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# 3. Invoking `gzip`

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.
``--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: time stamp 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.
``--license'`
``-L'`
  Display the `gzip` license then quit.
``--no-name'`
``-n'`
  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.
``--name'`
``-N'`
  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.
``--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`).
``--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`.
``--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).

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