Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages


home | help
GZIP(1)			    General Commands Manual		       GZIP(1)

       gzip, gunzip, zcat - compress or	expand files

       gzip [ -acdfhklLnNrtvV19	] [-S suffix] [	name ...  ]
       gunzip [	-acfhklLnNrtvV ] [-S suffix] [ name ...	 ]
       zcat [ -fhLV ] [	name ...  ]

       The  gzip  command reduces the size of the named	files using Lempel-Ziv
       coding (LZ77).  Whenever	possible, each file is replaced	 by  one  with
       the  extension  .gz, while keeping the same ownership modes, access and
       modification times.  (The default extension is z	for 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  gzip command 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, gzip trun-
       cates  it.  The gzip command 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  Names are not truncated on systems
       which do	not have a limit on file name length.

       By default, gzip	keeps the original file	name and timestamp in the com-
       pressed	file.  These  are used when decompressing the file with	the -N
       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 gzip -d
       or gunzip or zcat.  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 legal.

       gunzip takes 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.	 gunzip	also recognizes	the special extensions
       .tgz and	.taz as	shorthands for .tar.gz and .tar.Z respectively.	  When
       compressing, gzip uses the .tgz extension if necessary instead of trun-
       cating a	file with a .tar extension.

       gunzip can currently decompress files created by	gzip,  zip,  compress,
       compress	 -H  or	pack.  The detection of	the input format is automatic.
       When using the first two	formats, gunzip	checks a 32 bit	CRC. For  pack
       and gunzip checks the uncompressed length. The standard compress	format
       was not designed	to allow consistency checks. However gunzip  is	 some-
       times  able  to	detect	a bad .Z file. If you get an error when	uncom-
       pressing	a .Z file, do not assume that the .Z file  is  correct	simply
       because the standard uncompress does not	complain. This generally means
       that the	standard uncompress does not check its input, and happily gen-
       erates  garbage	output.	  The  SCO compress -H format (lzh compression
       method) does not	include	a CRC but also allows some consistency checks.

       Files created by	zip can	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 files to the	tar.gz format.
       To  extract a zip file with a single member, use	a command like 'gunzip
       <' or 'gunzip -S .zip'.  To extract zip files with  sev-
       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 ratio 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.

       -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

       -d --decompress --uncompress

       -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-

       -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
	      suffixes to try, when deriving an	output file name from an input
	      file name.

	      Use synchronous output.  With this option, gzip is  less	likely
	      to  lose	data during a system crash, but	it can be considerably

       -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

       -# --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  com-
	      pression	method	(best  compression).   The default compression
	      level is -6 (that	is, biased towards high	compression at expense
	      of speed).

	      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

       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


	     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,

	     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.

       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	 prob-
       lems  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

       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 "$@"

       znew(1),	zcmp(1), zmore(1), zforce(1), gzexe(1),	zip(1),	unzip(1), com-

       The gzip	file format is specified in P. Deutsch,	GZIP file format spec-
       ification 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).

       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 damaged. 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.	Recom-
	      press  the file with gzip, which compresses better and uses less

       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

       gunzip: corrupt input
	      A	SIGSEGV	violation was detected which usually  means  that  the
	      input 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.

       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
       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.

       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.

       Report bugs to:
       GNU gzip	home page: <>
       General help using GNU software:	<>

       Copyright (C) 1998-1999,	2001-2002, 2012, 2015-2022 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)


Want to link to this manual page? Use this URL:

home | help