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GZIP(1) General Commands Manual GZIP(1)
1mNAME0m
gzip, gunzip, zcat - compress or expand files
1mSYNOPSIS0m
1mgzip 22m[ 1m-acdfhklLnNrtvV19 22m] [1m-S suffix22m] [ 4mname24m 4m...24m ]
1mgunzip 22m[ 1m-acfhklLnNrtvV 22m] [1m-S suffix22m] [ 4mname24m 4m...24m ]
1mzcat 22m[ 1m-fhLV 22m] [ 4mname24m 4m...24m ]
1mDESCRIPTION0m
The 1mgzip 22mcommand reduces the size of the named files using Lempel-Ziv
coding (LZ77). Whenever possible, each file is replaced by one with
the extension 1m.gz22m, while keeping the same ownership modes, access and
modification times. (The default extension is 1mz 22mfor MSDOS, OS/2 FAT,
Windows NT FAT and Atari.) If no files are specified, or if a file
name is "-", the standard input is compressed to the standard output.
The 1mgzip 22mcommand will only attempt to compress regular files. In par-
ticular, it will ignore symbolic links.
If the compressed file name is too long for its file system, 1mgzip 22mtrun-
cates it. The 1mgzip 22mcommand attempts to truncate only the parts of the
file name longer than 3 characters. (A part is delimited by dots.) If
the name consists of small parts only, the longest parts are truncated.
For example, if file names are limited to 14 characters, gzip.msdos.exe
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, 1mgzip 22mkeeps the original file name and timestamp in the com-
pressed file. These are used when decompressing the file with the 1m-N0m
option. This is useful when the compressed file name was truncated or
when the timestamp was not preserved after a file transfer.
Compressed files can be restored to their original form using 1mgzip -d0m
or 1mgunzip 22mor 1mzcat22m. If the original name saved in the compressed file
is not suitable for its file system, a new name is constructed from the
original one to make it valid.
1mgunzip 22mtakes a list of files on its command line and replaces each file
whose name ends with .gz, -gz, .z, -z, or _z (ignoring case) and which
begins with the correct magic number with an uncompressed file without
the original extension. 1mgunzip 22malso recognizes the special extensions
1m.tgz 22mand 1m.taz 22mas shorthands for 1m.tar.gz 22mand 1m.tar.Z 22mrespectively. When
compressing, 1mgzip 22muses the 1m.tgz 22mextension if necessary instead of trun-
cating a file with a 1m.tar 22mextension.
1mgunzip 22mcan currently decompress files created by 1mgzip22m, 1mzip22m, 1mcompress22m,
1mcompress -H 22mor 1mpack22m. The detection of the input format is automatic.
When using the first two formats, 1mgunzip 22mchecks a 32 bit CRC. For 1mpack0m
and 1mgunzip 22mchecks the uncompressed length. The standard 1mcompress 22mfor-
mat was not designed to allow consistency checks. However 1mgunzip 22mis
sometimes able to detect a bad .Z file. If you get an error when un-
compressing a .Z file, do not assume that the .Z file is correct simply
because the standard 1muncompress 22mdoes not complain. This generally
means that the standard 1muncompress 22mdoes not check its input, and hap-
pily generates garbage output. The SCO compress -H format (lzh com-
pression method) does not include a CRC but also allows some consis-
tency checks.
Files created by 1mzip 22mcan be uncompressed by gzip only if they have a
single member compressed with the 'deflation' method. This feature is
only intended to help conversion of tar.zip files to the tar.gz format.
To extract a 1mzip 22mfile with a single member, use a command like '1mgunzip0m
1m<foo.zip22m' or '1mgunzip -S .zip foo.zip22m'. To extract zip files with sev-
eral members, use 1munzip 22minstead of 1mgunzip22m.
The 1mzcat 22mcommand is identical to 1mgunzip -c22m. (On some systems, 1mzcat 22mmay
be installed as 1mgzcat 22mto preserve the original link to 1mcompress22m.) 1mzcat0m
uncompresses either a list of files on the command line or its standard
input and writes the uncompressed data on standard output. 1mzcat 22mwill
uncompress files that have the correct magic number whether they have a
1m.gz 22msuffix or not.
The 1mgzip 22mcommand uses the Lempel-Ziv algorithm used in 1mzip 22mand 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
better than that achieved by LZW (as used in 1mcompress22m), Huffman coding
(as used in 1mpack22m), or adaptive Huffman coding (1mcompact22m).
Compression is always performed, even if the compressed file is
slightly larger than the original. The worst case expansion is a few
bytes for the gzip file header, plus 5 bytes per 32 KiB block, or an
expansion ratio of 0.015% for large files. The actual number of used
disk blocks almost never increases.
1mgzip 22mnormally preserves the mode and modification timestamp of a file
when compressing or decompressing. If you have appropriate privileges,
it also preserves the file's owner and group.
1mOPTIONS0m
1m-a --ascii0m
Ascii text mode: convert end-of-lines using local conventions.
This option is supported only on some non-Unix systems. For MS-
DOS, CR LF is converted to LF when compressing, and LF is con-
verted to CR LF when decompressing.
1m-c --stdout --to-stdout0m
Write output on standard output; keep original files unchanged.
If there are several input files, the output consists of a se-
quence of independently compressed members. To obtain better
compression, concatenate all input files before compressing
them.
1m-d --decompress --uncompress0m
Decompress.
1m-f --force0m
Force compression or decompression even if the file has multiple
links or the corresponding file already exists, or if the com-
pressed data is read from or written to a terminal. If the in-
put data is not in a format recognized by 1mgzip22m, and if the op-
tion --stdout is also given, copy the input data without change
to the standard output: let 1mzcat 22mbehave as 1mcat22m. If 1m-f 22mis not
given, and when not running in the background, 1mgzip 22mprompts to
verify whether an existing file should be overwritten.
1m-h --help0m
Display a help screen and quit.
1m-k --keep0m
Keep (don't delete) input files during compression or decompres-
sion.
1m-l --list0m
For each compressed file, list the following fields:
compressed size: size of the compressed file
uncompressed size: size of the uncompressed file
ratio: compression ratio (0.0% if unknown)
uncompressed_name: name of the uncompressed file
The uncompressed size is given as -1 for files not in gzip for-
mat, such as compressed .Z files. To get the uncompressed size
for such a file, you can use:
zcat file.Z | wc -c
In combination with the --verbose option, the following fields
are also displayed:
method: compression method
crc: the 32-bit CRC of the uncompressed data
date & time: timestamp for the uncompressed file
The compression methods currently supported are deflate, com-
press, lzh (SCO compress -H) and pack. The crc is given as
ffffffff for a file not in gzip format.
With --name, the uncompressed name, date and time are those
stored within the compress file if present.
With --verbose, the size totals and compression ratio for all
files is also displayed, unless some sizes are unknown. With
--quiet, the title and totals lines are not displayed.
1m-L --license0m
Display the 1mgzip 22mlicense and quit.
1m-n --no-name0m
When compressing, do not save the original file name and time-
stamp 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 1mgzip 22msuffix
from the compressed file name) and do not restore the original
timestamp if present (copy it from the compressed file). This
option is the default when decompressing.
1m-N --name0m
When compressing, always save the original file name, and save
the seconds part of the original modification timestamp if the
original is a regular file and its timestamp is at least 1
(1970-01-01 00:00:01 UTC) and is less than 2**32 (2106-02-07
06:28:16 UTC, assuming leap seconds are not counted); this is
the default. When decompressing, restore from the saved file
name and 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.
1m-q --quiet0m
Suppress all warnings.
1m-r --recursive0m
Travel the directory structure recursively. If any of the file
names specified on the command line are directories, 1mgzip 22mwill
descend into the directory and compress all the files it finds
there (or decompress them in the case of 1mgunzip 22m).
1m-S .suf --suffix .suf0m
When compressing, use suffix .suf instead of .gz. Any non-empty
suffix can be given, but suffixes other than .z and .gz should
be avoided to avoid confusion when files are transferred to
other systems.
When decompressing, add .suf to the beginning of the list of
suffixes to try, when deriving an output file name from an input
file name.
1m--synchronous0m
Use synchronous output. With this option, 1mgzip 22mis less likely
to lose data during a system crash, but it can be considerably
slower.
1m-t --test0m
Test. Check the compressed file integrity then quit.
1m-v --verbose0m
Verbose. Display the name and percentage reduction for each
file compressed or decompressed.
1m-V --version0m
Version. Display the version number and compilation options
then quit.
1m-# --fast --best0m
Regulate the speed of compression using the specified digit 1m#22m,
where 1m-1 22mor 1m--fast 22mindicates the fastest compression method
(less compression) and 1m-9 22mor 1m--best 22mindicates the slowest com-
pression method (best compression). The default compression
level is 1m-6 22m(that is, biased towards high compression at expense
of speed).
1m--rsyncable0m
When you synchronize a compressed file between two computers,
this option allows rsync to transfer only files that were
changed in the archive instead of the entire archive. Normally,
after a change is made to any file in the archive, the compres-
sion algorithm can generate a new version of the archive that
does not match the previous version of the archive. In this
case, rsync transfers the entire new version of the archive to
the remote computer. With this option, rsync can transfer only
the changed files as well as a small amount of metadata that is
required to update the archive structure in the area that was
changed.
1mADVANCED USAGE0m
Multiple compressed files can be concatenated. In this case, 1mgunzip0m
will extract all members at once. For example:
gzip -c file1 > foo.gz
gzip -c file2 >> foo.gz
Then
gunzip -c foo
is equivalent to
cat file1 file2
In case of damage to one member of a .gz file, other members can still
be recovered (if the damaged member is removed). However, you can get
better compression by compressing all members at once:
cat file1 file2 | gzip > foo.gz
compresses better than
gzip -c file1 file2 > foo.gz
If you want to recompress concatenated files to get better compression,
do:
gzip -cd old.gz | gzip > new.gz
If a compressed file consists of several members, the uncompressed size
and CRC reported by the --list option applies to the last member only.
If you need the uncompressed size for all members, you can use:
gzip -cd file.gz | wc -c
If you wish to create a single archive file with multiple members so
that members can later be extracted independently, use an archiver such
as tar or zip. GNU tar supports the -z option to invoke gzip transpar-
ently. gzip is designed as a complement to tar, not as a replacement.
1mENVIRONMENT0m
The obsolescent environment variable 1mGZIP 22mcan hold a set of default op-
tions for 1mgzip22m. These options are interpreted first and can be over-
written by explicit command line parameters. As this can cause prob-
lems when using scripts, this feature is supported only for options
that are reasonably likely to not cause too much harm, and 1mgzip 22mwarns
if it is used. This feature will be removed in a future release of
1mgzip22m.
You can use an alias or script instead. For example, if 1mgzip 22mis in the
directory 1m/usr/bin 22myou can prepend 1m$HOME/bin 22mto your 1mPATH 22mand create an
executable script 1m$HOME/bin/gzip 22mcontaining the following:
#! /bin/sh
export PATH=/usr/bin
exec gzip -9 "$@"
1mSEE ALSO0m
1mznew22m(1), 1mzcmp22m(1), 1mzmore22m(1), 1mzforce22m(1), 1mgzexe22m(1), 1mzip22m(1), 1munzip22m(1), 1mcom-0m
1mpress22m(1)
The 1mgzip 22mfile format is specified in P. Deutsch, GZIP file format spec-
ification version 4.3, 1m<https://www.ietf.org/rfc/rfc1952.txt>22m, Internet
RFC 1952 (May 1996). The 1mzip 22mdeflation format is specified in P.
Deutsch, DEFLATE Compressed Data Format Specification version 1.3,
1m<https://www.ietf.org/rfc/rfc1951.txt>22m, Internet RFC 1951 (May 1996).
1mDIAGNOSTICS0m
Exit status is normally 0; if an error occurs, exit status is 1. If a
warning occurs, exit status is 2.
Usage: gzip [-cdfhklLnNrtvV19] [-S suffix] [file ...]
Invalid options were specified on the command line.
4mfile24m: not in gzip format
The file specified to 1mgunzip 22mhas not been compressed.
4mfile24m: Corrupt input.
Use zcat to recover some data. The compressed file has been
damaged. The data up to the point of failure can be recovered
using
zcat 4mfile24m > recover
4mfile24m: compressed with 4mxx24m bits, can only handle 4myy24m bits
1mFile 22mwas compressed (using LZW) by a program that could deal
with more bits than the decompress code on this machine. Recom-
press the file with gzip, which compresses better and uses less
memory.
4mfile24m: already has .gz suffix -- unchanged
The file is assumed to be already compressed. Rename the file
and try again.
4mfile24m already exists; do you wish to overwrite (y or n)?
Respond "y" if you want the output file to be replaced; "n" if
not.
gunzip: corrupt input
A SIGSEGV violation was detected which usually means that the
input file has been corrupted.
4mxx.x%24m Percentage of the input saved by compression.
(Relevant only for 1m-v 22mand 1m-l22m.)
-- not a regular file or directory: ignored
When the input file is not a regular file or directory, (e.g., a
symbolic link, socket, FIFO, device file), it is left unaltered.
-- has 4mxx24m other links: unchanged
The input file has links; it is left unchanged. See 1mln22m(1) for
more information. Use the 1m-f 22mflag to force compression of mul-
tiply-linked files.
1mCAVEATS0m
When writing compressed data to a tape, it is generally necessary to
pad the output with zeroes up to a block boundary. When the data is
read and the whole block is passed to 1mgunzip 22mfor decompression, 1mgunzip0m
detects that there is extra trailing garbage after the compressed data
and emits a warning by default. You can use the --quiet option to sup-
press the warning.
1mBUGS0m
In some rare cases, the --best option gives worse compression than the
default compression level (-6). On some highly redundant files, 1mcom-0m
1mpress 22mcompresses better than 1mgzip22m.
1mREPORTING BUGS0m
Report bugs to: bug-gzip@gnu.org
GNU gzip home page: <https://www.gnu.org/software/gzip/>
General help using GNU software: <https://www.gnu.org/gethelp/>
1mCOPYRIGHT NOTICE0m
Copyright (C) 1998-1999, 2001-2002, 2012, 2015-2023 Free Software Foun-
dation, Inc.
Copyright (C) 1992, 1993 Jean-loup Gailly
Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.
Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the en-
tire resulting derived work is distributed under the terms of a permis-
sion notice identical to this one.
Permission is granted to copy and distribute translations of this man-
ual into another language, under the above conditions for modified ver-
sions, except that this permission notice may be stated in a transla-
tion approved by the Foundation.
local GZIP(1)
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