compact(1)                                             compact(1)



     NAME
          compact, uncompact, ccat - compress and uncompress files

     SYNOPSIS
          compact [name...]

          uncompact [name...]

          ccat [file...]

     DESCRIPTION
          compact compresses the named files using an adaptive Huffman
          code.  If no filenames are given, the standard input is com-
          pacted to the standard output.  compact operates as an on-
          line algorithm.  Each time a byte is read, it is encoded im-
          mediately 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 prefix a decoding tree to the
          compressed file since the encoder and the decoder start in
          the same state and stay synchronized.  Furthermore, compact
          and uncompact can operate as filters.  In particular, the
          command sequence

             | compact | uncompact |

          operates as a (very slow) no-op.

          When an argument file is given, it is compacted and the
          resulting file is placed in file.C.  file 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.

          uncompact restores the original file from a file compressed
          by compact. If no filenames are given, the standard input is
          uncompacted to the standard output.

          ccat cats the original file from a file compressed by com-
          pact, without uncompressing the file.

     RESTRICTION
          The last segment of the filename must contain fewer than
          thirteen characters to allow space for the appended .C.






     April, 1990                                                     1

     compact(1)                                             compact(1)



     FILES
          /usr/ucb/compact
          /usr/ucb/ccat
          /usr/ucb/uncompact
          *.C

     SEE ALSO
          pack(1),
          Gallager, Robert G., Variations on a Theme of Huffman,
          I.E.E.E. Transactions on Information Theory, vol. IT-24, no.
          6, November 1978, pp. 668-674.












































     2                                                     April, 1990