compact(1) compact(1)
NAME
compact, uncompact, ccat - compress and uncompress files,
and cat them
SYNOPSIS
compact [ name ... ]
uncompact [ name ... ]
ccat [ file ... ]
DESCRIPTION
compact compresses the named files using an adaptive Huffman
code. If no file names 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 prepend 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,
... | 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 file names 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'.
FILES
*.C compacted file created by compact, removed by
uncompact
Page 1 CX/UX User's Reference Manual
compact(1) compact(1)
SEE ALSO
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.
AUTHOR
Colin L. Mc Master
Page 2 CX/UX User's Reference Manual