pack(1)pack(1)Name
pack, pcat, unpack - compress and expand files
Syntaxpack [ - ] [ -f ] name...
pcat name...
unpack name...
Description
The command stores 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 forces packing of name. Using
this option you can cause an entire directory to be packed even if some
of the files cannot benefit from it. If is successful, name is
removed. Packed files can be restored to their original form using or
The command uses Huffman (minimum redundancy) codes on a byte-by-byte
basis. If a hyphen (-) is used as an argument, an internal flag is set
that causes the number of times each byte is used, its relative fre‐
quency, and the code for the byte to be printed on the standard output.
Additional occurrences of a hyphen (-) in place of name causes 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 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 ver‐
sions are about 90% of the original size.
The command returns a value that is the number of files that it failed
to compress.
No packing occurs if one of the following is true:
· The file appears packed.
· The file name exceeds 12 characters.
· The file has links.
· The file is a directory.
· The file cannot be opened.
· No disk storage blocks can be saved by packing.
· A file called already exists.
· The .z file cannot be created.
· An I/O error occurred during processing.
The last segment of the file name must not exceed 12 characters to
allow space for the appended .z extension. Directories cannot be com‐
pressed.
The command does for packed files what does for ordinary files, except
that can not 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 (without
destroying name.z) use the command:
pcat name >nnn
The command returns the number of files it was unable to unpack. Fail‐
ure 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.
The command expands files created by 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 modi‐
fication dates, and owner as those of the packed file.
The command returns a value that is the number of files it was unable
to unpack. Failure occurs for the same reasons that it occurs in as
well as for the following:
a file with the unpacked name already exists;
if the unpacked file cannot be created.
This command is present only for compatibility. In general, the com‐
mand runs faster and gives better compression.
See Alsocat(1), compress(1)pack(1)
