GZIP(1)                                                                                                                                           GZIP(1)

NAME
       gzip, gunzip, zcat - compress or expand files

SYNOPSIS
       gzip [ -acdfhlLnNrtvV19 ] [-S suffix] [ 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 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, _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 generally means that the standard uncom-
       press 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 distribu-
       tion 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.

       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 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 back-
              ground, 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 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 decompress-
              ing.

       -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 confusion 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  compres-
              sion)  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  bet-
       ter 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), 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 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 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 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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