GZIP linux command manual

GZIP(1)                                                                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 mod-
       ification 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 partic-
       ular, 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 trun-
       cated 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, _z or .Z 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  con-
       sistency 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 for-
       mat. To extract zip files with several members, use unzip  instead  of

       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 stan-
       dard 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 dis-
       tribution 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.

       -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

       -d --decompress --uncompress

       -f --force
              Force  compression or decompression even if the file has multi-
              ple 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 ouput: 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 for-
              mat,  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, com-
              press, 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 ).

       -S .suf --suffix .suf
              Use  suffix  .suf  instead of .gz. Any suffix can be given, but
              suffixes other than .z and .gz should be avoided to avoid  con-
              fusion  when  files  are  transferred to other systems.  A null
              suffix forces gunzip to  try decompression on all  given  files
              regardless of suffix, as in:

                  gunzip -S "" *       (*.* for MSDOS)

              Previous  versions of gzip used the .z suffix. This was changed
              to avoid a conflict with pack(1).

       -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  com-
              pression  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 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  compres-
       sion, 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  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,  , Internet RFC 1951 (May

       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

       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 unal-

       -- 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 mul-
              tiply-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 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.)

       The  gzip  format  represents  the  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  uncom-
       pressed file's true size:

             zcat file.gz | wc -c

       The  --list option reports sizes as -1 and crc as ffffffff if the com-
       pressed 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, com-
       press compresses better than gzip.

       Copyright (C) 1998, 1999, 2001 Free Software Foundation, Inc.
       Copyright (C) 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 per-
       mission notice identical to this one.

       Permission is granted to copy and distribute translations of this man-
       ual into another language, under the  above  conditions  for  modified
       versions, except that this permission notice may be stated in a trans-
       lation approved by the Foundation.

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