gzip(1) - phpMan

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GZIP(1)                                                                GZIP(1)



NAME
       gzip, gunzip, zcat - compress or expand files

SYNOPSIS
       gzip [ -acdfhlLnNrtvV19 ] [-S suffix] [--rsyncable] [ name ...  ]
       gunzip [ -acfhlLnNrtvV ] [-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  speci-
       fied,  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  charac-
       ters,  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, _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  respec-
       tively.   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 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  con-
       version 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 compres-
       sion obtained depends on the size of the input and the distribution of common  sub-
       strings.   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  com-
       press), 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.

       The gzip file format is specified in P. Deutsch,  GZIP  file  format  specification
       version  4.3,  <ftp://ftp.isi.edu/in-notes/rfc1952.txt>,  Internet  RFC  1952  (May
       1996).  The zip deflation format is specified in  P.  Deutsch,  DEFLATE  Compressed
       Data  Format  Specification  version 1.3, <ftp://ftp.isi.edu/in-notes/rfc1951.txt>,
       Internet RFC 1951 (May 1996).


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 recog-
              nized 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.

       -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 dis-
              played:

                  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  trun-
              cated.) 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  speci-
              fied  on the command line are directories, gzip will descend into the direc-
              tory 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 con-
              fusion 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.

              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  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 com-
       pressing 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  comple-
       ment 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),
       pack(1), compact(1)

       The  gzip  file  format  is specified in P. Deutsch, GZIP file format specification
       version  4.3,  <ftp://ftp.isi.edu/in-notes/rfc1952.txt>,  Internet  RFC  1952  (May
       1996).   The  zip  deflation  format is specified in P. Deutsch, DEFLATE Compressed
       Data Format Specification  version  1.3,  <ftp://ftp.isi.edu/in-notes/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 [-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.)

       -- 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 informa-
              tion. 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 com-
       pression level (-6). On some highly redundant  files,  compress  compresses  better
       than gzip.

COPYRIGHT NOTICE
       Copyright (C) 1998, 1999, 2001, 2002 Free Software Foundation, Inc.
       Copyright (C) 1992, 1993 Jean-loup Gailly

       Permission  is  granted  to make and distribute verbatim copies of this manual pro-
       vided 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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