pack(1)

pack, pcat, unpack -- compress and expand files

Synopsis

pack [-] [-f] name . . .

pcat name . . .

unpack name . . . .

Description

pack attempts to store the specified files in a compressed form. Wherever possible (and useful), each input file name is replaced by a packed file name.z with the same access modes, access and modified dates, and owner as those of name. The -f option will force packing of name. This is useful for causing an entire directory to be packed even if some of the files will not benefit. If pack is successful, name will be removed. Packed files can be restored to their original form using unpack or pcat.

pack uses Huffman (minimum redundancy) codes on a byte-by-byte basis. If the ``-'' argument is used, an internal flag is set that causes the number of times each byte is used, its relative frequency, and the code for the byte to be printed on the standard output. Additional occurrences of - in place of name will cause the internal flag to be set and reset.

The amount of compression obtained depends on the size of the input file and the character frequency distribution. Because a decoding tree forms the first part of each .z file, it is usually not worthwhile to pack files smaller than three blocks, unless the character frequency distribution is very skewed, which may occur with printer plots or pictures.

Typically, text files are reduced to 60-75% of their original size. Load modules, which use a larger character set and have a more uniform distribution of characters, show little compression, the packed versions being about 90% of the original size.

pack returns a value that is the number of files that it failed to compress.

No packing will occur if:

The file appears to be already packed.
The file has links.
The file is a directory.
The file cannot be opened.
No disk storage blocks will be saved by packing.
A file called name.z already exists.
The .z file cannot be created.
An I/O error occurred during processing.
The file size is over 16 MB.
The file name has more than NAME_MAX minus two characters: pack uses two characters to append .z to the file name.

pcat does for packed files what cat(1) does for ordinary files, except that pcat cannot be used as a filter. The specified files are unpacked and written to the standard output. Thus to view a packed file named name.z use: pcat name.z or just: pcat name. To make an unpacked copy, say nnn, of a packed file named name.z (without destroying name.z) use the command: pcat name >nnn.

pcat returns the number of files it was unable to unpack. Failure may occur if:

The file name (including the .z) has more than NAME_MAX characters.
The file cannot be opened.
The file does not appear to be the output of pack.

unpack expands files created by pack. For each file name specified in the command, a search is made for a file called name.z (or just name, if name ends in .z). If this file appears to be a packed file, it is replaced by its expanded version. The new file has the .z suffix stripped from its name, and has the same access modes, access and modification dates, and owner as those of the packed file.

unpack returns a value that is the number of files it was unable to unpack. Failure may occur for the same reasons that it may in pcat, or if a file with the unpacked name already exists.

Files

/usr/lib/locale/locale/LC_MESSAGES/uxdfm: language-specific message file (see LANG on environ(5).)

References

cat(1), compress(1)