\input texinfo @c -*-texinfo-*-
@c %**start of header
@setfilename gzip.info
+@documentencoding UTF-8
@include version.texi
@settitle GNU Gzip
@finalout
(version @value{VERSION}, @value{UPDATED}),
and documents commands for compressing and decompressing data.
-Copyright @copyright{} 1998-1999, 2001-2002, 2006-2007, 2009-2013 Free Software
+Copyright @copyright{} 1998-1999, 2001-2002, 2006-2007, 2009-2016 Free Software
Foundation, Inc.
Copyright @copyright{} 1992, 1993 Jean-loup Gailly
@chapter Overview
@cindex overview
-@command{gzip} reduces the size of the named files using Lempel-Ziv coding
+@command{gzip} reduces the size of the named files using Lempel--Ziv coding
(LZ77). Whenever possible, each file is replaced by one with the
extension @samp{.gz}, while keeping the same ownership modes, access and
modification times. (The default extension is @samp{-gz} for @abbr{VMS},
@samp{z} for @abbr{MSDOS}, @abbr{OS/2} @abbr{FAT} and Atari.)
If no files are specified or
-if a file name is "-", the standard input is compressed to the standard
+if a file name is @file{-}, the standard input is compressed to the standard
output. @command{gzip} will only attempt to compress regular files. In
particular, it will ignore symbolic links.
also allows some consistency checks.
Files created by @command{zip} can be uncompressed by @command{gzip} only if
-they have a single member compressed with the 'deflation' method. This
+they have a single member compressed with the ``deflation'' method. This
feature is only intended to help conversion of @file{tar.zip} files to
the @file{tar.gz} format. To extract a @command{zip} file with a single
member, use a command like @samp{gunzip <foo.zip} or @samp{gunzip -S
will uncompress files that have the correct magic number whether they
have a @samp{.gz} suffix or not.
-@command{gzip} uses the Lempel-Ziv algorithm used in @command{zip} and
+@command{gzip} uses the Lempel--Ziv algorithm used in @command{zip} and
@abbr{PKZIP}@.
The amount of compression obtained depends on the size of the input and
the distribution of common substrings. Typically, text such as source
-code or English is reduced by 60-70%. Compression is generally much
+code or English is reduced by 60--70%. Compression is generally much
better than that achieved by @abbr{LZW} (as used in @command{compress}), Huffman
coding (as used in @command{pack}), or adaptive Huffman coding
(@command{compact}).
disk blocks almost never increases. @command{gzip} normally preserves the mode,
ownership and time stamps of files when compressing or decompressing.
-The @command{gzip} file format is specified in P. Deutsch, @sc{gzip} file
+The @command{gzip} file format is specified in P. Deutsch, GZIP file
format specification version 4.3,
@uref{http://www.ietf.org/rfc/rfc1952.txt, Internet @abbr{RFC} 1952} (May
1996). The @command{zip} deflation format is specified in P. Deutsch,
-@sc{deflate} Compressed Data Format Specification version 1.3,
+DEFLATE Compressed Data Format Specification version 1.3,
@uref{http://www.ietf.org/rfc/rfc1951.txt, Internet @abbr{RFC} 1951} (May
1996).
-N, --name save or restore the original name and time stamp
-q, --quiet suppress all warnings
-r, --recursive operate recursively on directories
+ --rsyncable make rsync-friendly archive
-S, --suffix=SUF use suffix SUF on compressed files
+ --synchronous synchronous output (safer if system crashes, but slower)
-t, --test test compressed file integrity
-v, --verbose verbose mode
-V, --version display version number
into the directory and compress all the files it finds there (or
decompress them in the case of @command{gunzip}).
+@item --rsyncable
+Cater better to the @command{rsync} program by periodically resetting
+the internal structure of the compressed data stream. This lets the
+@code{rsync} program take advantage of similarities in the uncompressed
+input when synchronizing two files compressed with this flag. The cost:
+the compressed output is usually about one percent larger.
+
@item --suffix @var{suf}
@itemx -S @var{suf}
Use suffix @var{suf} instead of @samp{.gz}. Any suffix can be
Previous versions of gzip used the @samp{.z} suffix. This was changed to
avoid a conflict with @command{pack}.
+@item --synchronous
+Use synchronous output, by transferring output data to the output
+file's storage device when the file system supports this. Because
+file system data can be cached, without this option if the system
+crashes around the time a command like @samp{gzip FOO} is run the user
+might lose both @file{FOO} and @file{FOO.gz}; this is the default with
+@command{gzip}, just as it is the default with most applications that
+move data. When this option is used, @command{gzip} is safer but can
+be considerably slower.
+
@item --test
@itemx -t
Test. Check the compressed file integrity.
@chapter Environment
@cindex Environment
-The environment variable @env{GZIP} can hold a set of default options for
-@command{gzip}. These options are interpreted first and can be overwritten by
-explicit command line parameters. For example:
+The obsolescent environment variable @env{GZIP} can hold a set of
+default options for @command{gzip}. These options are interpreted
+first and can be overwritten by explicit command line parameters. As
+this can cause problems when using scripts, this feature is supported
+only for options that are reasonably likely to not cause too much
+harm, and @command{gzip} warns if it is used. This feature will be
+removed in a future release of @command{gzip}.
+
+You can use an alias or script instead. For example, if
+@command{gzip} is in the directory @samp{/usr/bin} you can prepend
+@file{$HOME/bin} to your @env{PATH} and create an executable script
+@file{$HOME/bin/gzip} containing the following:
@example
-for sh: GZIP="-8v --name"; export GZIP
-for csh: setenv GZIP "-8v --name"
-for MSDOS: set GZIP=-8v --name
+#! /bin/sh
+export PATH=/usr/bin
+exec gzip -9 "$@@"
@end example
-On @abbr{VMS}, the name of the environment variable is @env{GZIP_OPT}, to
-avoid a conflict with the symbol set for invocation of the program.
+On @abbr{VMS}, the name of the obsolescent environment variable is
+@env{GZIP_OPT}, to avoid a conflict with the symbol set for invocation
+of the program.
@node Tapes
@chapter Using @command{gzip} on tapes
the whole block is passed to @command{gunzip} for decompression,
@command{gunzip} detects that there is extra trailing garbage after the
compressed data and emits a warning by default if the garbage contains
-nonzero bytes. You have to use the
-@option{--quiet} option to suppress the warning. This option can be set in the
-@env{GZIP} environment variable, as in:
-
-@example
-for sh: GZIP="-q" tar -xfz --block-compress /dev/rst0
-for csh: (setenv GZIP "-q"; tar -xfz --block-compress /dev/rst0)
-@end example
-
-In the above example, @command{gzip} is invoked implicitly by the @option{-z}
-option of @acronym{GNU} @command{tar}. Make sure that the same block
-size (@option{-b}
-option of @command{tar}) is used for reading and writing compressed data on
-tapes. (This example assumes you are using the @acronym{GNU} version of
-@command{tar}.)
+nonzero bytes. You can use the @option{--quiet} option to suppress
+the warning.
@node Problems
@chapter Reporting Bugs
projects / debian / gzip / blobdiff