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gunzip

Name
     gzip, gunzip, gzcat - compress or expand files

Synopsis
     gzip [ -acdfhlLnNrtvV19 ] [-S suffix] [ name ... ]
     gunzip [ -acfhlLnNrtvV ] [-S suffix] [ name ... ]
     gzcat [ -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 exten-
     sion 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  out-
     put.   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  del-
     imited  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 gzcat. 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 exten-
     sion.  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 generally means that the standard uncompress
     does not check its input, and happily generates garbage out-
     put.   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.

     gzcat is identical to gunzip -c. (On some systems, gzcat may
     be  installed  as  ggzcat  to  preserve the original link to
     compress.) gzcat uncompresses either a list of files on  the
     command   line   or   its  standard  input  and  writes  the
     uncompressed data on standard output.  gzcat 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.   Typi-
     cally,  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 expan-
     sion 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  con-
          ventions.  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 out-
          put 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 writ-
          ten 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 stan-
          dard output: let gzcat 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:

              gzcat 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 decompress-
          ing, 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 direc-
          tories,  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.

          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 compres-
          sion).  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 indepen-
     dently, 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 invo-
     cation of the program.

Attributes
     See attributes(5) for descriptions of the  following  attri-
     butes:

     box; cbp-1 | cbp-1 l | l .  ATTRIBUTE TYPE ATTRIBUTE VALUE =
     Availability   compress/gzip = Stability Committed

See Also
     gznew(1), gzcmp(1), gzmore(1), gzforce(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/innotes/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 gzcat to recover some data.
          The compressed file has been damaged. The  data  up  to
          the point of failure can be recovered using

                gzcat 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 boun-
     dary. 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 warn-
     ing  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 com-
     mand to discover a large uncompressed file's true size:

           gzcat 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  compres-
     sion than the default compression 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 provided the copyright notice and this per-
     mission notice are preserved on all copies.

     Permission is granted to copy and distribute  modified  ver-
     sions of this manual under the conditions for verbatim copy-
     ing, provided that the entire resulting derived work is dis-
     tributed 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 condi-
     tions for modified versions,  except  that  this  permission
     notice  may be stated in a translation approved by the Foun-
     dation.

Notes
     This  software  was   built   from   source   available   at
     https://java.net/projects/solaris-userland.    The  original
     community       source       was       downloaded       from
     ftp://ftp.gnu.org/gnu/gzip/gzip-1.5.tar.gz

     Further information about this software can be found on  the
     open        source        community        website        at
     http://www.gnu.org/software/gzip/.
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