4BSD/usr/man/man1/compact.1

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.TH COMPACT 1
.UC 4
.SH NAME
compact, uncompact, ccat \- compress and uncompress files, and cat them
.SH SYNOPSIS
.B compact
[ name ... ]
.br
.B uncompact
[
name ...
]
.br
.B ccat
[ file ... ]
.SH DESCRIPTION
.I Compact
compresses the named files using an adaptive
Huffman code.  If no file names are given,
then the standard input is compacted to
the standard output.
.I 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,
.I compact
and
.I uncompact
can operate as filters.
In particular,
.sp
	... | compact | uncompact | ...
.br
.sp
operates as a (very slow) no-op.
.PP
When an argument
.I file
is given,
it is compacted
and the resulting file is placed in
.I file.C;
.I 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.
.PP
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.
.PP
.I Uncompact
restores the original file from
a file compressed by
.I compact.
If no file names are given,
then the standard input is uncompacted to
the standard output.
.PP
.I Ccat
cats the original file from
a file compressed by
.I compact,
without uncompressing the file.
.SH RESTRICTION
The last segment of the filename must
contain fewer than thirteen characters
to allow space for the appended '.C'.
.SH FILES
.ta 1i
*.C	compacted file created by compact, removed by uncompact
.SH "SEE ALSO"
Gallager, Robert G., "Variations on a Theme of Huffman",
.I "I.E.E.E.  Transactions on Information Theory,"
vol. IT-24, no. 6, November 1978, pp. 668 - 674.
.SH AUTHOR
Colin L. Mc Master
.SH BUGS