eral members, use unzip instead of gunzip.
The zcat command is identical to gunzip -c. (On some systems, zcat may
be installed as gzcat to preserve the original link to compress.) zcat
uncompresses either a list of files on the command line or its standard
input and writes the uncompressed data on standard output. zcat will
uncompress files that have the correct magic number whether they have a
.gz suffix or not.
The gzip command uses the Lempel-Ziv algorithm used in zip and 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 compress), Huffman coding
(as used in pack), or adaptive Huffman coding (compact).
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 ra-
tio of 0.015% for large files. The actual number of used disk blocks
almost never increases.
gzip normally 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.
OPTIONS
-a --ascii
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.
-c --stdout --to-stdout
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.
-d --decompress --uncompress
Decompress.
-f --force
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 input
data is not in a format recognized by gzip, and if the option
--stdout is also given, copy the input data without change to the
standard output: let zcat behave as cat. If -f is not given, and
when not running in the background, gzip prompts to verify
whether an existing file should be overwritten.
-h --help
Display a help screen and quit.
-k --keep
Keep (don't delete) input files during compression or decompres-
sion.
-l --list
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.
-L --license
Display the gzip license and quit.
-n --no-name
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 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
is the default when decompressing.
-N --name
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.
-q --quiet
Suppress all warnings.
-r --recursive
Travel the directory structure recursively. If any of the file
names specified on the command line are directories, gzip will
descend into the directory and compress all the files it finds
there (or decompress them in the case of gunzip ).
-S .suf --suffix .suf
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 suf-
fixes to try, when deriving an output file name from an input
file name.
--synchronous
Use synchronous output. With this option, gzip is less likely to
lose data during a system crash, but it can be considerably
slower.
-t --test
Test. Check the compressed file integrity then quit.
-v --verbose
Verbose. Display the name and percentage reduction for each file
compressed or decompressed.
-V --version
Version. Display the version number and compilation options then
quit.
-# --fast --best
Regulate the speed of compression using the specified digit #,
where -1 or --fast indicates the fastest compression method (less
compression) and -9 or --best indicates the slowest compression
method (best compression). The default compression level is -6
(that is, biased towards high compression at expense of speed).
--rsyncable
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 compression algo-
rithm 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.
ADVANCED USAGE
Multiple compressed files can be concatenated. In this case, gunzip
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.
ENVIRONMENT
The obsolescent environment variable GZIP can hold a set of default op-
tions for gzip. These options are interpreted first and can be over-
written 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 gzip warns if it is
used. This feature will be removed in a future release of gzip.
You can use an alias or script instead. For example, if gzip is in the
directory /usr/bin you can prepend $HOME/bin to your PATH and create an
executable script $HOME/bin/gzip containing the following:
#! /bin/sh
export PATH=/usr/bin
exec gzip -9 "$@"
SEE ALSO
znew(1), zcmp(1), zmore(1), zforce(1), gzexe(1), zip(1), unzip(1), com-
press(1)
The gzip file format is specified in P. Deutsch, GZIP file format speci-
fication version 4.3, , Internet
RFC 1952 (May 1996). The zip deflation format is specified in P.
Deutsch, DEFLATE Compressed Data Format Specification version 1.3,
, Internet RFC 1951 (May 1996).
DIAGNOSTICS
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.
file: not in gzip format
The file specified to gunzip has not been compressed.
file: Corrupt input.
Use zcat to recover some data. The compressed file has been dam-
aged. The data up to the point of failure can be recovered using
zcat file > recover
file: compressed with xx bits, can only handle yy bits
File was compressed (using LZW) by a program that could deal with
more bits than the decompress code on this machine. Recompress
the file with gzip, which compresses better and uses less memory.
file: already has .gz suffix -- unchanged
The file is assumed to be already compressed. Rename the file
and try again.
file 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 in-
put file has been corrupted.
xx.x% Percentage of the input saved by compression.
(Relevant only for -v and -l.)
-- 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 xx other links: unchanged
The input file has links; it is left unchanged. See ln(1) for
more information. Use the -f flag to force compression of multi-
ply-linked files.
CAVEATS
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 gunzip for decompression, gunzip de-
tects that there is extra trailing garbage after the compressed data and
emits a warning by default. You can use the --quiet option to suppress
the warning.
BUGS
In some rare cases, the --best option gives worse compression than the
default compression level (-6). On some highly redundant files, com-
press compresses better than gzip.
REPORTING BUGS
Report bugs to: bug-gzip@gnu.org
GNU gzip home page:
General help using GNU software:
COPYRIGHT NOTICE
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 pre-
served 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 manual
into another language, under the above conditions for modified versions,
except that this permission notice may be stated in a translation ap-
proved by the Foundation.
local GZIP(1)
