manpagez: man pages & more
man gzcat(1)
Home | html | info | man
gzip(1)                                                                gzip(1)


       gzip, gunzip, zcat - compress or expand files


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


       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 z for MSDOS, OS/2 FAT,  Win-
       dows  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 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  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 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.


       -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

       -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  time-
              stamp;  this  is  the  default.  When decompressing, restore the
              original file name and timestamp if present. This option is use-
              ful  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.

       -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
       options 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.


       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 (C) 1998-1999, 2001-2002, 2012, 2015-2018 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
       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.

                                     local                             gzip(1)

gzip 1.9 - Generated Thu Jan 11 16:49:19 CST 2018
© 2000-2024
Individual documents may contain additional copyright information.