(gzip.info)Invoking gzip

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3 Invoking ‘gzip’
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The format for running the ‘gzip’ program is:

     gzip OPTION ...

   ‘gzip’ supports the following options:

‘--stdout’
‘--to-stdout’
‘-c’
     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.

‘--decompress’
‘--uncompress’
‘-d’
     Decompress.

‘--force’
‘-f’
     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 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.

‘--help’
‘-h’
     Print an informative help message describing the options then quit.

‘--keep’
‘-k’
     Keep (don’t delete) input files during compression or
     decompression.

‘--list’
‘-l’
     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 (deflate,compress,lzh,pack)
          crc: the 32-bit CRC of the uncompressed data
          date & time: timestamp for the uncompressed file

     The CRC is given as ffffffff for a file not in gzip format.

     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.

     The ‘gzip’ format represents the input size modulo 2^32, so the
     uncompressed size and compression ratio are listed incorrectly for
     uncompressed files 4 GiB 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

‘--license’
‘-L’
     Display the ‘gzip’ license then quit.

‘--no-name’
‘-n’
     When compressing, do not save the original file name and timestamp
     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 timestamp if
     present (copy it from the compressed file).  This option is the
     default when decompressing.

‘--name’
‘-N’
     When compressing, always save the original file name and timestamp;
     this is the default.  When decompressing, restore the original file
     name and timestamp if present.  This option is useful on systems
     which have a limit on file name length or when the timestamp has
     been lost after a file transfer.

‘--quiet’
‘-q’
     Suppress all warning messages.

‘--recursive’
‘-r’
     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’).

‘--rsyncable’
     Cater better to the ‘rsync’ program by periodically resetting the
     internal structure of the compressed data stream.  This lets the
     ‘rsync’ program take advantage of similarities in the uncompressed
     input when synchronizing two files compressed with this flag.  The
     cost: the compressed output is usually about one percent larger.

‘--suffix SUF’
‘-S 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’.

‘--synchronous’
     Use synchronous output, by transferring output data to the output
     file’s storage device when the file system supports this.  Because
     file system data can be cached, without this option if the system
     crashes around the time a command like ‘gzip FOO’ is run the user
     might lose both ‘FOO’ and ‘FOO.gz’; this is the default with
     ‘gzip’, just as it is the default with most applications that move
     data.  When this option is used, ‘gzip’ is safer but can be
     considerably slower.

‘--test’
‘-t’
     Test.  Check the compressed file integrity.

‘--verbose’
‘-v’
     Verbose.  Display the name and percentage reduction for each file
     compressed.

‘--version’
‘-V’
     Version.  Display the version number and compilation options, then
     quit.

‘--fast’
‘--best’
‘-N’
     Regulate the speed of compression using the specified digit N,
     where ‘-1’ or ‘--fast’ indicates the fastest compression method
     (less compression) and ‘--best’ or ‘-9’ indicates the slowest
     compression method (optimal compression).  The default compression
     level is ‘-6’ (that is, biased towards high compression at expense
     of speed).