compact, uncompact, ccat - compact and uncompact files, and cat them
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. 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, and can operate as filters. In par‐
operates as a (very slow) no-op.
When an argument file is given, it is compacted, the resulting file is
placed in 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
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
restores the original file from a file compressed by If no file names
are specified, standard input is uncompacted and sent to the standard
writes the specified c_file, compressed by to standard output, without
uncompressing the file.
The commands recognize the following operands:
cfile Compacted file.
sfile Source file to compact or uncompact. If no file names
are given, the commands use standard input and sent to
the standard output. places the compacted file in
Access Control Lists (ACLs)
On systems that implement access control lists, when a new file is cre‐
ated 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) and aclv(5)). In JFS file systems,
files created by or do not inherit their parent directory's default ACL
entries (if any), but instead retain their original ACLs. When a file
being compacted or uncompacted resides on a JFS file system, and the
compacted or uncompacted file resides on an HFS file system (or vice
versa), as the result of or the use of or as a filter, optional ACL
entries are lost.
These commands return the following values upon completion:
0 Completed successfully.
>0 An error occurred.
On short-file-name systems, the last segment of the file name must con‐
tain 12 or fewer characters to allow space for the appended
Access control list entries of networked files are summarized (as
returned in by but not copied to the new file (see stat(2)).
was developed by Colin L. Mc Master.
compacted file created by compact, removed by uncompact
SEE ALSOcompress(1), pack(1), acl(5), aclv(5).
Gallager, Robert G., "Variations on a Theme of Huffman," vol. IT-24,
no. 6, November 1978, pp. 668 - 674.