Provided by: gzip_1.6-5ubuntu2_amd64 bug

NAME

       gzip, gunzip, zcat - compress or expand files

SYNOPSIS

       gzip [ -acdfhklLnNrtvV19 ] [--rsyncable] [-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  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: 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.

       -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 ).

       --rsyncable
              While  compressing,  synchronize  the output occasionally based on the input.  This
              increases size by less than 1 percent most  cases,  but  means  that  the  rsync(1)
              program  can  take  advantage  of  similarities  in  the  uncompressed  input  when
              synchronizing two  files  compressed  with  this  flag.   gunzip  cannot  tell  the
              difference  between  a  compressed  file  created with this option, and one created
              without it.

       -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.

       -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).

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 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. For
       example:
             for sh:    GZIP="-8v --name"; export GZIP
             for csh:   setenv GZIP "-8v --name"
             for MSDOS: set GZIP=-8v --name

       On Vax/VMS, the name of the 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.

       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 -- no change
              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 have to  use  the  --quiet  option  to
       suppress the warning. This option can be set in the GZIP environment variable as in:
         for sh:  GZIP="-q"  tar -xfz --block-compress /dev/rst0
         for csh: (setenv GZIP -q; tar -xfz --block-compr /dev/rst0

       In  the  above  example, gzip is invoked implicitly by the -z option of GNU tar. Make sure
       that the same block size (-b option of tar) is used for  reading  and  writing  compressed
       data on tapes.  (This example assumes you are using the GNU version of tar.)

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 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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