GZIP(1) 														   GZIP(1)



NAME
       gzip, gunzip, zcat - compress or expand files

SYNOPSIS
       gzip [ -acdfhlLnNrtvV19 ] [-S suffix] [ name ...  ]
       gunzip [ -acfhlLnNrtvV ] [-S suffix] [ name ...	]
       zcat [ -fhLV ] [ name ...  ]

DESCRIPTION
       Gzip  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
       -gz  for  VMS,  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.  Gzip will only attempt to compress regular files.	In particular,	it
       will ignore symbolic links.

       If  the	compressed file name is too long for its file system, gzip truncates it.  Gzip 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, gzip keeps the original file name and timestamp in the compressed 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 time stamp was not pre‐
       served 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 com‐
       pressing, gzip uses the .tgz extension if necessary instead of truncating 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 for‐
       mat  is	automatic.  When using the first two formats, gunzip checks a 32 bit CRC. For pack, gunzip checks the uncompressed
       length. The standard compress format was not designed to allow consistency checks. However  gunzip  is  sometimes  able	to
       detect  a  bad  .Z file. If you get an error when uncompressing 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  generates 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 tar.zip files to the tar.gz format.  To extract a zip file with a sin‐
       gle member, use a command like gunzip ,  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).


OPTIONS
       -a --ascii
	      Ascii  text  mode: convert end-of-lines using local conventions. This option is supported only on some non-Unix sys‐
	      tems. For MSDOS, CR LF is converted to LF when compressing, and LF is converted 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  con‐
	      sists  of  a sequence 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  compressed  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 exist‐
	      ing file should be overwritten.

       -h --help
	      Display a help screen and quit.

       -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 format, such as compressed .Z files. To  get  the  uncom‐
	      pressed 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: time stamp for the uncompressed file

	      The compression methods currently supported are deflate, compress, 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 time  stamp;  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 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.


       -t --test
	      Test. Check the compressed file integrity.

       -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).

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 transparently. gzip is designed as a comple‐
       ment to tar, not as a replacement.

ENVIRONMENT
       The environment variable GZIP can hold a set of default options for gzip.  These options are interpreted first and  can	be
       overwritten by explicit command line parameters. For example:
	     for sh:	GZIP="-8v --name"; export GZIP
	     for csh:	setenv GZIP "-8v --name"
	     for MSDOS: set GZIP=-8v --name

       On Vax/VMS, the name of the environment variable is GZIP_OPT, to avoid a conflict with the symbol set for invocation of the
       program.

SEE ALSO
       znew(1), zcmp(1), zmore(1), zforce(1), gzexe(1), zip(1), unzip(1), compress(1)

       The   gzip   file   format   is	 specified   in   P.   Deutsch,   GZIP	 file	format	  specification    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 [-cdfhlLnNrtvV19] [-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.	Recompress the file with gzip, which compresses better and uses less memory.

       file: already has .gz suffix -- no change
	      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 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 compres‐
	      sion of multiply-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 detects that there is extra trail‐
       ing garbage after the compressed data and emits a warning by default. You have to use the --quiet option  to  suppress  the
       warning. This option can be set in the GZIP environment variable as in:
	 for sh:  GZIP="-q"  tar -xfz --block-compress /dev/rst0
	 for csh: (setenv GZIP -q; tar -xfz --block-compr /dev/rst0

       In the above example, gzip is invoked implicitly by the -z option of GNU tar. Make sure that the same block size (-b option
       of tar) is used for reading and writing compressed data on tapes.  (This example assumes you are using the GNU  version	of
       tar.)

BUGS
       The  gzip  format represents the input size modulo 2^32, so the --list option reports incorrect uncompressed sizes and com‐
       pression ratios for uncompressed files 4 GB and larger.	To work around this problem, you can use the following command	to
       discover a large uncompressed file's true size:

	     zcat file.gz | wc -c

       The --list option reports sizes as -1 and crc as ffffffff if the compressed file is on a non seekable media.

       In  some  rare  cases,  the  --best  option gives worse compression than the default compression level (-6). On some highly
       redundant files, compress compresses better than gzip.

COPYRIGHT NOTICE
       Copyright © 1998, 1999, 2001, 2002 Free Software Foundation, Inc.
       Copyright © 1992, 1993 Jean-loup Gailly

       Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this  permis‐
       sion 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 entire resulting derived work is distributed under the terms of a permission  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 approved by the Foundation.



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