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 NAME
      gzip, gunzip, zcat - compress or expand files

 SYNOPSIS
      gzip [ -acdfhklLnNrtvV19 ] [-S suffix] [ name ... ]
      gunzip [ -acfhklLnNrtvV ] [-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 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 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 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
      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



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      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
      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 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.

 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
           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 consists of a
           sequence of independently compressed members. To obtain better
           compression, concatenate all input files before compressing them.

      -d --decompress --uncompress
           Decompress.





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      -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 existing file should be overwritten.

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

      -k --keep
           Keep (don't delete) input files during compression or
           decompression.

      -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 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,
           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.



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      -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.

      --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.

      -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.




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      -# --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
           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 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



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      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 complement to tar, not as a
      replacement.

 ENVIRONMENT
      The obsolescent 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.  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 "$@"

      On VMS, the name of the obsolescent 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, <http://www.ietf.org/rfc/rfc1952.txt>,
      Internet RFC 1952 (May 1996).  The zip deflation format is specified
      in P. Deutsch, DEFLATE Compressed Data Format Specification version
      1.3, <http://www.ietf.org/rfc/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 [-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.




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      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 -- 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
           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
           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 trailing garbage after the compressed data
      and emits a warning by default.  You can use the --quiet option to
      suppress the warning.

 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



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      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 c 1998-1999, 2001-2002, 2012, 2015-2016 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
      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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