
+reads and executes commands from '~/.bashrc', if that file exists and is
+readable. It will not do this if invoked as 'sh'. The '--norc' option
+may be used to inhibit this behavior, and the '--rcfile' option may be
+used to force another file to be read, but neither 'rshd' nor 'sshd'
+generally invoke the shell with those options or allow them to be
+specified.
+
+Invoked with unequal effective and real UID/GIDs
+................................................
+
+If Bash is started with the effective user (group) id not equal to the
+real user (group) id, and the '-p' option is not supplied, no startup
+files are read, shell functions are not inherited from the environment,
+the 'SHELLOPTS', 'BASHOPTS', 'CDPATH', and 'GLOBIGNORE' variables, if
+they appear in the environment, are ignored, and the effective user id
+is set to the real user id. If the '-p' option is supplied at
+invocation, the startup behavior is the same, but the effective user id
+is not reset.
+
+
+File: bash.info, Node: Interactive Shells, Next: Bash Conditional Expressions, Prev: Bash Startup Files, Up: Bash Features
+
+6.3 Interactive Shells
+======================
+
+* Menu:
+
+* What is an Interactive Shell?:: What determines whether a shell is Interactive.
+* Is this Shell Interactive?:: How to tell if a shell is interactive.
+* Interactive Shell Behavior:: What changes in an interactive shell?
+
+
+File: bash.info, Node: What is an Interactive Shell?, Next: Is this Shell Interactive?, Up: Interactive Shells
+
+6.3.1 What is an Interactive Shell?
+-----------------------------------
+
+An interactive shell is one started without non-option arguments (unless
+'-s' is specified) and without specifying the '-c' option, whose input
+and error output are both connected to terminals (as determined by
+'isatty(3)'), or one started with the '-i' option.
+
+ An interactive shell generally reads from and writes to a user's
+terminal.
+
+ The '-s' invocation option may be used to set the positional
+parameters when an interactive shell is started.
+
+
+File: bash.info, Node: Is this Shell Interactive?, Next: Interactive Shell Behavior, Prev: What is an Interactive Shell?, Up: Interactive Shells
+
+6.3.2 Is this Shell Interactive?
+--------------------------------
+
+To determine within a startup script whether or not Bash is running
+interactively, test the value of the '-' special parameter. It contains
+'i' when the shell is interactive. For example:
+
+ case "$-" in
+ *i*) echo This shell is interactive ;;
+ *) echo This shell is not interactive ;;
+ esac
+
+ Alternatively, startup scripts may examine the variable 'PS1'; it is
+unset in non-interactive shells, and set in interactive shells. Thus:
+
+ if [ -z "$PS1" ]; then
+ echo This shell is not interactive
+ else
+ echo This shell is interactive
+ fi
+
+
+File: bash.info, Node: Interactive Shell Behavior, Prev: Is this Shell Interactive?, Up: Interactive Shells
+
+6.3.3 Interactive Shell Behavior
+--------------------------------
+
+When the shell is running interactively, it changes its behavior in
+several ways.
+
+ 1. Startup files are read and executed as described in *note Bash
+ Startup Files::.
+
+ 2. Job Control (*note Job Control::) is enabled by default. When job
+ control is in effect, Bash ignores the keyboard-generated job
+ control signals 'SIGTTIN', 'SIGTTOU', and 'SIGTSTP'.
+
+ 3. Bash expands and displays 'PS1' before reading the first line of a
+ command, and expands and displays 'PS2' before reading the second
+ and subsequent lines of a multi-line command. Bash expands and
+ displays 'PS0' after it reads a command but before executing it.
+ See *note Controlling the Prompt::, for a complete list of prompt
+ string escape sequences.
+
+ 4. Bash executes the values of the set elements of the
+ 'PROMPT_COMMAND' array variable as commands before printing the
+ primary prompt, '$PS1' (*note Bash Variables::).
+
+ 5. Readline (*note Command Line Editing::) is used to read commands
+ from the user's terminal.
+
+ 6. Bash inspects the value of the 'ignoreeof' option to 'set -o'
+ instead of exiting immediately when it receives an 'EOF' on its
+ standard input when reading a command (*note The Set Builtin::).
+
+ 7. Command history (*note Bash History Facilities::) and history
+ expansion (*note History Interaction::) are enabled by default.
+ Bash will save the command history to the file named by '$HISTFILE'
+ when a shell with history enabled exits.
+
+ 8. Alias expansion (*note Aliases::) is performed by default.
+
+ 9. In the absence of any traps, Bash ignores 'SIGTERM' (*note
+ Signals::).
+
+ 10. In the absence of any traps, 'SIGINT' is caught and handled (*note
+ Signals::). 'SIGINT' will interrupt some shell builtins.
+
+ 11. An interactive login shell sends a 'SIGHUP' to all jobs on exit if
+ the 'huponexit' shell option has been enabled (*note Signals::).
+
+ 12. The '-n' invocation option is ignored, and 'set -n' has no effect
+ (*note The Set Builtin::).
+
+ 13. Bash will check for mail periodically, depending on the values of
+ the 'MAIL', 'MAILPATH', and 'MAILCHECK' shell variables (*note Bash
+ Variables::).
+
+ 14. Expansion errors due to references to unbound shell variables
+ after 'set -u' has been enabled will not cause the shell to exit
+ (*note The Set Builtin::).
+
+ 15. The shell will not exit on expansion errors caused by VAR being
+ unset or null in '${VAR:?WORD}' expansions (*note Shell Parameter
+ Expansion::).
+
+ 16. Redirection errors encountered by shell builtins will not cause
+ the shell to exit.
+
+ 17. When running in POSIX mode, a special builtin returning an error
+ status will not cause the shell to exit (*note Bash POSIX Mode::).
+
+ 18. A failed 'exec' will not cause the shell to exit (*note Bourne
+ Shell Builtins::).
+
+ 19. Parser syntax errors will not cause the shell to exit.
+
+ 20. If the 'cdspell' shell option is enabled, the shell will attempt
+ simple spelling correction for directory arguments to the 'cd'
+ builtin (see the description of the 'cdspell' option to the 'shopt'
+ builtin in *note The Shopt Builtin::). The 'cdspell' option is
+ only effective in interactive shells.
+
+ 21. The shell will check the value of the 'TMOUT' variable and exit if
+ a command is not read within the specified number of seconds after
+ printing '$PS1' (*note Bash Variables::).
+
+
+File: bash.info, Node: Bash Conditional Expressions, Next: Shell Arithmetic, Prev: Interactive Shells, Up: Bash Features
+
+6.4 Bash Conditional Expressions
+================================
+
+Conditional expressions are used by the '[[' compound command (*note
+Conditional Constructs::) and the 'test' and '[' builtin commands (*note
+Bourne Shell Builtins::). The 'test' and '[' commands determine their
+behavior based on the number of arguments; see the descriptions of those
+commands for any other command-specific actions.
+
+ Expressions may be unary or binary, and are formed from the following
+primaries. Unary expressions are often used to examine the status of a
+file. There are string operators and numeric comparison operators as
+well. Bash handles several filenames specially when they are used in
+expressions. If the operating system on which Bash is running provides
+these special files, Bash will use them; otherwise it will emulate them
+internally with this behavior: If the FILE argument to one of the
+primaries is of the form '/dev/fd/N', then file descriptor N is checked.
+If the FILE argument to one of the primaries is one of '/dev/stdin',
+'/dev/stdout', or '/dev/stderr', file descriptor 0, 1, or 2,
+respectively, is checked.
+
+ When used with '[[', the '<' and '>' operators sort lexicographically
+using the current locale. The 'test' command uses ASCII ordering.
+
+ Unless otherwise specified, primaries that operate on files follow
+symbolic links and operate on the target of the link, rather than the
+link itself.
+
+'-a FILE'
+ True if FILE exists.
+
+'-b FILE'
+ True if FILE exists and is a block special file.
+
+'-c FILE'
+ True if FILE exists and is a character special file.
+
+'-d FILE'
+ True if FILE exists and is a directory.
+
+'-e FILE'
+ True if FILE exists.
+
+'-f FILE'
+ True if FILE exists and is a regular file.
+
+'-g FILE'
+ True if FILE exists and its set-group-id bit is set.
+
+'-h FILE'
+ True if FILE exists and is a symbolic link.
+
+'-k FILE'
+ True if FILE exists and its "sticky" bit is set.
+
+'-p FILE'
+ True if FILE exists and is a named pipe (FIFO).
+
+'-r FILE'
+ True if FILE exists and is readable.
+
+'-s FILE'
+ True if FILE exists and has a size greater than zero.
+
+'-t FD'
+ True if file descriptor FD is open and refers to a terminal.
+
+'-u FILE'
+ True if FILE exists and its set-user-id bit is set.
+
+'-w FILE'
+ True if FILE exists and is writable.
+
+'-x FILE'
+ True if FILE exists and is executable.
+
+'-G FILE'
+ True if FILE exists and is owned by the effective group id.
+
+'-L FILE'
+ True if FILE exists and is a symbolic link.
+
+'-N FILE'
+ True if FILE exists and has been modified since it was last read.
+
+'-O FILE'
+ True if FILE exists and is owned by the effective user id.
+
+'-S FILE'
+ True if FILE exists and is a socket.
+
+'FILE1 -ef FILE2'
+ True if FILE1 and FILE2 refer to the same device and inode numbers.
+
+'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 than FILE2, or if FILE2 exists and FILE1
+ does not.
+
+'-o OPTNAME'
+ True if the shell option OPTNAME is enabled. The list of options
+ appears in the description of the '-o' option to the 'set' builtin
+ (*note The Set Builtin::).
+
+'-v VARNAME'
+ True if the shell variable VARNAME is set (has been assigned a
+ value).
+
+'-R VARNAME'
+ True if the shell variable VARNAME is set and is a name reference.
+
+'-z STRING'
+ True if the length of STRING is zero.
+
+'-n STRING'
+'STRING'
+ True if the length of STRING is non-zero.
+
+'STRING1 == STRING2'
+'STRING1 = STRING2'
+ True if the strings are equal. When used with the '[[' command,
+ this performs pattern matching as described above (*note
+ Conditional Constructs::).
+
+ '=' should be used with the 'test' command for POSIX conformance.
+
+'STRING1 != STRING2'
+ True if the strings are not equal.
+
+'STRING1 < STRING2'
+ True if STRING1 sorts before STRING2 lexicographically.
+
+'STRING1 > STRING2'
+ True if STRING1 sorts after STRING2 lexicographically.
+
+'ARG1 OP ARG2'
+ 'OP' is one of '-eq', '-ne', '-lt', '-le', '-gt', or '-ge'. These
+ arithmetic binary operators return true if ARG1 is equal to, not
+ equal to, less than, less than or equal to, greater than, or
+ greater than or equal to ARG2, respectively. ARG1 and ARG2 may be
+ positive or negative integers. When used with the '[[' command,
+ ARG1 and ARG2 are evaluated as arithmetic expressions (*note Shell
+ Arithmetic::).
+
+
+File: bash.info, Node: Shell Arithmetic, Next: Aliases, Prev: Bash Conditional Expressions, Up: Bash Features
+
+6.5 Shell Arithmetic
+====================
+
+The shell allows arithmetic expressions to be evaluated, as one of the
+shell expansions or by using the '((' compound command, the 'let'
+builtin, or the '-i' option to the 'declare' builtin.
+
+ Evaluation is done in fixed-width integers with no check for
+overflow, though division by 0 is trapped and flagged as an error. The
+operators and their precedence, associativity, and values are the same
+as in the C language. The following list of operators is grouped into
+levels of equal-precedence operators. The levels are listed in order of
+decreasing precedence.
+
+'ID++ ID--'
+ variable post-increment and post-decrement
+
+'++ID --ID'
+ variable pre-increment and pre-decrement
+
+'- +'
+ unary minus and plus
+
+'! ~'
+ logical and bitwise negation
+
+'**'
+ exponentiation
+
+'* / %'
+ multiplication, division, remainder
+
+'+ -'
+ addition, subtraction
+
+'<< >>'
+ left and right bitwise shifts
+
+'<= >= < >'
+ comparison
+
+'== !='
+ equality and inequality
+
+'&'
+ bitwise AND
+
+'^'
+ bitwise exclusive OR
+
+'|'
+ bitwise OR
+
+'&&'
+ logical AND
+
+'||'
+ logical OR
+
+'expr ? expr : expr'
+ conditional operator
+
+'= *= /= %= += -= <<= >>= &= ^= |='
+ assignment
+
+'expr1 , expr2'
+ comma
+
+ Shell variables are allowed as operands; parameter expansion is
+performed before the expression is evaluated. Within an expression,
+shell variables may also be referenced by name without using the
+parameter expansion syntax. A shell variable that is null or unset
+evaluates to 0 when referenced by name without using the parameter
+expansion syntax. The value of a variable is evaluated as an arithmetic
+expression when it is referenced, or when a variable which has been
+given the 'integer' attribute using 'declare -i' is assigned a value. A
+null value evaluates to 0. A shell variable need not have its 'integer'
+attribute turned on to be used in an expression.
+
+ Integer constants follow the C language definition, without suffixes
+or character constants. Constants with a leading 0 are interpreted as
+octal numbers. A leading '0x' or '0X' denotes hexadecimal. Otherwise,
+numbers take the form [BASE'#']N, where the optional BASE is a decimal
+number between 2 and 64 representing the arithmetic base, and N is a
+number in that base. If BASE'#' is omitted, then base 10 is used. When
+specifying N, if a non-digit is required, the digits greater than 9 are
+represented by the lowercase letters, the uppercase letters, '@', and
+'_', in that order. If BASE is less than or equal to 36, lowercase and
+uppercase letters may be used interchangeably to represent numbers
+between 10 and 35.
+
+ Operators are evaluated in order of precedence. Sub-expressions in
+parentheses are evaluated first and may override the precedence rules
+above.
+
+
+File: bash.info, Node: Aliases, Next: Arrays, Prev: Shell Arithmetic, Up: Bash Features
+
+6.6 Aliases
+===========
+
+"Aliases" allow a string to be substituted for a word when it is used as
+the first word of a simple command. The shell maintains a list of
+aliases that may be set and unset with the 'alias' and 'unalias' builtin
+commands.
+
+ The first word of each simple command, if unquoted, is checked to see
+if it has an alias. If so, that word is replaced by the text of the
+alias. The characters '/', '$', '`', '=' and any of the shell
+metacharacters or quoting characters listed above may not appear in an
+alias name. The replacement text may contain any valid shell input,
+including shell metacharacters. The first word of the replacement text
+is tested for aliases, but a word that is identical to an alias being
+expanded is not expanded a second time. This means that one may alias
+'ls' to '"ls -F"', for instance, and Bash does not try to recursively
+expand the replacement text. If the last character of the alias value
+is a 'blank', then the next command word following the alias is also
+checked for alias expansion.
+
+ Aliases are created and listed with the 'alias' command, and removed
+with the 'unalias' command.
+
+ There is no mechanism for using arguments in the replacement text, as
+in 'csh'. If arguments are needed, use a shell function (*note Shell
+Functions::).
+
+ Aliases are not expanded when the shell is not interactive, unless
+the 'expand_aliases' shell option is set using 'shopt' (*note The Shopt
+Builtin::).
+
+ The rules concerning the definition and use of aliases are somewhat
+confusing. Bash always reads at least one complete line of input, and
+all lines that make up a compound command, before executing any of the
+commands on that line or the compound command. Aliases are expanded
+when a command is read, not when it is executed. Therefore, an alias
+definition appearing on the same line as another command does not take
+effect until the next line of input is read. The commands following the
+alias definition on that line are not affected by the new alias. This
+behavior is also an issue when functions are executed. Aliases are
+expanded when a function definition is read, not when the function is
+executed, because a function definition is itself a command. As a
+consequence, aliases defined in a function are not available until after
+that function is executed. To be safe, always put alias definitions on
+a separate line, and do not use 'alias' in compound commands.
+
+ For almost every purpose, shell functions are preferred over aliases.
+
+
+File: bash.info, Node: Arrays, Next: The Directory Stack, Prev: Aliases, Up: Bash Features
+
+6.7 Arrays
+==========
+
+Bash provides one-dimensional indexed and associative array variables.
+Any variable may be used as an indexed array; the 'declare' builtin will
+explicitly declare an array. There is no maximum limit on the size of
+an array, nor any requirement that members be indexed or assigned
+contiguously. Indexed arrays are referenced using integers (including
+arithmetic expressions (*note Shell Arithmetic::)) and are zero-based;
+associative arrays use arbitrary strings. Unless otherwise noted,
+indexed array indices must be non-negative integers.
+
+ An indexed array is created automatically if any variable is assigned
+to using the syntax
+ NAME[SUBSCRIPT]=VALUE
+
+The SUBSCRIPT is treated as an arithmetic expression that must evaluate
+to a number. To explicitly declare an array, use
+ declare -a NAME
+The syntax
+ declare -a NAME[SUBSCRIPT]
+is also accepted; the SUBSCRIPT is ignored.
+
+Associative arrays are created using
+ declare -A NAME
+
+ Attributes may be specified for an array variable using the 'declare'
+and 'readonly' builtins. Each attribute applies to all members of an
+array.
+
+ Arrays are assigned to using compound assignments of the form
+ NAME=(VALUE1 VALUE2 ... )
+where each VALUE may be of the form '[SUBSCRIPT]='STRING. Indexed array
+assignments do not require anything but STRING. When assigning to
+indexed arrays, if the optional subscript is supplied, that index is
+assigned to; otherwise the index of the element assigned is the last
+index assigned to by the statement plus one. Indexing starts at zero.
+
+ Each VALUE in the list undergoes all the shell expansions described
+above (*note Shell Expansions::).
+
+ When assigning to an associative array, the words in a compound
+assignment may be either assignment statements, for which the subscript
+is required, or a list of words that is interpreted as a sequence of
+alternating keys and values: NAME=(KEY1 VALUE1 KEY2 VALUE2 ... ). These
+are treated identically to NAME=( [KEY1]=VALUE1 [KEY2]=VALUE2 ... ).
+The first word in the list determines how the remaining words are
+interpreted; all assignments in a list must be of the same type. When
+using key/value pairs, the keys may not be missing or empty; a final
+missing value is treated like the empty string.
+
+ This syntax is also accepted by the 'declare' builtin. Individual
+array elements may be assigned to using the 'NAME[SUBSCRIPT]=VALUE'
+syntax introduced above.
+
+ When assigning to an indexed array, if NAME is subscripted by a
+negative number, that number is interpreted as relative to one greater
+than the maximum index of NAME, so negative indices count back from the
+end of the array, and an index of -1 references the last element.
+
+ The '+=' operator will append to an array variable when assigning
+using the compound assignment syntax; see *note Shell Parameters::
+above.
+
+ Any element of an array may be referenced using '${NAME[SUBSCRIPT]}'.
+The braces are required to avoid conflicts with the shell's filename
+expansion operators. If the SUBSCRIPT is '@' or '*', the word expands
+to all members of the array NAME. These subscripts differ only when the
+word appears within double quotes. If the word is double-quoted,
+'${NAME[*]}' expands to a single word with the value of each array
+member separated by the first character of the 'IFS' variable, and
+'${NAME[@]}' expands each element of NAME to a separate word. When
+there are no array members, '${NAME[@]}' expands to nothing. If the
+double-quoted expansion occurs within a word, the expansion of the first
+parameter is joined with the beginning part of the original word, and
+the expansion of the last parameter is joined with the last part of the
+original word. This is analogous to the expansion of the special
+parameters '@' and '*'. '${#NAME[SUBSCRIPT]}' expands to the length of
+'${NAME[SUBSCRIPT]}'. If SUBSCRIPT is '@' or '*', the expansion is the
+number of elements in the array. If the SUBSCRIPT used to reference an
+element of an indexed array evaluates to a number less than zero, it is
+interpreted as relative to one greater than the maximum index of the
+array, so negative indices count back from the end of the array, and an
+index of -1 refers to the last element.
+
+ Referencing an array variable without a subscript is equivalent to
+referencing with a subscript of 0. Any reference to a variable using a
+valid subscript is legal, and 'bash' will create an array if necessary.
+
+ An array variable is considered set if a subscript has been assigned
+a value. The null string is a valid value.
+
+ It is possible to obtain the keys (indices) of an array as well as
+the values. ${!NAME[@]} and ${!NAME[*]} expand to the indices assigned
+in array variable NAME. The treatment when in double quotes is similar
+to the expansion of the special parameters '@' and '*' within double
+quotes.
+
+ The 'unset' builtin is used to destroy arrays. 'unset
+NAME[SUBSCRIPT]' destroys the array element at index SUBSCRIPT.
+Negative subscripts to indexed arrays are interpreted as described
+above. Unsetting the last element of an array variable does not unset
+the variable. 'unset NAME', where NAME is an array, removes the entire
+array. 'unset NAME[SUBSCRIPT]' behaves differently depending on the
+array type when given a subscript of '*' or '@'. When NAME is an
+associative array, it removes the element with key '*' or '@'. If NAME
+is an indexed array, 'unset' removes all of the elements, but does not
+remove the array itself.
+
+ When using a variable name with a subscript as an argument to a
+command, such as with 'unset', without using the word expansion syntax
+described above, the argument is subject to the shell's filename
+expansion. If filename expansion is not desired, the argument should be
+quoted.
+
+ The 'declare', 'local', and 'readonly' builtins each accept a '-a'
+option to specify an indexed array and a '-A' option to specify an
+associative array. If both options are supplied, '-A' takes precedence.
+The 'read' builtin accepts a '-a' option to assign a list of words read
+from the standard input to an array, and can read values from the
+standard input into individual array elements. The 'set' and 'declare'
+builtins display array values in a way that allows them to be reused as
+input.
+
+
+File: bash.info, Node: The Directory Stack, Next: Controlling the Prompt, Prev: Arrays, Up: Bash Features
+
+6.8 The Directory Stack
+=======================
+
+* Menu:
+
+* Directory Stack Builtins:: Bash builtin commands to manipulate
+ the directory stack.
+
+The directory stack is a list of recently-visited directories. The
+'pushd' builtin adds directories to the stack as it changes the current
+directory, and the 'popd' builtin removes specified directories from the
+stack and changes the current directory to the directory removed. The
+'dirs' builtin displays the contents of the directory stack. The
+current directory is always the "top" of the directory stack.
+
+ The contents of the directory stack are also visible as the value of
+the 'DIRSTACK' shell variable.
+
+
+File: bash.info, Node: Directory Stack Builtins, Up: The Directory Stack
+
+6.8.1 Directory Stack Builtins
+------------------------------
+
+'dirs'
+ dirs [-clpv] [+N | -N]
+
+ Display the list of currently remembered directories. Directories
+ are added to the list with the 'pushd' command; the 'popd' command
+ removes directories from the list. The current directory is always
+ the first directory in the stack.
+
+ '-c'
+ Clears the directory stack by deleting all of the elements.
+ '-l'
+ Produces a listing using full pathnames; the default listing
+ format uses a tilde to denote the home directory.
+ '-p'
+ Causes 'dirs' to print the directory stack with one entry per
+ line.
+ '-v'
+ Causes 'dirs' to print the directory stack with one entry per
+ line, prefixing each entry with its index in the stack.
+ '+N'
+ Displays the Nth directory (counting from the left of the list
+ printed by 'dirs' when invoked without options), starting with
+ zero.
+ '-N'
+ Displays the Nth directory (counting from the right of the
+ list printed by 'dirs' when invoked without options), starting
+ with zero.
+
+'popd'
+ popd [-n] [+N | -N]
+
+ Removes elements from the directory stack. The elements are
+ numbered from 0 starting at the first directory listed by 'dirs';
+ that is, 'popd' is equivalent to 'popd +0'.
+
+ When no arguments are given, 'popd' removes the top directory from
+ the stack and changes to the new top directory.
+
+ Arguments, if supplied, have the following meanings:
+
+ '-n'
+ Suppresses the normal change of directory when removing
+ directories from the stack, so that only the stack is
+ manipulated.
+ '+N'
+ Removes the Nth directory (counting from the left of the list
+ printed by 'dirs'), starting with zero, from the stack.
+ '-N'
+ Removes the Nth directory (counting from the right of the list
+ printed by 'dirs'), starting with zero, from the stack.
+
+ If the top element of the directory stack is modified, and the '-n'
+ option was not supplied, 'popd' uses the 'cd' builtin to change to
+ the directory at the top of the stack. If the 'cd' fails, 'popd'
+ returns a non-zero value.
+
+ Otherwise, 'popd' returns an unsuccessful status if an invalid
+ option is encountered, the directory stack is empty, or a
+ non-existent directory stack entry is specified.
+
+ If the 'popd' command is successful, Bash runs 'dirs' to show the
+ final contents of the directory stack, and the return status is 0.
+
+'pushd'
+ pushd [-n] [+N | -N | DIR]
+
+ Adds a directory to the top of the directory stack, or rotates the
+ stack, making the new top of the stack the current working
+ directory. With no arguments, 'pushd' exchanges the top two
+ elements of the directory stack.
+
+ Arguments, if supplied, have the following meanings:
+
+ '-n'
+ Suppresses the normal change of directory when rotating or
+ adding directories to the stack, so that only the stack is
+ manipulated.
+ '+N'
+ Brings the Nth directory (counting from the left of the list
+ printed by 'dirs', starting with zero) to the top of the list
+ by rotating the stack.
+ '-N'
+ Brings the Nth directory (counting from the right of the list
+ printed by 'dirs', starting with zero) to the top of the list
+ by rotating the stack.
+ 'DIR'
+ Makes DIR be the top of the stack.
+
+ After the stack has been modified, if the '-n' option was not
+ supplied, 'pushd' uses the 'cd' builtin to change to the directory
+ at the top of the stack. If the 'cd' fails, 'pushd' returns a
+ non-zero value.
+
+ Otherwise, if no arguments are supplied, 'pushd' returns 0 unless
+ the directory stack is empty. When rotating the directory stack,
+ 'pushd' returns 0 unless the directory stack is empty or a
+ non-existent directory stack element is specified.
+
+ If the 'pushd' command is successful, Bash runs 'dirs' to show the
+ final contents of the directory stack.
+
+
+File: bash.info, Node: Controlling the Prompt, Next: The Restricted Shell, Prev: The Directory Stack, Up: Bash Features
+
+6.9 Controlling the Prompt
+==========================
+
+Bash examines the value of the array variable 'PROMPT_COMMAND' just
+before printing each primary prompt. If any elements in
+'PROMPT_COMMAND' are set and non-null, Bash executes each value, in
+numeric order, just as if it had been typed on the command line.
+
+ In addition, the following table describes the special characters
+which can appear in the prompt variables 'PS0', 'PS1', 'PS2', and 'PS4':
+
+'\a'
+ A bell character.
+'\d'
+ The date, in "Weekday Month Date" format (e.g., "Tue May 26").
+'\D{FORMAT}'
+ The FORMAT is passed to 'strftime'(3) and the result is inserted
+ into the prompt string; an empty FORMAT results in a
+ locale-specific time representation. The braces are required.
+'\e'
+ An escape character.
+'\h'
+ The hostname, up to the first '.'.
+'\H'
+ The hostname.
+'\j'
+ The number of jobs currently managed by the shell.
+'\l'
+ The basename of the shell's terminal device name.
+'\n'
+ A newline.
+'\r'
+ A carriage return.
+'\s'
+ The name of the shell, the basename of '$0' (the portion following
+ the final slash).
+'\t'
+ The time, in 24-hour HH:MM:SS format.
+'\T'
+ The time, in 12-hour HH:MM:SS format.
+'\@'
+ The time, in 12-hour am/pm format.
+'\A'
+ The time, in 24-hour HH:MM format.
+'\u'
+ The username of the current user.
+'\v'
+ The version of Bash (e.g., 2.00)
+'\V'
+ The release of Bash, version + patchlevel (e.g., 2.00.0)
+'\w'
+ The value of the 'PWD' shell variable ('$PWD'), with '$HOME'
+ abbreviated with a tilde (uses the '$PROMPT_DIRTRIM' variable).
+'\W'
+ The basename of '$PWD', with '$HOME' abbreviated with a tilde.
+'\!'
+ The history number of this command.
+'\#'
+ The command number of this command.
+'\$'
+ If the effective uid is 0, '#', otherwise '$'.
+'\NNN'
+ The character whose ASCII code is the octal value NNN.
+'\\'
+ A backslash.
+'\['
+ Begin a sequence of non-printing characters. This could be used to
+ embed a terminal control sequence into the prompt.
+'\]'
+ End a sequence of non-printing characters.
+
+ The command number and the history number are usually different: the
+history number of a command is its position in the history list, which
+may include commands restored from the history file (*note Bash History
+Facilities::), while the command number is the position in the sequence
+of commands executed during the current shell session.
+
+ After the string is decoded, it is expanded via parameter expansion,
+command substitution, arithmetic expansion, and quote removal, subject
+to the value of the 'promptvars' shell option (*note The Shopt
+Builtin::). This can have unwanted side effects if escaped portions of
+the string appear within command substitution or contain characters
+special to word expansion.
+
+
+File: bash.info, Node: The Restricted Shell, Next: Bash POSIX Mode, Prev: Controlling the Prompt, Up: Bash Features
+
+6.10 The Restricted Shell
+=========================
+
+If Bash is started with the name 'rbash', or the '--restricted' or '-r'
+option is supplied at invocation, the shell becomes restricted. A
+restricted shell is used to set up an environment more controlled than
+the standard shell. A restricted shell behaves identically to 'bash'
+with the exception that the following are disallowed or not performed:
+
+ * Changing directories with the 'cd' builtin.
+ * Setting or unsetting the values of the 'SHELL', 'PATH', 'HISTFILE',
+ 'ENV', or 'BASH_ENV' variables.
+ * Specifying command names containing slashes.
+ * Specifying a filename containing a slash as an argument to the '.'
+ builtin command.
+ * Specifying a filename containing a slash as an argument to the
+ 'history' builtin command.
+ * Specifying a filename containing a slash as an argument to the '-p'
+ option to the 'hash' builtin command.
+ * Importing function definitions from the shell environment at
+ startup.
+ * Parsing the value of 'SHELLOPTS' from the shell environment at
+ startup.
+ * Redirecting output using the '>', '>|', '<>', '>&', '&>', and '>>'
+ redirection operators.
+ * Using the 'exec' builtin to replace the shell with another command.
+ * Adding or deleting builtin commands with the '-f' and '-d' options
+ to the 'enable' builtin.
+ * Using the 'enable' builtin command to enable disabled shell
+ builtins.
+ * Specifying the '-p' option to the 'command' builtin.
+ * Turning off restricted mode with 'set +r' or 'shopt -u
+ restricted_shell'.
+
+ These restrictions are enforced after any startup files are read.
+
+ When a command that is found to be a shell script is executed (*note
+Shell Scripts::), 'rbash' turns off any restrictions in the shell
+spawned to execute the script.
+
+ The restricted shell mode is only one component of a useful
+restricted environment. It should be accompanied by setting 'PATH' to a
+value that allows execution of only a few verified commands (commands
+that allow shell escapes are particularly vulnerable), changing the
+current directory to a non-writable directory other than '$HOME' after
+login, not allowing the restricted shell to execute shell scripts, and
+cleaning the environment of variables that cause some commands to modify
+their behavior (e.g., 'VISUAL' or 'PAGER').
+
+ Modern systems provide more secure ways to implement a restricted
+environment, such as 'jails', 'zones', or 'containers'.
+
+
+File: bash.info, Node: Bash POSIX Mode, Next: Shell Compatibility Mode, Prev: The Restricted Shell, Up: Bash Features
+
+6.11 Bash POSIX Mode
+====================
+
+Starting Bash with the '--posix' command-line option or executing 'set
+-o posix' while Bash is running will cause Bash to conform more closely
+to the POSIX standard by changing the behavior to match that specified
+by POSIX in areas where the Bash default differs.
+
+ When invoked as 'sh', Bash enters POSIX mode after reading the
+startup files.
+
+ The following list is what's changed when 'POSIX mode' is in effect:
+
+ 1. Bash ensures that the 'POSIXLY_CORRECT' variable is set.
+
+ 2. When a command in the hash table no longer exists, Bash will
+ re-search '$PATH' to find the new location. This is also available
+ with 'shopt -s checkhash'.
+
+ 3. Bash will not insert a command without the execute bit set into the
+ command hash table, even if it returns it as a (last-ditch) result
+ from a '$PATH' search.
+
+ 4. The message printed by the job control code and builtins when a job
+ exits with a non-zero status is 'Done(status)'.
+
+ 5. The message printed by the job control code and builtins when a job
+ is stopped is 'Stopped(SIGNAME)', where SIGNAME is, for example,
+ 'SIGTSTP'.
+
+ 6. Alias expansion is always enabled, even in non-interactive shells.
+
+ 7. Reserved words appearing in a context where reserved words are
+ recognized do not undergo alias expansion.
+
+ 8. Alias expansion is performed when initially parsing a command
+ substitution. The default mode generally defers it, when enabled,
+ until the command substitution is executed. This means that
+ command substitution will not expand aliases that are defined after
+ the command substitution is initially parsed (e.g., as part of a
+ function definition).
+
+ 9. The POSIX 'PS1' and 'PS2' expansions of '!' to the history number
+ and '!!' to '!' are enabled, and parameter expansion is performed
+ on the values of 'PS1' and 'PS2' regardless of the setting of the
+ 'promptvars' option.
+
+ 10. The POSIX startup files are executed ('$ENV') rather than the
+ normal Bash files.
+
+ 11. Tilde expansion is only performed on assignments preceding a
+ command name, rather than on all assignment statements on the line.
+
+ 12. The default history file is '~/.sh_history' (this is the default
+ value of '$HISTFILE').
+
+ 13. Redirection operators do not perform filename expansion on the
+ word in the redirection unless the shell is interactive.
+
+ 14. Redirection operators do not perform word splitting on the word in
+ the redirection.
+
+ 15. Function names must be valid shell 'name's. That is, they may not
+ contain characters other than letters, digits, and underscores, and
+ may not start with a digit. Declaring a function with an invalid
+ name causes a fatal syntax error in non-interactive shells.
+
+ 16. Function names may not be the same as one of the POSIX special
+ builtins.
+
+ 17. POSIX special builtins are found before shell functions during
+ command lookup.
+
+ 18. When printing shell function definitions (e.g., by 'type'), Bash
+ does not print the 'function' keyword.
+
+ 19. Literal tildes that appear as the first character in elements of
+ the 'PATH' variable are not expanded as described above under *note
+ Tilde Expansion::.
+
+ 20. The 'time' reserved word may be used by itself as a command. When
+ used in this way, it displays timing statistics for the shell and
+ its completed children. The 'TIMEFORMAT' variable controls the
+ format of the timing information.
+
+ 21. When parsing and expanding a ${...} expansion that appears within
+ double quotes, single quotes are no longer special and cannot be
+ used to quote a closing brace or other special character, unless
+ the operator is one of those defined to perform pattern removal.
+ In this case, they do not have to appear as matched pairs.
+
+ 22. The parser does not recognize 'time' as a reserved word if the
+ next token begins with a '-'.
+
+ 23. The '!' character does not introduce history expansion within a
+ double-quoted string, even if the 'histexpand' option is enabled.
+
+ 24. If a POSIX special builtin returns an error status, a
+ non-interactive shell exits. The fatal errors are those listed in
+ the POSIX standard, and include things like passing incorrect
+ options, redirection errors, variable assignment errors for
+ assignments preceding the command name, and so on.
+
+ 25. A non-interactive shell exits with an error status if a variable
+ assignment error occurs when no command name follows the assignment
+ statements. A variable assignment error occurs, for example, when
+ trying to assign a value to a readonly variable.
+
+ 26. A non-interactive shell exits with an error status if a variable
+ assignment error occurs in an assignment statement preceding a
+ special builtin, but not with any other simple command. For any
+ other simple command, the shell aborts execution of that command,
+ and execution continues at the top level ("the shell shall not
+ perform any further processing of the command in which the error
+ occurred").
+
+ 27. A non-interactive shell exits with an error status if the
+ iteration variable in a 'for' statement or the selection variable
+ in a 'select' statement is a readonly variable.
+
+ 28. Non-interactive shells exit if FILENAME in '.' FILENAME is not
+ found.
+
+ 29. Non-interactive shells exit if a syntax error in an arithmetic
+ expansion results in an invalid expression.
+
+ 30. Non-interactive shells exit if a parameter expansion error occurs.
+
+ 31. Non-interactive shells exit if there is a syntax error in a script
+ read with the '.' or 'source' builtins, or in a string processed by
+ the 'eval' builtin.
+
+ 32. While variable indirection is available, it may not be applied to
+ the '#' and '?' special parameters.
+
+ 33. Expanding the '*' special parameter in a pattern context where the
+ expansion is double-quoted does not treat the '$*' as if it were
+ double-quoted.
+
+ 34. Assignment statements preceding POSIX special builtins persist in
+ the shell environment after the builtin completes.
+
+ 35. The 'command' builtin does not prevent builtins that take
+ assignment statements as arguments from expanding them as
+ assignment statements; when not in POSIX mode, assignment builtins
+ lose their assignment statement expansion properties when preceded
+ by 'command'.
+
+ 36. The 'bg' builtin uses the required format to describe each job
+ placed in the background, which does not include an indication of
+ whether the job is the current or previous job.
+
+ 37. The output of 'kill -l' prints all the signal names on a single
+ line, separated by spaces, without the 'SIG' prefix.
+
+ 38. The 'kill' builtin does not accept signal names with a 'SIG'
+ prefix.
+
+ 39. The 'export' and 'readonly' builtin commands display their output
+ in the format required by POSIX.
+
+ 40. The 'trap' builtin displays signal names without the leading
+ 'SIG'.
+
+ 41. The 'trap' builtin doesn't check the first argument for a possible
+ signal specification and revert the signal handling to the original
+ disposition if it is, unless that argument consists solely of
+ digits and is a valid signal number. If users want to reset the
+ handler for a given signal to the original disposition, they should
+ use '-' as the first argument.
+
+ 42. 'trap -p' displays signals whose dispositions are set to SIG_DFL
+ and those that were ignored when the shell started.
+
+ 43. The '.' and 'source' builtins do not search the current directory
+ for the filename argument if it is not found by searching 'PATH'.
+
+ 44. Enabling POSIX mode has the effect of setting the
+ 'inherit_errexit' option, so subshells spawned to execute command
+ substitutions inherit the value of the '-e' option from the parent
+ shell. When the 'inherit_errexit' option is not enabled, Bash
+ clears the '-e' option in such subshells.
+
+ 45. Enabling POSIX mode has the effect of setting the 'shift_verbose'
+ option, so numeric arguments to 'shift' that exceed the number of
+ positional parameters will result in an error message.
+
+ 46. When the 'alias' builtin displays alias definitions, it does not
+ display them with a leading 'alias ' unless the '-p' option is
+ supplied.
+
+ 47. When the 'set' builtin is invoked without options, it does not
+ display shell function names and definitions.
+
+ 48. When the 'set' builtin is invoked without options, it displays
+ variable values without quotes, unless they contain shell
+ metacharacters, even if the result contains nonprinting characters.
+
+ 49. When the 'cd' builtin is invoked in logical mode, and the pathname
+ constructed from '$PWD' and the directory name supplied as an
+ argument does not refer to an existing directory, 'cd' will fail
+ instead of falling back to physical mode.
+
+ 50. When the 'cd' builtin cannot change a directory because the length
+ of the pathname constructed from '$PWD' and the directory name
+ supplied as an argument exceeds 'PATH_MAX' when all symbolic links
+ are expanded, 'cd' will fail instead of attempting to use only the
+ supplied directory name.
+
+ 51. The 'pwd' builtin verifies that the value it prints is the same as
+ the current directory, even if it is not asked to check the file
+ system with the '-P' option.
+
+ 52. When listing the history, the 'fc' builtin does not include an
+ indication of whether or not a history entry has been modified.
+
+ 53. The default editor used by 'fc' is 'ed'.
+
+ 54. The 'type' and 'command' builtins will not report a non-executable
+ file as having been found, though the shell will attempt to execute
+ such a file if it is the only so-named file found in '$PATH'.
+
+ 55. The 'vi' editing mode will invoke the 'vi' editor directly when
+ the 'v' command is run, instead of checking '$VISUAL' and
+ '$EDITOR'.
+
+ 56. When the 'xpg_echo' option is enabled, Bash does not attempt to
+ interpret any arguments to 'echo' as options. Each argument is
+ displayed, after escape characters are converted.
+
+ 57. The 'ulimit' builtin uses a block size of 512 bytes for the '-c'
+ and '-f' options.
+
+ 58. The arrival of 'SIGCHLD' when a trap is set on 'SIGCHLD' does not
+ interrupt the 'wait' builtin and cause it to return immediately.
+ The trap command is run once for each child that exits.
+
+ 59. The 'read' builtin may be interrupted by a signal for which a trap
+ has been set. If Bash receives a trapped signal while executing
+ 'read', the trap handler executes and 'read' returns an exit status
+ greater than 128.
+
+ 60. The 'printf' builtin uses 'double' (via 'strtod') to convert
+ arguments corresponding to floating point conversion specifiers,
+ instead of 'long double' if it's available. The 'L' length
+ modifier forces 'printf' to use 'long double' if it's available.
+
+ 61. Bash removes an exited background process's status from the list
+ of such statuses after the 'wait' builtin is used to obtain it.
+
+ There is other POSIX behavior that Bash does not implement by default
+even when in POSIX mode. Specifically:
+
+ 1. The 'fc' builtin checks '$EDITOR' as a program to edit history
+ entries if 'FCEDIT' is unset, rather than defaulting directly to
+ 'ed'. 'fc' uses 'ed' if 'EDITOR' is unset.
+
+ 2. As noted above, Bash requires the 'xpg_echo' option to be enabled
+ for the 'echo' builtin to be fully conformant.
+
+ Bash can be configured to be POSIX-conformant by default, by
+specifying the '--enable-strict-posix-default' to 'configure' when
+building (*note Optional Features::).
+
+
+File: bash.info, Node: Shell Compatibility Mode, Prev: Bash POSIX Mode, Up: Bash Features
+
+6.12 Shell Compatibility Mode
+=============================
+
+Bash-4.0 introduced the concept of a "shell compatibility level",
+specified as a set of options to the shopt builtin ('compat31',
+'compat32', 'compat40', 'compat41', and so on). There is only one
+current compatibility level - each option is mutually exclusive. The
+compatibility level is intended to allow users to select behavior from
+previous versions that is incompatible with newer versions while they
+migrate scripts to use current features and behavior. It's intended to
+be a temporary solution.
+
+ This section does not mention behavior that is standard for a
+particular version (e.g., setting 'compat32' means that quoting the rhs
+of the regexp matching operator quotes special regexp characters in the
+word, which is default behavior in bash-3.2 and subsequent versions).
+
+ If a user enables, say, 'compat32', it may affect the behavior of
+other compatibility levels up to and including the current compatibility
+level. The idea is that each compatibility level controls behavior that
+changed in that version of Bash, but that behavior may have been present
+in earlier versions. For instance, the change to use locale-based
+comparisons with the '[[' command came in bash-4.1, and earlier versions
+used ASCII-based comparisons, so enabling 'compat32' will enable
+ASCII-based comparisons as well. That granularity may not be sufficient
+for all uses, and as a result users should employ compatibility levels
+carefully. Read the documentation for a particular feature to find out
+the current behavior.
+
+ Bash-4.3 introduced a new shell variable: 'BASH_COMPAT'. The value
+assigned to this variable (a decimal version number like 4.2, or an
+integer corresponding to the 'compat'NN option, like 42) determines the
+compatibility level.
+
+ Starting with bash-4.4, Bash has begun deprecating older
+compatibility levels. Eventually, the options will be removed in favor
+of 'BASH_COMPAT'.
+
+ Bash-5.0 is the final version for which there will be an individual
+shopt option for the previous version. Users should use 'BASH_COMPAT'
+on bash-5.0 and later versions.
+
+ The following table describes the behavior changes controlled by each
+compatibility level setting. The 'compat'NN tag is used as shorthand
+for setting the compatibility level to NN using one of the following
+mechanisms. For versions prior to bash-5.0, the compatibility level may
+be set using the corresponding 'compat'NN shopt option. For bash-4.3
+and later versions, the 'BASH_COMPAT' variable is preferred, and it is
+required for bash-5.1 and later versions.
+
+'compat31'
+ * quoting the rhs of the '[[' command's regexp matching operator
+ (=~) has no special effect
+
+'compat32'
+ * interrupting a command list such as "a ; b ; c" causes the
+ execution of the next command in the list (in bash-4.0 and
+ later versions, the shell acts as if it received the
+ interrupt, so interrupting one command in a list aborts the
+ execution of the entire list)
+
+'compat40'
+ * the '<' and '>' operators to the '[[' command do not consider
+ the current locale when comparing strings; they use ASCII
+ ordering. Bash versions prior to bash-4.1 use ASCII collation
+ and strcmp(3); bash-4.1 and later use the current locale's
+ collation sequence and strcoll(3).
+
+'compat41'
+ * in posix mode, 'time' may be followed by options and still be
+ recognized as a reserved word (this is POSIX interpretation
+ 267)
+ * in posix mode, the parser requires that an even number of
+ single quotes occur in the WORD portion of a double-quoted
+ ${...} parameter expansion and treats them specially, so that
+ characters within the single quotes are considered quoted
+ (this is POSIX interpretation 221)
+
+'compat42'
+ * the replacement string in double-quoted pattern substitution
+ does not undergo quote removal, as it does in versions after
+ bash-4.2
+ * in posix mode, single quotes are considered special when
+ expanding the WORD portion of a double-quoted ${...} parameter
+ expansion and can be used to quote a closing brace or other
+ special character (this is part of POSIX interpretation 221);
+ in later versions, single quotes are not special within
+ double-quoted word expansions
+
+'compat43'
+ * the shell does not print a warning message if an attempt is
+ made to use a quoted compound assignment as an argument to
+ declare (e.g., declare -a foo='(1 2)'). Later versions warn
+ that this usage is deprecated
+ * word expansion errors are considered non-fatal errors that
+ cause the current command to fail, even in posix mode (the
+ default behavior is to make them fatal errors that cause the
+ shell to exit)
+ * when executing a shell function, the loop state
+ (while/until/etc.) is not reset, so 'break' or 'continue' in
+ that function will break or continue loops in the calling
+ context. Bash-4.4 and later reset the loop state to prevent
+ this
+
+'compat44'
+ * the shell sets up the values used by 'BASH_ARGV' and
+ 'BASH_ARGC' so they can expand to the shell's positional
+ parameters even if extended debugging mode is not enabled
+ * a subshell inherits loops from its parent context, so 'break'
+ or 'continue' will cause the subshell to exit. Bash-5.0 and
+ later reset the loop state to prevent the exit
+ * variable assignments preceding builtins like 'export' and
+ 'readonly' that set attributes continue to affect variables
+ with the same name in the calling environment even if the
+ shell is not in posix mode
+
+'compat50 (set using BASH_COMPAT)'
+ * Bash-5.1 changed the way '$RANDOM' is generated to introduce
+ slightly more randomness. If the shell compatibility level is
+ set to 50 or lower, it reverts to the method from bash-5.0 and
+ previous versions, so seeding the random number generator by
+ assigning a value to 'RANDOM' will produce the same sequence
+ as in bash-5.0
+ * If the command hash table is empty, Bash versions prior to
+ bash-5.1 printed an informational message to that effect, even
+ when producing output that can be reused as input. Bash-5.1
+ suppresses that message when the '-l' option is supplied.
+
+'compat51 (set using BASH_COMPAT)'
+ * The 'unset' builtin will unset the array 'a' given an argument
+ like 'a[@]'. Bash-5.2 will unset an element with key '@'
+ (associative arrays) or remove all the elements without
+ unsetting the array (indexed arrays)
+ * arithmetic commands ( ((...)) ) and the expressions in an
+ arithmetic for statement can be expanded more than once
+ * expressions used as arguments to arithmetic operators in the
+ '[[' conditional command can be expanded more than once
+ * the expressions in substring parameter brace expansion can be
+ expanded more than once
+ * the expressions in the $(( ... )) word expansion can be
+ expanded more than once
+ * arithmetic expressions used as indexed array subscripts can be
+ expanded more than once
+ * 'test -v', when given an argument of 'A[@]', where A is an
+ existing associative array, will return true if the array has
+ any set elements. Bash-5.2 will look for and report on a key
+ named '@'
+ * the ${PARAMETER[:]=VALUE} word expansion will return VALUE,
+ before any variable-specific transformations have been
+ performed (e.g., converting to lowercase). Bash-5.2 will
+ return the final value assigned to the variable.
+ * Parsing command substitutions will behave as if extended glob
+ (*note The Shopt Builtin::) is enabled, so that parsing a
+ command substitution containing an extglob pattern (say, as
+ part of a shell function) will not fail. This assumes the
+ intent is to enable extglob before the command is executed and
+ word expansions are performed. It will fail at word expansion
+ time if extglob hasn't been enabled by the time the command is
+ executed.
+
+
+File: bash.info, Node: Job Control, Next: Command Line Editing, Prev: Bash Features, Up: Top
+
+7 Job Control
+*************
+
+This chapter discusses what job control is, how it works, and how Bash
+allows you to access its facilities.
+
+* Menu:
+
+* Job Control Basics:: How job control works.
+* Job Control Builtins:: Bash builtin commands used to interact
+ with job control.
+* Job Control Variables:: Variables Bash uses to customize job
+ control.
+
+
+File: bash.info, Node: Job Control Basics, Next: Job Control Builtins, Up: Job Control
+
+7.1 Job Control Basics
+======================
+
+Job control refers to the ability to selectively stop (suspend) the
+execution of processes and continue (resume) their execution at a later
+point. A user typically employs this facility via an interactive
+interface supplied jointly by the operating system kernel's terminal
+driver and Bash.
+
+ The shell associates a JOB with each pipeline. It keeps a table of
+currently executing jobs, which may be listed with the 'jobs' command.
+When Bash starts a job asynchronously, it prints a line that looks like:
+ [1] 25647
+indicating that this job is job number 1 and that the process ID of the
+last process in the pipeline associated with this job is 25647. All of
+the processes in a single pipeline are members of the same job. Bash
+uses the JOB abstraction as the basis for job control.
+
+ To facilitate the implementation of the user interface to job
+control, the operating system maintains the notion of a current terminal
+process group ID. Members of this process group (processes whose
+process group ID is equal to the current terminal process group ID)
+receive keyboard-generated signals such as 'SIGINT'. These processes
+are said to be in the foreground. Background processes are those whose
+process group ID differs from the terminal's; such processes are immune
+to keyboard-generated signals. Only foreground processes are allowed to
+read from or, if the user so specifies with 'stty tostop', write to the
+terminal. Background processes which attempt to read from (write to
+when 'stty tostop' is in effect) the terminal are sent a 'SIGTTIN'
+('SIGTTOU') signal by the kernel's terminal driver, which, unless
+caught, suspends the process.
+
+ If the operating system on which Bash is running supports job
+control, Bash contains facilities to use it. Typing the "suspend"
+character (typically '^Z', Control-Z) while a process is running causes
+that process to be stopped and returns control to Bash. Typing the
+"delayed suspend" character (typically '^Y', Control-Y) causes the
+process to be stopped when it attempts to read input from the terminal,
+and control to be returned to Bash. The user then manipulates the state
+of this job, using the 'bg' command to continue it in the background,
+the 'fg' command to continue it in the foreground, or the 'kill' command
+to kill it. A '^Z' takes effect immediately, and has the additional
+side effect of causing pending output and typeahead to be discarded.
+
+ There are a number of ways to refer to a job in the shell. The
+character '%' introduces a job specification ("jobspec").
+
+ Job number 'n' may be referred to as '%n'. The symbols '%%' and '%+'
+refer to the shell's notion of the current job, which is the last job
+stopped while it was in the foreground or started in the background. A
+single '%' (with no accompanying job specification) also refers to the
+current job. The previous job may be referenced using '%-'. If there
+is only a single job, '%+' and '%-' can both be used to refer to that
+job. In output pertaining to jobs (e.g., the output of the 'jobs'
+command), the current job is always flagged with a '+', and the previous
+job with a '-'.
+
+ A job may also be referred to using a prefix of the name used to
+start it, or using a substring that appears in its command line. For
+example, '%ce' refers to a stopped job whose command name begins with
+'ce'. Using '%?ce', on the other hand, refers to any job containing the
+string 'ce' in its command line. If the prefix or substring matches
+more than one job, Bash reports an error.
+
+ Simply naming a job can be used to bring it into the foreground: '%1'
+is a synonym for 'fg %1', bringing job 1 from the background into the
+foreground. Similarly, '%1 &' resumes job 1 in the background,
+equivalent to 'bg %1'
+
+ The shell learns immediately whenever a job changes state. Normally,
+Bash waits until it is about to print a prompt before reporting changes
+in a job's status so as to not interrupt any other output. If the '-b'
+option to the 'set' builtin is enabled, Bash reports such changes
+immediately (*note The Set Builtin::). Any trap on 'SIGCHLD' is
+executed for each child process that exits.
+
+ If an attempt to exit Bash is made while jobs are stopped, (or
+running, if the 'checkjobs' option is enabled - see *note The Shopt
+Builtin::), the shell prints a warning message, and if the 'checkjobs'
+option is enabled, lists the jobs and their statuses. The 'jobs'
+command may then be used to inspect their status. If a second attempt
+to exit is made without an intervening command, Bash does not print
+another warning, and any stopped jobs are terminated.
+
+ When the shell is waiting for a job or process using the 'wait'
+builtin, and job control is enabled, 'wait' will return when the job
+changes state. The '-f' option causes 'wait' to wait until the job or
+process terminates before returning.
+
+
+File: bash.info, Node: Job Control Builtins, Next: Job Control Variables, Prev: Job Control Basics, Up: Job Control
+
+7.2 Job Control Builtins
+========================
+
+'bg'
+ bg [JOBSPEC ...]
+
+ Resume each suspended job JOBSPEC in the background, as if it had
+ been started with '&'. If JOBSPEC is not supplied, the current job
+ is used. The return status is zero unless it is run when job
+ control is not enabled, or, when run with job control enabled, any
+ JOBSPEC was not found or specifies a job that was started without
+ job control.
+
+'fg'
+ fg [JOBSPEC]
+
+ Resume the job JOBSPEC in the foreground and make it the current
+ job. If JOBSPEC is not supplied, the current job is used. The
+ return status is that of the command placed into the foreground, or
+ non-zero if run when job control is disabled or, when run with job
+ control enabled, JOBSPEC does not specify a valid job or JOBSPEC
+ specifies a job that was started without job control.
+
+'jobs'
+ jobs [-lnprs] [JOBSPEC]
+ jobs -x COMMAND [ARGUMENTS]
+
+ The first form lists the active jobs. The options have the
+ following meanings:
+
+ '-l'
+ List process IDs in addition to the normal information.
+
+ '-n'
+ Display information only about jobs that have changed status
+ since the user was last notified of their status.
+
+ '-p'
+ List only the process ID of the job's process group leader.
+
+ '-r'
+ Display only running jobs.
+
+ '-s'
+ Display only stopped jobs.
+
+ If JOBSPEC is given, output is restricted to information about that
+ job. If JOBSPEC is not supplied, the status of all jobs is listed.
+
+ If the '-x' option is supplied, 'jobs' replaces any JOBSPEC found
+ in COMMAND or ARGUMENTS with the corresponding process group ID,
+ and executes COMMAND, passing it ARGUMENTs, returning its exit
+ status.
+
+'kill'
+ kill [-s SIGSPEC] [-n SIGNUM] [-SIGSPEC] JOBSPEC or PID
+ kill -l|-L [EXIT_STATUS]
+
+ Send a signal specified by SIGSPEC or SIGNUM to the process named
+ by job specification JOBSPEC or process ID PID. SIGSPEC is either
+ a case-insensitive signal name such as 'SIGINT' (with or without
+ the 'SIG' prefix) or a signal number; SIGNUM is a signal number.
+ If SIGSPEC and SIGNUM are not present, 'SIGTERM' is used. The '-l'
+ option lists the signal names. If any arguments are supplied when
+ '-l' is given, the names of the signals corresponding to the
+ arguments are listed, and the return status is zero. EXIT_STATUS
+ is a number specifying a signal number or the exit status of a
+ process terminated by a signal. The '-L' option is equivalent to
+ '-l'. The return status is zero if at least one signal was
+ successfully sent, or non-zero if an error occurs or an invalid
+ option is encountered.
+
+'wait'
+ wait [-fn] [-p VARNAME] [JOBSPEC or PID ...]
+
+ Wait until the child process specified by each process ID PID or
+ job specification JOBSPEC exits and return the exit status of the
+ last command waited for. If a job spec is given, all processes in
+ the job are waited for. If no arguments are given, 'wait' waits
+ for all running background jobs and the last-executed process
+ substitution, if its process id is the same as $!, and the return
+ status is zero. If the '-n' option is supplied, 'wait' waits for a
+ single job from the list of PIDs or JOBSPECs or, if no arguments
+ are supplied, any job, to complete and returns its exit status. If
+ none of the supplied arguments is a child of the shell, or if no
+ arguments are supplied and the shell has no unwaited-for children,
+ the exit status is 127. If the '-p' option is supplied, the
+ process or job identifier of the job for which the exit status is
+ returned is assigned to the variable VARNAME named by the option
+ argument. The variable will be unset initially, before any
+ assignment. This is useful only when the '-n' option is supplied.
+ Supplying the '-f' option, when job control is enabled, forces
+ 'wait' to wait for each PID or JOBSPEC to terminate before
+ returning its status, instead of returning when it changes status.
+ If neither JOBSPEC nor PID specifies an active child process of the
+ shell, the return status is 127. If 'wait' is interrupted by a
+ signal, the return status will be greater than 128, as described
+ above (*note Signals::). Otherwise, the return status is the exit
+ status of the last process or job waited for.
+
+'disown'
+ disown [-ar] [-h] [JOBSPEC ... | PID ... ]
+
+ Without options, remove each JOBSPEC from the table of active jobs.
+ If the '-h' option is given, the job is not removed from the table,
+ but is marked so that 'SIGHUP' is not sent to the job if the shell
+ receives a 'SIGHUP'. If JOBSPEC is not present, and neither the
+ '-a' nor the '-r' option is supplied, the current job is used. If
+ no JOBSPEC is supplied, the '-a' option means to remove or mark all
+ jobs; the '-r' option without a JOBSPEC argument restricts
+ operation to running jobs.
+
+'suspend'
+ suspend [-f]
+
+ Suspend the execution of this shell until it receives a 'SIGCONT'
+ signal. A login shell, or a shell without job control enabled,
+ cannot be suspended; the '-f' option can be used to override this
+ and force the suspension. The return status is 0 unless the shell
+ is a login shell or job control is not enabled and '-f' is not
+ supplied.
+
+ When job control is not active, the 'kill' and 'wait' builtins do not
+accept JOBSPEC arguments. They must be supplied process IDs.
+
+
+File: bash.info, Node: Job Control Variables, Prev: Job Control Builtins, Up: Job Control
+
+7.3 Job Control Variables
+=========================
+
+'auto_resume'
+ This variable controls how the shell interacts with the user and
+ job control. If this variable exists then single word simple
+ commands without redirections are treated as candidates for
+ resumption of an existing job. There is no ambiguity allowed; if
+ there is more than one job beginning with the string typed, then
+ the most recently accessed job will be selected. The name of a
+ stopped job, in this context, is the command line used to start it.
+ If this variable is set to the value 'exact', the string supplied
+ must match the name of a stopped job exactly; if set to
+ 'substring', the string supplied needs to match a substring of the
+ name of a stopped job. The 'substring' value provides
+ functionality analogous to the '%?' job ID (*note Job Control
+ Basics::). If set to any other value, the supplied string must be
+ a prefix of a stopped job's name; this provides functionality
+ analogous to the '%' job ID.
+
+
+File: bash.info, Node: Command Line Editing, Next: Using History Interactively, Prev: Job Control, Up: Top
+
+8 Command Line Editing
+**********************
+
+This chapter describes the basic features of the GNU command line
+editing interface. Command line editing is provided by the Readline
+library, which is used by several different programs, including Bash.
+Command line editing is enabled by default when using an interactive
+shell, unless the '--noediting' option is supplied at shell invocation.
+Line editing is also used when using the '-e' option to the 'read'
+builtin command (*note Bash Builtins::). By default, the line editing
+commands are similar to those of Emacs. A vi-style line editing
+interface is also available. Line editing can be enabled at any time
+using the '-o emacs' or '-o vi' options to the 'set' builtin command
+(*note The Set Builtin::), or disabled using the '+o emacs' or '+o vi'
+options to 'set'.
+
+* Menu:
+
+* Introduction and Notation:: Notation used in this text.
+* Readline Interaction:: The minimum set of commands for editing a line.
+* Readline Init File:: Customizing Readline from a user's view.
+* Bindable Readline Commands:: A description of most of the Readline commands
+ available for binding
+* Readline vi Mode:: A short description of how to make Readline
+ behave like the vi editor.
+* Programmable Completion:: How to specify the possible completions for
+ a specific command.
+* Programmable Completion Builtins:: Builtin commands to specify how to
+ complete arguments for a particular command.
+* A Programmable Completion Example:: An example shell function for
+ generating possible completions.
+
+
+File: bash.info, Node: Introduction and Notation, Next: Readline Interaction, Up: Command Line Editing
+
+8.1 Introduction to Line Editing
+================================
+
+The following paragraphs describe the notation used to represent
+keystrokes.
+
+ The text 'C-k' is read as 'Control-K' and describes the character
+produced when the <k> key is pressed while the Control key is depressed.
+
+ The text 'M-k' is read as 'Meta-K' and describes the character
+produced when the Meta key (if you have one) is depressed, and the <k>
+key is pressed. The Meta key is labeled <ALT> on many keyboards. On
+keyboards with two keys labeled <ALT> (usually to either side of the
+space bar), the <ALT> on the left side is generally set to work as a
+Meta key. The <ALT> key on the right may also be configured to work as
+a Meta key or may be configured as some other modifier, such as a
+Compose key for typing accented characters.
+
+ If you do not have a Meta or <ALT> key, or another key working as a
+Meta key, the identical keystroke can be generated by typing <ESC>
+_first_, and then typing <k>. Either process is known as "metafying"
+the <k> key.
+
+ The text 'M-C-k' is read as 'Meta-Control-k' and describes the
+character produced by "metafying" 'C-k'.
+
+ In addition, several keys have their own names. Specifically, <DEL>,
+<ESC>, <LFD>, <SPC>, <RET>, and <TAB> all stand for themselves when seen
+in this text, or in an init file (*note Readline Init File::). If your
+keyboard lacks a <LFD> key, typing <C-j> will produce the desired
+character. The <RET> key may be labeled <Return> or <Enter> on some
+keyboards.
+
+
+File: bash.info, Node: Readline Interaction, Next: Readline Init File, Prev: Introduction and Notation, Up: Command Line Editing
+
+8.2 Readline Interaction
+========================
+
+Often during an interactive session you type in a long line of text,
+only to notice that the first word on the line is misspelled. The
+Readline library gives you a set of commands for manipulating the text
+as you type it in, allowing you to just fix your typo, and not forcing
+you to retype the majority of the line. Using these editing commands,
+you move the cursor to the place that needs correction, and delete or
+insert the text of the corrections. Then, when you are satisfied with
+the line, you simply press <RET>. You do not have to be at the end of
+the line to press <RET>; the entire line is accepted regardless of the
+location of the cursor within the line.
+
+* Menu:
+
+* Readline Bare Essentials:: The least you need to know about Readline.
+* Readline Movement Commands:: Moving about the input line.
+* Readline Killing Commands:: How to delete text, and how to get it back!
+* Readline Arguments:: Giving numeric arguments to commands.
+* Searching:: Searching through previous lines.
+
+
+File: bash.info, Node: Readline Bare Essentials, Next: Readline Movement Commands, Up: Readline Interaction
+
+8.2.1 Readline Bare Essentials
+------------------------------
+
+In order to enter characters into the line, simply type them. The typed
+character appears where the cursor was, and then the cursor moves one
+space to the right. If you mistype a character, you can use your erase
+character to back up and delete the mistyped character.
+
+ Sometimes you may mistype a character, and not notice the error until
+you have typed several other characters. In that case, you can type
+'C-b' to move the cursor to the left, and then correct your mistake.
+Afterwards, you can move the cursor to the right with 'C-f'.
+
+ When you add text in the middle of a line, you will notice that
+characters to the right of the cursor are 'pushed over' to make room for
+the text that you have inserted. Likewise, when you delete text behind
+the cursor, characters to the right of the cursor are 'pulled back' to
+fill in the blank space created by the removal of the text. A list of
+the bare essentials for editing the text of an input line follows.
+
+'C-b'
+ Move back one character.
+'C-f'
+ Move forward one character.
+<DEL> or <Backspace>
+ Delete the character to the left of the cursor.
+'C-d'
+ Delete the character underneath the cursor.
+Printing characters
+ Insert the character into the line at the cursor.
+'C-_' or 'C-x C-u'
+ Undo the last editing command. You can undo all the way back to an
+ empty line.
+
+(Depending on your configuration, the <Backspace> key might be set to
+delete the character to the left of the cursor and the <DEL> key set to
+delete the character underneath the cursor, like 'C-d', rather than the
+character to the left of the cursor.)
+
+
+File: bash.info, Node: Readline Movement Commands, Next: Readline Killing Commands, Prev: Readline Bare Essentials, Up: Readline Interaction
+
+8.2.2 Readline Movement Commands
+--------------------------------
+
+The above table describes the most basic keystrokes that you need in
+order to do editing of the input line. For your convenience, many other
+commands have been added in addition to 'C-b', 'C-f', 'C-d', and <DEL>.
+Here are some commands for moving more rapidly about the line.
+
+'C-a'
+ Move to the start of the line.
+'C-e'
+ Move to the end of the line.
+'M-f'
+ Move forward a word, where a word is composed of letters and
+ digits.
+'M-b'
+ Move backward a word.
+'C-l'
+ Clear the screen, reprinting the current line at the top.
+
+ Notice how 'C-f' moves forward a character, while 'M-f' moves forward
+a word. It is a loose convention that control keystrokes operate on
+characters while meta keystrokes operate on words.
+
+
+File: bash.info, Node: Readline Killing Commands, Next: Readline Arguments, Prev: Readline Movement Commands, Up: Readline Interaction
+
+8.2.3 Readline Killing Commands
+-------------------------------
+
+"Killing" text means to delete the text from the line, but to save it
+away for later use, usually by "yanking" (re-inserting) it back into the
+line. ('Cut' and 'paste' are more recent jargon for 'kill' and 'yank'.)
+
+ If the description for a command says that it 'kills' text, then you
+can be sure that you can get the text back in a different (or the same)
+place later.
+
+ When you use a kill command, the text is saved in a "kill-ring". Any
+number of consecutive kills save all of the killed text together, so
+that when you yank it back, you get it all. The kill ring is not line
+specific; the text that you killed on a previously typed line is
+available to be yanked back later, when you are typing another line.
+
+ Here is the list of commands for killing text.
+
+'C-k'
+ Kill the text from the current cursor position to the end of the
+ line.
+
+'M-d'
+ Kill from the cursor to the end of the current word, or, if between
+ words, to the end of the next word. Word boundaries are the same
+ as those used by 'M-f'.
+
+'M-<DEL>'
+ Kill from the cursor to the start of the current word, or, if
+ between words, to the start of the previous word. Word boundaries
+ are the same as those used by 'M-b'.
+
+'C-w'
+ Kill from the cursor to the previous whitespace. This is different
+ than 'M-<DEL>' because the word boundaries differ.
+
+ Here is how to "yank" the text back into the line. Yanking means to
+copy the most-recently-killed text from the kill buffer.
+
+'C-y'
+ Yank the most recently killed text back into the buffer at the
+ cursor.
+
+'M-y'
+ Rotate the kill-ring, and yank the new top. You can only do this
+ if the prior command is 'C-y' or 'M-y'.
+
+
+File: bash.info, Node: Readline Arguments, Next: Searching, Prev: Readline Killing Commands, Up: Readline Interaction
+
+8.2.4 Readline Arguments
+------------------------
+
+You can pass numeric arguments to Readline commands. Sometimes the
+argument acts as a repeat count, other times it is the sign of the
+argument that is significant. If you pass a negative argument to a
+command which normally acts in a forward direction, that command will
+act in a backward direction. For example, to kill text back to the
+start of the line, you might type 'M-- C-k'.
+
+ The general way to pass numeric arguments to a command is to type
+meta digits before the command. If the first 'digit' typed is a minus
+sign ('-'), then the sign of the argument will be negative. Once you
+have typed one meta digit to get the argument started, you can type the
+remainder of the digits, and then the command. For example, to give the
+'C-d' command an argument of 10, you could type 'M-1 0 C-d', which will
+delete the next ten characters on the input line.
+
+
+File: bash.info, Node: Searching, Prev: Readline Arguments, Up: Readline Interaction
+
+8.2.5 Searching for Commands in the History
+-------------------------------------------
+
+Readline provides commands for searching through the command history
+(*note Bash History Facilities::) for lines containing a specified
+string. There are two search modes: "incremental" and
+"non-incremental".
+
+ Incremental searches begin before the user has finished typing the
+search string. As each character of the search string is typed,
+Readline displays the next entry from the history matching the string
+typed so far. An incremental search requires only as many characters as
+needed to find the desired history entry. To search backward in the
+history for a particular string, type 'C-r'. Typing 'C-s' searches
+forward through the history. The characters present in the value of the
+'isearch-terminators' variable are used to terminate an incremental
+search. If that variable has not been assigned a value, the <ESC> and
+'C-J' characters will terminate an incremental search. 'C-g' will abort
+an incremental search and restore the original line. When the search is
+terminated, the history entry containing the search string becomes the
+current line.
+
+ To find other matching entries in the history list, type 'C-r' or
+'C-s' as appropriate. This will search backward or forward in the
+history for the next entry matching the search string typed so far. Any
+other key sequence bound to a Readline command will terminate the search
+and execute that command. For instance, a <RET> will terminate the
+search and accept the line, thereby executing the command from the
+history list. A movement command will terminate the search, make the
+last line found the current line, and begin editing.
+
+ Readline remembers the last incremental search string. If two 'C-r's
+are typed without any intervening characters defining a new search
+string, any remembered search string is used.
+
+ Non-incremental searches read the entire search string before
+starting to search for matching history lines. The search string may be
+typed by the user or be part of the contents of the current line.
+
+
+File: bash.info, Node: Readline Init File, Next: Bindable Readline Commands, Prev: Readline Interaction, Up: Command Line Editing
+
+8.3 Readline Init File
+======================
+
+Although the Readline library comes with a set of Emacs-like keybindings
+installed by default, it is possible to use a different set of
+keybindings. Any user can customize programs that use Readline by
+putting commands in an "inputrc" file, conventionally in their home
+directory. The name of this file is taken from the value of the shell
+variable 'INPUTRC'. If that variable is unset, the default is
+'~/.inputrc'. If that file does not exist or cannot be read, the
+ultimate default is '/etc/inputrc'. The 'bind' builtin command can also
+be used to set Readline keybindings and variables. *Note Bash
+Builtins::.
+
+ When a program which uses the Readline library starts up, the init
+file is read, and the key bindings are set.
+
+ In addition, the 'C-x C-r' command re-reads this init file, thus
+incorporating any changes that you might have made to it.
+
+* Menu:
+
+* Readline Init File Syntax:: Syntax for the commands in the inputrc file.
+
+* Conditional Init Constructs:: Conditional key bindings in the inputrc file.
+
+* Sample Init File:: An example inputrc file.
+
+
+File: bash.info, Node: Readline Init File Syntax, Next: Conditional Init Constructs, Up: Readline Init File
+
+8.3.1 Readline Init File Syntax
+-------------------------------
+
+There are only a few basic constructs allowed in the Readline init file.
+Blank lines are ignored. Lines beginning with a '#' are comments.
+Lines beginning with a '$' indicate conditional constructs (*note
+Conditional Init Constructs::). Other lines denote variable settings
+and key bindings.
+
+Variable Settings
+ You can modify the run-time behavior of Readline by altering the
+ values of variables in Readline using the 'set' command within the
+ init file. The syntax is simple:
+
+ set VARIABLE VALUE
+
+ Here, for example, is how to change from the default Emacs-like key
+ binding to use 'vi' line editing commands:
+
+ set editing-mode vi
+
+ Variable names and values, where appropriate, are recognized
+ without regard to case. Unrecognized variable names are ignored.
+
+ Boolean variables (those that can be set to on or off) are set to
+ on if the value is null or empty, ON (case-insensitive), or 1. Any
+ other value results in the variable being set to off.
+
+ The 'bind -V' command lists the current Readline variable names and
+ values. *Note Bash Builtins::.
+
+ A great deal of run-time behavior is changeable with the following
+ variables.
+
+ 'active-region-start-color'
+ A string variable that controls the text color and background
+ when displaying the text in the active region (see the
+ description of 'enable-active-region' below). This string
+ must not take up any physical character positions on the
+ display, so it should consist only of terminal escape
+ sequences. It is output to the terminal before displaying the
+ text in the active region. This variable is reset to the
+ default value whenever the terminal type changes. The default
+ value is the string that puts the terminal in standout mode,
+ as obtained from the terminal's terminfo description. A
+ sample value might be '\e[01;33m'.
+
+ 'active-region-end-color'
+ A string variable that "undoes" the effects of
+ 'active-region-start-color' and restores "normal" terminal
+ display appearance after displaying text in the active region.
+ This string must not take up any physical character positions
+ on the display, so it should consist only of terminal escape
+ sequences. It is output to the terminal after displaying the
+ text in the active region. This variable is reset to the
+ default value whenever the terminal type changes. The default
+ value is the string that restores the terminal from standout
+ mode, as obtained from the terminal's terminfo description. A
+ sample value might be '\e[0m'.
+
+ 'bell-style'
+ Controls what happens when Readline wants to ring the terminal
+ bell. If set to 'none', Readline never rings the bell. If
+ set to 'visible', Readline uses a visible bell if one is
+ available. If set to 'audible' (the default), Readline
+ attempts to ring the terminal's bell.
+
+ 'bind-tty-special-chars'
+ If set to 'on' (the default), Readline attempts to bind the
+ control characters treated specially by the kernel's terminal
+ driver to their Readline equivalents.
+
+ 'blink-matching-paren'
+ If set to 'on', Readline attempts to briefly move the cursor
+ to an opening parenthesis when a closing parenthesis is
+ inserted. The default is 'off'.
+
+ 'colored-completion-prefix'
+ If set to 'on', when listing completions, Readline displays
+ the common prefix of the set of possible completions using a
+ different color. The color definitions are taken from the
+ value of the 'LS_COLORS' environment variable. If there is a
+ color definition in 'LS_COLORS' for the custom suffix
+ 'readline-colored-completion-prefix', Readline uses this color
+ for the common prefix instead of its default. The default is
+ 'off'.
+
+ 'colored-stats'
+ If set to 'on', Readline displays possible completions using
+ different colors to indicate their file type. The color
+ definitions are taken from the value of the 'LS_COLORS'
+ environment variable. The default is 'off'.
+
+ 'comment-begin'
+ The string to insert at the beginning of the line when the
+ 'insert-comment' command is executed. The default value is
+ '"#"'.
+
+ 'completion-display-width'
+ The number of screen columns used to display possible matches
+ when performing completion. The value is ignored if it is
+ less than 0 or greater than the terminal screen width. A
+ value of 0 will cause matches to be displayed one per line.
+ The default value is -1.
+
+ 'completion-ignore-case'
+ If set to 'on', Readline performs filename matching and
+ completion in a case-insensitive fashion. The default value
+ is 'off'.
+
+ 'completion-map-case'
+ If set to 'on', and COMPLETION-IGNORE-CASE is enabled,
+ Readline treats hyphens ('-') and underscores ('_') as
+ equivalent when performing case-insensitive filename matching
+ and completion. The default value is 'off'.
+
+ 'completion-prefix-display-length'
+ The length in characters of the common prefix of a list of
+ possible completions that is displayed without modification.
+ When set to a value greater than zero, common prefixes longer
+ than this value are replaced with an ellipsis when displaying
+ possible completions.
+
+ 'completion-query-items'
+ The number of possible completions that determines when the
+ user is asked whether the list of possibilities should be
+ displayed. If the number of possible completions is greater
+ than or equal to this value, Readline will ask whether or not
+ the user wishes to view them; otherwise, they are simply
+ listed. This variable must be set to an integer value greater
+ than or equal to zero. A zero value means Readline should
+ never ask; negative values are treated as zero. The default
+ limit is '100'.
+
+ 'convert-meta'
+ If set to 'on', Readline will convert characters with the
+ eighth bit set to an ASCII key sequence by stripping the
+ eighth bit and prefixing an <ESC> character, converting them
+ to a meta-prefixed key sequence. The default value is 'on',
+ but will be set to 'off' if the locale is one that contains
+ eight-bit characters. This variable is dependent on the
+ 'LC_CTYPE' locale category, and may change if the locale is
+ changed.
+
+ 'disable-completion'
+ If set to 'On', Readline will inhibit word completion.
+ Completion characters will be inserted into the line as if
+ they had been mapped to 'self-insert'. The default is 'off'.
+
+ 'echo-control-characters'
+ When set to 'on', on operating systems that indicate they
+ support it, Readline echoes a character corresponding to a
+ signal generated from the keyboard. The default is 'on'.
+
+ 'editing-mode'
+ The 'editing-mode' variable controls which default set of key
+ bindings is used. By default, Readline starts up in Emacs
+ editing mode, where the keystrokes are most similar to Emacs.
+ This variable can be set to either 'emacs' or 'vi'.
+
+ 'emacs-mode-string'
+ If the SHOW-MODE-IN-PROMPT variable is enabled, this string is
+ displayed immediately before the last line of the primary
+ prompt when emacs editing mode is active. The value is
+ expanded like a key binding, so the standard set of meta- and
+ control prefixes and backslash escape sequences is available.
+ Use the '\1' and '\2' escapes to begin and end sequences of
+ non-printing characters, which can be used to embed a terminal
+ control sequence into the mode string. The default is '@'.
+
+ 'enable-active-region'
+ The "point" is the current cursor position, and "mark" refers
+ to a saved cursor position (*note Commands For Moving::). The
+ text between the point and mark is referred to as the
+ "region". When this variable is set to 'On', Readline allows
+ certain commands to designate the region as "active". When
+ the region is active, Readline highlights the text in the
+ region using the value of the 'active-region-start-color',
+ which defaults to the string that enables the terminal's
+ standout mode. The active region shows the text inserted by
+ bracketed-paste and any matching text found by incremental and
+ non-incremental history searches. The default is 'On'.
+
+ 'enable-bracketed-paste'
+ When set to 'On', Readline configures the terminal to insert
+ each paste into the editing buffer as a single string of
+ characters, instead of treating each character as if it had
+ been read from the keyboard. This is called putting the
+ terminal into "bracketed paste mode"; it prevents Readline
+ from executing any editing commands bound to key sequences
+ appearing in the pasted text. The default is 'On'.
+
+ 'enable-keypad'
+ When set to 'on', Readline will try to enable the application
+ keypad when it is called. Some systems need this to enable
+ the arrow keys. The default is 'off'.
+
+ 'enable-meta-key'
+ When set to 'on', Readline will try to enable any meta
+ modifier key the terminal claims to support when it is called.
+ On many terminals, the meta key is used to send eight-bit
+ characters. The default is 'on'.
+
+ 'expand-tilde'
+ If set to 'on', tilde expansion is performed when Readline
+ attempts word completion. The default is 'off'.
+
+ 'history-preserve-point'
+ If set to 'on', the history code attempts to place the point
+ (the current cursor position) at the same location on each
+ history line retrieved with 'previous-history' or
+ 'next-history'. The default is 'off'.
+
+ 'history-size'
+ Set the maximum number of history entries saved in the history
+ list. If set to zero, any existing history entries are
+ deleted and no new entries are saved. If set to a value less
+ than zero, the number of history entries is not limited. By
+ default, the number of history entries is not limited. If an
+ attempt is made to set HISTORY-SIZE to a non-numeric value,
+ the maximum number of history entries will be set to 500.
+
+ 'horizontal-scroll-mode'
+ This variable can be set to either 'on' or 'off'. Setting it
+ to 'on' means that the text of the lines being edited will
+ scroll horizontally on a single screen line when they are
+ longer than the width of the screen, instead of wrapping onto
+ a new screen line. This variable is automatically set to 'on'
+ for terminals of height 1. By default, this variable is set
+ to 'off'.
+
+ 'input-meta'
+ If set to 'on', Readline will enable eight-bit input (it will
+ not clear the eighth bit in the characters it reads),
+ regardless of what the terminal claims it can support. The
+ default value is 'off', but Readline will set it to 'on' if
+ the locale contains eight-bit characters. The name
+ 'meta-flag' is a synonym for this variable. This variable is
+ dependent on the 'LC_CTYPE' locale category, and may change if
+ the locale is changed.
+
+ 'isearch-terminators'
+ The string of characters that should terminate an incremental
+ search without subsequently executing the character as a
+ command (*note Searching::). If this variable has not been
+ given a value, the characters <ESC> and 'C-J' will terminate
+ an incremental search.
+
+ 'keymap'
+ Sets Readline's idea of the current keymap for key binding
+ commands. Built-in 'keymap' names are 'emacs',
+ 'emacs-standard', 'emacs-meta', 'emacs-ctlx', 'vi', 'vi-move',
+ 'vi-command', and 'vi-insert'. 'vi' is equivalent to
+ 'vi-command' ('vi-move' is also a synonym); 'emacs' is
+ equivalent to 'emacs-standard'. Applications may add
+ additional names. The default value is 'emacs'. The value of
+ the 'editing-mode' variable also affects the default keymap.
+
+ 'keyseq-timeout'
+ Specifies the duration Readline will wait for a character when
+ reading an ambiguous key sequence (one that can form a
+ complete key sequence using the input read so far, or can take
+ additional input to complete a longer key sequence). If no
+ input is received within the timeout, Readline will use the
+ shorter but complete key sequence. Readline uses this value
+ to determine whether or not input is available on the current
+ input source ('rl_instream' by default). The value is
+ specified in milliseconds, so a value of 1000 means that
+ Readline will wait one second for additional input. If this
+ variable is set to a value less than or equal to zero, or to a
+ non-numeric value, Readline will wait until another key is
+ pressed to decide which key sequence to complete. The default
+ value is '500'.
+
+ 'mark-directories'
+ If set to 'on', completed directory names have a slash
+ appended. The default is 'on'.
+
+ 'mark-modified-lines'
+ This variable, when set to 'on', causes Readline to display an
+ asterisk ('*') at the start of history lines which have been
+ modified. This variable is 'off' by default.
+
+ 'mark-symlinked-directories'
+ If set to 'on', completed names which are symbolic links to
+ directories have a slash appended (subject to the value of
+ 'mark-directories'). The default is 'off'.
+
+ 'match-hidden-files'
+ This variable, when set to 'on', causes Readline to match
+ files whose names begin with a '.' (hidden files) when
+ performing filename completion. If set to 'off', the leading
+ '.' must be supplied by the user in the filename to be
+ completed. This variable is 'on' by default.
+
+ 'menu-complete-display-prefix'
+ If set to 'on', menu completion displays the common prefix of
+ the list of possible completions (which may be empty) before
+ cycling through the list. The default is 'off'.
+
+ 'output-meta'
+ If set to 'on', Readline will display characters with the
+ eighth bit set directly rather than as a meta-prefixed escape
+ sequence. The default is 'off', but Readline will set it to
+ 'on' if the locale contains eight-bit characters. This
+ variable is dependent on the 'LC_CTYPE' locale category, and
+ may change if the locale is changed.
+
+ 'page-completions'
+ If set to 'on', Readline uses an internal 'more'-like pager to
+ display a screenful of possible completions at a time. This
+ variable is 'on' by default.
+
+ 'print-completions-horizontally'
+ If set to 'on', Readline will display completions with matches
+ sorted horizontally in alphabetical order, rather than down
+ the screen. The default is 'off'.
+
+ 'revert-all-at-newline'
+ If set to 'on', Readline will undo all changes to history
+ lines before returning when 'accept-line' is executed. By
+ default, history lines may be modified and retain individual
+ undo lists across calls to 'readline()'. The default is
+ 'off'.
+
+ 'show-all-if-ambiguous'
+ This alters the default behavior of the completion functions.
+ If set to 'on', words which have more than one possible
+ completion cause the matches to be listed immediately instead
+ of ringing the bell. The default value is 'off'.
+
+ 'show-all-if-unmodified'
+ This alters the default behavior of the completion functions
+ in a fashion similar to SHOW-ALL-IF-AMBIGUOUS. If set to
+ 'on', words which have more than one possible completion
+ without any possible partial completion (the possible
+ completions don't share a common prefix) cause the matches to
+ be listed immediately instead of ringing the bell. The
+ default value is 'off'.
+
+ 'show-mode-in-prompt'
+ If set to 'on', add a string to the beginning of the prompt
+ indicating the editing mode: emacs, vi command, or vi
+ insertion. The mode strings are user-settable (e.g.,
+ EMACS-MODE-STRING). The default value is 'off'.
+
+ 'skip-completed-text'
+ If set to 'on', this alters the default completion behavior
+ when inserting a single match into the line. It's only active
+ when performing completion in the middle of a word. If
+ enabled, Readline does not insert characters from the
+ completion that match characters after point in the word being
+ completed, so portions of the word following the cursor are
+ not duplicated. For instance, if this is enabled, attempting
+ completion when the cursor is after the 'e' in 'Makefile' will
+ result in 'Makefile' rather than 'Makefilefile', assuming
+ there is a single possible completion. The default value is
+ 'off'.
+
+ 'vi-cmd-mode-string'
+ If the SHOW-MODE-IN-PROMPT variable is enabled, this string is
+ displayed immediately before the last line of the primary
+ prompt when vi editing mode is active and in command mode.
+ The value is expanded like a key binding, so the standard set
+ of meta- and control prefixes and backslash escape sequences
+ is available. Use the '\1' and '\2' escapes to begin and end
+ sequences of non-printing characters, which can be used to
+ embed a terminal control sequence into the mode string. The
+ default is '(cmd)'.
+
+ 'vi-ins-mode-string'
+ If the SHOW-MODE-IN-PROMPT variable is enabled, this string is
+ displayed immediately before the last line of the primary
+ prompt when vi editing mode is active and in insertion mode.
+ The value is expanded like a key binding, so the standard set
+ of meta- and control prefixes and backslash escape sequences
+ is available. Use the '\1' and '\2' escapes to begin and end
+ sequences of non-printing characters, which can be used to
+ embed a terminal control sequence into the mode string. The
+ default is '(ins)'.
+
+ 'visible-stats'
+ If set to 'on', a character denoting a file's type is appended
+ to the filename when listing possible completions. The
+ default is 'off'.
+
+Key Bindings
+ The syntax for controlling key bindings in the init file is simple.
+ First you need to find the name of the command that you want to
+ change. The following sections contain tables of the command name,
+ the default keybinding, if any, and a short description of what the
+ command does.
+
+ Once you know the name of the command, simply place on a line in
+ the init file the name of the key you wish to bind the command to,
+ a colon, and then the name of the command. There can be no space
+ between the key name and the colon - that will be interpreted as
+ part of the key name. The name of the key can be expressed in
+ different ways, depending on what you find most comfortable.
+
+ In addition to command names, Readline allows keys to be bound to a
+ string that is inserted when the key is pressed (a MACRO).
+
+ The 'bind -p' command displays Readline function names and bindings
+ in a format that can be put directly into an initialization file.
+ *Note Bash Builtins::.
+
+ KEYNAME: FUNCTION-NAME or MACRO
+ KEYNAME is the name of a key spelled out in English. For
+ example:
+ Control-u: universal-argument
+ Meta-Rubout: backward-kill-word
+ Control-o: "> output"
+
+ In the example above, 'C-u' is bound to the function
+ 'universal-argument', 'M-DEL' is bound to the function
+ 'backward-kill-word', and 'C-o' is bound to run the macro
+ expressed on the right hand side (that is, to insert the text
+ '> output' into the line).
+
+ A number of symbolic character names are recognized while
+ processing this key binding syntax: DEL, ESC, ESCAPE, LFD,
+ NEWLINE, RET, RETURN, RUBOUT, SPACE, SPC, and TAB.
+
+ "KEYSEQ": FUNCTION-NAME or MACRO
+ KEYSEQ differs from KEYNAME above in that strings denoting an
+ entire key sequence can be specified, by placing the key
+ sequence in double quotes. Some GNU Emacs style key escapes
+ can be used, as in the following example, but the special
+ character names are not recognized.
+
+ "\C-u": universal-argument
+ "\C-x\C-r": re-read-init-file
+ "\e[11~": "Function Key 1"
+
+ In the above example, 'C-u' is again bound to the function
+ 'universal-argument' (just as it was in the first example),
+ ''C-x' 'C-r'' is bound to the function 're-read-init-file',
+ and '<ESC> <[> <1> <1> <~>' is bound to insert the text
+ 'Function Key 1'.
+
+ The following GNU Emacs style escape sequences are available when
+ specifying key sequences:
+
+ '\C-'
+ control prefix
+ '\M-'
+ meta prefix
+ '\e'
+ an escape character
+ '\\'
+ backslash
+ '\"'
+ <">, a double quotation mark
+ '\''
+ <'>, a single quote or apostrophe
+
+ In addition to the GNU Emacs style escape sequences, a second set
+ of backslash escapes is available:
+
+ '\a'
+ alert (bell)
+ '\b'
+ backspace
+ '\d'
+ delete
+ '\f'
+ form feed
+ '\n'
+ newline
+ '\r'
+ carriage return
+ '\t'
+ horizontal tab
+ '\v'
+ vertical tab
+ '\NNN'
+ the eight-bit character whose value is the octal value NNN
+ (one to three digits)
+ '\xHH'
+ the eight-bit character whose value is the hexadecimal value
+ HH (one or two hex digits)
+
+ When entering the text of a macro, single or double quotes must be
+ used to indicate a macro definition. Unquoted text is assumed to
+ be a function name. In the macro body, the backslash escapes
+ described above are expanded. Backslash will quote any other
+ character in the macro text, including '"' and '''. For example,
+ the following binding will make ''C-x' \' insert a single '\' into
+ the line:
+ "\C-x\\": "\\"
+
+
+File: bash.info, Node: Conditional Init Constructs, Next: Sample Init File, Prev: Readline Init File Syntax, Up: Readline Init File
+
+8.3.2 Conditional Init Constructs
+---------------------------------
+
+Readline implements a facility similar in spirit to the conditional
+compilation features of the C preprocessor which allows key bindings and
+variable settings to be performed as the result of tests. There are
+four parser directives used.
+
+'$if'
+ The '$if' construct allows bindings to be made based on the editing
+ mode, the terminal being used, or the application using Readline.
+ The text of the test, after any comparison operator, extends to the
+ end of the line; unless otherwise noted, no characters are required
+ to isolate it.
+
+ 'mode'
+ The 'mode=' form of the '$if' directive is used to test
+ whether Readline is in 'emacs' or 'vi' mode. This may be used
+ in conjunction with the 'set keymap' command, for instance, to
+ set bindings in the 'emacs-standard' and 'emacs-ctlx' keymaps
+ only if Readline is starting out in 'emacs' mode.
+
+ 'term'
+ The 'term=' form may be used to include terminal-specific key
+ bindings, perhaps to bind the key sequences output by the
+ terminal's function keys. The word on the right side of the
+ '=' is tested against both the full name of the terminal and
+ the portion of the terminal name before the first '-'. This
+ allows 'sun' to match both 'sun' and 'sun-cmd', for instance.
+
+ 'version'
+ The 'version' test may be used to perform comparisons against
+ specific Readline versions. The 'version' expands to the
+ current Readline version. The set of comparison operators
+ includes '=' (and '=='), '!=', '<=', '>=', '<', and '>'. The
+ version number supplied on the right side of the operator
+ consists of a major version number, an optional decimal point,
+ and an optional minor version (e.g., '7.1'). If the minor
+ version is omitted, it is assumed to be '0'. The operator may
+ be separated from the string 'version' and from the version
+ number argument by whitespace. The following example sets a
+ variable if the Readline version being used is 7.0 or newer:
+ $if version >= 7.0
+ set show-mode-in-prompt on
+ $endif
+
+ 'application'
+ The APPLICATION construct is used to include
+ application-specific settings. Each program using the
+ Readline library sets the APPLICATION NAME, and you can test
+ for a particular value. This could be used to bind key
+ sequences to functions useful for a specific program. For
+ instance, the following command adds a key sequence that
+ quotes the current or previous word in Bash:
+ $if Bash
+ # Quote the current or previous word
+ "\C-xq": "\eb\"\ef\""
+ $endif
+
+ 'variable'
+ The VARIABLE construct provides simple equality tests for
+ Readline variables and values. The permitted comparison
+ operators are '=', '==', and '!='. The variable name must be
+ separated from the comparison operator by whitespace; the
+ operator may be separated from the value on the right hand
+ side by whitespace. Both string and boolean variables may be
+ tested. Boolean variables must be tested against the values
+ ON and OFF. The following example is equivalent to the
+ 'mode=emacs' test described above:
+ $if editing-mode == emacs
+ set show-mode-in-prompt on
+ $endif
+
+'$endif'
+ This command, as seen in the previous example, terminates an '$if'
+ command.
+
+'$else'
+ Commands in this branch of the '$if' directive are executed if the
+ test fails.
+
+'$include'
+ This directive takes a single filename as an argument and reads
+ commands and bindings from that file. For example, the following
+ directive reads from '/etc/inputrc':
+ $include /etc/inputrc
+
+
+File: bash.info, Node: Sample Init File, Prev: Conditional Init Constructs, Up: Readline Init File
+
+8.3.3 Sample Init File
+----------------------
+
+Here is an example of an INPUTRC file. This illustrates key binding,
+variable assignment, and conditional syntax.
+
+ # This file controls the behaviour of line input editing for
+ # programs that use the GNU Readline library. Existing
+ # programs include FTP, Bash, and GDB.
+ #
+ # You can re-read the inputrc file with C-x C-r.
+ # Lines beginning with '#' are comments.
+ #
+ # First, include any system-wide bindings and variable
+ # assignments from /etc/Inputrc
+ $include /etc/Inputrc
+
+ #
+ # Set various bindings for emacs mode.
+
+ set editing-mode emacs
+
+ $if mode=emacs
+
+ Meta-Control-h: backward-kill-word Text after the function name is ignored
+
+ #
+ # Arrow keys in keypad mode
+ #
+ #"\M-OD": backward-char
+ #"\M-OC": forward-char
+ #"\M-OA": previous-history
+ #"\M-OB": next-history
+ #
+ # Arrow keys in ANSI mode
+ #
+ "\M-[D": backward-char
+ "\M-[C": forward-char
+ "\M-[A": previous-history
+ "\M-[B": next-history
+ #
+ # Arrow keys in 8 bit keypad mode
+ #
+ #"\M-\C-OD": backward-char
+ #"\M-\C-OC": forward-char
+ #"\M-\C-OA": previous-history
+ #"\M-\C-OB": next-history
+ #
+ # Arrow keys in 8 bit ANSI mode
+ #
+ #"\M-\C-[D": backward-char
+ #"\M-\C-[C": forward-char
+ #"\M-\C-[A": previous-history
+ #"\M-\C-[B": next-history
+
+ C-q: quoted-insert
+
+ $endif
+
+ # An old-style binding. This happens to be the default.
+ TAB: complete
+
+ # Macros that are convenient for shell interaction
+ $if Bash
+ # edit the path
+ "\C-xp": "PATH=${PATH}\e\C-e\C-a\ef\C-f"
+ # prepare to type a quoted word --
+ # insert open and close double quotes
+ # and move to just after the open quote
+ "\C-x\"": "\"\"\C-b"
+ # insert a backslash (testing backslash escapes
+ # in sequences and macros)
+ "\C-x\\": "\\"
+ # Quote the current or previous word
+ "\C-xq": "\eb\"\ef\""
+ # Add a binding to refresh the line, which is unbound
+ "\C-xr": redraw-current-line
+ # Edit variable on current line.
+ "\M-\C-v": "\C-a\C-k$\C-y\M-\C-e\C-a\C-y="
+ $endif
+
+ # use a visible bell if one is available
+ set bell-style visible
+
+ # don't strip characters to 7 bits when reading
+ set input-meta on
+
+ # allow iso-latin1 characters to be inserted rather
+ # than converted to prefix-meta sequences
+ set convert-meta off
+
+ # display characters with the eighth bit set directly
+ # rather than as meta-prefixed characters
+ set output-meta on
+
+ # if there are 150 or more possible completions for a word,
+ # ask whether or not the user wants to see all of them
+ set completion-query-items 150
+
+ # For FTP
+ $if Ftp
+ "\C-xg": "get \M-?"
+ "\C-xt": "put \M-?"
+ "\M-.": yank-last-arg
+ $endif
+
+
+File: bash.info, Node: Bindable Readline Commands, Next: Readline vi Mode, Prev: Readline Init File, Up: Command Line Editing
+
+8.4 Bindable Readline Commands
+==============================
+
+* Menu:
+
+* Commands For Moving:: Moving about the line.
+* Commands For History:: Getting at previous lines.
+* Commands For Text:: Commands for changing text.
+* Commands For Killing:: Commands for killing and yanking.
+* Numeric Arguments:: Specifying numeric arguments, repeat counts.
+* Commands For Completion:: Getting Readline to do the typing for you.
+* Keyboard Macros:: Saving and re-executing typed characters
+* Miscellaneous Commands:: Other miscellaneous commands.
+
+This section describes Readline commands that may be bound to key
+sequences. You can list your key bindings by executing 'bind -P' or,
+for a more terse format, suitable for an INPUTRC file, 'bind -p'.
+(*Note Bash Builtins::.) Command names without an accompanying key
+sequence are unbound by default.
+
+ In the following descriptions, "point" refers to the current cursor
+position, and "mark" refers to a cursor position saved by the 'set-mark'
+command. The text between the point and mark is referred to as the
+"region".
+
+
+File: bash.info, Node: Commands For Moving, Next: Commands For History, Up: Bindable Readline Commands
+
+8.4.1 Commands For Moving
+-------------------------
+
+'beginning-of-line (C-a)'
+ Move to the start of the current line.
+
+'end-of-line (C-e)'
+ Move to the end of the line.
+
+'forward-char (C-f)'
+ Move forward a character.
+
+'backward-char (C-b)'
+ Move back a character.
+
+'forward-word (M-f)'
+ Move forward to the end of the next word. Words are composed of
+ letters and digits.
+
+'backward-word (M-b)'
+ Move back to the start of the current or previous word. Words are
+ composed of letters and digits.
+
+'shell-forward-word (M-C-f)'
+ Move forward to the end of the next word. Words are delimited by
+ non-quoted shell metacharacters.
+
+'shell-backward-word (M-C-b)'
+ Move back to the start of the current or previous word. Words are
+ delimited by non-quoted shell metacharacters.
+
+'previous-screen-line ()'
+ Attempt to move point to the same physical screen column on the
+ previous physical screen line. This will not have the desired
+ effect if the current Readline line does not take up more than one
+ physical line or if point is not greater than the length of the
+ prompt plus the screen width.
+
+'next-screen-line ()'
+ Attempt to move point to the same physical screen column on the
+ next physical screen line. This will not have the desired effect
+ if the current Readline line does not take up more than one
+ physical line or if the length of the current Readline line is not
+ greater than the length of the prompt plus the screen width.
+
+'clear-display (M-C-l)'
+ Clear the screen and, if possible, the terminal's scrollback
+ buffer, then redraw the current line, leaving the current line at
+ the top of the screen.
+
+'clear-screen (C-l)'
+ Clear the screen, then redraw the current line, leaving the current
+ line at the top of the screen.
+
+'redraw-current-line ()'
+ Refresh the current line. By default, this is unbound.
+
+
+File: bash.info, Node: Commands For History, Next: Commands For Text, Prev: Commands For Moving, Up: Bindable Readline Commands
+
+8.4.2 Commands For Manipulating The History
+-------------------------------------------
+
+'accept-line (Newline or Return)'
+ Accept the line regardless of where the cursor is. If this line is
+ non-empty, add it to the history list according to the setting of
+ the 'HISTCONTROL' and 'HISTIGNORE' variables. If this line is a
+ modified history line, then restore the history line to its
+ original state.
+
+'previous-history (C-p)'
+ Move 'back' through the history list, fetching the previous
+ command.
+
+'next-history (C-n)'
+ Move 'forward' through the history list, fetching the next command.
+
+'beginning-of-history (M-<)'
+ Move to the first line in the history.
+
+'end-of-history (M->)'
+ Move to the end of the input history, i.e., the line currently
+ being entered.
+
+'reverse-search-history (C-r)'
+ Search backward starting at the current line and moving 'up'
+ through the history as necessary. This is an incremental search.
+ This command sets the region to the matched text and activates the
+ mark.
+
+'forward-search-history (C-s)'
+ Search forward starting at the current line and moving 'down'
+ through the history as necessary. This is an incremental search.
+ This command sets the region to the matched text and activates the
+ mark.
+
+'non-incremental-reverse-search-history (M-p)'
+ Search backward starting at the current line and moving 'up'
+ through the history as necessary using a non-incremental search for
+ a string supplied by the user. The search string may match
+ anywhere in a history line.
+
+'non-incremental-forward-search-history (M-n)'
+ Search forward starting at the current line and moving 'down'
+ through the history as necessary using a non-incremental search for
+ a string supplied by the user. The search string may match
+ anywhere in a history line.
+
+'history-search-forward ()'
+ Search forward through the history for the string of characters
+ between the start of the current line and the point. The search
+ string must match at the beginning of a history line. This is a
+ non-incremental search. By default, this command is unbound.
+
+'history-search-backward ()'
+ Search backward through the history for the string of characters
+ between the start of the current line and the point. The search
+ string must match at the beginning of a history line. This is a
+ non-incremental search. By default, this command is unbound.
+
+'history-substring-search-forward ()'
+ Search forward through the history for the string of characters
+ between the start of the current line and the point. The search
+ string may match anywhere in a history line. This is a
+ non-incremental search. By default, this command is unbound.
+
+'history-substring-search-backward ()'
+ Search backward through the history for the string of characters
+ between the start of the current line and the point. The search
+ string may match anywhere in a history line. This is a
+ non-incremental search. By default, this command is unbound.
+
+'yank-nth-arg (M-C-y)'
+ Insert the first argument to the previous command (usually the
+ second word on the previous line) at point. With an argument N,
+ insert the Nth word from the previous command (the words in the
+ previous command begin with word 0). A negative argument inserts
+ the Nth word from the end of the previous command. Once the
+ argument N is computed, the argument is extracted as if the '!N'
+ history expansion had been specified.
+
+'yank-last-arg (M-. or M-_)'
+ Insert last argument to the previous command (the last word of the
+ previous history entry). With a numeric argument, behave exactly
+ like 'yank-nth-arg'. Successive calls to 'yank-last-arg' move back
+ through the history list, inserting the last word (or the word
+ specified by the argument to the first call) of each line in turn.
+ Any numeric argument supplied to these successive calls determines
+ the direction to move through the history. A negative argument
+ switches the direction through the history (back or forward). The
+ history expansion facilities are used to extract the last argument,
+ as if the '!$' history expansion had been specified.
+
+'operate-and-get-next (C-o)'
+ Accept the current line for return to the calling application as if
+ a newline had been entered, and fetch the next line relative to the
+ current line from the history for editing. A numeric argument, if
+ supplied, specifies the history entry to use instead of the current
+ line.
+
+'fetch-history ()'
+ With a numeric argument, fetch that entry from the history list and
+ make it the current line. Without an argument, move back to the
+ first entry in the history list.
+
+
+File: bash.info, Node: Commands For Text, Next: Commands For Killing, Prev: Commands For History, Up: Bindable Readline Commands
+
+8.4.3 Commands For Changing Text
+--------------------------------
+
+'end-of-file (usually C-d)'
+ The character indicating end-of-file as set, for example, by
+ 'stty'. If this character is read when there are no characters on
+ the line, and point is at the beginning of the line, Readline
+ interprets it as the end of input and returns EOF.
+
+'delete-char (C-d)'
+ Delete the character at point. If this function is bound to the
+ same character as the tty EOF character, as 'C-d' commonly is, see
+ above for the effects.
+
+'backward-delete-char (Rubout)'
+ Delete the character behind the cursor. A numeric argument means
+ to kill the characters instead of deleting them.
+
+'forward-backward-delete-char ()'
+ Delete the character under the cursor, unless the cursor is at the
+ end of the line, in which case the character behind the cursor is
+ deleted. By default, this is not bound to a key.
+
+'quoted-insert (C-q or C-v)'
+ Add the next character typed to the line verbatim. This is how to
+ insert key sequences like 'C-q', for example.
+
+'self-insert (a, b, A, 1, !, ...)'
+ Insert yourself.
+
+'bracketed-paste-begin ()'
+ This function is intended to be bound to the "bracketed paste"
+ escape sequence sent by some terminals, and such a binding is
+ assigned by default. It allows Readline to insert the pasted text
+ as a single unit without treating each character as if it had been
+ read from the keyboard. The characters are inserted as if each one
+ was bound to 'self-insert' instead of executing any editing
+ commands.
+
+ Bracketed paste sets the region (the characters between point and
+ the mark) to the inserted text. It uses the concept of an _active
+ mark_: when the mark is active, Readline redisplay uses the
+ terminal's standout mode to denote the region.
+
+'transpose-chars (C-t)'
+ Drag the character before the cursor forward over the character at
+ the cursor, moving the cursor forward as well. If the insertion
+ point is at the end of the line, then this transposes the last two
+ characters of the line. Negative arguments have no effect.
+
+'transpose-words (M-t)'
+ Drag the word before point past the word after point, moving point
+ past that word as well. If the insertion point is at the end of
+ the line, this transposes the last two words on the line.
+
+'upcase-word (M-u)'
+ Uppercase the current (or following) word. With a negative
+ argument, uppercase the previous word, but do not move the cursor.
+
+'downcase-word (M-l)'
+ Lowercase the current (or following) word. With a negative
+ argument, lowercase the previous word, but do not move the cursor.
+
+'capitalize-word (M-c)'
+ Capitalize the current (or following) word. With a negative
+ argument, capitalize the previous word, but do not move the cursor.
+
+'overwrite-mode ()'
+ Toggle overwrite mode. With an explicit positive numeric argument,
+ switches to overwrite mode. With an explicit non-positive numeric
+ argument, switches to insert mode. This command affects only
+ 'emacs' mode; 'vi' mode does overwrite differently. Each call to
+ 'readline()' starts in insert mode.
+
+ In overwrite mode, characters bound to 'self-insert' replace the
+ text at point rather than pushing the text to the right.
+ Characters bound to 'backward-delete-char' replace the character
+ before point with a space.
+
+ By default, this command is unbound.
+
+
+File: bash.info, Node: Commands For Killing, Next: Numeric Arguments, Prev: Commands For Text, Up: Bindable Readline Commands
+
+8.4.4 Killing And Yanking
+-------------------------
+
+'kill-line (C-k)'
+ Kill the text from point to the end of the line. With a negative
+ numeric argument, kill backward from the cursor to the beginning of
+ the current line.
+
+'backward-kill-line (C-x Rubout)'
+ Kill backward from the cursor to the beginning of the current line.
+ With a negative numeric argument, kill forward from the cursor to
+ the end of the current line.
+
+'unix-line-discard (C-u)'
+ Kill backward from the cursor to the beginning of the current line.
+
+'kill-whole-line ()'
+ Kill all characters on the current line, no matter where point is.
+ By default, this is unbound.
+
+'kill-word (M-d)'
+ Kill from point to the end of the current word, or if between
+ words, to the end of the next word. Word boundaries are the same
+ as 'forward-word'.
+
+'backward-kill-word (M-<DEL>)'
+ Kill the word behind point. Word boundaries are the same as
+ 'backward-word'.
+
+'shell-kill-word (M-C-d)'
+ Kill from point to the end of the current word, or if between
+ words, to the end of the next word. Word boundaries are the same
+ as 'shell-forward-word'.
+
+'shell-backward-kill-word ()'
+ Kill the word behind point. Word boundaries are the same as
+ 'shell-backward-word'.
+
+'shell-transpose-words (M-C-t)'
+ Drag the word before point past the word after point, moving point
+ past that word as well. If the insertion point is at the end of
+ the line, this transposes the last two words on the line. Word
+ boundaries are the same as 'shell-forward-word' and
+ 'shell-backward-word'.
+
+'unix-word-rubout (C-w)'
+ Kill the word behind point, using white space as a word boundary.
+ The killed text is saved on the kill-ring.
+
+'unix-filename-rubout ()'
+ Kill the word behind point, using white space and the slash
+ character as the word boundaries. The killed text is saved on the
+ kill-ring.
+
+'delete-horizontal-space ()'
+ Delete all spaces and tabs around point. By default, this is
+ unbound.
+
+'kill-region ()'
+ Kill the text in the current region. By default, this command is
+ unbound.
+
+'copy-region-as-kill ()'
+ Copy the text in the region to the kill buffer, so it can be yanked
+ right away. By default, this command is unbound.
+
+'copy-backward-word ()'
+ Copy the word before point to the kill buffer. The word boundaries
+ are the same as 'backward-word'. By default, this command is
+ unbound.
+
+'copy-forward-word ()'
+ Copy the word following point to the kill buffer. The word
+ boundaries are the same as 'forward-word'. By default, this
+ command is unbound.
+
+'yank (C-y)'
+ Yank the top of the kill ring into the buffer at point.
+
+'yank-pop (M-y)'
+ Rotate the kill-ring, and yank the new top. You can only do this
+ if the prior command is 'yank' or 'yank-pop'.
+
+
+File: bash.info, Node: Numeric Arguments, Next: Commands For Completion, Prev: Commands For Killing, Up: Bindable Readline Commands
+
+8.4.5 Specifying Numeric Arguments
+----------------------------------
+
+'digit-argument (M-0, M-1, ... M--)'
+ Add this digit to the argument already accumulating, or start a new
+ argument. 'M--' starts a negative argument.
+
+'universal-argument ()'
+ This is another way to specify an argument. If this command is
+ followed by one or more digits, optionally with a leading minus
+ sign, those digits define the argument. If the command is followed
+ by digits, executing 'universal-argument' again ends the numeric
+ argument, but is otherwise ignored. As a special case, if this
+ command is immediately followed by a character that is neither a
+ digit nor minus sign, the argument count for the next command is
+ multiplied by four. The argument count is initially one, so
+ executing this function the first time makes the argument count
+ four, a second time makes the argument count sixteen, and so on.
+ By default, this is not bound to a key.
+
+
+File: bash.info, Node: Commands For Completion, Next: Keyboard Macros, Prev: Numeric Arguments, Up: Bindable Readline Commands
+
+8.4.6 Letting Readline Type For You
+-----------------------------------
+
+'complete (<TAB>)'
+ Attempt to perform completion on the text before point. The actual
+ completion performed is application-specific. Bash attempts
+ completion treating the text as a variable (if the text begins with
+ '$'), username (if the text begins with '~'), hostname (if the text
+ begins with '@'), or command (including aliases and functions) in
+ turn. If none of these produces a match, filename completion is
+ attempted.
+
+'possible-completions (M-?)'
+ List the possible completions of the text before point. When
+ displaying completions, Readline sets the number of columns used
+ for display to the value of 'completion-display-width', the value
+ of the environment variable 'COLUMNS', or the screen width, in that
+ order.
+
+'insert-completions (M-*)'
+ Insert all completions of the text before point that would have
+ been generated by 'possible-completions'.
+
+'menu-complete ()'
+ Similar to 'complete', but replaces the word to be completed with a
+ single match from the list of possible completions. Repeated
+ execution of 'menu-complete' steps through the list of possible
+ completions, inserting each match in turn. At the end of the list
+ of completions, the bell is rung (subject to the setting of
+ 'bell-style') and the original text is restored. An argument of N
+ moves N positions forward in the list of matches; a negative
+ argument may be used to move backward through the list. This
+ command is intended to be bound to <TAB>, but is unbound by
+ default.
+
+'menu-complete-backward ()'
+ Identical to 'menu-complete', but moves backward through the list
+ of possible completions, as if 'menu-complete' had been given a
+ negative argument.
+
+'delete-char-or-list ()'
+ Deletes the character under the cursor if not at the beginning or
+ end of the line (like 'delete-char'). If at the end of the line,
+ behaves identically to 'possible-completions'. This command is
+ unbound by default.
+
+'complete-filename (M-/)'
+ Attempt filename completion on the text before point.
+
+'possible-filename-completions (C-x /)'
+ List the possible completions of the text before point, treating it
+ as a filename.
+
+'complete-username (M-~)'
+ Attempt completion on the text before point, treating it as a
+ username.
+
+'possible-username-completions (C-x ~)'
+ List the possible completions of the text before point, treating it
+ as a username.
+
+'complete-variable (M-$)'
+ Attempt completion on the text before point, treating it as a shell
+ variable.
+
+'possible-variable-completions (C-x $)'
+ List the possible completions of the text before point, treating it
+ as a shell variable.
+
+'complete-hostname (M-@)'
+ Attempt completion on the text before point, treating it as a
+ hostname.
+
+'possible-hostname-completions (C-x @)'
+ List the possible completions of the text before point, treating it
+ as a hostname.
+
+'complete-command (M-!)'
+ Attempt completion on the text before point, treating it as a
+ command name. Command completion attempts to match the text
+ against aliases, reserved words, shell functions, shell builtins,
+ and finally executable filenames, in that order.
+
+'possible-command-completions (C-x !)'
+ List the possible completions of the text before point, treating it
+ as a command name.
+
+'dynamic-complete-history (M-<TAB>)'
+ Attempt completion on the text before point, comparing the text
+ against lines from the history list for possible completion
+ matches.
+
+'dabbrev-expand ()'
+ Attempt menu completion on the text before point, comparing the
+ text against lines from the history list for possible completion
+ matches.
+
+'complete-into-braces (M-{)'
+ Perform filename completion and insert the list of possible
+ completions enclosed within braces so the list is available to the
+ shell (*note Brace Expansion::).
+
+
+File: bash.info, Node: Keyboard Macros, Next: Miscellaneous Commands, Prev: Commands For Completion, Up: Bindable Readline Commands
+
+8.4.7 Keyboard Macros
+---------------------
+
+'start-kbd-macro (C-x ()'
+ Begin saving the characters typed into the current keyboard macro.
+
+'end-kbd-macro (C-x ))'
+ Stop saving the characters typed into the current keyboard macro
+ and save the definition.
+
+'call-last-kbd-macro (C-x e)'
+ Re-execute the last keyboard macro defined, by making the
+ characters in the macro appear as if typed at the keyboard.
+
+'print-last-kbd-macro ()'
+ Print the last keyboard macro defined in a format suitable for the
+ INPUTRC file.
+
+
+File: bash.info, Node: Miscellaneous Commands, Prev: Keyboard Macros, Up: Bindable Readline Commands
+
+8.4.8 Some Miscellaneous Commands
+---------------------------------
+
+'re-read-init-file (C-x C-r)'
+ Read in the contents of the INPUTRC file, and incorporate any
+ bindings or variable assignments found there.
+
+'abort (C-g)'
+ Abort the current editing command and ring the terminal's bell
+ (subject to the setting of 'bell-style').
+
+'do-lowercase-version (M-A, M-B, M-X, ...)'
+ If the metafied character X is upper case, run the command that is
+ bound to the corresponding metafied lower case character. The
+ behavior is undefined if X is already lower case.
+
+'prefix-meta (<ESC>)'
+ Metafy the next character typed. This is for keyboards without a
+ meta key. Typing '<ESC> f' is equivalent to typing 'M-f'.
+
+'undo (C-_ or C-x C-u)'
+ Incremental undo, separately remembered for each line.
+
+'revert-line (M-r)'
+ Undo all changes made to this line. This is like executing the
+ 'undo' command enough times to get back to the beginning.
+
+'tilde-expand (M-&)'
+ Perform tilde expansion on the current word.
+
+'set-mark (C-@)'
+ Set the mark to the point. If a numeric argument is supplied, the
+ mark is set to that position.
+
+'exchange-point-and-mark (C-x C-x)'
+ Swap the point with the mark. The current cursor position is set
+ to the saved position, and the old cursor position is saved as the
+ mark.
+
+'character-search (C-])'
+ A character is read and point is moved to the next occurrence of
+ that character. A negative argument searches for previous
+ occurrences.
+
+'character-search-backward (M-C-])'
+ A character is read and point is moved to the previous occurrence
+ of that character. A negative argument searches for subsequent
+ occurrences.
+
+'skip-csi-sequence ()'
+ Read enough characters to consume a multi-key sequence such as
+ those defined for keys like Home and End. Such sequences begin
+ with a Control Sequence Indicator (CSI), usually ESC-[. If this
+ sequence is bound to "\e[", keys producing such sequences will have
+ no effect unless explicitly bound to a Readline command, instead of
+ inserting stray characters into the editing buffer. This is
+ unbound by default, but usually bound to ESC-[.
+
+'insert-comment (M-#)'
+ Without a numeric argument, the value of the 'comment-begin'
+ variable is inserted at the beginning of the current line. If a
+ numeric argument is supplied, this command acts as a toggle: if the
+ characters at the beginning of the line do not match the value of
+ 'comment-begin', the value is inserted, otherwise the characters in
+ 'comment-begin' are deleted from the beginning of the line. In
+ either case, the line is accepted as if a newline had been typed.
+ The default value of 'comment-begin' causes this command to make
+ the current line a shell comment. If a numeric argument causes the
+ comment character to be removed, the line will be executed by the
+ shell.
+
+'dump-functions ()'
+ Print all of the functions and their key bindings to the Readline
+ output stream. If a numeric argument is supplied, the output is
+ formatted in such a way that it can be made part of an INPUTRC
+ file. This command is unbound by default.
+
+'dump-variables ()'
+ Print all of the settable variables and their values to the
+ Readline output stream. If a numeric argument is supplied, the
+ output is formatted in such a way that it can be made part of an
+ INPUTRC file. This command is unbound by default.
+
+'dump-macros ()'
+ Print all of the Readline key sequences bound to macros and the
+ strings they output. If a numeric argument is supplied, the output
+ is formatted in such a way that it can be made part of an INPUTRC
+ file. This command is unbound by default.
+
+'spell-correct-word (C-x s)'
+ Perform spelling correction on the current word, treating it as a
+ directory or filename, in the same way as the 'cdspell' shell
+ option. Word boundaries are the same as those used by
+ 'shell-forward-word'.
+
+'glob-complete-word (M-g)'
+ The word before point is treated as a pattern for pathname
+ expansion, with an asterisk implicitly appended. This pattern is
+ used to generate a list of matching file names for possible
+ completions.
+
+'glob-expand-word (C-x *)'
+ The word before point is treated as a pattern for pathname
+ expansion, and the list of matching file names is inserted,
+ replacing the word. If a numeric argument is supplied, a '*' is
+ appended before pathname expansion.
+
+'glob-list-expansions (C-x g)'
+ The list of expansions that would have been generated by
+ 'glob-expand-word' is displayed, and the line is redrawn. If a
+ numeric argument is supplied, a '*' is appended before pathname
+ expansion.
+
+'display-shell-version (C-x C-v)'
+ Display version information about the current instance of Bash.
+
+'shell-expand-line (M-C-e)'
+ Expand the line as the shell does. This performs alias and history
+ expansion as well as all of the shell word expansions (*note Shell
+ Expansions::).
+
+'history-expand-line (M-^)'
+ Perform history expansion on the current line.
+
+'magic-space ()'
+ Perform history expansion on the current line and insert a space
+ (*note History Interaction::).
+
+'alias-expand-line ()'
+ Perform alias expansion on the current line (*note Aliases::).
+
+'history-and-alias-expand-line ()'
+ Perform history and alias expansion on the current line.
+
+'insert-last-argument (M-. or M-_)'
+ A synonym for 'yank-last-arg'.
+
+'edit-and-execute-command (C-x C-e)'
+ Invoke an editor on the current command line, and execute the
+ result as shell commands. Bash attempts to invoke '$VISUAL',
+ '$EDITOR', and 'emacs' as the editor, in that order.
+
+
+File: bash.info, Node: Readline vi Mode, Next: Programmable Completion, Prev: Bindable Readline Commands, Up: Command Line Editing
+
+8.5 Readline vi Mode
+====================
+
+While the Readline library does not have a full set of 'vi' editing
+functions, it does contain enough to allow simple editing of the line.
+The Readline 'vi' mode behaves as specified in the POSIX standard.
+
+ In order to switch interactively between 'emacs' and 'vi' editing
+modes, use the 'set -o emacs' and 'set -o vi' commands (*note The Set
+Builtin::). The Readline default is 'emacs' mode.
+
+ When you enter a line in 'vi' mode, you are already placed in
+'insertion' mode, as if you had typed an 'i'. Pressing <ESC> switches
+you into 'command' mode, where you can edit the text of the line with
+the standard 'vi' movement keys, move to previous history lines with 'k'
+and subsequent lines with 'j', and so forth.
+
+
+File: bash.info, Node: Programmable Completion, Next: Programmable Completion Builtins, Prev: Readline vi Mode, Up: Command Line Editing
+
+8.6 Programmable Completion
+===========================
+
+When word completion is attempted for an argument to a command for which
+a completion specification (a COMPSPEC) has been defined using the
+'complete' builtin (*note Programmable Completion Builtins::), the
+programmable completion facilities are invoked.
+
+ First, the command name is identified. If a compspec has been
+defined for that command, the compspec is used to generate the list of
+possible completions for the word. If the command word is the empty
+string (completion attempted at the beginning of an empty line), any
+compspec defined with the '-E' option to 'complete' is used. If the
+command word is a full pathname, a compspec for the full pathname is
+searched for first. If no compspec is found for the full pathname, an
+attempt is made to find a compspec for the portion following the final
+slash. If those searches do not result in a compspec, any compspec
+defined with the '-D' option to 'complete' is used as the default. If
+there is no default compspec, Bash attempts alias expansion on the
+command word as a final resort, and attempts to find a compspec for the
+command word from any successful expansion
+
+ Once a compspec has been found, it is used to generate the list of
+matching words. If a compspec is not found, the default Bash completion
+described above (*note Commands For Completion::) is performed.
+
+ First, the actions specified by the compspec are used. Only matches
+which are prefixed by the word being completed are returned. When the
+'-f' or '-d' option is used for filename or directory name completion,
+the shell variable 'FIGNORE' is used to filter the matches. *Note Bash
+Variables::, for a description of 'FIGNORE'.
+
+ Any completions specified by a filename expansion pattern to the '-G'
+option are generated next. The words generated by the pattern need not
+match the word being completed. The 'GLOBIGNORE' shell variable is not
+used to filter the matches, but the 'FIGNORE' shell variable is used.
+
+ Next, the string specified as the argument to the '-W' option is
+considered. The string is first split using the characters in the 'IFS'
+special variable as delimiters. Shell quoting is honored within the
+string, in order to provide a mechanism for the words to contain shell
+metacharacters or characters in the value of 'IFS'. Each word is then
+expanded using brace expansion, tilde expansion, parameter and variable
+expansion, command substitution, and arithmetic expansion, as described
+above (*note Shell Expansions::). The results are split using the rules
+described above (*note Word Splitting::). The results of the expansion
+are prefix-matched against the word being completed, and the matching
+words become the possible completions.
+
+ After these matches have been generated, any shell function or
+command specified with the '-F' and '-C' options is invoked. When the
+command or function is invoked, the 'COMP_LINE', 'COMP_POINT',
+'COMP_KEY', and 'COMP_TYPE' variables are assigned values as described
+above (*note Bash Variables::). If a shell function is being invoked,
+the 'COMP_WORDS' and 'COMP_CWORD' variables are also set. When the
+function or command is invoked, the first argument ($1) is the name of
+the command whose arguments are being completed, the second argument
+($2) is the word being completed, and the third argument ($3) is the
+word preceding the word being completed on the current command line. No
+filtering of the generated completions against the word being completed
+is performed; the function or command has complete freedom in generating
+the matches.
+
+ Any function specified with '-F' is invoked first. The function may
+use any of the shell facilities, including the 'compgen' and 'compopt'
+builtins described below (*note Programmable Completion Builtins::), to
+generate the matches. It must put the possible completions in the
+'COMPREPLY' array variable, one per array element.
+
+ Next, any command specified with the '-C' option is invoked in an
+environment equivalent to command substitution. It should print a list
+of completions, one per line, to the standard output. Backslash may be
+used to escape a newline, if necessary.
+
+ After all of the possible completions are generated, any filter
+specified with the '-X' option is applied to the list. The filter is a
+pattern as used for pathname expansion; a '&' in the pattern is replaced
+with the text of the word being completed. A literal '&' may be escaped
+with a backslash; the backslash is removed before attempting a match.
+Any completion that matches the pattern will be removed from the list.
+A leading '!' negates the pattern; in this case any completion not
+matching the pattern will be removed. If the 'nocasematch' shell option
+(see the description of 'shopt' in *note The Shopt Builtin::) is
+enabled, the match is performed without regard to the case of alphabetic
+characters.
+
+ Finally, any prefix and suffix specified with the '-P' and '-S'
+options are added to each member of the completion list, and the result
+is returned to the Readline completion code as the list of possible
+completions.
+
+ If the previously-applied actions do not generate any matches, and
+the '-o dirnames' option was supplied to 'complete' when the compspec
+was defined, directory name completion is attempted.
+
+ If the '-o plusdirs' option was supplied to 'complete' when the
+compspec was defined, directory name completion is attempted and any
+matches are added to the results of the other actions.
+
+ By default, if a compspec is found, whatever it generates is returned
+to the completion code as the full set of possible completions. The
+default Bash completions are not attempted, and the Readline default of
+filename completion is disabled. If the '-o bashdefault' option was
+supplied to 'complete' when the compspec was defined, the default Bash
+completions are attempted if the compspec generates no matches. If the
+'-o default' option was supplied to 'complete' when the compspec was
+defined, Readline's default completion will be performed if the compspec
+(and, if attempted, the default Bash completions) generate no matches.
+
+ When a compspec indicates that directory name completion is desired,
+the programmable completion functions force Readline to append a slash
+to completed names which are symbolic links to directories, subject to
+the value of the MARK-DIRECTORIES Readline variable, regardless of the
+setting of the MARK-SYMLINKED-DIRECTORIES Readline variable.
+
+ There is some support for dynamically modifying completions. This is
+most useful when used in combination with a default completion specified
+with '-D'. It's possible for shell functions executed as completion
+handlers to indicate that completion should be retried by returning an
+exit status of 124. If a shell function returns 124, and changes the
+compspec associated with the command on which completion is being
+attempted (supplied as the first argument when the function is
+executed), programmable completion restarts from the beginning, with an
+attempt to find a new compspec for that command. This allows a set of
+completions to be built dynamically as completion is attempted, rather
+than being loaded all at once.
+
+ For instance, assuming that there is a library of compspecs, each
+kept in a file corresponding to the name of the command, the following
+default completion function would load completions dynamically:
+
+ _completion_loader()
+ {
+ . "/etc/bash_completion.d/$1.sh" >/dev/null 2>&1 && return 124
+ }
+ complete -D -F _completion_loader -o bashdefault -o default
+
+
+File: bash.info, Node: Programmable Completion Builtins, Next: A Programmable Completion Example, Prev: Programmable Completion, Up: Command Line Editing
+
+8.7 Programmable Completion Builtins
+====================================
+
+Three builtin commands are available to manipulate the programmable
+completion facilities: one to specify how the arguments to a particular
+command are to be completed, and two to modify the completion as it is
+happening.
+
+'compgen'
+ compgen [OPTION] [WORD]
+
+ Generate possible completion matches for WORD according to the
+ OPTIONs, which may be any option accepted by the 'complete' builtin
+ with the exception of '-p' and '-r', and write the matches to the
+ standard output. When using the '-F' or '-C' options, the various
+ shell variables set by the programmable completion facilities,
+ while available, will not have useful values.
+
+ The matches will be generated in the same way as if the
+ programmable completion code had generated them directly from a
+ completion specification with the same flags. If WORD is
+ specified, only those completions matching WORD will be displayed.
+
+ The return value is true unless an invalid option is supplied, or
+ no matches were generated.
+
+'complete'
+ complete [-abcdefgjksuv] [-o COMP-OPTION] [-DEI] [-A ACTION] [-G GLOBPAT]
+ [-W WORDLIST] [-F FUNCTION] [-C COMMAND] [-X FILTERPAT]
+ [-P PREFIX] [-S SUFFIX] NAME [NAME ...]
+ complete -pr [-DEI] [NAME ...]
+
+ Specify how arguments to each NAME should be completed. If the
+ '-p' option is supplied, or if no options are supplied, existing
+ completion specifications are printed in a way that allows them to
+ be reused as input. The '-r' option removes a completion
+ specification for each NAME, or, if no NAMEs are supplied, all
+ completion specifications. The '-D' option indicates that other
+ supplied options and actions should apply to the "default" command
+ completion; that is, completion attempted on a command for which no
+ completion has previously been defined. The '-E' option indicates
+ that other supplied options and actions should apply to "empty"
+ command completion; that is, completion attempted on a blank line.
+ The '-I' option indicates that other supplied options and actions
+ should apply to completion on the initial non-assignment word on
+ the line, or after a command delimiter such as ';' or '|', which is
+ usually command name completion. If multiple options are supplied,
+ the '-D' option takes precedence over '-E', and both take
+ precedence over '-I'. If any of '-D', '-E', or '-I' are supplied,
+ any other NAME arguments are ignored; these completions only apply
+ to the case specified by the option.
+
+ The process of applying these completion specifications when word
+ completion is attempted is described above (*note Programmable
+ Completion::).
+
+ Other options, if specified, have the following meanings. The
+ arguments to the '-G', '-W', and '-X' options (and, if necessary,
+ the '-P' and '-S' options) should be quoted to protect them from
+ expansion before the 'complete' builtin is invoked.
+
+ '-o COMP-OPTION'
+ The COMP-OPTION controls several aspects of the compspec's
+ behavior beyond the simple generation of completions.
+ COMP-OPTION may be one of:
+
+ 'bashdefault'
+ Perform the rest of the default Bash completions if the
+ compspec generates no matches.
+
+ 'default'
+ Use Readline's default filename completion if the
+ compspec generates no matches.
+
+ 'dirnames'
+ Perform directory name completion if the compspec
+ generates no matches.
+
+ 'filenames'
+ Tell Readline that the compspec generates filenames, so
+ it can perform any filename-specific processing (like
+ adding a slash to directory names, quoting special
+ characters, or suppressing trailing spaces). This option
+ is intended to be used with shell functions specified
+ with '-F'.
+
+ 'noquote'
+ Tell Readline not to quote the completed words if they
+ are filenames (quoting filenames is the default).
+
+ 'nosort'
+ Tell Readline not to sort the list of possible
+ completions alphabetically.
+
+ 'nospace'
+ Tell Readline not to append a space (the default) to
+ words completed at the end of the line.
+
+ 'plusdirs'
+ After any matches defined by the compspec are generated,
+ directory name completion is attempted and any matches
+ are added to the results of the other actions.
+
+ '-A ACTION'
+ The ACTION may be one of the following to generate a list of
+ possible completions:
+
+ 'alias'
+ Alias names. May also be specified as '-a'.
+
+ 'arrayvar'
+ Array variable names.
+
+ 'binding'
+ Readline key binding names (*note Bindable Readline
+ Commands::).
+
+ 'builtin'
+ Names of shell builtin commands. May also be specified
+ as '-b'.
+
+ 'command'
+ Command names. May also be specified as '-c'.
+
+ 'directory'
+ Directory names. May also be specified as '-d'.
+
+ 'disabled'
+ Names of disabled shell builtins.
+
+ 'enabled'
+ Names of enabled shell builtins.
+
+ 'export'
+ Names of exported shell variables. May also be specified
+ as '-e'.
+
+ 'file'
+ File names. May also be specified as '-f'.
+
+ 'function'
+ Names of shell functions.
+
+ 'group'
+ Group names. May also be specified as '-g'.
+
+ 'helptopic'
+ Help topics as accepted by the 'help' builtin (*note Bash
+ Builtins::).
+
+ 'hostname'
+ Hostnames, as taken from the file specified by the
+ 'HOSTFILE' shell variable (*note Bash Variables::).
+
+ 'job'
+ Job names, if job control is active. May also be
+ specified as '-j'.
+
+ 'keyword'
+ Shell reserved words. May also be specified as '-k'.
+
+ 'running'
+ Names of running jobs, if job control is active.
+
+ 'service'
+ Service names. May also be specified as '-s'.
+
+ 'setopt'
+ Valid arguments for the '-o' option to the 'set' builtin
+ (*note The Set Builtin::).
+
+ 'shopt'
+ Shell option names as accepted by the 'shopt' builtin
+ (*note Bash Builtins::).
+
+ 'signal'
+ Signal names.
+
+ 'stopped'
+ Names of stopped jobs, if job control is active.
+
+ 'user'
+ User names. May also be specified as '-u'.
+
+ 'variable'
+ Names of all shell variables. May also be specified as
+ '-v'.
+
+ '-C COMMAND'
+ COMMAND is executed in a subshell environment, and its output
+ is used as the possible completions. Arguments are passed as
+ with the '-F' option.
+
+ '-F FUNCTION'
+ The shell function FUNCTION is executed in the current shell
+ environment. When it is executed, $1 is the name of the
+ command whose arguments are being completed, $2 is the word
+ being completed, and $3 is the word preceding the word being
+ completed, as described above (*note Programmable
+ Completion::). When it finishes, the possible completions are
+ retrieved from the value of the 'COMPREPLY' array variable.
+
+ '-G GLOBPAT'
+ The filename expansion pattern GLOBPAT is expanded to generate
+ the possible completions.
+
+ '-P PREFIX'
+ PREFIX is added at the beginning of each possible completion
+ after all other options have been applied.
+
+ '-S SUFFIX'
+ SUFFIX is appended to each possible completion after all other
+ options have been applied.
+
+ '-W WORDLIST'
+ The WORDLIST is split using the characters in the 'IFS'
+ special variable as delimiters, and each resultant word is
+ expanded. The possible completions are the members of the
+ resultant list which match the word being completed.
+
+ '-X FILTERPAT'
+ FILTERPAT is a pattern as used for filename expansion. It is
+ applied to the list of possible completions generated by the
+ preceding options and arguments, and each completion matching
+ FILTERPAT is removed from the list. A leading '!' in
+ FILTERPAT negates the pattern; in this case, any completion
+ not matching FILTERPAT is removed.
+
+ The return value is true unless an invalid option is supplied, an
+ option other than '-p' or '-r' is supplied without a NAME argument,
+ an attempt is made to remove a completion specification for a NAME
+ for which no specification exists, or an error occurs adding a
+ completion specification.
+
+'compopt'
+ compopt [-o OPTION] [-DEI] [+o OPTION] [NAME]
+ Modify completion options for each NAME according to the OPTIONs,
+ or for the currently-executing completion if no NAMEs are supplied.
+ If no OPTIONs are given, display the completion options for each
+ NAME or the current completion. The possible values of OPTION are
+ those valid for the 'complete' builtin described above. The '-D'
+ option indicates that other supplied options should apply to the
+ "default" command completion; that is, completion attempted on a
+ command for which no completion has previously been defined. The
+ '-E' option indicates that other supplied options should apply to
+ "empty" command completion; that is, completion attempted on a
+ blank line. The '-I' option indicates that other supplied options
+ should apply to completion on the initial non-assignment word on
+ the line, or after a command delimiter such as ';' or '|', which is
+ usually command name completion.
+
+ If multiple options are supplied, the '-D' option takes precedence
+ over '-E', and both take precedence over '-I'
+
+ The return value is true unless an invalid option is supplied, an
+ attempt is made to modify the options for a NAME for which no
+ completion specification exists, or an output error occurs.
+
+
+File: bash.info, Node: A Programmable Completion Example, Prev: Programmable Completion Builtins, Up: Command Line Editing
+
+8.8 A Programmable Completion Example
+=====================================
+
+The most common way to obtain additional completion functionality beyond
+the default actions 'complete' and 'compgen' provide is to use a shell
+function and bind it to a particular command using 'complete -F'.
+
+ The following function provides completions for the 'cd' builtin. It
+is a reasonably good example of what shell functions must do when used
+for completion. This function uses the word passed as '$2' to determine
+the directory name to complete. You can also use the 'COMP_WORDS' array
+variable; the current word is indexed by the 'COMP_CWORD' variable.
+
+ The function relies on the 'complete' and 'compgen' builtins to do
+much of the work, adding only the things that the Bash 'cd' does beyond
+accepting basic directory names: tilde expansion (*note Tilde
+Expansion::), searching directories in $CDPATH, which is described above
+(*note Bourne Shell Builtins::), and basic support for the 'cdable_vars'
+shell option (*note The Shopt Builtin::). '_comp_cd' modifies the value
+of IFS so that it contains only a newline to accommodate file names
+containing spaces and tabs - 'compgen' prints the possible completions
+it generates one per line.
+
+ Possible completions go into the COMPREPLY array variable, one
+completion per array element. The programmable completion system
+retrieves the completions from there when the function returns.
+
+ # A completion function for the cd builtin
+ # based on the cd completion function from the bash_completion package
+ _comp_cd()
+ {
+ local IFS=$' \t\n' # normalize IFS
+ local cur _skipdot _cdpath
+ local i j k
+
+ # Tilde expansion, which also expands tilde to full pathname
+ case "$2" in
+ \~*) eval cur="$2" ;;
+ *) cur=$2 ;;
+ esac
+
+ # no cdpath or absolute pathname -- straight directory completion
+ if [[ -z "${CDPATH:-}" ]] || [[ "$cur" == @(./*|../*|/*) ]]; then
+ # compgen prints paths one per line; could also use while loop
+ IFS=$'\n'
+ COMPREPLY=( $(compgen -d -- "$cur") )
+ IFS=$' \t\n'
+ # CDPATH+directories in the current directory if not in CDPATH
+ else
+ IFS=$'\n'
+ _skipdot=false
+ # preprocess CDPATH to convert null directory names to .
+ _cdpath=${CDPATH/#:/.:}
+ _cdpath=${_cdpath//::/:.:}
+ _cdpath=${_cdpath/%:/:.}
+ for i in ${_cdpath//:/$'\n'}; do
+ if [[ $i -ef . ]]; then _skipdot=true; fi
+ k="${#COMPREPLY[@]}"
+ for j in $( compgen -d -- "$i/$cur" ); do
+ COMPREPLY[k++]=${j#$i/} # cut off directory
+ done
+ done
+ $_skipdot || COMPREPLY+=( $(compgen -d -- "$cur") )
+ IFS=$' \t\n'
+ fi
+
+ # variable names if appropriate shell option set and no completions
+ if shopt -q cdable_vars && [[ ${#COMPREPLY[@]} -eq 0 ]]; then
+ COMPREPLY=( $(compgen -v -- "$cur") )
+ fi
+
+ return 0
+ }
+
+ We install the completion function using the '-F' option to
+'complete':
+
+ # Tell readline to quote appropriate and append slashes to directories;
+ # use the bash default completion for other arguments
+ complete -o filenames -o nospace -o bashdefault -F _comp_cd cd
+
+Since we'd like Bash and Readline to take care of some of the other
+details for us, we use several other options to tell Bash and Readline
+what to do. The '-o filenames' option tells Readline that the possible
+completions should be treated as filenames, and quoted appropriately.
+That option will also cause Readline to append a slash to filenames it
+can determine are directories (which is why we might want to extend
+'_comp_cd' to append a slash if we're using directories found via
+CDPATH: Readline can't tell those completions are directories). The '-o
+nospace' option tells Readline to not append a space character to the
+directory name, in case we want to append to it. The '-o bashdefault'
+option brings in the rest of the "Bash default" completions - possible
+completions that Bash adds to the default Readline set. These include
+things like command name completion, variable completion for words
+beginning with '$' or '${', completions containing pathname expansion
+patterns (*note Filename Expansion::), and so on.
+
+ Once installed using 'complete', '_comp_cd' will be called every time
+we attempt word completion for a 'cd' command.
+
+ Many more examples - an extensive collection of completions for most
+of the common GNU, Unix, and Linux commands - are available as part of
+the bash_completion project. This is installed by default on many
+GNU/Linux distributions. Originally written by Ian Macdonald, the
+project now lives at <https://github.com/scop/bash-completion/>. There
+are ports for other systems such as Solaris and Mac OS X.
+
+ An older version of the bash_completion package is distributed with
+bash in the 'examples/complete' subdirectory.
+
+
+File: bash.info, Node: Using History Interactively, Next: Installing Bash, Prev: Command Line Editing, Up: Top
+
+9 Using History Interactively
+*****************************
+
+This chapter describes how to use the GNU History Library interactively,
+from a user's standpoint. It should be considered a user's guide. For
+information on using the GNU History Library in other programs, see the
+GNU Readline Library Manual.
+
+* Menu:
+
+* Bash History Facilities:: How Bash lets you manipulate your command
+ history.
+* Bash History Builtins:: The Bash builtin commands that manipulate
+ the command history.
+* History Interaction:: What it feels like using History as a user.
+
+
+File: bash.info, Node: Bash History Facilities, Next: Bash History Builtins, Up: Using History Interactively
+
+9.1 Bash History Facilities
+===========================
+
+When the '-o history' option to the 'set' builtin is enabled (*note The
+Set Builtin::), the shell provides access to the "command history", the
+list of commands previously typed. The value of the 'HISTSIZE' shell
+variable is used as the number of commands to save in a history list.
+The text of the last '$HISTSIZE' commands (default 500) is saved. The
+shell stores each command in the history list prior to parameter and
+variable expansion but after history expansion is performed, subject to
+the values of the shell variables 'HISTIGNORE' and 'HISTCONTROL'.
+
+ When the shell starts up, the history is initialized from the file
+named by the 'HISTFILE' variable (default '~/.bash_history'). The file
+named by the value of 'HISTFILE' is truncated, if necessary, to contain
+no more than the number of lines specified by the value of the
+'HISTFILESIZE' variable. When a shell with history enabled exits, the
+last '$HISTSIZE' lines are copied from the history list to the file
+named by '$HISTFILE'. If the 'histappend' shell option is set (*note
+Bash Builtins::), the lines are appended to the history file, otherwise
+the history file is overwritten. If 'HISTFILE' is unset, or if the
+history file is unwritable, the history is not saved. After saving the
+history, the history file is truncated to contain no more than
+'$HISTFILESIZE' lines. If 'HISTFILESIZE' is unset, or set to null, a
+non-numeric value, or a numeric value less than zero, the history file
+is not truncated.
+
+ If the 'HISTTIMEFORMAT' is set, the time stamp information associated
+with each history entry is written to the history file, marked with the
+history comment character. When the history file is read, lines
+beginning with the history comment character followed immediately by a
+digit are interpreted as timestamps for the following history entry.
+
+ The builtin command 'fc' may be used to list or edit and re-execute a
+portion of the history list. The 'history' builtin may be used to
+display or modify the history list and manipulate the history file.
+When using command-line editing, search commands are available in each
+editing mode that provide access to the history list (*note Commands For
+History::).
+
+ The shell allows control over which commands are saved on the history
+list. The 'HISTCONTROL' and 'HISTIGNORE' variables may be set to cause
+the shell to save only a subset of the commands entered. The 'cmdhist'
+shell option, if enabled, causes the shell to attempt to save each line
+of a multi-line command in the same history entry, adding semicolons
+where necessary to preserve syntactic correctness. The 'lithist' shell
+option causes the shell to save the command with embedded newlines
+instead of semicolons. The 'shopt' builtin is used to set these
+options. *Note The Shopt Builtin::, for a description of 'shopt'.
+
+
+File: bash.info, Node: Bash History Builtins, Next: History Interaction, Prev: Bash History Facilities, Up: Using History Interactively
+
+9.2 Bash History Builtins
+=========================
+
+Bash provides two builtin commands which manipulate the history list and
+history file.
+
+'fc'
+ fc [-e ENAME] [-lnr] [FIRST] [LAST]
+ fc -s [PAT=REP] [COMMAND]
+
+ The first form selects a range of commands from FIRST to LAST from
+ the history list and displays or edits and re-executes them. Both
+ FIRST and LAST may be specified as a string (to locate the most
+ recent command beginning with that string) or as a number (an index
+ into the history list, where a negative number is used as an offset
+ from the current command number).
+
+ When listing, a FIRST or LAST of 0 is equivalent to -1 and -0 is
+ equivalent to the current command (usually the 'fc' command);
+ otherwise 0 is equivalent to -1 and -0 is invalid.
+
+ If LAST is not specified, it is set to FIRST. If FIRST is not
+ specified, it is set to the previous command for editing and -16
+ for listing. If the '-l' flag is given, the commands are listed on
+ standard output. The '-n' flag suppresses the command numbers when
+ listing. The '-r' flag reverses the order of the listing.
+ Otherwise, the editor given by ENAME is invoked on a file
+ containing those commands. If ENAME is not given, the value of the
+ following variable expansion is used: '${FCEDIT:-${EDITOR:-vi}}'.
+ This says to use the value of the 'FCEDIT' variable if set, or the
+ value of the 'EDITOR' variable if that is set, or 'vi' if neither
+ is set. When editing is complete, the edited commands are echoed
+ and executed.
+
+ In the second form, COMMAND is re-executed after each instance of
+ PAT in the selected command is replaced by REP. COMMAND is
+ interpreted the same as FIRST above.
+
+ A useful alias to use with the 'fc' command is 'r='fc -s'', so that
+ typing 'r cc' runs the last command beginning with 'cc' and typing
+ 'r' re-executes the last command (*note Aliases::).
+
+'history'
+ history [N]
+ history -c
+ history -d OFFSET
+ history -d START-END
+ history [-anrw] [FILENAME]
+ history -ps ARG
+
+ With no options, display the history list with line numbers. Lines
+ prefixed with a '*' have been modified. An argument of N lists
+ only the last N lines. If the shell variable 'HISTTIMEFORMAT' is
+ set and not null, it is used as a format string for STRFTIME to
+ display the time stamp associated with each displayed history
+ entry. No intervening blank is printed between the formatted time
+ stamp and the history line.
+
+ Options, if supplied, have the following meanings:
+
+ '-c'
+ Clear the history list. This may be combined with the other
+ options to replace the history list completely.
+
+ '-d OFFSET'
+ Delete the history entry at position OFFSET. If OFFSET is
+ positive, it should be specified as it appears when the
+ history is displayed. If OFFSET is negative, it is
+ interpreted as relative to one greater than the last history
+ position, so negative indices count back from the end of the
+ history, and an index of '-1' refers to the current 'history
+ -d' command.
+
+ '-d START-END'
+ Delete the range of history entries between positions START
+ and END, inclusive. Positive and negative values for START
+ and END are interpreted as described above.
+
+ '-a'
+ Append the new history lines to the history file. These are
+ history lines entered since the beginning of the current Bash
+ session, but not already appended to the history file.
+
+ '-n'
+ Append the history lines not already read from the history
+ file to the current history list. These are lines appended to
+ the history file since the beginning of the current Bash
+ session.
+
+ '-r'
+ Read the history file and append its contents to the history
+ list.
+
+ '-w'
+ Write out the current history list to the history file.
+
+ '-p'
+ Perform history substitution on the ARGs and display the
+ result on the standard output, without storing the results in
+ the history list.
+
+ '-s'
+ The ARGs are added to the end of the history list as a single
+ entry.
+
+ If a FILENAME argument is supplied when any of the '-w', '-r',
+ '-a', or '-n' options is used, Bash uses FILENAME as the history
+ file. If not, then the value of the 'HISTFILE' variable is used.
+
+ The return value is 0 unless an invalid option is encountered, an
+ error occurs while reading or writing the history file, an invalid
+ OFFSET or range is supplied as an argument to '-d', or the history
+ expansion supplied as an argument to '-p' fails.
+
+
+File: bash.info, Node: History Interaction, Prev: Bash History Builtins, Up: Using History Interactively
+
+9.3 History Expansion
+=====================
+
+The History library provides a history expansion feature that is similar
+to the history expansion provided by 'csh'. This section describes the
+syntax used to manipulate the history information.
+
+ History expansions introduce words from the history list into the
+input stream, making it easy to repeat commands, insert the arguments to
+a previous command into the current input line, or fix errors in
+previous commands quickly.
+
+ History expansion is performed immediately after a complete line is
+read, before the shell breaks it into words, and is performed on each
+line individually. Bash attempts to inform the history expansion
+functions about quoting still in effect from previous lines.
+
+ History expansion takes place in two parts. The first is to
+determine which line from the history list should be used during
+substitution. The second is to select portions of that line for
+inclusion into the current one. The line selected from the history is
+called the "event", and the portions of that line that are acted upon
+are called "words". Various "modifiers" are available to manipulate the
+selected words. The line is broken into words in the same fashion that
+Bash does, so that several words surrounded by quotes are considered one
+word. History expansions are introduced by the appearance of the
+history expansion character, which is '!' by default.
+
+ History expansion implements shell-like quoting conventions: a
+backslash can be used to remove the special handling for the next
+character; single quotes enclose verbatim sequences of characters, and
+can be used to inhibit history expansion; and characters enclosed within
+double quotes may be subject to history expansion, since backslash can
+escape the history expansion character, but single quotes may not, since
+they are not treated specially within double quotes.
+
+ When using the shell, only '\' and ''' may be used to escape the
+history expansion character, but the history expansion character is also
+treated as quoted if it immediately precedes the closing double quote in
+a double-quoted string.
+
+ Several shell options settable with the 'shopt' builtin (*note The
+Shopt Builtin::) may be used to tailor the behavior of history
+expansion. If the 'histverify' shell option is enabled, and Readline is
+being used, history substitutions are not immediately passed to the
+shell parser. Instead, the expanded line is reloaded into the Readline
+editing buffer for further modification. If Readline is being used, and
+the 'histreedit' shell option is enabled, a failed history expansion
+will be reloaded into the Readline editing buffer for correction. The
+'-p' option to the 'history' builtin command may be used to see what a
+history expansion will do before using it. The '-s' option to the
+'history' builtin may be used to add commands to the end of the history
+list without actually executing them, so that they are available for
+subsequent recall. This is most useful in conjunction with Readline.
+
+ The shell allows control of the various characters used by the
+history expansion mechanism with the 'histchars' variable, as explained
+above (*note Bash Variables::). The shell uses the history comment
+character to mark history timestamps when writing the history file.
+
+* Menu:
+
+* Event Designators:: How to specify which history line to use.
+* Word Designators:: Specifying which words are of interest.
+* Modifiers:: Modifying the results of substitution.
+
+
+File: bash.info, Node: Event Designators, Next: Word Designators, Up: History Interaction
+
+9.3.1 Event Designators
+-----------------------
+
+An event designator is a reference to a command line entry in the
+history list. Unless the reference is absolute, events are relative to
+the current position in the history list.
+
+'!'
+ Start a history substitution, except when followed by a space, tab,
+ the end of the line, '=' or '(' (when the 'extglob' shell option is
+ enabled using the 'shopt' builtin).
+
+'!N'
+ Refer to command line N.
+
+'!-N'
+ Refer to the command N lines back.
+
+'!!'
+ Refer to the previous command. This is a synonym for '!-1'.
+
+'!STRING'
+ Refer to the most recent command preceding the current position in
+ the history list starting with STRING.
+
+'!?STRING[?]'
+ Refer to the most recent command preceding the current position in
+ the history list containing STRING. The trailing '?' may be
+ omitted if the STRING is followed immediately by a newline. If
+ STRING is missing, the string from the most recent search is used;
+ it is an error if there is no previous search string.
+
+'^STRING1^STRING2^'
+ Quick Substitution. Repeat the last command, replacing STRING1
+ with STRING2. Equivalent to '!!:s^STRING1^STRING2^'.
+
+'!#'
+ The entire command line typed so far.
+
+
+File: bash.info, Node: Word Designators, Next: Modifiers, Prev: Event Designators, Up: History Interaction
+
+9.3.2 Word Designators
+----------------------
+
+Word designators are used to select desired words from the event. A ':'
+separates the event specification from the word designator. It may be
+omitted if the word designator begins with a '^', '$', '*', '-', or '%'.
+Words are numbered from the beginning of the line, with the first word
+being denoted by 0 (zero). Words are inserted into the current line
+separated by single spaces.
+
+ For example,
+
+'!!'
+ designates the preceding command. When you type this, the
+ preceding command is repeated in toto.
+
+'!!:$'
+ designates the last argument of the preceding command. This may be
+ shortened to '!$'.
+
+'!fi:2'
+ designates the second argument of the most recent command starting
+ with the letters 'fi'.
+
+ Here are the word designators:
+
+'0 (zero)'
+ The '0'th word. For many applications, this is the command word.
+
+'N'
+ The Nth word.
+
+'^'
+ The first argument; that is, word 1.
+
+'$'
+ The last argument.
+
+'%'
+ The first word matched by the most recent '?STRING?' search, if the
+ search string begins with a character that is part of a word.
+
+'X-Y'
+ A range of words; '-Y' abbreviates '0-Y'.
+
+'*'
+ All of the words, except the '0'th. This is a synonym for '1-$'.
+ It is not an error to use '*' if there is just one word in the
+ event; the empty string is returned in that case.
+
+'X*'
+ Abbreviates 'X-$'
+
+'X-'
+ Abbreviates 'X-$' like 'X*', but omits the last word. If 'x' is
+ missing, it defaults to 0.
+
+ If a word designator is supplied without an event specification, the
+previous command is used as the event.
+
+
+File: bash.info, Node: Modifiers, Prev: Word Designators, Up: History Interaction
+
+9.3.3 Modifiers
+---------------
+
+After the optional word designator, you can add a sequence of one or
+more of the following modifiers, each preceded by a ':'. These modify,
+or edit, the word or words selected from the history event.
+
+'h'
+ Remove a trailing pathname component, leaving only the head.
+
+'t'
+ Remove all leading pathname components, leaving the tail.
+
+'r'
+ Remove a trailing suffix of the form '.SUFFIX', leaving the
+ basename.
+
+'e'
+ Remove all but the trailing suffix.
+
+'p'
+ Print the new command but do not execute it.
+
+'q'
+ Quote the substituted words, escaping further substitutions.
+
+'x'
+ Quote the substituted words as with 'q', but break into words at
+ spaces, tabs, and newlines. The 'q' and 'x' modifiers are mutually
+ exclusive; the last one supplied is used.
+
+'s/OLD/NEW/'
+ Substitute NEW for the first occurrence of OLD in the event line.
+ Any character may be used as the delimiter in place of '/'. The
+ delimiter may be quoted in OLD and NEW with a single backslash. If
+ '&' appears in NEW, it is replaced by OLD. A single backslash will
+ quote the '&'. If OLD is null, it is set to the last OLD
+ substituted, or, if no previous history substitutions took place,
+ the last STRING in a !?STRING'[?]' search. If NEW is null, each
+ matching OLD is deleted. The final delimiter is optional if it is
+ the last character on the input line.
+
+'&'
+ Repeat the previous substitution.
+
+'g'
+'a'
+ Cause changes to be applied over the entire event line. Used in
+ conjunction with 's', as in 'gs/OLD/NEW/', or with '&'.
+
+'G'
+ Apply the following 's' or '&' modifier once to each word in the
+ event.
+
+
+File: bash.info, Node: Installing Bash, Next: Reporting Bugs, Prev: Using History Interactively, Up: Top
+
+10 Installing Bash
+******************
+
+This chapter provides basic instructions for installing Bash on the
+various supported platforms. The distribution supports the GNU
+operating systems, nearly every version of Unix, and several non-Unix
+systems such as BeOS and Interix. Other independent ports exist for
+MS-DOS, OS/2, and Windows platforms.
+
+* Menu:
+
+* Basic Installation:: Installation instructions.
+* Compilers and Options:: How to set special options for various
+ systems.
+* Compiling For Multiple Architectures:: How to compile Bash for more
+ than one kind of system from
+ the same source tree.
+* Installation Names:: How to set the various paths used by the installation.
+* Specifying the System Type:: How to configure Bash for a particular system.
+* Sharing Defaults:: How to share default configuration values among GNU
+ programs.
+* Operation Controls:: Options recognized by the configuration program.
+* Optional Features:: How to enable and disable optional features when
+ building Bash.
+
+
+File: bash.info, Node: Basic Installation, Next: Compilers and Options, Up: Installing Bash
+
+10.1 Basic Installation
+=======================
+
+These are installation instructions for Bash.
+
+ The simplest way to compile Bash is:
+
+ 1. 'cd' to the directory containing the source code and type
+ './configure' to configure Bash for your system. If you're using
+ 'csh' on an old version of System V, you might need to type 'sh
+ ./configure' instead to prevent 'csh' from trying to execute
+ 'configure' itself.
+
+ Running 'configure' takes some time. While running, it prints
+ messages telling which features it is checking for.
+
+ 2. Type 'make' to compile Bash and build the 'bashbug' bug reporting
+ script.
+
+ 3. Optionally, type 'make tests' to run the Bash test suite.
+
+ 4. Type 'make install' to install 'bash' and 'bashbug'. This will
+ also install the manual pages and Info file, message translation
+ files, some supplemental documentation, a number of example
+ loadable builtin commands, and a set of header files for developing
+ loadable builtins. You may need additional privileges to install
+ 'bash' to your desired destination, so 'sudo make install' might be
+ required. More information about controlling the locations where
+ 'bash' and other files are installed is below (*note Installation
+ Names::).
+
+ The 'configure' shell script attempts to guess correct values for
+various system-dependent variables used during compilation. It uses
+those values to create a 'Makefile' in each directory of the package
+(the top directory, the 'builtins', 'doc', 'po', and 'support'
+directories, each directory under 'lib', and several others). It also
+creates a 'config.h' file containing system-dependent definitions.
+Finally, it creates a shell script named 'config.status' that you can
+run in the future to recreate the current configuration, a file
+'config.cache' that saves the results of its tests to speed up
+reconfiguring, and a file 'config.log' containing compiler output
+(useful mainly for debugging 'configure'). If at some point
+'config.cache' contains results you don't want to keep, you may remove
+or edit it.
+
+ To find out more about the options and arguments that the 'configure'
+script understands, type
+
+ bash-4.2$ ./configure --help
+
+at the Bash prompt in your Bash source directory.
+
+ If you want to build Bash in a directory separate from the source
+directory - to build for multiple architectures, for example - just use
+the full path to the configure script. The following commands will
+build bash in a directory under '/usr/local/build' from the source code
+in '/usr/local/src/bash-4.4':
+
+ mkdir /usr/local/build/bash-4.4
+ cd /usr/local/build/bash-4.4
+ bash /usr/local/src/bash-4.4/configure
+ make
+
+ See *note Compiling For Multiple Architectures:: for more information
+about building in a directory separate from the source.
+
+ If you need to do unusual things to compile Bash, please try to
+figure out how 'configure' could check whether or not to do them, and
+mail diffs or instructions to <bash-maintainers@gnu.org> so they can be
+considered for the next release.
+
+ The file 'configure.ac' is used to create 'configure' by a program
+called Autoconf. You only need 'configure.ac' if you want to change it
+or regenerate 'configure' using a newer version of Autoconf. If you do
+this, make sure you are using Autoconf version 2.69 or newer.
+
+ You can remove the program binaries and object files from the source
+code directory by typing 'make clean'. To also remove the files that
+'configure' created (so you can compile Bash for a different kind of
+computer), type 'make distclean'.
+
+
+File: bash.info, Node: Compilers and Options, Next: Compiling For Multiple Architectures, Prev: Basic Installation, Up: Installing Bash
+
+10.2 Compilers and Options
+==========================
+
+Some systems require unusual options for compilation or linking that the
+'configure' script does not know about. You can give 'configure'
+initial values for variables by setting them in the environment. Using
+a Bourne-compatible shell, you can do that on the command line like
+this:
+
+ CC=c89 CFLAGS=-O2 LIBS=-lposix ./configure
+
+ On systems that have the 'env' program, you can do it like this:
+
+ env CPPFLAGS=-I/usr/local/include LDFLAGS=-s ./configure
+
+ The configuration process uses GCC to build Bash if it is available.
+
+
+File: bash.info, Node: Compiling For Multiple Architectures, Next: Installation Names, Prev: Compilers and Options, Up: Installing Bash
+
+10.3 Compiling For Multiple Architectures
+=========================================
+
+You can compile Bash for more than one kind of computer at the same
+time, by placing the object files for each architecture in their own
+directory. To do this, you must use a version of 'make' that supports
+the 'VPATH' variable, such as GNU 'make'. 'cd' to the directory where
+you want the object files and executables to go and run the 'configure'
+script from the source directory (*note Basic Installation::). You may
+need to supply the '--srcdir=PATH' argument to tell 'configure' where
+the source files are. 'configure' automatically checks for the source
+code in the directory that 'configure' is in and in '..'.
+
+ If you have to use a 'make' that does not support the 'VPATH'
+variable, you can compile Bash for one architecture at a time in the
+source code directory. After you have installed Bash for one
+architecture, use 'make distclean' before reconfiguring for another
+architecture.
+
+ Alternatively, if your system supports symbolic links, you can use
+the 'support/mkclone' script to create a build tree which has symbolic
+links back to each file in the source directory. Here's an example that
+creates a build directory in the current directory from a source
+directory '/usr/gnu/src/bash-2.0':
+
+ bash /usr/gnu/src/bash-2.0/support/mkclone -s /usr/gnu/src/bash-2.0 .
+
+The 'mkclone' script requires Bash, so you must have already built Bash
+for at least one architecture before you can create build directories
+for other architectures.
+
+
+File: bash.info, Node: Installation Names, Next: Specifying the System Type, Prev: Compiling For Multiple Architectures, Up: Installing Bash
+
+10.4 Installation Names
+=======================
+
+By default, 'make install' will install into '/usr/local/bin',
+'/usr/local/man', etc.; that is, the "installation prefix" defaults to
+'/usr/local'. You can specify an installation prefix other than
+'/usr/local' by giving 'configure' the option '--prefix=PATH', or by
+specifying a value for the 'prefix' 'make' variable when running 'make
+install' (e.g., 'make install prefix=PATH'). The 'prefix' variable
+provides a default for 'exec_prefix' and other variables used when
+installing bash.
+
+ You can specify separate installation prefixes for
+architecture-specific files and architecture-independent files. If you
+give 'configure' the option '--exec-prefix=PATH', 'make install' will
+use PATH as the prefix for installing programs and libraries.
+Documentation and other data files will still use the regular prefix.
+
+ If you would like to change the installation locations for a single
+run, you can specify these variables as arguments to 'make': 'make
+install exec_prefix=/' will install 'bash' and 'bashbug' into '/bin'
+instead of the default '/usr/local/bin'.
+
+ If you want to see the files bash will install and where it will
+install them without changing anything on your system, specify the
+variable 'DESTDIR' as an argument to 'make'. Its value should be the
+absolute directory path you'd like to use as the root of your sample
+installation tree. For example,
+
+ mkdir /fs1/bash-install
+ make install DESTDIR=/fs1/bash-install
+
+will install 'bash' into '/fs1/bash-install/usr/local/bin/bash', the
+documentation into directories within
+'/fs1/bash-install/usr/local/share', the example loadable builtins into
+'/fs1/bash-install/usr/local/lib/bash', and so on. You can use the
+usual 'exec_prefix' and 'prefix' variables to alter the directory paths
+beneath the value of 'DESTDIR'.
+
+ The GNU Makefile standards provide a more complete description of
+these variables and their effects.
+
+
+File: bash.info, Node: Specifying the System Type, Next: Sharing Defaults, Prev: Installation Names, Up: Installing Bash
+
+10.5 Specifying the System Type
+===============================
+
+There may be some features 'configure' can not figure out automatically,
+but needs to determine by the type of host Bash will run on. Usually
+'configure' can figure that out, but if it prints a message saying it
+can not guess the host type, give it the '--host=TYPE' option. 'TYPE'
+can either be a short name for the system type, such as 'sun4', or a
+canonical name with three fields: 'CPU-COMPANY-SYSTEM' (e.g.,
+'i386-unknown-freebsd4.2').
+
+ See the file 'support/config.sub' for the possible values of each
+field.
+
+
+File: bash.info, Node: Sharing Defaults, Next: Operation Controls, Prev: Specifying the System Type, Up: Installing Bash
+
+10.6 Sharing Defaults
+=====================
+
+If you want to set default values for 'configure' scripts to share, you
+can create a site shell script called 'config.site' that gives default
+values for variables like 'CC', 'cache_file', and 'prefix'. 'configure'
+looks for 'PREFIX/share/config.site' if it exists, then
+'PREFIX/etc/config.site' if it exists. Or, you can set the
+'CONFIG_SITE' environment variable to the location of the site script.
+A warning: the Bash 'configure' looks for a site script, but not all
+'configure' scripts do.
+
+
+File: bash.info, Node: Operation Controls, Next: Optional Features, Prev: Sharing Defaults, Up: Installing Bash
+
+10.7 Operation Controls
+=======================
+
+'configure' recognizes the following options to control how it operates.
+
+'--cache-file=FILE'
+ Use and save the results of the tests in FILE instead of
+ './config.cache'. Set FILE to '/dev/null' to disable caching, for
+ debugging 'configure'.
+
+'--help'
+ Print a summary of the options to 'configure', and exit.
+
+'--quiet'
+'--silent'
+'-q'
+ Do not print messages saying which checks are being made.
+
+'--srcdir=DIR'
+ Look for the Bash source code in directory DIR. Usually
+ 'configure' can determine that directory automatically.
+
+'--version'
+ Print the version of Autoconf used to generate the 'configure'
+ script, and exit.
+
+ 'configure' also accepts some other, not widely used, boilerplate
+options. 'configure --help' prints the complete list.
+
+
+File: bash.info, Node: Optional Features, Prev: Operation Controls, Up: Installing Bash
+
+10.8 Optional Features
+======================
+
+The Bash 'configure' has a number of '--enable-FEATURE' options, where
+FEATURE indicates an optional part of Bash. There are also several
+'--with-PACKAGE' options, where PACKAGE is something like 'bash-malloc'
+or 'purify'. To turn off the default use of a package, use
+'--without-PACKAGE'. To configure Bash without a feature that is
+enabled by default, use '--disable-FEATURE'.
+
+ Here is a complete list of the '--enable-' and '--with-' options that
+the Bash 'configure' recognizes.
+
+'--with-afs'
+ Define if you are using the Andrew File System from Transarc.
+
+'--with-bash-malloc'
+ Use the Bash version of 'malloc' in the directory 'lib/malloc'.
+ This is not the same 'malloc' that appears in GNU libc, but an
+ older version originally derived from the 4.2 BSD 'malloc'. This
+ 'malloc' is very fast, but wastes some space on each allocation.
+ This option is enabled by default. The 'NOTES' file contains a
+ list of systems for which this should be turned off, and
+ 'configure' disables this option automatically for a number of
+ systems.
+
+'--with-curses'
+ Use the curses library instead of the termcap library. This should
+ be supplied if your system has an inadequate or incomplete termcap
+ database.
+
+'--with-gnu-malloc'
+ A synonym for '--with-bash-malloc'.
+
+'--with-installed-readline[=PREFIX]'
+ Define this to make Bash link with a locally-installed version of
+ Readline rather than the version in 'lib/readline'. This works
+ only with Readline 5.0 and later versions. If PREFIX is 'yes' or
+ not supplied, 'configure' uses the values of the make variables
+ 'includedir' and 'libdir', which are subdirectories of 'prefix' by
+ default, to find the installed version of Readline if it is not in
+ the standard system include and library directories. If PREFIX is
+ 'no', Bash links with the version in 'lib/readline'. If PREFIX is
+ set to any other value, 'configure' treats it as a directory
+ pathname and looks for the installed version of Readline in
+ subdirectories of that directory (include files in PREFIX/'include'
+ and the library in PREFIX/'lib').
+
+'--with-libintl-prefix[=PREFIX]'
+ Define this to make Bash link with a locally-installed version of
+ the libintl library instead of the version in 'lib/intl'.
+
+'--with-libiconv-prefix[=PREFIX]'
+ Define this to make Bash look for libiconv in PREFIX instead of the
+ standard system locations. There is no version included with Bash.
+
+'--enable-minimal-config'
+ This produces a shell with minimal features, close to the
+ historical Bourne shell.
+
+ There are several '--enable-' options that alter how Bash is
+compiled, linked, and installed, rather than changing run-time features.
+
+'--enable-largefile'
+ Enable support for large files
+ (http://www.unix.org/version2/whatsnew/lfs20mar.html) if the
+ operating system requires special compiler options to build
+ programs which can access large files. This is enabled by default,
+ if the operating system provides large file support.
+
+'--enable-profiling'
+ This builds a Bash binary that produces profiling information to be
+ processed by 'gprof' each time it is executed.
+
+'--enable-separate-helpfiles'
+ Use external files for the documentation displayed by the 'help'
+ builtin instead of storing the text internally.
+
+'--enable-static-link'
+ This causes Bash to be linked statically, if 'gcc' is being used.
+ This could be used to build a version to use as root's shell.
+
+ The 'minimal-config' option can be used to disable all of the
+following options, but it is processed first, so individual options may
+be enabled using 'enable-FEATURE'.
+
+ All of the following options except for 'alt-array-implementation',
+'disabled-builtins', 'direxpand-default', 'strict-posix-default', and
+'xpg-echo-default' are enabled by default, unless the operating system
+does not provide the necessary support.
+
+'--enable-alias'
+ Allow alias expansion and include the 'alias' and 'unalias'
+ builtins (*note Aliases::).
+
+'--enable-alt-array-implementation'
+ This builds bash using an alternate implementation of arrays (*note
+ Arrays::) that provides faster access at the expense of using more
+ memory (sometimes many times more, depending on how sparse an array
+ is).
+
+'--enable-arith-for-command'
+ Include support for the alternate form of the 'for' command that
+ behaves like the C language 'for' statement (*note Looping
+ Constructs::).
+
+'--enable-array-variables'
+ Include support for one-dimensional array shell variables (*note
+ Arrays::).
+
+'--enable-bang-history'
+ Include support for 'csh'-like history substitution (*note History
+ Interaction::).
+
+'--enable-brace-expansion'
+ Include 'csh'-like brace expansion ( 'b{a,b}c' ==> 'bac bbc' ).
+ See *note Brace Expansion::, for a complete description.
+
+'--enable-casemod-attributes'
+ Include support for case-modifying attributes in the 'declare'
+ builtin and assignment statements. Variables with the 'uppercase'
+ attribute, for example, will have their values converted to
+ uppercase upon assignment.
+
+'--enable-casemod-expansion'
+ Include support for case-modifying word expansions.
+
+'--enable-command-timing'
+ Include support for recognizing 'time' as a reserved word and for
+ displaying timing statistics for the pipeline following 'time'
+ (*note Pipelines::). This allows pipelines as well as shell
+ builtins and functions to be timed.
+
+'--enable-cond-command'
+ Include support for the '[[' conditional command. (*note
+ Conditional Constructs::).
+
+'--enable-cond-regexp'
+ Include support for matching POSIX regular expressions using the
+ '=~' binary operator in the '[[' conditional command. (*note
+ Conditional Constructs::).
+
+'--enable-coprocesses'
+ Include support for coprocesses and the 'coproc' reserved word
+ (*note Pipelines::).
+
+'--enable-debugger'
+ Include support for the bash debugger (distributed separately).
+
+'--enable-dev-fd-stat-broken'
+ If calling 'stat' on /dev/fd/N returns different results than
+ calling 'fstat' on file descriptor N, supply this option to enable
+ a workaround. This has implications for conditional commands that
+ test file attributes.
+
+'--enable-direxpand-default'
+ Cause the 'direxpand' shell option (*note The Shopt Builtin::) to
+ be enabled by default when the shell starts. It is normally
+ disabled by default.
+
+'--enable-directory-stack'
+ Include support for a 'csh'-like directory stack and the 'pushd',
+ 'popd', and 'dirs' builtins (*note The Directory Stack::).
+
+'--enable-disabled-builtins'
+ Allow builtin commands to be invoked via 'builtin xxx' even after
+ 'xxx' has been disabled using 'enable -n xxx'. See *note Bash
+ Builtins::, for details of the 'builtin' and 'enable' builtin
+ commands.
+
+'--enable-dparen-arithmetic'
+ Include support for the '((...))' command (*note Conditional
+ Constructs::).
+
+'--enable-extended-glob'
+ Include support for the extended pattern matching features
+ described above under *note Pattern Matching::.
+
+'--enable-extended-glob-default'
+ Set the default value of the 'extglob' shell option described above
+ under *note The Shopt Builtin:: to be enabled.
+
+'--enable-function-import'
+ Include support for importing function definitions exported by
+ another instance of the shell from the environment. This option is
+ enabled by default.
+
+'--enable-glob-asciirange-default'
+ Set the default value of the 'globasciiranges' shell option
+ described above under *note The Shopt Builtin:: to be enabled.
+ This controls the behavior of character ranges when used in pattern
+ matching bracket expressions.
+
+'--enable-help-builtin'
+ Include the 'help' builtin, which displays help on shell builtins
+ and variables (*note Bash Builtins::).
+
+'--enable-history'
+ Include command history and the 'fc' and 'history' builtin commands
+ (*note Bash History Facilities::).
+
+'--enable-job-control'
+ This enables the job control features (*note Job Control::), if the
+ operating system supports them.
+
+'--enable-multibyte'
+ This enables support for multibyte characters if the operating
+ system provides the necessary support.
+
+'--enable-net-redirections'
+ This enables the special handling of filenames of the form
+ '/dev/tcp/HOST/PORT' and '/dev/udp/HOST/PORT' when used in
+ redirections (*note Redirections::).
+
+'--enable-process-substitution'
+ This enables process substitution (*note Process Substitution::) if
+ the operating system provides the necessary support.
+
+'--enable-progcomp'
+ Enable the programmable completion facilities (*note Programmable
+ Completion::). If Readline is not enabled, this option has no
+ effect.
+
+'--enable-prompt-string-decoding'
+ Turn on the interpretation of a number of backslash-escaped
+ characters in the '$PS0', '$PS1', '$PS2', and '$PS4' prompt
+ strings. See *note Controlling the Prompt::, for a complete list
+ of prompt string escape sequences.
+
+'--enable-readline'
+ Include support for command-line editing and history with the Bash
+ version of the Readline library (*note Command Line Editing::).
+
+'--enable-restricted'
+ Include support for a "restricted shell". If this is enabled,
+ Bash, when called as 'rbash', enters a restricted mode. See *note
+ The Restricted Shell::, for a description of restricted mode.
+
+'--enable-select'
+ Include the 'select' compound command, which allows the generation
+ of simple menus (*note Conditional Constructs::).
+
+'--enable-single-help-strings'
+ Store the text displayed by the 'help' builtin as a single string
+ for each help topic. This aids in translating the text to
+ different languages. You may need to disable this if your compiler
+ cannot handle very long string literals.
+
+'--enable-strict-posix-default'
+ Make Bash POSIX-conformant by default (*note Bash POSIX Mode::).
+
+'--enable-translatable-strings'
+ Enable support for '$"STRING"' translatable strings (*note Locale
+ Translation::).
+
+'--enable-usg-echo-default'
+ A synonym for '--enable-xpg-echo-default'.
+
+'--enable-xpg-echo-default'
+ Make the 'echo' builtin expand backslash-escaped characters by
+ default, without requiring the '-e' option. This sets the default
+ value of the 'xpg_echo' shell option to 'on', which makes the Bash
+ 'echo' behave more like the version specified in the Single Unix
+ Specification, version 3. *Note Bash Builtins::, for a description
+ of the escape sequences that 'echo' recognizes.
+
+ The file 'config-top.h' contains C Preprocessor '#define' statements
+for options which are not settable from 'configure'. Some of these are
+not meant to be changed; beware of the consequences if you do. Read the
+comments associated with each definition for more information about its
+effect.
+
+
+File: bash.info, Node: Reporting Bugs, Next: Major Differences From The Bourne Shell, Prev: Installing Bash, Up: Top
+
+Appendix A Reporting Bugs
+*************************
+
+Please report all bugs you find in Bash. But first, you should make
+sure that it really is a bug, and that it appears in the latest version
+of Bash. The latest version of Bash is always available for FTP from
+<ftp://ftp.gnu.org/pub/gnu/bash/> and from
+<http://git.savannah.gnu.org/cgit/bash.git/snapshot/bash-master.tar.gz>.
+
+ Once you have determined that a bug actually exists, use the
+'bashbug' command to submit a bug report. If you have a fix, you are
+encouraged to mail that as well! Suggestions and 'philosophical' bug
+reports may be mailed to <bug-bash@gnu.org> or posted to the Usenet
+newsgroup 'gnu.bash.bug'.
+
+ All bug reports should include:
+ * The version number of Bash.
+ * The hardware and operating system.
+ * The compiler used to compile Bash.
+ * A description of the bug behaviour.
+ * A short script or 'recipe' which exercises the bug and may be used
+ to reproduce it.
+
+'bashbug' inserts the first three items automatically into the template
+it provides for filing a bug report.
+
+ Please send all reports concerning this manual to <bug-bash@gnu.org>.
+
+
+File: bash.info, Node: Major Differences From The Bourne Shell, Next: GNU Free Documentation License, Prev: Reporting Bugs, Up: Top
+
+Appendix B Major Differences From The Bourne Shell
+**************************************************
+
+Bash implements essentially the same grammar, parameter and variable
+expansion, redirection, and quoting as the Bourne Shell. Bash uses the
+POSIX standard as the specification of how these features are to be
+implemented. There are some differences between the traditional Bourne
+shell and Bash; this section quickly details the differences of
+significance. A number of these differences are explained in greater
+depth in previous sections. This section uses the version of 'sh'
+included in SVR4.2 (the last version of the historical Bourne shell) as
+the baseline reference.
+
+ * Bash is POSIX-conformant, even where the POSIX specification
+ differs from traditional 'sh' behavior (*note Bash POSIX Mode::).
+
+ * Bash has multi-character invocation options (*note Invoking
+ Bash::).
+
+ * Bash has command-line editing (*note Command Line Editing::) and
+ the 'bind' builtin.
+
+ * Bash provides a programmable word completion mechanism (*note
+ Programmable Completion::), and builtin commands 'complete',
+ 'compgen', and 'compopt', to manipulate it.
+
+ * Bash has command history (*note Bash History Facilities::) and the
+ 'history' and 'fc' builtins to manipulate it. The Bash history
+ list maintains timestamp information and uses the value of the
+ 'HISTTIMEFORMAT' variable to display it.
+
+ * Bash implements 'csh'-like history expansion (*note History
+ Interaction::).
+
+ * Bash has one-dimensional array variables (*note Arrays::), and the
+ appropriate variable expansions and assignment syntax to use them.
+ Several of the Bash builtins take options to act on arrays. Bash
+ provides a number of built-in array variables.
+
+ * The '$'...'' quoting syntax, which expands ANSI-C backslash-escaped
+ characters in the text between the single quotes, is supported
+ (*note ANSI-C Quoting::).
+
+ * Bash supports the '$"..."' quoting syntax to do locale-specific
+ translation of the characters between the double quotes. The '-D',
+ '--dump-strings', and '--dump-po-strings' invocation options list
+ the translatable strings found in a script (*note Locale
+ Translation::).
+
+ * Bash implements the '!' keyword to negate the return value of a
+ pipeline (*note Pipelines::). Very useful when an 'if' statement
+ needs to act only if a test fails. The Bash '-o pipefail' option
+ to 'set' will cause a pipeline to return a failure status if any
+ command fails.
+
+ * Bash has the 'time' reserved word and command timing (*note
+ Pipelines::). The display of the timing statistics may be
+ controlled with the 'TIMEFORMAT' variable.
+
+ * Bash implements the 'for (( EXPR1 ; EXPR2 ; EXPR3 ))' arithmetic
+ for command, similar to the C language (*note Looping
+ Constructs::).
+
+ * Bash includes the 'select' compound command, which allows the
+ generation of simple menus (*note Conditional Constructs::).
+
+ * Bash includes the '[[' compound command, which makes conditional
+ testing part of the shell grammar (*note Conditional Constructs::),
+ including optional regular expression matching.
+
+ * Bash provides optional case-insensitive matching for the 'case' and
+ '[[' constructs.
+
+ * Bash includes brace expansion (*note Brace Expansion::) and tilde
+ expansion (*note Tilde Expansion::).
+
+ * Bash implements command aliases and the 'alias' and 'unalias'
+ builtins (*note Aliases::).
+
+ * Bash provides shell arithmetic, the '((' compound command (*note
+ Conditional Constructs::), and arithmetic expansion (*note Shell
+ Arithmetic::).
+
+ * Variables present in the shell's initial environment are
+ automatically exported to child processes. The Bourne shell does
+ not normally do this unless the variables are explicitly marked
+ using the 'export' command.
+
+ * Bash supports the '+=' assignment operator, which appends to the
+ value of the variable named on the left hand side.
+
+ * Bash includes the POSIX pattern removal '%', '#', '%%' and '##'
+ expansions to remove leading or trailing substrings from variable
+ values (*note Shell Parameter Expansion::).
+
+ * The expansion '${#xx}', which returns the length of '${xx}', is
+ supported (*note Shell Parameter Expansion::).
+
+ * The expansion '${var:'OFFSET'[:'LENGTH']}', which expands to the
+ substring of 'var''s value of length LENGTH, beginning at OFFSET,
+ is present (*note Shell Parameter Expansion::).
+
+ * The expansion '${VAR/[/]'PATTERN'[/'REPLACEMENT']}', which matches
+ PATTERN and replaces it with REPLACEMENT in the value of VAR, is
+ available (*note Shell Parameter Expansion::).
+
+ * The expansion '${!PREFIX*}' expansion, which expands to the names
+ of all shell variables whose names begin with PREFIX, is available
+ (*note Shell Parameter Expansion::).
+
+ * Bash has indirect variable expansion using '${!word}' (*note Shell
+ Parameter Expansion::).
+
+ * Bash can expand positional parameters beyond '$9' using '${NUM}'.
+
+ * The POSIX '$()' form of command substitution is implemented (*note
+ Command Substitution::), and preferred to the Bourne shell's '``'
+ (which is also implemented for backwards compatibility).
+
+ * Bash has process substitution (*note Process Substitution::).
+
+ * Bash automatically assigns variables that provide information about
+ the current user ('UID', 'EUID', and 'GROUPS'), the current host
+ ('HOSTTYPE', 'OSTYPE', 'MACHTYPE', and 'HOSTNAME'), and the
+ instance of Bash that is running ('BASH', 'BASH_VERSION', and
+ 'BASH_VERSINFO'). *Note Bash Variables::, for details.
+
+ * The 'IFS' variable is used to split only the results of expansion,
+ not all words (*note Word Splitting::). This closes a longstanding
+ shell security hole.
+
+ * The filename expansion bracket expression code uses '!' and '^' to
+ negate the set of characters between the brackets. The Bourne
+ shell uses only '!'.
+
+ * Bash implements the full set of POSIX filename expansion operators,
+ including character classes, equivalence classes, and collating
+ symbols (*note Filename Expansion::).
+
+ * Bash implements extended pattern matching features when the
+ 'extglob' shell option is enabled (*note Pattern Matching::).
+
+ * It is possible to have a variable and a function with the same
+ name; 'sh' does not separate the two name spaces.
+
+ * Bash functions are permitted to have local variables using the
+ 'local' builtin, and thus useful recursive functions may be written
+ (*note Bash Builtins::).
+
+ * Variable assignments preceding commands affect only that command,
+ even builtins and functions (*note Environment::). In 'sh', all
+ variable assignments preceding commands are global unless the
+ command is executed from the file system.
+
+ * Bash performs filename expansion on filenames specified as operands
+ to input and output redirection operators (*note Redirections::).
+
+ * Bash contains the '<>' redirection operator, allowing a file to be
+ opened for both reading and writing, and the '&>' redirection
+ operator, for directing standard output and standard error to the
+ same file (*note Redirections::).
+
+ * Bash includes the '<<<' redirection operator, allowing a string to
+ be used as the standard input to a command.
+
+ * Bash implements the '[n]<&WORD' and '[n]>&WORD' redirection
+ operators, which move one file descriptor to another.
+
+ * Bash treats a number of filenames specially when they are used in
+ redirection operators (*note Redirections::).
+
+ * Bash can open network connections to arbitrary machines and
+ services with the redirection operators (*note Redirections::).
+
+ * The 'noclobber' option is available to avoid overwriting existing
+ files with output redirection (*note The Set Builtin::). The '>|'
+ redirection operator may be used to override 'noclobber'.
+
+ * The Bash 'cd' and 'pwd' builtins (*note Bourne Shell Builtins::)
+ each take '-L' and '-P' options to switch between logical and
+ physical modes.
+
+ * Bash allows a function to override a builtin with the same name,
+ and provides access to that builtin's functionality within the
+ function via the 'builtin' and 'command' builtins (*note Bash
+ Builtins::).
+
+ * The 'command' builtin allows selective disabling of functions when
+ command lookup is performed (*note Bash Builtins::).
+
+ * Individual builtins may be enabled or disabled using the 'enable'
+ builtin (*note Bash Builtins::).
+
+ * The Bash 'exec' builtin takes additional options that allow users
+ to control the contents of the environment passed to the executed
+ command, and what the zeroth argument to the command is to be
+ (*note Bourne Shell Builtins::).
+
+ * Shell functions may be exported to children via the environment
+ using 'export -f' (*note Shell Functions::).
+
+ * The Bash 'export', 'readonly', and 'declare' builtins can take a
+ '-f' option to act on shell functions, a '-p' option to display
+ variables with various attributes set in a format that can be used
+ as shell input, a '-n' option to remove various variable
+ attributes, and 'name=value' arguments to set variable attributes
+ and values simultaneously.
+
+ * The Bash 'hash' builtin allows a name to be associated with an
+ arbitrary filename, even when that filename cannot be found by
+ searching the '$PATH', using 'hash -p' (*note Bourne Shell
+ Builtins::).
+
+ * Bash includes a 'help' builtin for quick reference to shell
+ facilities (*note Bash Builtins::).
+
+ * The 'printf' builtin is available to display formatted output
+ (*note Bash Builtins::).
+
+ * The Bash 'read' builtin (*note Bash Builtins::) will read a line
+ ending in '\' with the '-r' option, and will use the 'REPLY'
+ variable as a default if no non-option arguments are supplied. The
+ Bash 'read' builtin also accepts a prompt string with the '-p'
+ option and will use Readline to obtain the line when given the '-e'
+ option. The 'read' builtin also has additional options to control
+ input: the '-s' option will turn off echoing of input characters as
+ they are read, the '-t' option will allow 'read' to time out if
+ input does not arrive within a specified number of seconds, the
+ '-n' option will allow reading only a specified number of
+ characters rather than a full line, and the '-d' option will read
+ until a particular character rather than newline.
+
+ * The 'return' builtin may be used to abort execution of scripts
+ executed with the '.' or 'source' builtins (*note Bourne Shell
+ Builtins::).
+
+ * Bash includes the 'shopt' builtin, for finer control of shell
+ optional capabilities (*note The Shopt Builtin::), and allows these
+ options to be set and unset at shell invocation (*note Invoking
+ Bash::).
+
+ * Bash has much more optional behavior controllable with the 'set'
+ builtin (*note The Set Builtin::).
+
+ * The '-x' ('xtrace') option displays commands other than simple
+ commands when performing an execution trace (*note The Set
+ Builtin::).
+
+ * The 'test' builtin (*note Bourne Shell Builtins::) is slightly
+ different, as it implements the POSIX algorithm, which specifies
+ the behavior based on the number of arguments.
+
+ * Bash includes the 'caller' builtin, which displays the context of
+ any active subroutine call (a shell function or a script executed
+ with the '.' or 'source' builtins). This supports the Bash
+ debugger.
+
+ * The 'trap' builtin (*note Bourne Shell Builtins::) allows a 'DEBUG'
+ pseudo-signal specification, similar to 'EXIT'. Commands specified
+ with a 'DEBUG' trap are executed before every simple command, 'for'
+ command, 'case' command, 'select' command, every arithmetic 'for'
+ command, and before the first command executes in a shell function.
+ The 'DEBUG' trap is not inherited by shell functions unless the
+ function has been given the 'trace' attribute or the 'functrace'
+ option has been enabled using the 'shopt' builtin. The 'extdebug'
+ shell option has additional effects on the 'DEBUG' trap.
+
+ The 'trap' builtin (*note Bourne Shell Builtins::) allows an 'ERR'
+ pseudo-signal specification, similar to 'EXIT' and 'DEBUG'.
+ Commands specified with an 'ERR' trap are executed after a simple
+ command fails, with a few exceptions. The 'ERR' trap is not
+ inherited by shell functions unless the '-o errtrace' option to the
+ 'set' builtin is enabled.
+
+ The 'trap' builtin (*note Bourne Shell Builtins::) allows a
+ 'RETURN' pseudo-signal specification, similar to 'EXIT' and
+ 'DEBUG'. Commands specified with a 'RETURN' trap are executed
+ before execution resumes after a shell function or a shell script
+ executed with '.' or 'source' returns. The 'RETURN' trap is not
+ inherited by shell functions unless the function has been given the
+ 'trace' attribute or the 'functrace' option has been enabled using
+ the 'shopt' builtin.
+
+ * The Bash 'type' builtin is more extensive and gives more
+ information about the names it finds (*note Bash Builtins::).
+
+ * The Bash 'umask' builtin permits a '-p' option to cause the output
+ to be displayed in the form of a 'umask' command that may be reused
+ as input (*note Bourne Shell Builtins::).
+
+ * Bash implements a 'csh'-like directory stack, and provides the
+ 'pushd', 'popd', and 'dirs' builtins to manipulate it (*note The
+ Directory Stack::). Bash also makes the directory stack visible as
+ the value of the 'DIRSTACK' shell variable.
+
+ * Bash interprets special backslash-escaped characters in the prompt
+ strings when interactive (*note Controlling the Prompt::).
+
+ * The Bash restricted mode is more useful (*note The Restricted
+ Shell::); the SVR4.2 shell restricted mode is too limited.
+
+ * The 'disown' builtin can remove a job from the internal shell job
+ table (*note Job Control Builtins::) or suppress the sending of
+ 'SIGHUP' to a job when the shell exits as the result of a 'SIGHUP'.
+
+ * Bash includes a number of features to support a separate debugger
+ for shell scripts.
+
+ * The SVR4.2 shell has two privilege-related builtins ('mldmode' and
+ 'priv') not present in Bash.
+
+ * Bash does not have the 'stop' or 'newgrp' builtins.
+
+ * Bash does not use the 'SHACCT' variable or perform shell
+ accounting.
+
+ * The SVR4.2 'sh' uses a 'TIMEOUT' variable like Bash uses 'TMOUT'.
+
+More features unique to Bash may be found in *note Bash Features::.
+
+B.1 Implementation Differences From The SVR4.2 Shell
+====================================================
+
+Since Bash is a completely new implementation, it does not suffer from
+many of the limitations of the SVR4.2 shell. For instance:
+
+ * Bash does not fork a subshell when redirecting into or out of a
+ shell control structure such as an 'if' or 'while' statement.
+
+ * Bash does not allow unbalanced quotes. The SVR4.2 shell will
+ silently insert a needed closing quote at 'EOF' under certain
+ circumstances. This can be the cause of some hard-to-find errors.
+
+ * The SVR4.2 shell uses a baroque memory management scheme based on
+ trapping 'SIGSEGV'. If the shell is started from a process with
+ 'SIGSEGV' blocked (e.g., by using the 'system()' C library function
+ call), it misbehaves badly.
+
+ * In a questionable attempt at security, the SVR4.2 shell, when
+ invoked without the '-p' option, will alter its real and effective
+ UID and GID if they are less than some magic threshold value,
+ commonly 100. This can lead to unexpected results.
+
+ * The SVR4.2 shell does not allow users to trap 'SIGSEGV', 'SIGALRM',
+ or 'SIGCHLD'.
+
+ * The SVR4.2 shell does not allow the 'IFS', 'MAILCHECK', 'PATH',
+ 'PS1', or 'PS2' variables to be unset.
+
+ * The SVR4.2 shell treats '^' as the undocumented equivalent of '|'.
+
+ * Bash allows multiple option arguments when it is invoked ('-x -v');
+ the SVR4.2 shell allows only one option argument ('-xv'). In fact,
+ some versions of the shell dump core if the second argument begins
+ with a '-'.
+
+ * The SVR4.2 shell exits a script if any builtin fails; Bash exits a
+ script only if one of the POSIX special builtins fails, and only
+ for certain failures, as enumerated in the POSIX standard.
+
+ * The SVR4.2 shell behaves differently when invoked as 'jsh' (it
+ turns on job control).
+
+
+File: bash.info, Node: GNU Free Documentation License, Next: Indexes, Prev: Major Differences From The Bourne Shell, Up: Top
+
+Appendix C GNU Free Documentation License
+*****************************************
+
+ Version 1.3, 3 November 2008
+
+ Copyright (C) 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
+ <http://fsf.org/>
+
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
+
+ 0. PREAMBLE
+
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+ functional and useful document "free" in the sense of freedom: to
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+ 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.
+ It complements the GNU General Public License, which is a copyleft
+ license designed for free software.
+
+ We have designed this License in order to use it for manuals for
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+ free program should come with manuals providing the same freedoms
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+ recommend this License principally for works whose purpose is
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+
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+ 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
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+ 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
+ <http://www.gnu.org/copyleft/>.
+
+ 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: bash.info, Node: Indexes, Prev: GNU Free Documentation License, Up: Top
+
+Appendix D Indexes
+******************
+
+* Menu:
+
+* Builtin Index:: Index of Bash builtin commands.
+* Reserved Word Index:: Index of Bash reserved words.
+* Variable Index:: Quick reference helps you find the
+ variable you want.
+* Function Index:: Index of bindable Readline functions.
+* Concept Index:: General index for concepts described in
+ this manual.
+
+
+File: bash.info, Node: Builtin Index, Next: Reserved Word Index, Up: Indexes
+
+D.1 Index of Shell Builtin Commands
+===================================
+
+
+* Menu:
+
+* .: Bourne Shell Builtins.
+ (line 17)
+* :: Bourne Shell Builtins.
+ (line 11)
+* [: Bourne Shell Builtins.
+ (line 275)
+* alias: Bash Builtins. (line 11)
+* bg: Job Control Builtins.
+ (line 7)
+* bind: Bash Builtins. (line 21)
+* break: Bourne Shell Builtins.
+ (line 37)
+* builtin: Bash Builtins. (line 108)
+* caller: Bash Builtins. (line 117)
+* cd: Bourne Shell Builtins.
+ (line 45)
+* command: Bash Builtins. (line 134)
+* compgen: Programmable Completion Builtins.
+ (line 12)
+* complete: Programmable Completion Builtins.
+ (line 30)
+* compopt: Programmable Completion Builtins.
+ (line 238)
+* continue: Bourne Shell Builtins.
+ (line 90)
+* declare: Bash Builtins. (line 154)
+* dirs: Directory Stack Builtins.
+ (line 7)
+* disown: Job Control Builtins.
+ (line 104)
+* echo: Bash Builtins. (line 257)
+* enable: Bash Builtins. (line 306)
+* eval: Bourne Shell Builtins.
+ (line 99)
+* exec: Bourne Shell Builtins.
+ (line 107)
+* exit: Bourne Shell Builtins.
+ (line 125)
+* export: Bourne Shell Builtins.
+ (line 132)
+* fc: Bash History Builtins.
+ (line 10)
+* fg: Job Control Builtins.
+ (line 17)
+* getopts: Bourne Shell Builtins.
+ (line 148)
+* hash: Bourne Shell Builtins.
+ (line 192)
+* help: Bash Builtins. (line 342)
+* history: Bash History Builtins.
+ (line 46)
+* jobs: Job Control Builtins.
+ (line 27)
+* kill: Job Control Builtins.
+ (line 58)
+* let: Bash Builtins. (line 361)
+* local: Bash Builtins. (line 369)
+* logout: Bash Builtins. (line 385)
+* mapfile: Bash Builtins. (line 390)
+* popd: Directory Stack Builtins.
+ (line 35)
+* printf: Bash Builtins. (line 436)
+* pushd: Directory Stack Builtins.
+ (line 69)
+* pwd: Bourne Shell Builtins.
+ (line 212)
+* read: Bash Builtins. (line 488)
+* readarray: Bash Builtins. (line 585)
+* readonly: Bourne Shell Builtins.
+ (line 222)
+* return: Bourne Shell Builtins.
+ (line 241)
+* set: The Set Builtin. (line 11)
+* shift: Bourne Shell Builtins.
+ (line 262)
+* shopt: The Shopt Builtin. (line 9)
+* source: Bash Builtins. (line 594)
+* suspend: Job Control Builtins.
+ (line 116)
+* test: Bourne Shell Builtins.
+ (line 275)
+* times: Bourne Shell Builtins.
+ (line 360)
+* trap: Bourne Shell Builtins.
+ (line 366)
+* type: Bash Builtins. (line 599)
+* typeset: Bash Builtins. (line 631)
+* ulimit: Bash Builtins. (line 637)
+* umask: Bourne Shell Builtins.
+ (line 415)
+* unalias: Bash Builtins. (line 743)
+* unset: Bourne Shell Builtins.
+ (line 433)
+* wait: Job Control Builtins.
+ (line 76)
+
+
+File: bash.info, Node: Reserved Word Index, Next: Variable Index, Prev: Builtin Index, Up: Indexes
+
+D.2 Index of Shell Reserved Words
+=================================
+
+
+* Menu:
+
+* !: Pipelines. (line 9)
+* [[: Conditional Constructs.
+ (line 126)
+* ]]: Conditional Constructs.
+ (line 126)
+* {: Command Grouping. (line 21)
+* }: Command Grouping. (line 21)
+* case: Conditional Constructs.
+ (line 28)
+* do: Looping Constructs. (line 12)
+* done: Looping Constructs. (line 12)
+* elif: Conditional Constructs.
+ (line 7)
+* else: Conditional Constructs.
+ (line 7)
+* esac: Conditional Constructs.
+ (line 28)
+* fi: Conditional Constructs.
+ (line 7)
+* for: Looping Constructs. (line 32)
+* function: Shell Functions. (line 13)
+* if: Conditional Constructs.
+ (line 7)
+* in: Conditional Constructs.
+ (line 28)
+* select: Conditional Constructs.
+ (line 84)
+* then: Conditional Constructs.
+ (line 7)
+* time: Pipelines. (line 9)
+* until: Looping Constructs. (line 12)
+* while: Looping Constructs. (line 22)
+
+
+File: bash.info, Node: Variable Index, Next: Function Index, Prev: Reserved Word Index, Up: Indexes
+
+D.3 Parameter and Variable Index
+================================
+
+
+* Menu:
+
+* !: Special Parameters. (line 55)
+* #: Special Parameters. (line 39)
+* $: Special Parameters. (line 51)
+* $!: Special Parameters. (line 56)
+* $#: Special Parameters. (line 40)
+* $$: Special Parameters. (line 52)
+* $*: Special Parameters. (line 10)
+* $-: Special Parameters. (line 47)
+* $0: Special Parameters. (line 61)
+* $?: Special Parameters. (line 43)
+* $@: Special Parameters. (line 23)
+* $_: Bash Variables. (line 14)
+* *: Special Parameters. (line 9)
+* -: Special Parameters. (line 46)
+* 0: Special Parameters. (line 60)
+* ?: Special Parameters. (line 42)
+* @: Special Parameters. (line 22)
+* _: Bash Variables. (line 13)
+* active-region-end-color: Readline Init File Syntax.
+ (line 51)
+* active-region-start-color: Readline Init File Syntax.
+ (line 38)
+* auto_resume: Job Control Variables.
+ (line 6)
+* BASH: Bash Variables. (line 23)
+* BASHOPTS: Bash Variables. (line 26)
+* BASHPID: Bash Variables. (line 35)
+* BASH_ALIASES: Bash Variables. (line 42)
+* BASH_ARGC: Bash Variables. (line 51)
+* BASH_ARGV: Bash Variables. (line 64)
+* BASH_ARGV0: Bash Variables. (line 76)
+* BASH_CMDS: Bash Variables. (line 84)
+* BASH_COMMAND: Bash Variables. (line 93)
+* BASH_COMPAT: Bash Variables. (line 100)
+* BASH_ENV: Bash Variables. (line 116)
+* BASH_EXECUTION_STRING: Bash Variables. (line 122)
+* BASH_LINENO: Bash Variables. (line 125)
+* BASH_LOADABLES_PATH: Bash Variables. (line 133)
+* BASH_REMATCH: Bash Variables. (line 137)
+* BASH_SOURCE: Bash Variables. (line 145)
+* BASH_SUBSHELL: Bash Variables. (line 152)
+* BASH_VERSINFO: Bash Variables. (line 158)
+* BASH_VERSION: Bash Variables. (line 181)
+* BASH_XTRACEFD: Bash Variables. (line 184)
+* bell-style: Readline Init File Syntax.
+ (line 64)
+* bind-tty-special-chars: Readline Init File Syntax.
+ (line 71)
+* blink-matching-paren: Readline Init File Syntax.
+ (line 76)
+* CDPATH: Bourne Shell Variables.
+ (line 9)
+* CHILD_MAX: Bash Variables. (line 195)
+* colored-completion-prefix: Readline Init File Syntax.
+ (line 81)
+* colored-stats: Readline Init File Syntax.
+ (line 91)
+* COLUMNS: Bash Variables. (line 202)
+* comment-begin: Readline Init File Syntax.
+ (line 97)
+* completion-display-width: Readline Init File Syntax.
+ (line 102)
+* completion-ignore-case: Readline Init File Syntax.
+ (line 109)
+* completion-map-case: Readline Init File Syntax.
+ (line 114)
+* completion-prefix-display-length: Readline Init File Syntax.
+ (line 120)
+* completion-query-items: Readline Init File Syntax.
+ (line 127)
+* COMPREPLY: Bash Variables. (line 254)
+* COMP_CWORD: Bash Variables. (line 208)
+* COMP_KEY: Bash Variables. (line 237)
+* COMP_LINE: Bash Variables. (line 214)
+* COMP_POINT: Bash Variables. (line 219)
+* COMP_TYPE: Bash Variables. (line 227)
+* COMP_WORDBREAKS: Bash Variables. (line 241)
+* COMP_WORDS: Bash Variables. (line 247)
+* convert-meta: Readline Init File Syntax.
+ (line 138)
+* COPROC: Bash Variables. (line 260)
+* DIRSTACK: Bash Variables. (line 264)
+* disable-completion: Readline Init File Syntax.
+ (line 148)
+* echo-control-characters: Readline Init File Syntax.
+ (line 153)
+* editing-mode: Readline Init File Syntax.
+ (line 158)
+* EMACS: Bash Variables. (line 274)
+* emacs-mode-string: Readline Init File Syntax.
+ (line 164)
+* enable-active-region: Readline Init File Syntax.
+ (line 174)
+* enable-bracketed-paste: Readline Init File Syntax.
+ (line 187)
+* enable-keypad: Readline Init File Syntax.
+ (line 196)
+* ENV: Bash Variables. (line 279)
+* EPOCHREALTIME: Bash Variables. (line 284)
+* EPOCHSECONDS: Bash Variables. (line 292)
+* EUID: Bash Variables. (line 299)
+* EXECIGNORE: Bash Variables. (line 303)
+* expand-tilde: Readline Init File Syntax.
+ (line 207)
+* FCEDIT: Bash Variables. (line 316)
+* FIGNORE: Bash Variables. (line 320)
+* FUNCNAME: Bash Variables. (line 326)
+* FUNCNEST: Bash Variables. (line 343)
+* GLOBIGNORE: Bash Variables. (line 348)
+* GROUPS: Bash Variables. (line 355)
+* histchars: Bash Variables. (line 361)
+* HISTCMD: Bash Variables. (line 376)
+* HISTCONTROL: Bash Variables. (line 382)
+* HISTFILE: Bash Variables. (line 398)
+* HISTFILESIZE: Bash Variables. (line 402)
+* HISTIGNORE: Bash Variables. (line 413)
+* history-preserve-point: Readline Init File Syntax.
+ (line 211)
+* history-size: Readline Init File Syntax.
+ (line 217)
+* HISTSIZE: Bash Variables. (line 433)
+* HISTTIMEFORMAT: Bash Variables. (line 440)
+* HOME: Bourne Shell Variables.
+ (line 13)
+* horizontal-scroll-mode: Readline Init File Syntax.
+ (line 226)
+* HOSTFILE: Bash Variables. (line 448)
+* HOSTNAME: Bash Variables. (line 459)
+* HOSTTYPE: Bash Variables. (line 462)
+* IFS: Bourne Shell Variables.
+ (line 18)
+* IGNOREEOF: Bash Variables. (line 465)
+* input-meta: Readline Init File Syntax.
+ (line 235)
+* INPUTRC: Bash Variables. (line 475)
+* INSIDE_EMACS: Bash Variables. (line 479)
+* isearch-terminators: Readline Init File Syntax.
+ (line 245)
+* keymap: Readline Init File Syntax.
+ (line 252)
+* LANG: Creating Internationalized Scripts.
+ (line 51)
+* LANG <1>: Bash Variables. (line 485)
+* LC_ALL: Bash Variables. (line 489)
+* LC_COLLATE: Bash Variables. (line 493)
+* LC_CTYPE: Bash Variables. (line 500)
+* LC_MESSAGES: Creating Internationalized Scripts.
+ (line 51)
+* LC_MESSAGES <1>: Bash Variables. (line 505)
+* LC_NUMERIC: Bash Variables. (line 509)
+* LC_TIME: Bash Variables. (line 513)
+* LINENO: Bash Variables. (line 517)
+* LINES: Bash Variables. (line 522)
+* MACHTYPE: Bash Variables. (line 528)
+* MAIL: Bourne Shell Variables.
+ (line 22)
+* MAILCHECK: Bash Variables. (line 532)
+* MAILPATH: Bourne Shell Variables.
+ (line 27)
+* MAPFILE: Bash Variables. (line 540)
+* mark-modified-lines: Readline Init File Syntax.
+ (line 282)
+* mark-symlinked-directories: Readline Init File Syntax.
+ (line 287)
+* match-hidden-files: Readline Init File Syntax.
+ (line 292)
+* menu-complete-display-prefix: Readline Init File Syntax.
+ (line 299)
+* meta-flag: Readline Init File Syntax.
+ (line 235)
+* OLDPWD: Bash Variables. (line 544)
+* OPTARG: Bourne Shell Variables.
+ (line 34)
+* OPTERR: Bash Variables. (line 547)
+* OPTIND: Bourne Shell Variables.
+ (line 38)
+* OSTYPE: Bash Variables. (line 551)
+* output-meta: Readline Init File Syntax.
+ (line 304)
+* page-completions: Readline Init File Syntax.
+ (line 312)
+* PATH: Bourne Shell Variables.
+ (line 42)
+* PIPESTATUS: Bash Variables. (line 554)
+* POSIXLY_CORRECT: Bash Variables. (line 559)
+* PPID: Bash Variables. (line 569)
+* PROMPT_COMMAND: Bash Variables. (line 573)
+* PROMPT_DIRTRIM: Bash Variables. (line 579)
+* PS0: Bash Variables. (line 585)
+* PS1: Bourne Shell Variables.
+ (line 48)
+* PS2: Bourne Shell Variables.
+ (line 53)
+* PS3: Bash Variables. (line 590)
+* PS4: Bash Variables. (line 595)
+* PWD: Bash Variables. (line 603)
+* RANDOM: Bash Variables. (line 606)
+* READLINE_ARGUMENT: Bash Variables. (line 612)
+* READLINE_LINE: Bash Variables. (line 616)
+* READLINE_MARK: Bash Variables. (line 620)
+* READLINE_POINT: Bash Variables. (line 626)
+* REPLY: Bash Variables. (line 630)
+* revert-all-at-newline: Readline Init File Syntax.
+ (line 322)
+* SECONDS: Bash Variables. (line 633)
+* SHELL: Bash Variables. (line 642)
+* SHELLOPTS: Bash Variables. (line 647)
+* SHLVL: Bash Variables. (line 656)
+* show-all-if-ambiguous: Readline Init File Syntax.
+ (line 329)
+* show-all-if-unmodified: Readline Init File Syntax.
+ (line 335)
+* show-mode-in-prompt: Readline Init File Syntax.
+ (line 344)
+* skip-completed-text: Readline Init File Syntax.
+ (line 350)
+* SRANDOM: Bash Variables. (line 661)
+* TEXTDOMAIN: Creating Internationalized Scripts.
+ (line 51)
+* TEXTDOMAINDIR: Creating Internationalized Scripts.
+ (line 51)
+* TIMEFORMAT: Bash Variables. (line 670)
+* TMOUT: Bash Variables. (line 708)
+* TMPDIR: Bash Variables. (line 720)
+* UID: Bash Variables. (line 724)
+* vi-cmd-mode-string: Readline Init File Syntax.
+ (line 363)
+* vi-ins-mode-string: Readline Init File Syntax.
+ (line 374)
+* visible-stats: Readline Init File Syntax.
+ (line 385)
+
+
+File: bash.info, Node: Function Index, Next: Concept Index, Prev: Variable Index, Up: Indexes
+
+D.4 Function Index
+==================
+
+
+* Menu:
+
+* abort (C-g): Miscellaneous Commands.
+ (line 10)
+* accept-line (Newline or Return): Commands For History.
+ (line 6)
+* alias-expand-line (): Miscellaneous Commands.
+ (line 131)
+* backward-char (C-b): Commands For Moving. (line 15)
+* backward-delete-char (Rubout): Commands For Text. (line 17)
+* backward-kill-line (C-x Rubout): Commands For Killing.
+ (line 11)
+* backward-kill-word (M-<DEL>): Commands For Killing.
+ (line 28)
+* backward-word (M-b): Commands For Moving. (line 22)
+* beginning-of-history (M-<): Commands For History.
+ (line 20)
+* beginning-of-line (C-a): Commands For Moving. (line 6)
+* bracketed-paste-begin (): Commands For Text. (line 33)
+* call-last-kbd-macro (C-x e): Keyboard Macros. (line 13)
+* capitalize-word (M-c): Commands For Text. (line 66)
+* character-search (C-]): Miscellaneous Commands.
+ (line 42)
+* character-search-backward (M-C-]): Miscellaneous Commands.
+ (line 47)
+* clear-display (M-C-l): Commands For Moving. (line 48)
+* clear-screen (C-l): Commands For Moving. (line 53)
+* complete (<TAB>): Commands For Completion.
+ (line 6)
+* complete-command (M-!): Commands For Completion.
+ (line 80)
+* complete-filename (M-/): Commands For Completion.
+ (line 49)
+* complete-hostname (M-@): Commands For Completion.
+ (line 72)
+* complete-into-braces (M-{): Commands For Completion.
+ (line 100)
+* complete-username (M-~): Commands For Completion.
+ (line 56)
+* complete-variable (M-$): Commands For Completion.
+ (line 64)
+* copy-backward-word (): Commands For Killing.
+ (line 69)
+* copy-forward-word (): Commands For Killing.
+ (line 74)
+* copy-region-as-kill (): Commands For Killing.
+ (line 65)
+* dabbrev-expand (): Commands For Completion.
+ (line 95)
+* delete-char (C-d): Commands For Text. (line 12)
+* delete-char-or-list (): Commands For Completion.
+ (line 43)
+* delete-horizontal-space (): Commands For Killing.
+ (line 57)
+* digit-argument (M-0, M-1, ... M--): Numeric Arguments. (line 6)
+* display-shell-version (C-x C-v): Miscellaneous Commands.
+ (line 116)
+* do-lowercase-version (M-A, M-B, M-X, ...): Miscellaneous Commands.
+ (line 14)
+* downcase-word (M-l): Commands For Text. (line 62)
+* dump-functions (): Miscellaneous Commands.
+ (line 74)
+* dump-macros (): Miscellaneous Commands.
+ (line 86)
+* dump-variables (): Miscellaneous Commands.
+ (line 80)
+* dynamic-complete-history (M-<TAB>): Commands For Completion.
+ (line 90)
+* edit-and-execute-command (C-x C-e): Miscellaneous Commands.
+ (line 140)
+* end-kbd-macro (C-x )): Keyboard Macros. (line 9)
+* end-of-file (usually C-d): Commands For Text. (line 6)
+* end-of-history (M->): Commands For History.
+ (line 23)
+* end-of-line (C-e): Commands For Moving. (line 9)
+* exchange-point-and-mark (C-x C-x): Miscellaneous Commands.
+ (line 37)
+* fetch-history (): Commands For History.
+ (line 103)
+* forward-backward-delete-char (): Commands For Text. (line 21)
+* forward-char (C-f): Commands For Moving. (line 12)
+* forward-search-history (C-s): Commands For History.
+ (line 33)
+* forward-word (M-f): Commands For Moving. (line 18)
+* glob-complete-word (M-g): Miscellaneous Commands.
+ (line 98)
+* glob-expand-word (C-x *): Miscellaneous Commands.
+ (line 104)
+* glob-list-expansions (C-x g): Miscellaneous Commands.
+ (line 110)
+* history-and-alias-expand-line (): Miscellaneous Commands.
+ (line 134)
+* history-expand-line (M-^): Miscellaneous Commands.
+ (line 124)
+* history-search-backward (): Commands For History.
+ (line 57)
+* history-search-forward (): Commands For History.
+ (line 51)
+* history-substring-search-backward (): Commands For History.
+ (line 69)
+* history-substring-search-forward (): Commands For History.
+ (line 63)
+* insert-comment (M-#): Miscellaneous Commands.
+ (line 61)
+* insert-completions (M-*): Commands For Completion.
+ (line 22)
+* insert-last-argument (M-. or M-_): Miscellaneous Commands.
+ (line 137)
+* kill-line (C-k): Commands For Killing.
+ (line 6)
+* kill-region (): Commands For Killing.
+ (line 61)
+* kill-whole-line (): Commands For Killing.
+ (line 19)
+* kill-word (M-d): Commands For Killing.
+ (line 23)
+* magic-space (): Miscellaneous Commands.
+ (line 127)
+* menu-complete (): Commands For Completion.
+ (line 26)
+* menu-complete-backward (): Commands For Completion.
+ (line 38)
+* next-history (C-n): Commands For History.
+ (line 17)
+* next-screen-line (): Commands For Moving. (line 41)
+* non-incremental-forward-search-history (M-n): Commands For History.
+ (line 45)
+* non-incremental-reverse-search-history (M-p): Commands For History.
+ (line 39)
+* operate-and-get-next (C-o): Commands For History.
+ (line 96)
+* overwrite-mode (): Commands For Text. (line 70)
+* possible-command-completions (C-x !): Commands For Completion.
+ (line 86)
+* possible-completions (M-?): Commands For Completion.
+ (line 15)
+* possible-filename-completions (C-x /): Commands For Completion.
+ (line 52)
+* possible-hostname-completions (C-x @): Commands For Completion.
+ (line 76)
+* possible-username-completions (C-x ~): Commands For Completion.
+ (line 60)
+* possible-variable-completions (C-x $): Commands For Completion.
+ (line 68)
+* prefix-meta (<ESC>): Miscellaneous Commands.
+ (line 19)
+* previous-history (C-p): Commands For History.
+ (line 13)
+* previous-screen-line (): Commands For Moving. (line 34)
+* print-last-kbd-macro (): Keyboard Macros. (line 17)
+* quoted-insert (C-q or C-v): Commands For Text. (line 26)
+* re-read-init-file (C-x C-r): Miscellaneous Commands.
+ (line 6)
+* redraw-current-line (): Commands For Moving. (line 57)
+* reverse-search-history (C-r): Commands For History.
+ (line 27)
+* revert-line (M-r): Miscellaneous Commands.
+ (line 26)
+* self-insert (a, b, A, 1, !, ...): Commands For Text. (line 30)
+* set-mark (C-@): Miscellaneous Commands.
+ (line 33)
+* shell-backward-kill-word (): Commands For Killing.
+ (line 37)
+* shell-backward-word (M-C-b): Commands For Moving. (line 30)
+* shell-expand-line (M-C-e): Miscellaneous Commands.
+ (line 119)
+* shell-forward-word (M-C-f): Commands For Moving. (line 26)
+* shell-kill-word (M-C-d): Commands For Killing.
+ (line 32)
+* shell-transpose-words (M-C-t): Commands For Killing.
+ (line 41)
+* skip-csi-sequence (): Miscellaneous Commands.
+ (line 52)
+* spell-correct-word (C-x s): Miscellaneous Commands.
+ (line 92)
+* start-kbd-macro (C-x (): Keyboard Macros. (line 6)
+* tilde-expand (M-&): Miscellaneous Commands.
+ (line 30)
+* transpose-chars (C-t): Commands For Text. (line 47)
+* transpose-words (M-t): Commands For Text. (line 53)
+* undo (C-_ or C-x C-u): Miscellaneous Commands.
+ (line 23)
+* universal-argument (): Numeric Arguments. (line 10)
+* unix-filename-rubout (): Commands For Killing.
+ (line 52)
+* unix-line-discard (C-u): Commands For Killing.
+ (line 16)
+* unix-word-rubout (C-w): Commands For Killing.
+ (line 48)
+* upcase-word (M-u): Commands For Text. (line 58)
+* yank (C-y): Commands For Killing.
+ (line 79)
+* yank-last-arg (M-. or M-_): Commands For History.
+ (line 84)
+* yank-nth-arg (M-C-y): Commands For History.
+ (line 75)
+* yank-pop (M-y): Commands For Killing.
+ (line 82)
+
+
+File: bash.info, Node: Concept Index, Prev: Function Index, Up: Indexes
+
+D.5 Concept Index
+=================
+
+
+* Menu:
+
+* alias expansion: Aliases. (line 6)
+* arithmetic evaluation: Shell Arithmetic. (line 6)
+* arithmetic expansion: Arithmetic Expansion.
+ (line 6)
+* arithmetic, shell: Shell Arithmetic. (line 6)
+* arrays: Arrays. (line 6)
+* background: Job Control Basics. (line 6)
+* Bash configuration: Basic Installation. (line 6)
+* Bash installation: Basic Installation. (line 6)
+* Bourne shell: Basic Shell Features.
+ (line 6)
+* brace expansion: Brace Expansion. (line 6)
+* builtin: Definitions. (line 17)
+* command editing: Readline Bare Essentials.
+ (line 6)
+* command execution: Command Search and Execution.
+ (line 6)
+* command expansion: Simple Command Expansion.
+ (line 6)
+* command history: Bash History Facilities.
+ (line 6)
+* command search: Command Search and Execution.
+ (line 6)
+* command substitution: Command Substitution.
+ (line 6)
+* command timing: Pipelines. (line 9)
+* commands, compound: Compound Commands. (line 6)
+* commands, conditional: Conditional Constructs.
+ (line 6)
+* commands, grouping: Command Grouping. (line 6)
+* commands, lists: Lists. (line 6)
+* commands, looping: Looping Constructs. (line 6)
+* commands, pipelines: Pipelines. (line 6)
+* commands, shell: Shell Commands. (line 6)
+* commands, simple: Simple Commands. (line 6)
+* comments, shell: Comments. (line 6)
+* Compatibility Level: Shell Compatibility Mode.
+ (line 6)
+* Compatibility Mode: Shell Compatibility Mode.
+ (line 6)
+* completion builtins: Programmable Completion Builtins.
+ (line 6)
+* configuration: Basic Installation. (line 6)
+* control operator: Definitions. (line 21)
+* coprocess: Coprocesses. (line 6)
+* directory stack: The Directory Stack. (line 6)
+* editing command lines: Readline Bare Essentials.
+ (line 6)
+* environment: Environment. (line 6)
+* evaluation, arithmetic: Shell Arithmetic. (line 6)
+* event designators: Event Designators. (line 6)
+* execution environment: Command Execution Environment.
+ (line 6)
+* exit status: Definitions. (line 26)
+* exit status <1>: Exit Status. (line 6)
+* expansion: Shell Expansions. (line 6)
+* expansion, arithmetic: Arithmetic Expansion.
+ (line 6)
+* expansion, brace: Brace Expansion. (line 6)
+* expansion, filename: Filename Expansion. (line 9)
+* expansion, parameter: Shell Parameter Expansion.
+ (line 6)
+* expansion, pathname: Filename Expansion. (line 9)
+* expansion, tilde: Tilde Expansion. (line 6)
+* expressions, arithmetic: Shell Arithmetic. (line 6)
+* expressions, conditional: Bash Conditional Expressions.
+ (line 6)
+* field: Definitions. (line 30)
+* filename: Definitions. (line 35)
+* filename expansion: Filename Expansion. (line 9)
+* foreground: Job Control Basics. (line 6)
+* functions, shell: Shell Functions. (line 6)
+* history builtins: Bash History Builtins.
+ (line 6)
+* history events: Event Designators. (line 8)
+* history expansion: History Interaction. (line 6)
+* history list: Bash History Facilities.
+ (line 6)
+* History, how to use: A Programmable Completion Example.
+ (line 113)
+* identifier: Definitions. (line 51)
+* initialization file, readline: Readline Init File. (line 6)
+* installation: Basic Installation. (line 6)
+* interaction, readline: Readline Interaction.
+ (line 6)
+* interactive shell: Invoking Bash. (line 131)
+* interactive shell <1>: Interactive Shells. (line 6)
+* internationalization: Locale Translation. (line 6)
+* internationalized scripts: Creating Internationalized Scripts.
+ (line 3)
+* job: Definitions. (line 38)
+* job control: Definitions. (line 42)
+* job control <1>: Job Control Basics. (line 6)
+* kill ring: Readline Killing Commands.
+ (line 18)
+* killing text: Readline Killing Commands.
+ (line 6)
+* localization: Locale Translation. (line 6)
+* login shell: Invoking Bash. (line 128)
+* matching, pattern: Pattern Matching. (line 6)
+* metacharacter: Definitions. (line 46)
+* name: Definitions. (line 51)
+* native languages: Locale Translation. (line 6)
+* notation, readline: Readline Bare Essentials.
+ (line 6)
+* operator, shell: Definitions. (line 57)
+* parameter expansion: Shell Parameter Expansion.
+ (line 6)
+* parameters: Shell Parameters. (line 6)
+* parameters, positional: Positional Parameters.
+ (line 6)
+* parameters, special: Special Parameters. (line 6)
+* pathname expansion: Filename Expansion. (line 9)
+* pattern matching: Pattern Matching. (line 6)
+* pipeline: Pipelines. (line 6)
+* POSIX: Definitions. (line 9)
+* POSIX Mode: Bash POSIX Mode. (line 6)
+* process group: Definitions. (line 62)
+* process group ID: Definitions. (line 66)
+* process substitution: Process Substitution.
+ (line 6)
+* programmable completion: Programmable Completion.
+ (line 6)
+* prompting: Controlling the Prompt.
+ (line 6)
+* quoting: Quoting. (line 6)
+* quoting, ANSI: ANSI-C Quoting. (line 6)
+* Readline, how to use: Job Control Variables.
+ (line 23)
+* redirection: Redirections. (line 6)
+* reserved word: Definitions. (line 70)
+* reserved words: Reserved Words. (line 6)
+* restricted shell: The Restricted Shell.
+ (line 6)
+* return status: Definitions. (line 75)
+* shell arithmetic: Shell Arithmetic. (line 6)
+* shell function: Shell Functions. (line 6)
+* shell script: Shell Scripts. (line 6)
+* shell variable: Shell Parameters. (line 6)
+* shell, interactive: Interactive Shells. (line 6)
+* signal: Definitions. (line 78)
+* signal handling: Signals. (line 6)
+* special builtin: Definitions. (line 82)
+* special builtin <1>: Special Builtins. (line 6)
+* startup files: Bash Startup Files. (line 6)
+* string translations: Creating Internationalized Scripts.
+ (line 3)
+* suspending jobs: Job Control Basics. (line 6)
+* tilde expansion: Tilde Expansion. (line 6)
+* token: Definitions. (line 86)
+* translation, native languages: Locale Translation. (line 6)
+* variable, shell: Shell Parameters. (line 6)
+* variables, readline: Readline Init File Syntax.
+ (line 37)
+* word: Definitions. (line 90)
+* word splitting: Word Splitting. (line 6)
+* yanking text: Readline Killing Commands.
+ (line 6)
+
+
+
+Tag Table:
+Node: Top896
+Node: Introduction2815
+Node: What is Bash?3028
+Node: What is a shell?4139
+Node: Definitions6674
+Node: Basic Shell Features9622
+Node: Shell Syntax10838
+Node: Shell Operation11861
+Node: Quoting13151
+Node: Escape Character14452
+Node: Single Quotes14934
+Node: Double Quotes15279
+Node: ANSI-C Quoting16554
+Node: Locale Translation17861
+Node: Creating Internationalized Scripts19169
+Node: Comments23283
+Node: Shell Commands23898
+Node: Reserved Words24833
+Node: Simple Commands25586
+Node: Pipelines26237
+Node: Lists29233
+Node: Compound Commands31025
+Node: Looping Constructs32034
+Node: Conditional Constructs34526
+Node: Command Grouping49011
+Node: Coprocesses50486
+Node: GNU Parallel53146
+Node: Shell Functions54060
+Node: Shell Parameters61942
+Node: Positional Parameters66327
+Node: Special Parameters67226
+Node: Shell Expansions70437
+Node: Brace Expansion72561
+Node: Tilde Expansion75292
+Node: Shell Parameter Expansion77910
+Node: Command Substitution96258
+Node: Arithmetic Expansion97610
+Node: Process Substitution98575
+Node: Word Splitting99692
+Node: Filename Expansion101633
+Node: Pattern Matching104379
+Node: Quote Removal109378
+Node: Redirections109670
+Node: Executing Commands119327
+Node: Simple Command Expansion119994
+Node: Command Search and Execution122101
+Node: Command Execution Environment124476
+Node: Environment127508
+Node: Exit Status129168
+Node: Signals130949
+Node: Shell Scripts134395
+Node: Shell Builtin Commands137419
+Node: Bourne Shell Builtins139454
+Node: Bash Builtins160917
+Node: Modifying Shell Behavior191770
+Node: The Set Builtin192112
+Node: The Shopt Builtin202710
+Node: Special Builtins218619
+Node: Shell Variables219595
+Node: Bourne Shell Variables220029
+Node: Bash Variables222130
+Node: Bash Features254942
+Node: Invoking Bash255952
+Node: Bash Startup Files261962
+Node: Interactive Shells267090
+Node: What is an Interactive Shell?267498
+Node: Is this Shell Interactive?268144
+Node: Interactive Shell Behavior268956
+Node: Bash Conditional Expressions272582
+Node: Shell Arithmetic277221
+Node: Aliases280162
+Node: Arrays282772
+Node: The Directory Stack289160
+Node: Directory Stack Builtins289941
+Node: Controlling the Prompt294198
+Node: The Restricted Shell297160
+Node: Bash POSIX Mode299767
+Node: Shell Compatibility Mode311682
+Node: Job Control320246
+Node: Job Control Basics320703
+Node: Job Control Builtins325702
+Node: Job Control Variables331494
+Node: Command Line Editing332647
+Node: Introduction and Notation334315
+Node: Readline Interaction335935
+Node: Readline Bare Essentials337123
+Node: Readline Movement Commands338909
+Node: Readline Killing Commands339866
+Node: Readline Arguments341784
+Node: Searching342825
+Node: Readline Init File345008
+Node: Readline Init File Syntax346266
+Node: Conditional Init Constructs369849
+Node: Sample Init File374042
+Node: Bindable Readline Commands377163
+Node: Commands For Moving378364
+Node: Commands For History380412
+Node: Commands For Text385403
+Node: Commands For Killing389049
+Node: Numeric Arguments392079
+Node: Commands For Completion393215
+Node: Keyboard Macros397403
+Node: Miscellaneous Commands398088
+Node: Readline vi Mode404030
+Node: Programmable Completion404934
+Node: Programmable Completion Builtins412711
+Node: A Programmable Completion Example423460
+Node: Using History Interactively428705
+Node: Bash History Facilities429386
+Node: Bash History Builtins432388
+Node: History Interaction437409
+Node: Event Designators441026
+Node: Word Designators442377
+Node: Modifiers444134
+Node: Installing Bash445939
+Node: Basic Installation447073
+Node: Compilers and Options450792
+Node: Compiling For Multiple Architectures451530
+Node: Installation Names453219
+Node: Specifying the System Type455325
+Node: Sharing Defaults456039
+Node: Operation Controls456709
+Node: Optional Features457664
+Node: Reporting Bugs468880
+Node: Major Differences From The Bourne Shell470152
+Node: GNU Free Documentation License486998
+Node: Indexes512172
+Node: Builtin Index512623
+Node: Reserved Word Index519447
+Node: Variable Index521892
+Node: Function Index538663
+Node: Concept Index552444
+
+End Tag Table
+
+
+Local Variables:
+coding: utf-8
+End:
generated by cgit v1.2.3 (git 2.39.1) at 2024-11-13 07:31:10 +0000