Info Catalog gzip: Advanced usage gzip: Top gzip: Tapes

gzip: Environment

 
 5 Environment
 *************
 
 The obsolescent 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.  As this can cause
 problems when using scripts, this feature is supported only for options
 that are reasonably likely to not cause too much harm, and ‘gzip’ warns
 if it is used.  This feature will be removed in a future release of
 ‘gzip’.
 
    You can use an alias or script instead.  For example, if ‘gzip’ is in
 the directory ‘/usr/bin’ you can prepend ‘$HOME/bin’ to your ‘PATH’ and
 create an executable script ‘$HOME/bin/gzip’ containing the following:
 
      #! /bin/sh
      export PATH=/usr/bin
      exec gzip -9 "$@"
 
    The following environment variables are applicable only when using
 ‘gzip’ on IBM Z mainframes supporting DEFLATE COMPRESSION CALL
 instruction:
 
 ‘DFLTCC’
      Whether DEFLATE COMPRESSION CALL should be used.  Default value is
      ‘1’.  Set this to ‘0’ to disable DEFLATE COMPRESSION CALL
      altogether.
 
 ‘DFLTCC_LEVEL_MASK’
      Compression levels on which DEFLATE COMPRESSION CALL should be
      used.  Represented as a bit mask in decimal or hexadecimal form,
      where each bit corresponds to a compression level.  Default value
      is ‘2’, which means level 1 only.  In order to make use of DEFLATE
      COMPRESSION CALL by default, that is, on levels 1-6, set this to
      ‘0x7e’.
 
 ‘DFLTCC_BLOCK_SIZE’
      Size of deflate blocks produced by DEFLATE COMPRESSION CALL in
      bytes in decimal or hexadecimal form.  Default value is ‘1048576’
      (1 megabyte).  When using DEFLATE COMPRESSION CALL to compress a
      file containing heterogeneous data (e.g.  a ‘.tar’ archive
      containing text and binary files), setting this to a smaller value
      may improve compression ratio.
 
 ‘DFLTCC_FIRST_FHT_BLOCK_SIZE’
      Size of the first fixed deflate block produced by DEFLATE
      COMPRESSION CALL in bytes in decimal or hexadecimal form.  Default
      value is ‘4096’ (4 kilobytes).  When using DEFLATE COMPRESSION CALL
      to compress a small file, setting this to a larger value may
      improve compression ratio.
 
 ‘DFLTCC_RIBM’
      Value of "Reserved for IBM" field of DEFLATE COMPRESSION CALL
      parameter block.  Default value is ‘0’.
 
 ‘SOURCE_DATE_EPOCH’
      If set to any value, disables compression with DEFLATE COMPRESSION
      CALL. This variable is normally set during reproducible builds, and
      in such cases DEFLATE COMPRESSION CALL needs to be disabled,
      because its output may be not reproducible.
 

Info Catalog gzip: Advanced usage gzip: Top gzip: Tapes