\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, 2009-2018 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},
+modification times. (The default extension is
@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.
is compressed to gzi.msd.exe.gz. Names are not truncated on systems
which do not have a limit on file name length.
-By default, @command{gzip} keeps the original file name and time stamp in
-the compressed file. These are used when decompressing the file with the
-@option{-N} option. This is useful when the compressed file name was
-truncated or when the time stamp was not preserved after a file
-transfer. However, due to limitations in the current @command{gzip} file
-format, fractional seconds are discarded. Also, time stamps must fall
-within the range 1970-01-01 00:00:00 through 2106-02-07 06:28:15
-@abbr{UTC}, and hosts whose operating systems use 32-bit time
-stamps are further restricted to time stamps no later than 2038-01-19
+By default, @command{gzip} keeps the original file name in the
+compressed file. This can be useful when decompressing the file with
+@option{-N} if the compressed file name was truncated after a file
+transfer.
+
+If the original is a regular file, @command{gzip} by default keeps its
+timestamp in the compressed file. This can be useful when
+decompressing the file with @option{-N} if the timestamp was not
+preserved after a file transfer.
+However, due to limitations in the current @command{gzip} file
+format, fractional seconds are discarded. Also, timestamps must fall
+within the range 1970-01-01 00:00:01 through 2106-02-07 06:28:15
+@abbr{UTC}, and hosts whose operating systems use 32-bit timestamps
+are further restricted to timestamps no later than 2038-01-19
03:14:07 @abbr{UTC}. The upper bounds assume the typical case
where leap seconds are ignored.
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}).
the @command{gzip} file header, plus 5 bytes every 32K block, or an expansion
ratio of 0.015% for large files. Note that the actual number of used
disk blocks almost never increases. @command{gzip} normally preserves the mode,
-ownership and time stamps of files when compressing or decompressing.
+ownership and timestamps 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
+@uref{https://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,
-@uref{http://www.ietf.org/rfc/rfc1951.txt, Internet @abbr{RFC} 1951} (May
+DEFLATE Compressed Data Format Specification version 1.3,
+@uref{https://www.ietf.org/rfc/rfc1951.txt, Internet @abbr{RFC} 1951} (May
1996).
@node Sample
-k, --keep keep (don't delete) input files
-l, --list list compressed file contents
-L, --license display software license
- -n, --no-name do not save or restore the original name and time stamp
- -N, --name save or restore the original name and time stamp
+ -n, --no-name do not save or restore the original name and timestamp
+ -N, --name save or restore the original name and timestamp
-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
@example
method: compression method (deflate,compress,lzh,pack)
crc: the 32-bit CRC of the uncompressed data
-date & time: time stamp for the uncompressed file
+date & time: timestamp for the uncompressed file
@end example
The @abbr{CRC} is given as ffffffff for a file not in gzip format.
@item --no-name
@itemx -n
-When compressing, do not save the original file name and time stamp by
+When compressing, do not save the original file name and timestamp by
default. (The original name is always saved if the name had to be
truncated.) When decompressing, do not restore the original file name
if present (remove only the @command{gzip}
suffix from the compressed file name) and do not restore the original
-time stamp if present (copy it from the compressed file). This option
+timestamp if present (copy it from the compressed file). This option
is the default when decompressing.
@item --name
@itemx -N
-When compressing, always save the original file name and time stamp; this
+When compressing, always save the original file name, and save
+the original timestamp if the original is a regular file; this
is the default. When decompressing, restore the original file name and
-time stamp if present. This option is useful on systems which have
-a limit on file name length or when the time stamp has been lost after
+timestamp if present. This option is useful on systems which have
+a limit on file name length or when the timestamp has been lost after
a file transfer.
@item --quiet
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.
-
@node Tapes
@chapter Using @command{gzip} on tapes
@cindex 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