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+\input texinfo @c -*-texinfo-*-
+@c %**start of header
+@setfilename zutils.info
+@documentencoding ISO-8859-15
+@settitle Zutils Manual
+@finalout
+@c %**end of header
+
+@set UPDATED 7 January 2023
+@set VERSION 1.12
+
+@dircategory Compression
+@direntry
+* Zutils: (zutils).             Utilities dealing with compressed files
+@end direntry
+
+
+@ifnothtml
+@titlepage
+@title Zutils
+@subtitle Utilities dealing with compressed files
+@subtitle for Zutils version @value{VERSION}, @value{UPDATED}
+@author by Antonio Diaz Diaz
+
+@page
+@vskip 0pt plus 1filll
+@end titlepage
+
+@contents
+@end ifnothtml
+
+@ifnottex
+@node Top
+@top
+
+This manual is for Zutils (version @value{VERSION}, @value{UPDATED}).
+
+@menu
+* Introduction::        Purpose and features of zutils
+* Common options::      Options common to all utilities
+* Configuration::       The configuration file zutils.conf
+* Zcat::                Concatenating compressed files
+* Zcmp::                Comparing compressed files byte by byte
+* Zdiff::               Comparing compressed files line by line
+* Zgrep::               Searching inside compressed files
+* Ztest::               Testing the integrity of compressed files
+* Zupdate::             Recompressing files to lzip format
+* Problems::            Reporting bugs
+* Concept index::       Index of concepts
+@end menu
+
+@sp 1
+Copyright @copyright{} 2009-2023 Antonio Diaz Diaz.
+
+This manual is free documentation: you have unlimited permission to copy,
+distribute, and modify it.
+@end ifnottex
+
+
+@node Introduction
+@chapter Introduction
+@cindex introduction
+
+@uref{http://www.nongnu.org/zutils/zutils.html,,Zutils}
+is a collection of utilities able to process any combination of
+compressed and uncompressed files transparently. If any file given,
+including standard input, is compressed, its decompressed content is used.
+Compressed files are decompressed on the fly; no temporary files are
+created. Data format is detected by its magic bytes, not by the file name
+extension.
+
+These utilities are not wrapper scripts but safer and more efficient C++
+programs. In particular the option @option{--recursive} is very efficient in
+those utilities supporting it.
+
+@noindent
+The utilities provided are @command{zcat}, @command{zcmp}, @command{zdiff},
+@command{zgrep}, @command{ztest}, and @command{zupdate}.@*
+The formats supported are bzip2, gzip,
+@uref{http://www.nongnu.org/lzip/lzip.html,,lzip}, xz, and zstd.@*
+Zutils uses external compressors. The compressor to be used for each format
+is configurable at runtime.
+
+@command{zcat}, @command{zcmp}, @command{zdiff}, and @command{zgrep} are
+improved replacements for the shell scripts provided by GNU gzip.
+@command{ztest} is unique to zutils. @command{zupdate} is similar to gzip's
+znew.
+
+NOTE: Bzip2 and lzip provide well-defined values of exit status, which makes
+them safe to use with zutils. Gzip and xz may return ambiguous warning
+values, making them less reliable back ends for zutils. Zstd currently does
+not even document its exit status in its man page.
+@xref{compressor-requirements}.
+
+FORMAT NOTE 1: The option @option{--format} allows the processing of a subset
+of formats in recursive mode and when trying compressed file names. For
+example, use the following command to search for the string @samp{foo} in
+gzip and lzip files only:
+@w{@samp{zgrep foo -r --format=gz,lz somedir somefile.tar}}.
+
+FORMAT NOTE 2: The standard POSIX compress format (.Z) is obsolete and is
+only supported through gzip. For this to work, the gzip program used (for
+example GNU gzip) must be able to decompress .Z files.
+
+LANGUAGE NOTE: Uncompressed = not compressed = plain data; it may never have
+been compressed. Decompressed is used to refer to data which have undergone
+the process of decompression.
+
+@sp 1
+Numbers given as arguments to options (positions, sizes) may be followed
+by a multiplier and an optional @samp{B} for "byte".
+
+Table of SI and binary prefixes (unit multipliers):
+
+@multitable {Prefix} {kilobyte  (10^3 = 1000)} {|} {Prefix} {kibibyte (2^10 = 1024)}
+@item Prefix @tab Value               @tab | @tab Prefix @tab Value
+@item k @tab kilobyte  (10^3 = 1000)  @tab | @tab Ki @tab kibibyte (2^10 = 1024)
+@item M @tab megabyte  (10^6)         @tab | @tab Mi @tab mebibyte (2^20)
+@item G @tab gigabyte  (10^9)         @tab | @tab Gi @tab gibibyte (2^30)
+@item T @tab terabyte  (10^12)        @tab | @tab Ti @tab tebibyte (2^40)
+@item P @tab petabyte  (10^15)        @tab | @tab Pi @tab pebibyte (2^50)
+@item E @tab exabyte   (10^18)        @tab | @tab Ei @tab exbibyte (2^60)
+@item Z @tab zettabyte (10^21)        @tab | @tab Zi @tab zebibyte (2^70)
+@item Y @tab yottabyte (10^24)        @tab | @tab Yi @tab yobibyte (2^80)
+@end multitable
+
+
+@node Common options
+@chapter Common options
+@cindex common options
+
+The following
+@uref{http://www.nongnu.org/arg-parser/manual/arg_parser_manual.html#Argument-syntax,,options}:
+are available in all the utilities. Rather than writing identical
+descriptions for each of the programs, they are described here.
+@ifnothtml
+@xref{Argument syntax,,,arg_parser}.
+@end ifnothtml
+
+@table @code
+@item -h
+@itemx --help
+Print an informative help message describing the options and exit.
+@command{zgrep} only supports the @option{--help} form of this option.
+
+@anchor{version}
+@item -V
+@itemx --version
+Print the version number on the standard output and exit.
+This version number should be included in all bug reports.
+In verbose mode, @command{zdiff} and @command{zgrep} print also the version
+of the diff or grep program used respectively. At verbosity level 1 (2 for
+@command{zdiff} and @command{zgrep}) or higher, print also the versions of
+the compressors used (perhaps limited by option @option{--format}). (The
+compressors used must support the option @option{-V} for this to work).
+
+@item -M @var{format_list}
+@itemx --format=@var{format_list}
+Process only the formats listed in the comma-separated @var{format_list}.
+Valid formats are @samp{bz2}, @samp{gz}, @samp{lz}, @samp{xz}, @samp{zst},
+and @samp{un} for @samp{uncompressed}, meaning "any file name without a
+known extension". This option excludes files based on extension, instead of
+format, because it is more efficient. The exclusion only applies to names
+generated automatically (for example when adding extensions to a file name
+or when operating recursively on directories). Files given in the command
+line are always processed.
+
+Each format in @var{format_list} enables file names with the following
+extensions:
+
+@multitable {bz2} {enables} {any other file name}
+@item bz2 @tab enables @tab .bz2 .tbz .tbz2
+@item gz  @tab enables @tab .gz .tgz .Z
+@item lz  @tab enables @tab .lz .tlz
+@item xz  @tab enables @tab .xz .txz
+@item zst @tab enables @tab .zst .tzst
+@item un  @tab enables @tab any other file name
+@end multitable
+
+@item -N
+@itemx --no-rcfile
+Don't read the runtime configuration file @file{zutils.conf}.
+
+@item --bz2=@var{command}
+@itemx --gz=@var{command}
+@itemx --lz=@var{command}
+@itemx --xz=@var{command}
+@itemx --zst=@var{command}
+Set program to be used as decompressor for the corresponding format.
+@var{command} may include arguments. For example
+@w{@option{--lz='plzip --threads=2'}}. @command{zupdate} uses @option{--lz}
+for compression, not for decompression (@pxref{lz-compressor}). The name of
+the program can't begin with @samp{-}. These options override the values set
+in @file{zutils.conf}. The compression program used must meet three
+requirements:
+
+@anchor{compressor-requirements}
+@enumerate
+@item
+When called with the option @option{-d} and without file names, it must read
+compressed data from the standard input and produce decompressed data on the
+standard output.
+@item
+If the option @option{-q} is passed to zutils, the compression program must
+also accept it.
+@item
+It must return 0 if no errors occurred, and a non-zero value otherwise.
+@end enumerate
+
+@end table
+
+
+@node Configuration
+@chapter The configuration file 'zutils.conf'
+@cindex zutils.conf
+
+@file{zutils.conf} is the runtime configuration file for zutils. In it you
+may define the compressor name and options to be used for each format.
+@file{zutils.conf} is optional; you don't need to install it in order to run
+zutils.
+
+The compressors specified in the command line override those specified
+in @file{zutils.conf}.
+
+You may copy the system @file{zutils.conf} file @file{$@{sysconfdir@}/zutils.conf}
+to @file{$XDG_CONFIG_HOME/zutils.conf} and customize these options as you like.
+(@env{XDG_CONFIG_HOME} defaults to @file{$HOME/.config}). The file syntax is
+fairly obvious (and there are further instructions in it):
+
+@enumerate
+@item
+Any line beginning with @samp{#} is a comment line.
+@item
+Each non-comment line defines the command to be used for the corresponding
+format, with the syntax:
+@example
+<format> = <compressor> [options]
+@end example
+where <format> is one of @samp{bz2}, @samp{gz}, @samp{lz}, @samp{xz}, or
+@samp{zst}.
+@end enumerate
+
+
+@node Zcat
+@chapter Zcat
+@cindex zcat
+
+@command{zcat} copies each @var{file} argument to standard output in
+sequence. If any file given is compressed, its decompressed content is
+copied. If a file given does not exist, and its name does not end with one
+of the known extensions, @command{zcat} tries the compressed file names
+corresponding to the formats supported. If a file fails to decompress,
+@command{zcat} continues copying the rest of the files.
+
+If a file is specified as @samp{-}, data are read from standard input,
+decompressed if needed, and sent to standard output. Data read from
+standard input must be of the same type; all uncompressed or all in the
+same compressed format.
+
+If no files are specified, recursive searches examine the current working
+directory, and nonrecursive searches read standard input.
+
+The format for running @command{zcat} is:
+
+@example
+zcat [@var{options}] [@var{files}]
+@end example
+
+@noindent
+Exit status is 0 if no errors occurred, 1 otherwise.
+
+@command{zcat} supports the following options:
+
+@table @code
+@item -A
+@itemx --show-all
+Equivalent to @option{-vET}.
+
+@item -b
+@itemx --number-nonblank
+Number all nonblank output lines, starting with 1. The line count is
+unlimited.
+
+@item -e
+Equivalent to @option{-vE}.
+
+@item -E
+@itemx --show-ends
+Print a @samp{$} after the end of each line.
+
+@item -n
+@itemx --number
+Number all output lines, starting with 1. The line count is unlimited.
+
+@item -O @var{format}
+@itemx --force-format=@var{format}
+Force the compressed format given. Valid values for @var{format} are
+@samp{bz2}, @samp{gz}, @samp{lz}, @samp{xz}, @samp{zst}, and @samp{un} for
+@samp{uncompressed}. If this option is used, the files are passed to the
+corresponding decompressor (or transmitted unmodified) without verifying
+their format, and the exact file name must be given. Other names won't be
+tried.
+
+@item -q
+@itemx --quiet
+Quiet operation. Suppress all messages.
+
+@item -r
+@itemx --recursive
+For each directory operand, read and process all files in that directory,
+recursively. Follow symbolic links given in the command line, but skip
+symbolic links that are encountered recursively.
+
+@item -R
+@itemx --dereference-recursive
+For each directory operand, read and process all files in that directory,
+recursively, following all symbolic links.
+
+@item -s
+@itemx --squeeze-blank
+Replace multiple adjacent blank lines with a single blank line.
+
+@item -t
+Equivalent to @option{-vT}.
+
+@item -T
+@itemx --show-tabs
+Print TAB characters as @samp{^I}.
+
+@item -v
+@itemx --show-nonprinting
+Print control characters except for LF (newline) and TAB using @samp{^}
+notation and precede characters larger than 127 with @samp{M-} (which
+stands for "meta").
+
+@item --verbose
+Verbose mode. Show error messages. Repeating it increases the verbosity
+level. @xref{version}.
+
+@end table
+
+
+@node Zcmp
+@chapter Zcmp
+@cindex zcmp
+
+@command{zcmp} compares two files and, if they differ, writes to standard
+output the first byte and line number where they differ. Bytes and lines are
+numbered starting with 1. A hyphen @samp{-} used as a @var{file} argument
+means standard input. If any file given is compressed, its decompressed
+content is used. Compressed files are decompressed on the fly; no temporary
+files are created.
+
+The format for running @command{zcmp} is:
+
+@example
+zcmp [@var{options}] @var{file1} [@var{file2}]
+@end example
+
+@noindent
+This compares @var{file1} to @var{file2}. The standard input is used only if
+@var{file1} or @var{file2} refers to standard input. If @var{file2} is
+omitted @command{zcmp} tries the following:
+
+@itemize -
+@item
+If @var{file1} is compressed, compares its decompressed contents with
+the corresponding uncompressed file (the name of @var{file1} with the
+extension removed).
+@item
+If @var{file1} is uncompressed, compares it with the decompressed
+contents of @var{file1}.[lz|bz2|gz|zst|xz] (the first one that is found).
+@end itemize
+
+@noindent
+An exit status of 0 means no differences were found, 1 means some
+differences were found, and 2 means trouble.
+
+@command{zcmp} supports the following options:
+
+@table @code
+@item -b
+@itemx --print-bytes
+Print the values of the differing bytes (in octal by default) followed by
+the bytes themselves in printable form. Print control bytes as a @samp{^}
+followed by a letter, and precede bytes larger than 127 with @samp{M-}
+(which stands for "meta").
+
+@item -H
+@itemx --hexadecimal
+Print the values of the differing bytes in hexadecimal instead of octal.
+
+@item -i @var{size}
+@itemx --ignore-initial=@var{size}
+Ignore any differences in the first @var{size} bytes of the input files.
+Treat files with fewer than @var{size} bytes as if they were empty. If
+@var{size} is in the form @samp{@var{size1}:@var{size2}}, ignore the
+first @var{size1} bytes of the first input file and the first
+@var{size2} bytes of the second input file.
+
+@item -l
+@itemx --list
+Print the byte numbers (in decimal) and values (in octal by default) of all
+differing bytes. Bytes are numbered starting with 1.
+
+@item -n @var{count}
+@itemx --bytes=@var{count}
+Compare at most @var{count} input bytes.
+
+@item -O [@var{format1}][,@var{format2}]
+@itemx --force-format=[@var{format1}][,@var{format2}]
+Force the compressed formats given. Any of @var{format1} or @var{format2}
+may be omitted and the corresponding format will be automatically detected.
+Valid values for @var{format} are @samp{bz2}, @samp{gz}, @samp{lz},
+@samp{xz}, @samp{zst}, and @samp{un} for @samp{uncompressed}. If at least
+one format is specified with this option, the file is passed to the
+corresponding decompressor (or transmitted unmodified) without verifying its
+format, and the exact file names of both @var{file1} and @var{file2} must be
+given. Other names won't be tried.
+
+@item -q
+@itemx --quiet
+@itemx --silent
+Suppress diagnostics written to standard error, even the
+@w{@samp{EOF on <name_of_shorter_file>}} diagnostic. Byte differences are
+still written to standard output. (@option{-q} produces no output except
+byte differences).
+
+@item -s
+@itemx --script
+Write nothing to standard output or standard error when files differ, not
+even the @w{@samp{EOF on <name_of_shorter_file>}} diagnostic; indicate
+differing files through exit status only. Diagnostic messages are still
+written to standard error when an error is encountered. (@option{-s}
+produces no output except error messages).
+
+@item -v
+@itemx --verbose
+Verbose mode. Undoes the effect of @option{--quiet}. Further -v's increase
+the verbosity level. @xref{version}.
+
+@end table
+
+Byte counts given as arguments to options may be expressed in decimal,
+hexadecimal, or octal (using the same syntax as integer constants in C++),
+and may be followed by a multiplier and an optional @samp{B} for "byte".
+
+Table of SI and binary prefixes (unit multipliers):
+
+@multitable {Prefix} {kilobyte  (10^3 = 1000)} {|} {Prefix} {kibibyte (2^10 = 1024)}
+@item Prefix @tab Value               @tab | @tab Prefix @tab Value
+@item k @tab kilobyte  (10^3 = 1000)  @tab | @tab Ki @tab kibibyte (2^10 = 1024)
+@item M @tab megabyte  (10^6)         @tab | @tab Mi @tab mebibyte (2^20)
+@item G @tab gigabyte  (10^9)         @tab | @tab Gi @tab gibibyte (2^30)
+@item T @tab terabyte  (10^12)        @tab | @tab Ti @tab tebibyte (2^40)
+@item P @tab petabyte  (10^15)        @tab | @tab Pi @tab pebibyte (2^50)
+@item E @tab exabyte   (10^18)        @tab | @tab Ei @tab exbibyte (2^60)
+@item Z @tab zettabyte (10^21)        @tab | @tab Zi @tab zebibyte (2^70)
+@item Y @tab yottabyte (10^24)        @tab | @tab Yi @tab yobibyte (2^80)
+@end multitable
+
+
+@node Zdiff
+@chapter Zdiff
+@cindex zdiff
+
+@command{zdiff} compares two files and, if they differ, writes to standard
+output the differences line by line. A hyphen @samp{-} used as a @var{file}
+argument means standard input. If any file given is compressed, its
+decompressed content is used. @command{zdiff} is a front end to the program
+diff and has the limitation that messages from diff refer to temporary file
+names instead of those specified.
+
+The format for running @command{zdiff} is:
+
+@example
+zdiff [@var{options}] @var{file1} [@var{file2}]
+@end example
+
+@noindent
+This compares @var{file1} to @var{file2}. The standard input is used only if
+@var{file1} or @var{file2} refers to standard input. If @var{file2} is
+omitted @command{zdiff} tries the following:
+
+@itemize -
+@item
+If @var{file1} is compressed, compares its decompressed contents with
+the corresponding uncompressed file (the name of @var{file1} with the
+extension removed).
+@item
+If @var{file1} is uncompressed, compares it with the decompressed
+contents of @var{file1}.[lz|bz2|gz|zst|xz] (the first one that is found).
+@end itemize
+
+@noindent
+An exit status of 0 means no differences were found, 1 means some
+differences were found, and 2 means trouble.
+
+@command{zdiff} supports the following options (some options only work if
+the diff program used supports them):
+
+@table @code
+@item -a
+@itemx --text
+Treat all files as text.
+
+@item -b
+@itemx --ignore-space-change
+Ignore changes in the amount of white space.
+
+@item -B
+@itemx --ignore-blank-lines
+Ignore changes whose lines are all blank.
+
+@item -c
+Use the context output format.
+
+@item -C @var{n}
+@itemx --context=@var{n}
+Same as -c but use @var{n} lines of context.
+
+@item -d
+@itemx --minimal
+Try hard to find a smaller set of changes.
+
+@item -E
+@itemx --ignore-tab-expansion
+Ignore changes due to tab expansion.
+
+@item -i
+@itemx --ignore-case
+Ignore case differences in file contents.
+
+@item -O [@var{format1}][,@var{format2}]
+@itemx --force-format=[@var{format1}][,@var{format2}]
+Force the compressed formats given. Any of @var{format1} or @var{format2}
+may be omitted and the corresponding format will be automatically detected.
+Valid values for @var{format} are @samp{bz2}, @samp{gz}, @samp{lz},
+@samp{xz}, @samp{zst}, and @samp{un} for @samp{uncompressed}. If at least
+one format is specified with this option, the file is passed to the
+corresponding decompressor (or transmitted unmodified) without verifying its
+format, and the exact file names of both @var{file1} and @var{file2} must be
+given. Other names won't be tried.
+
+@item -p
+@itemx --show-c-function
+Show which C function each change is in.
+
+@item -q
+@itemx --brief
+Output only whether files differ.
+
+@item -s
+@itemx --report-identical-files
+Report when two files are identical.
+
+@item -t
+@itemx --expand-tabs
+Expand tabs to spaces in output.
+
+@item -T
+@itemx --initial-tab
+Make tabs line up by prepending a tab.
+
+@item -u
+Use the unified output format.
+
+@item -U @var{n}
+@itemx --unified=@var{n}
+Same as -u but use @var{n} lines of context.
+
+@item -v
+@itemx --verbose
+When specified before @option{--version}, print the version of the diff
+program used. Further -v's increase the verbosity level. @xref{version}.
+
+@item -w
+@itemx --ignore-all-space
+Ignore all white space.
+
+@item -W @var{columns}
+@itemx --width=@var{columns}
+Output at most the specified number of print columns per line in side by
+side format.
+
+@item -y
+@itemx --side-by-side
+Use the side by side output format.
+
+@end table
+
+
+@node Zgrep
+@chapter Zgrep
+@cindex zgrep
+
+@command{zgrep} is a front end to the program grep that allows transparent
+search on any combination of compressed and uncompressed files. If any file
+given is compressed, its decompressed content is used. If a file given does
+not exist, and its name does not end with one of the known extensions,
+@command{zgrep} tries the compressed file names corresponding to the formats
+supported. If a file fails to decompress, @command{zgrep} continues
+searching the rest of the files.
+
+If a file is specified as @samp{-}, data are read from standard input,
+decompressed if needed, and fed to grep. Data read from standard input
+must be of the same type; all uncompressed or all in the same
+compressed format.
+
+If no files are specified, recursive searches examine the current working
+directory, and nonrecursive searches read standard input.
+
+For efficiency reasons, @command{zgrep} does not always read all its input.
+For example, the shell command @w{@samp{base64 -d foo | zgrep -q X}} can
+cause @command{zgrep} to exit immediately after reading a line containing
+@samp{X}, without bothering to read the rest of its input data. This in turn
+can cause base64 to exit with a nonzero status because base64 cannot write
+to its output pipe after @command{zgrep} exits.
+
+The format for running @command{zgrep} is:
+
+@example
+zgrep [@var{options}] @var{pattern} [@var{files}]
+@end example
+
+@noindent
+An exit status of 0 means at least one match was found, 1 means no
+matches were found, and 2 means trouble.
+
+@command{zgrep} supports the following options (Some options only work if
+the grep program used supports them. Options -h, -H, -r, -R, and -Z are
+managed by @command{zgrep} and not passed to grep):
+
+@table @code
+@item -a
+@itemx --text
+Treat all files as text.
+
+@item -A @var{n}
+@itemx --after-context=@var{n}
+Print @var{n} lines of trailing context.
+
+@item -b
+@itemx --byte-offset
+Print the byte offset of each line.
+
+@item -B @var{n}
+@itemx --before-context=@var{n}
+Print @var{n} lines of leading context.
+
+@item -c
+@itemx --count
+Only print a count of matching lines per file.
+
+@item -C @var{n}
+@itemx --context=@var{n}
+Print @var{n} lines of output context.
+
+@item --color[=@var{when}]
+Show matched strings in color. @var{when} is @samp{never}, @samp{always},
+or @samp{auto}.
+
+@item -e @var{pattern}
+@itemx --regexp=@var{pattern}
+Use @var{pattern} as the pattern to match.
+
+@item -E
+@itemx --extended-regexp
+Interpret @var{pattern} as an extended regular expression (ERE).
+
+@item -f @var{file}
+@itemx --file=@var{file}
+Obtain patterns from @var{file}, one per line.@*
+When searching in several files at once, command substitution can be used
+with @option{-e} to read @var{file} only once, for example if @var{file} is
+not a regular file:
+@w{@samp{zgrep -e "$(cat @var{file})" file1.lz file2.gz}}
+
+@item -F
+@itemx --fixed-strings
+Interpret @var{pattern} as a set of newline-separated strings.
+
+@item -G
+@itemx --basic-regexp
+Interpret @var{pattern} as a basic regular expression (BRE). This is the
+default.
+
+@item -h
+@itemx --no-filename
+Suppress the prefixing of file names on output when multiple files are
+searched.
+
+@item -H
+@itemx --with-filename
+Print the file name for each match.
+
+@item -i
+@itemx --ignore-case
+Ignore case distinctions.
+
+@item -I
+Ignore binary files.
+
+@item -l
+@itemx --files-with-matches
+Only print names of files containing at least one match. Stop reading each
+file on the first match.
+
+@item -L
+@itemx --files-without-match
+Only print names of files not containing any matches. Stop reading each file
+on the first match.@*
+Note: option -L fails (prints wrong results, returns wrong status, and even
+hangs) when using GNU grep versions 3.2 to 3.4 inclusive because of a wrong
+change in the exit status of grep, which was reverted in GNU grep 3.5.
+
+@item --label=@var{label}
+Display input actually coming from standard input as input coming from file
+@var{label}.
+
+@item --line-buffered
+Use line buffering on output. This may cause a performance penalty.
+
+@item -m @var{n}
+@itemx --max-count=@var{n}
+Stop after @var{n} matches.
+
+@item -n
+@itemx --line-number
+Prefix each matched line with its line number in the input file.
+
+@item -o
+@itemx --only-matching
+Show only the part of matching lines that actually matches @var{pattern}.
+
+@item -O @var{format}
+@itemx --force-format=@var{format}
+Force the compressed format given. Valid values for @var{format} are
+@samp{bz2}, @samp{gz}, @samp{lz}, @samp{xz}, @samp{zst}, and @samp{un} for
+@samp{uncompressed}. If this option is used, the files are passed to the
+corresponding decompressor (or transmitted unmodified) without verifying
+their format, and the exact file name must be given. Other names won't be
+tried.
+
+@item -P
+@itemx --perl-regexp
+Interpret @var{pattern} as a Perl-compatible regular expression (PCRE).
+
+@item -q
+@itemx --quiet
+@itemx --silent
+Suppress all messages. Exit immediately with zero status if any match is
+found, even if an error was detected.
+
+@item -r
+@itemx --recursive
+For each directory operand, read and process all files in that directory,
+recursively. Follow symbolic links given in the command line, but skip
+symbolic links that are encountered recursively.
+
+@item -R
+@itemx --dereference-recursive
+For each directory operand, read and process all files in that directory,
+recursively, following all symbolic links.
+
+@item -s
+@itemx --no-messages
+Suppress error messages about nonexistent or unreadable files.
+
+@item -T
+@itemx --initial-tab
+Make sure that the first character of actual line content lies on a tab
+stop, so that the alignment of tabs looks normal.
+
+@item -U
+@itemx --binary
+Use binary I/O on platforms affected by the bug known as "text mode I/O".
+(MS-DOS, MS-Windows, OS/2).
+
+@item -v
+@itemx --invert-match
+Select non-matching lines.
+
+@item --verbose
+Verbose mode. Show error messages. When specified before @option{--version},
+print the version of the grep program used. Repeating it increases the
+verbosity level. @xref{version}.
+
+@item -w
+@itemx --word-regexp
+Match only whole words.
+
+@item -x
+@itemx --line-regexp
+Match only whole lines.
+
+@item -Z
+@itemx --null
+Output a zero byte (the ASCII NUL character) instead of the character that
+normally follows a file name. For example, @w{@samp{zgrep -lZ}} outputs a
+zero byte after each file name instead of the usual newline. This option
+makes the output unambiguous, even in the presence of file names containing
+unusual characters like newlines.
+
+@end table
+
+
+@node Ztest
+@chapter Ztest
+@cindex ztest
+
+@command{ztest} verifies the integrity of the compressed files specified. It
+also warns if an uncompressed file has a compressed file name extension, or
+if a compressed file has a wrong compressed extension. Uncompressed files
+are otherwise ignored. If a file is specified as @samp{-}, the integrity of
+compressed data read from standard input is verified. Data read from
+standard input must be all in the same compressed format. If a file fails to
+decompress, does not exist, can't be opened, or is a terminal, @command{ztest}
+continues verifying the rest of the files. A final diagnostic is shown at
+verbosity level 1 or higher if any file fails the test when testing multiple
+files.
+
+If no files are specified, recursive searches examine the current working
+directory, and nonrecursive searches read standard input.
+
+Bzip2, gzip, and lzip are the primary formats. Xz and zstd are optional. If
+the decompressor for the xz or zstd formats is not found, the corresponding
+files are ignored.
+
+Note that error detection in the xz format is broken. First, some xz
+files lack integrity information. Second, not all xz decompressors can
+@uref{http://www.nongnu.org/lzip/xz_inadequate.html#fragmented,,verify the integrity}
+of all xz files. Third, section 2.1.1.2 'Stream Flags' of the
+@uref{http://tukaani.org/xz/xz-file-format.txt,,xz format specification}
+allows xz decompressors to produce garbage output without issuing any
+warning. Therefore, xz files can't always be verified as reliably as
+files in the other formats can.
+@c We can only hope that xz is soon abandoned.
+
+The format for running @command{ztest} is:
+
+@example
+ztest [@var{options}] [@var{files}]
+@end example
+
+@noindent
+Exit status is 0 if all compressed files verify OK, 1 if environmental
+problems (file not found, invalid command line options, I/O errors, etc),
+2 if any compressed file is corrupt or invalid, or if any file has an
+incorrect file name extension.
+
+@command{ztest} supports the following options:
+
+@table @code
+@item -O @var{format}
+@itemx --force-format=@var{format}
+Force the compressed format given. Valid values for @var{format} are
+@samp{bz2}, @samp{gz}, @samp{lz}, @samp{xz}, and @samp{zst}. If this option
+is used, the files are passed to the corresponding decompressor without
+verifying their format, and any files in a format that the decompressor
+can't understand will fail.
+
+@item -q
+@itemx --quiet
+Quiet operation. Suppress all messages.
+
+@item -r
+@itemx --recursive
+For each directory operand, read and process all files in that directory,
+recursively. Follow symbolic links given in the command line, but skip
+symbolic links that are encountered recursively.
+
+@item -R
+@itemx --dereference-recursive
+For each directory operand, read and process all files in that directory,
+recursively, following all symbolic links.
+
+@item -v
+@itemx --verbose
+Verbose mode. Show the verify status for each file processed. Further -v's
+increase the verbosity level. @xref{version}.
+
+@end table
+
+
+@node Zupdate
+@chapter Zupdate
+@cindex zupdate
+
+@command{zupdate} recompresses files from bzip2, gzip, xz, and zstd formats
+to lzip format. Each original is compared with the new file and then
+deleted. Only regular files with standard file name extensions are
+recompressed, other files are ignored. Compressed files are decompressed and
+then recompressed on the fly; no temporary files are created. If an error
+happens while recompressing a file, @command{zupdate} exits immediately
+without recompressing the rest of the files. The lzip format is chosen as
+destination because it is the most appropriate for long-term data archiving.
+
+If no files are specified, recursive searches examine the current working
+directory, and nonrecursive searches do nothing.
+
+If the lzip compressed version of a file already exists, the file is skipped
+unless the option @option{--force} is given. In this case, if the comparison
+with the existing lzip version fails, an error is returned and the original
+file is not deleted. The operation of @command{zupdate} is meant to be safe
+and not cause any data loss. Therefore, existing lzip compressed files are
+never overwritten nor deleted.
+
+Combining the options @option{--force} and @option{--keep}, as in
+@w{@samp{zupdate -f -k *.gz}}, verifies that there are no differences
+between each pair of files in a multiformat set of files.
+
+The names of the original files must have one of the following extensions:@*
+@samp{.bz2}, @samp{.gz}, @samp{.xz}, @samp{.zst}, or @samp{.Z}, which are
+recompressed to @samp{.lz};@*
+@samp{.tbz}, @samp{.tbz2}, @samp{.tgz}, @samp{.txz}, or @samp{.tzst}, which
+are recompressed to @samp{.tlz}.@*
+Keeping the combined extensions @w{(@samp{.tgz} ---> @samp{.tlz})} may be
+useful when recompressing Slackware packages, for example.
+
+Bzip2, gzip, and lzip are the primary formats. Xz and zstd are optional. If
+the decompressor for the xz or zstd formats is not found, the corresponding
+files are ignored.
+
+Recompressing a file is much like copying or moving it. Therefore
+@command{zupdate} preserves the access and modification dates, permissions,
+and, if you have appropriate privileges, ownership of the file just as
+@w{@samp{cp -p}} does. (If the user ID or the group ID can't be duplicated,
+the file permission bits S_ISUID and S_ISGID are cleared).
+
+The format for running @command{zupdate} is:
+
+@example
+zupdate [@var{options}] [@var{files}]
+@end example
+
+@noindent
+Exit status is 0 if all the compressed files were successfully recompressed
+(if needed), compared, and deleted (if requested). 1 if a non-fatal error
+occurred (file not found or not regular, or has invalid format, or can't be
+deleted). 2 if a fatal error occurred (invalid command line options,
+compressor can't be run, or comparison fails).
+
+@command{zupdate} supports the following options:
+
+@table @code
+@item -d @var{dir}
+@itemx --destdir=@var{dir}
+Write recompressed files to another directory, using @var{dir} as base
+directory, instead of writing them in the same directory as the original
+files. In recursive mode, this is done by replacing each directory specified
+in the command line with @var{dir} to produce the recompressed file names.
+For example, @w{@samp{zupdate -r -d @var{dir} ../a}} recompresses a file
+named @file{../a/b/c.gz} to @file{@var{dir}/b/c.lz}. Regular files specified
+in the command line are recompressed directly into @var{dir}. For example,
+@w{@samp{zupdate -d @var{dir} ../a/b/c.gz}} writes the recompressed file to
+@file{@var{dir}/c.lz}.
+
+This option allows recompressing files from a read-only file system to
+another place without the need to copy or link them to the destination
+directory first. (Remember to use option @option{--keep} when recompressing
+read-only files to avoid warnings about files that can't be deleted).
+
+@item -e
+@itemx --expand-extensions
+Expand combined file name extensions; recompress @samp{.tbz}, @samp{.tbz2},
+@samp{.tgz}, @samp{.txz}, and @samp{.tzst} to @samp{tar.lz}.
+
+@item -f
+@itemx --force
+Don't skip a file for which a lzip compressed version already exists.
+@option{--force} compares the content of the input file with the content
+of the existing lzip file and deletes the input file if both contents
+are identical.
+
+@item -i
+@itemx --ignore-errors
+Ignore non-fatal errors. (See exit status above).
+
+@item -k
+@itemx --keep
+Keep (don't delete) the input file after comparing it with the lzip file.
+Use it when recompressing files from a read-only file system. (See option
+@option{--destdir} above).
+
+@item -l
+@itemx --lzip-verbose
+Pass one option @option{-v} to the lzip compressor so that it shows the
+compression ratio for each file processed. Using lzip 1.15 or newer, a
+second @option{-l} shows the progress of compression. Use it together with
+@option{-v} to see the name of the file.
+
+@item -q
+@itemx --quiet
+Quiet operation. Suppress all messages.
+
+@item -r
+@itemx --recursive
+For each directory operand, read and process all files in that directory,
+recursively. Follow symbolic links given in the command line, but skip
+symbolic links that are encountered recursively.
+
+@item -R
+@itemx --dereference-recursive
+For each directory operand, read and process all files in that directory,
+recursively, following all symbolic links.
+
+@item -v
+@itemx --verbose
+Verbose mode. Show the files being processed. A second @option{-v} also shows
+the files being ignored and increases the verbosity level. @xref{version}.
+
+@item -0 .. -9
+Set the compression level of lzip. By default @command{zupdate} passes
+@option{-9} to lzip. Custom compression options can be passed to lzip with
+the option @option{--lz}. For example @w{@option{--lz='lzip -9 -s64MiB'}}.
+
+@anchor{lz-compressor}
+@item --lz=@var{command}
+Set compression command. @var{command} may include arguments. For example
+@w{@option{--lz='plzip --threads=2'}}. The name of the program can't begin
+with @samp{-}. This option overrides the value set in @file{zutils.conf}.
+The compression program used does not need to implement decompression
+(@pxref{compressor-requirements}), but it must implement at least the
+compression level option @option{-9} and the option @w{@option{-o @var{file}}}
+to write the compressed output to @var{file}.
+@uref{http://www.nongnu.org/lzip/manual/tarlz_manual.html,,tarlz} meets
+these requirements, and therefore can be used to recompress POSIX tar
+archives by using a command like
+@w{@samp{zupdate --lz='tarlz -9 -z --no-solid' archive.tar.gz}}.
+@ifnothtml
+@xref{Top,tarlz manual,,tarlz}.
+@end ifnothtml
+
+@end table
+
+
+@node Problems
+@chapter Reporting bugs
+@cindex bugs
+@cindex getting help
+
+There are probably bugs in zutils. There are certainly errors and
+omissions in this manual. If you report them, they will get fixed. If
+you don't, no one will ever know about them and they will remain unfixed
+for all eternity, if not longer.
+
+If you find a bug in zutils, please send electronic mail to
+@email{zutils-bug@@nongnu.org}. Include the version number, which you can
+find by running @w{@samp{zupdate --version}}.
+
+
+@node Concept index
+@unnumbered Concept index
+
+@printindex cp
+
+@bye