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[unix-history] / usr / man / cat.old / compact.0

COMPACT(1)          UNIX Programmer's Manual           COMPACT(1)



NAME
    compact, uncompact, ccat - compress and uncompress files,
    and cat them

SYNOPSIS
    compact [ -v ] [ name ... ]
    uncompact [ -v ] [ name ...  ]
    ccat [ -v ] [ file ... ]

DESCRIPTION
    _\bC_\bo_\bm_\bp_\ba_\bc_\bt compresses the named files using an adaptive Huffman
    code.  If no file names are given, the standard input is
    compacted to the standard output.  _\bC_\bo_\bm_\bp_\ba_\bc_\bt operates as an
    on-line algorithm.  Each time a byte is read, it is encoded
    immediately according to the current prefix code.  This code
    is an optimal Huffman code for the set of frequencies seen
    so far.  It is unnecessary to prepend a decoding tree to the
    compressed file since the encoder and the decoder start in
    the same state and stay synchronized.  Furthermore, _\bc_\bo_\bm_\bp_\ba_\bc_\bt
    and _\bu_\bn_\bc_\bo_\bm_\bp_\ba_\bc_\bt can operate as filters.  In particular,

         ... | compact | uncompact | ...

    operates as a (very slow) no-op.

    When an argument _\bf_\bi_\bl_\be is given, it is compacted and the
    resulting file is placed in _\bf_\bi_\bl_\be._\bC; _\bf_\bi_\bl_\be is unlinked.  The
    first two bytes of the compacted file code the fact that the
    file is compacted.  This code is used to prohibit recompac-
    tion.

    The amount of compression to be expected depends on the type
    of file being compressed.  Typical values of compression
    are: Text (38%), Pascal Source (43%), C Source (36%) and
    Binary (19%).  These values are the percentages of file
    bytes reduced.

    _\bU_\bn_\bc_\bo_\bm_\bp_\ba_\bc_\bt restores the original file from a file compressed
    by _\bc_\bo_\bm_\bp_\ba_\bc_\bt. If no file names are given, the standard input
    is uncompacted to the standard output.

    _\bC_\bc_\ba_\bt cats the original file from a file compressed by _\bc_\bo_\bm_\b-
    _\bp_\ba_\bc_\bt, without uncompressing the file (it is just a shell
    script which directs the uncompacted output to the standard
    output).

    _\bC_\bo_\bm_\bp_\ba_\bc_\bt, _\bu_\bn_\bc_\bo_\bm_\bp_\ba_\bc_\bt, and _\bc_\bc_\ba_\bt normally do their work
    silently.  If a -v flag is supplied, _\bc_\bo_\bm_\bp_\ba_\bc_\bt will report the
    compression percentage for each compacted file while _\bu_\bn_\bc_\bo_\bm_\b-
    _\bp_\ba_\bc_\bt and _\bc_\bc_\ba_\bt will print out the name of each file as
    they're uncompacted.




Printed 12/6/87          April 29, 1985                         1






COMPACT(1)          UNIX Programmer's Manual           COMPACT(1)



RESTRICTION
    The last segment of the filename must be short enough to
    allow space for the appended '.C'.

FILES
    *.C       compacted file created by compact, removed by
    uncompact

SEE ALSO
    Gallager, Robert G., `Variations on a Theme of Huffman',
    _\bI._\bE._\bE._\bE.  _\bT_\br_\ba_\bn_\bs_\ba_\bc_\bt_\bi_\bo_\bn_\bs _\bo_\bn _\bI_\bn_\bf_\bo_\br_\bm_\ba_\bt_\bi_\bo_\bn _\bT_\bh_\be_\bo_\br_\by, vol. IT-24,
    no. 6, November 1978, pp. 668 - 674.

AUTHOR
    Colin L. Mc Master








































Printed 12/6/87          April 29, 1985                         2