pack(1)

NAME

pack, pcat, unpack − compress and expand files

SYNOPSIS

pack [ − ] [ −f ] name ...

pcat name ...

unpack name ...

AVAILABILITY

SUNWesu

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 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 name has more than 12 characters;
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 last segment of the file name must contain no more than 12 characters to allow space for the appended .z extension. Directories cannot be compressed.

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 (exclusive of the .z) has more than 12 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, as well as for the following:

a file with the “unpacked” name already exists;
if the unpacked file cannot be created.

OPTIONS

−f Forces 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.

ENVIRONMENT

If any of the LC_∗ variables ( LC_CTYPE, LC_MESSAGES, LC_TIME, LC_COLLATE, LC_NUMERIC, and LC_MONETARY ) (see environ(5)) are not set in the environment, the operational behavior of pack for each corresponding locale category is determined by the value of the LANG environment variable. If LC_ALL is set, its contents are used to override both the LANG and the other LC_∗ variables. If none of the above variables is set in the environment, the "C" (U.S. style) locale determines how pack behaves.

LC_CTYPE
Determines how pack handles characters. When LC_CTYPE is set to a valid value, pack can display and handle text and filenames containing valid characters for that locale. pack can display and handle Extended Unix Code (EUC) characters where any individual character can be 1, 2, or 3 bytes wide. pack can also handle EUC characters of 1, 2, or more column widths. In the "C" locale, only characters from ISO 8859-1 are valid.

LC_MESSAGES
Determines how diagnostic and informative messages are presented. This includes the language and style of the messages, and the correct form of affirmative and negative responses. In the "C" locale, the messages are presented in the default form found in the program itself (in most cases, U.S. English).

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