NAME
compact, uncompact, ccat — compact and uncompact 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,
standard input is compacted and sent 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 attach a decoding tree
in front of the compressed file
because 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, the resulting file is placed in
file.C,
and
file
is unlinked.
The first two bytes of the compacted file
code the fact that the file is compacted.
These bytes are used to prohibit recompaction.
The amount of compression to be expected depends
on the type of file being compressed.
Typical file size reduction (in percent) through compression are:
Text, 38%; Pascal Source, 43%; C Source, 36%; and Binary, 19%.
uncompact
restores the original file from a file compressed by
compact.
If no file names are specified,
standard input is uncompacted and sent to the standard output.
ccat
cats the original file from a file compressed by
compact,
without uncompressing the file.
Access Control Lists (ACLs)
On systems that implement access control lists,
when a new file is created with the effective user and group
ID
of the caller, the original file's
ACL
is copied to the new file after being altered
to reflect any change in ownership (see
acl(5)).
WARNINGS
On short-filename systems,
the last segment of the file name
must contain 12 or fewer characters
to allow space for the appended
.C.
DEPENDENCIES
NFS
Access control list entries of networked files are summarized
(as returned in
st_mode
by
stat()),
but not copied to the new file (see
stat(2)).
FILES
- *.C
compacted file created by compact, removed by uncompact
SEE ALSO
compress(1),
pack(1),
acl(5).
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
compact
was developed by Colin L. Mc Master.
