Provided by: gzip_1.10-0ubuntu2_amd64 bug

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 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 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 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  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.

       -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: timestamp 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 timestamp 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  timestamp  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 timestamp; this is the
              default. When decompressing, restore  the  original  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.

       --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.

       -# --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 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 "$@"

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,  <https://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, <https://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.

       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

       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, 2012, 2015-2018 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 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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