noble (1) gzip.1.gz

Provided by: gzip_1.12-1ubuntu3_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

       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 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.

       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 group.

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 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.

       --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 then quit.

       -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

       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.

REPORTING BUGS

       Report bugs to: bug-gzip@gnu.org
       GNU gzip home page: <https://www.gnu.org/software/gzip/>
       General help using GNU software: <https://www.gnu.org/gethelp/>

       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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