compact(1)                                             compact(1)



NAME
     compact, uncompact, ccat - compress and uncompress files

SYNOPSIS
     compact [name]...

     uncompact [name]...

     ccat [file]...

ARGUMENTS
     file Specifies the file to be displayed.  If this argument
          is not given, the standard input is compacted or
          uncompacted to the standard output.

     name Specifies the files to be compacted or uncompacted.

DESCRIPTION
     compact compresses the named files using an adaptive Huffman
     code.  If no filenames are given, the standard input is
     compacted to the standard output.  compact 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 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 name 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
     recompaction.

     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.

     ccat cats the original file from a file compressed by
     compact, without uncompressing the file.




January 1992                                                    1

compact(1)                                             compact(1)



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

FILES
     /usr/ucb/compact
          Executable file
     /usr/ucb/uncompact
          Executable file
     /usr/ucb/ccat
          Executable file
     *.C  Compacted files

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                                                    January 1992