pack(1) User Commands pack(1)
pack, pcat, unpack - compress and expand files
pack [-f] [-] file...
The pack command attempts to store the specified files in a compressed
form. Wherever possible (and useful), each input file file is replaced
by a packed file file.z with the same access modes, access and modified
dates, and owner as those of file. If pack is successful, file will be
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 pic-
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 being about 90% of the original size.
pack returns a value that is the number of files that it failed to com-
No packing will occur if:
o the file appears to be already packed
o the file name has more than 14 - 2 bytes
o the file has links
o the file is a directory
o the file cannot be opened
o the file is empty
o no disk storage blocks will be saved by packing
o a file called file.z already exists
o the .z file cannot be created
o an I/O error occurred during processing.
The last segment of the file name must contain no more than 14 - 2
bytes to allow space for the appended .z extension. Directories cannot
The pcat command 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.
pcat returns the number of files it was unable to unpack. Failure may
o the file cannot be opened;
o the file does not appear to be the output of pack.
The unpack command expands files created by pack. For each file speci-
fied in the command, a search is made for a file called file.z (or just
file, if file 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.
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:
o a file with the ``unpacked'' name already exists;
o the unpacked file cannot be created.
o the filename (excluding the .z extension) has more than 14 bytes.
The following options are supported by pack:
-f Forces packing of file. This is useful for causing an entire
directory to be packed even if some of the files will not ben-
efit. Packed files can be restored to their original form
using unpack or pcat.
The following operands are supported:
file A path name of a file to be packed, unpacked, or
pcated; file can include or omit the .z suffix.
- 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 file will cause the inter-
nal flag to be set and reset.
See largefile(5) for the description of the behavior of pack, pcat, and
unpack when encountering files greater than or equal to 2 Gbyte ( 2**31
Example 1: Viewing a Packed File
To view a packed file named file.z use:
example% pcat file.z
example% pcat file
Example 2: Making and Unpacked Copy:
To make an unpacked copy, say nnn, of a packed file named file.z (with-
out destroying file.z) use the command:
example% pcat file >>nnn
See environ(5) for descriptions of the following environment variables
that affect the execution of pack, pcat, and unpack: LC_CTYPE, LC_MES-
SAGES, and NLSPATH.
The following exit values are returned:
0 Successful completion.
>>0 An error occurred. The number of files the command failed to
pack/unpack is returned.
See attributes(5) for descriptions of the following attributes:
tab() allbox; cw(2.750000i)| cw(2.750000i) lw(2.750000i)|
lw(2.750000i). ATTRIBUTE TYPEATTRIBUTE VALUE AvailabilitySUNWesu
cat(1), compress(1), zcat(1), attributes(5), environ(5), largefile( 5)
SunOS 5.10 20 Dec 1996 pack(1)