pack(1)
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pack, pcat, unpack Command
compress and expand files
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SYNTAX
pack [ - ] [ -f ] name ...
pcat name ...
unpack name ...
DESCRIPTION
Pack tries 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 (DG/UX
only) will force packing of name. This is useful for packing an
entire directory 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
prints the number of times each byte is used, its relative
frequency, and the code for the byte on the standard output.
Additional occurrences of - in place of name will set and reset
the internal flag.
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 are 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;
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pack(1)
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; or
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 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 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; or
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 as for pcat, if a file with the
unpacked name already exists, or if the unpacked file cannot be
created.
SEE ALSO
cat(1).
DG/UX 4.00 Page 2
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