Tribblix: manual page: unpack.1

PACK(1) User Commands PACK(1)

NAME

pack, pcat, unpack - compress and expand files

SYNOPSIS

pack [-f/] [-] file...

pcat file...

unpack [-/] file...

DESCRIPTION

pack
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 is removed.

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 can 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.

The pack utility returns a value that is the number of files that it
failed to compress. If that number exceeds 255, 255 is returned.

No packing occurs if:

o the file appears to be already packed

o the file name is too long to add the .z suffix

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 are 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 be short enough to allow space
for the appended .z extension. Directories cannot be compressed.

pcat
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 can
occur if:

o the file cannot be opened;

o the file does not appear to be the output of pack.

unpack
The unpack command expands files created by pack. For each file
specified 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 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 can occur for the same reasons that it can in pcat,
as well as for the following:

o a file with the unpacked name already exists;

o the unpacked file cannot be created.

OPTIONS

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 do not
benefit. Packed files can be restored to their original form
using unpack or pcat.

The following options are supported by pack and unpack:

-/
When packing or unpacking, copies any ACL and extended system
attributes associated with the source file to the target file.
If an ACL or extended system attributes cannot be copied, the
original file is retained, a diagnostic message is written to
stderr, and the final exit status is non-zero.

OPERANDS

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 causes the internal flag to be set and reset.

USAGE

See largefile(7) for the description of the behavior of pack, pcat,
and unpack when encountering files greater than or equal to 2 Gbyte
(2^31 bytes).

EXAMPLES

Example 1: Viewing a Packed File

To view a packed file named file.z use:

example% pcat file.z

or just:

example% pcat file

Example 2: Making an Unpacked Copy:

To make an unpacked copy, say nnn, of a packed file named file.z
(without destroying file.z) use the command:

example% pcat file >nnn

ENVIRONMENT VARIABLES

See environ(7) for descriptions of the following environment
variables that affect the execution of pack, pcat, and unpack:
LC_CTYPE, LC_MESSAGES, and NLSPATH.

EXIT STATUS

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. If the number of failures exceeds 255,
then 255 is returned.

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:

+---------------+-----------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+-----------------+
|CSI | Enabled |
+---------------+-----------------+