compact(1)

NAME

compact, uncompact, ccat − compress and uncompress files, and cat them

SYNTAX

compact [name...]
uncompact [name...]
ccat [file...]

DESCRIPTION

The compact command compresses the named files using an adaptive Huffman code. If no file names are given, the standard input is compacted to the standard output. The compact command 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 recompaction.

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.

The uncompact command 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.

The ccat command cats the original file from a file compressed by compact, without uncompressing the file.

RESTRICTIONS

The last segment of the file name must contain fewer than thirteen characters to allow space for the appended ’.C’.

FILES