HP-UX Reference (11i v2 03/08) - 1 User Commands A-M (vol 1)

c
compact(1) compact(1)
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, stan-
dard 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 syn-
chronized. 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) and aclv(5)). In JFS file systems, files created by
compact, uncom-
pact or ccat 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 com-
pacted or uncompacted file resides on an HFS file system (or vice versa), as the result of
ccat or the use
of
compact or uncompact as a filter, optional ACL entries are lost.
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)).
AUTHOR
compact was developed by Colin L. Mc Master.
FILES
*.C compacted file created by compact, removed by uncompact
SEE ALSO
compress(1), pack(1), acl(5), aclv(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.
HP-UX 11i Version 2: August 2003 − 1 − Hewlett-Packard Company Section 1−−109