GZIP(1)			    General Commands Manual		       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 modi-
       fication 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 particu-
       lar, it will ignore symbolic links.

       If the compressed file name is too long for its file system, gzip trun-
       cates  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 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 time stamp 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,
       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 single member, use a command like gunzip
       <foo.zip or gunzip -S .zip foo.zip.  To extract zip files with  several
       members, use unzip instead of gunzip.

       zcat  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.

       Gzip uses the Lempel-Ziv algorithm used in zip and PKZIP.   The	amount
       of  compression	obtained depends on the size of the input and the dis-
       tribution 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 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.  gzip preserves the mode,
       ownership and timestamps of files when compressing or decompressing.

       The gzip file format is specified in P. Deutsch, GZIP file format spec-
       ification version 4.3, <ftp://ftp.isi.edu/in-notes/rfc1952.txt>, Inter-
       net RFC 1952 (May 1996).	 The zip deflation format is specified	in  P.
       Deutsch,	 DEFLATE  Compressed  Data  Format  Specification version 1.3,
       <ftp://ftp.isi.edu/in-notes/rfc1951.txt>, 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 systems. For
	      MSDOS, 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
	      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  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.

       -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: time stamp 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  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.

	      pack(1).

       -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  com-
	      pression	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 transpar-
       ently. gzip is designed as a complement 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), com-
       press(1), pack(1), compact(1)

       The gzip file format is specified in P. Deutsch, GZIP file format spec-
       ification version 4.3, <ftp://ftp.isi.edu/in-notes/rfc1952.txt>, Inter-
       net RFC 1952 (May 1996).	 The zip deflation format is specified	in  P.
       Deutsch,	 DEFLATE  Compressed  Data  Format  Specification version 1.3,
       <ftp://ftp.isi.edu/in-notes/rfc1951.txt>, 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.	Recom-
	      press 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 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
       detects that there is extra trailing 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 compression 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  com-
       pressed 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,  com-
       press compresses better than gzip.

COPYRIGHT NOTICE
       Copyright (C) 1998, 1999, 2001, 2002 Free Software Foundation, 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
       entire  resulting derived work is distributed under the terms of a per-
       mission 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.



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