Provided by: gzip_1.12-1ubuntu1_amd64 bug


       gzip, gunzip, zcat - compress or expand files


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


       The  gzip  command  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.  The gzip command 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.  The  gzip
       command 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 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

       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 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.

       The  zcat  command  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.

       The  gzip  command  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
       per  32 KiB  block,  or an expansion ratio of 0.015% for large files. The actual number of
       used disk blocks almost never increases.

       gzip normally preserves the mode and modification timestamp of a file when compressing  or
       decompressing.  If you have appropriate privileges, it also preserves the file's owner and


       -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

       -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

       -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 save the seconds part  of
              the  original  modification  timestamp  if  the  original is a regular file and its
              timestamp is  at  least  1  (1970-01-01  00:00:01  UTC)  and  is  less  than  2**32
              (2106-02-07  06:28:16  UTC,  assuming  leap  seconds  are not counted); this is the
              default. When decompressing, restore from the saved  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.

              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 then quit.

       -v --verbose
              Verbose. Display the name and percentage reduction  for  each  file  compressed  or

       -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

              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.


       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, 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


       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 "$@"


       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).


       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

       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.


       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.


       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.


       Report bugs to:
       GNU gzip home page: <>
       General help using GNU software: <>


       Copyright © 1998-1999, 2001-2002, 2012, 2015-2022 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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