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GZIP(1)                                        General Commands Manual                                        GZIP(1)

       gzip, gunzip, zcat - compress or expand files

       gzip [ -acdfhlLnNrtvV19 ] [-S suffix] [ name ...  ]
       gunzip [ -acfhlLnNrtvV ] [-S suffix] [ name ...  ]
       zcat [ -fhLV ] [ name ...  ]

       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  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 decom‐
       pressing 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, 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 gener‐
       ally 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

       Files created by zip can be uncompressed by gzip only if they have a single member compressed with the 'defla‐
       tion'  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.

       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 num‐
       ber 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

       -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,  con‐
              catenate 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 with‐
              out 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.

       -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

              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.

              pressing, 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  decom‐
              press 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.


       -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).

       Multiple compressed files can be concatenated. In this case, gunzip will extract  all  members  at  once.  For

             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
             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 inde‐
       pendently, 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.

       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.

       znew(1), zcmp(1), zmore(1), zforce(1), gzexe(1), zip(1), unzip(1), compress(1), pack(1), compact(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,  <
       notes/rfc1951.txt>, 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 [-cdfhlLnNrtvV19] [-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.)

       --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.)

       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 © 1998, 1999, 2001, 2002 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  verba‐
       tim  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.

                                                        local                                                 GZIP(1)