pack, pcat, unpack - Compresses and expands files
pack [-f] [-] file[.z]...
unpack file[.z]...
pcat file[.z]...
Interfaces documented on this reference page conform to
industry standards as follows:
pack: XCU5.0
pcat: XCU5.0
unpack: XCU5.0
Refer to the standards(5) reference page for more information
about industry standards and associated tags.
Displays statistics about the input files. The statistics
are calculated from a Huffman minimum redundancy code tree
built on a byte-by-byte basis. Repeating the - (dash) on
the command line toggles this function. Forces compaction
of input files.
Note
These options are applicable to the pack command only.
A pathname of a file to be compressed or uncompressed.
If the suffix is included on the pack command, pack
searches for files without that suffix. If the
suffix is not included, the files created have the
original name with appended.
If the suffix is included on a pcat or unpack command,
the command processes files with that name.
If the suffix is not included, the command appends
to the file name.
Files created by the unpack command will not have
the suffix.
The pack command
The pack command stores the specified file in a compressed
form. The input file is replaced by a packed file with a
name derived from the original file name (file.z), with
the ownership, modes, access time and modification time of
the original file preserved, if the invoking process has
appropriate privileges.
Directories cannot be compressed.
If pack cannot create a smaller file, it stops processing
and reports that it is unable to save space, unless you
specify the -f option. (The -f option forces packing to
occur even if the files cannot benefit from packing.) A
failure to save space generally happens with small files
or files with uniform character distribution.
The amount of space saved depends on the size of the input
file and the character frequency distribution. Because a
decoding tree forms the first part of each file, you will
generally not be able to save space with files smaller
than three blocks. Typically, text files are reduced 25
to 40 percent.
Object files, which use a larger character set and have a
more uniform distribution of characters, show only a 10
percent reduction when packed.
The exit value of the pack command is the number of files
that it could not pack. Packing is not done under any one
of the following conditions: The file is already packed.
The file has links. The file is a directory. The file
cannot be opened. No storage blocks are saved by packing.
This is overridden by the -f option. A file called file.z
already exists. The file cannot be created. An I/O error
occurs during processing. The file is empty.
The pcat command [Toc] [Back]
The pcat command reads the specified files, unpacks them,
and writes them to standard output.
The exit value of pcat is the number of files it was
unable to unpack. A file cannot be unpacked if any one of
the following occurs: The file cannot be opened. The file
is not a packed file. [Tru64 UNIX] The file name (exclusive
of the has more than 12 bytes and it resides on a
System V file system.
The unpack command [Toc] [Back]
The unpack command expands files created by pack. For
each file specified, unpack searches for a file called
file.z. If this file is a packed file, unpack replaces it
by its expanded version. The unpack command names the new
file name by removing the suffix from file. The new file
has the same access modes, access and modification dates,
and owner as the original packed file.
The exit value is the number of files the unpack command
was unable to unpack. A file cannot be unpacked if any
one of the following occurs: The file cannot be opened.
The file is not a packed file. A file with the unpacked
file name already exists. The unpacked file cannot be
created.
The pack, pcat and unpack utilities are marked LEGACY in
XCU Issue 5. Both pcat and unpack operate only on files
ending in you specify a file name that does not end in
pcat and unpack add the suffix and search the directory
for a file name with that suffix. [Tru64 UNIX] The
unpack command writes a warning to standard output if the
file it is unpacking has links. The new unpacked file has
a different inode than the packed file from which it was
created. However, any other files linked to the packed
file's original inode still exist and are still packed.
[Tru64 UNIX] If pack is used on files residing on a System
V file system, the file names must contain no more
than 12 bytes to allow space for the added extension.
[Tru64 UNIX] If you try to use pack on a very small file,
you might receive the following message: pack filename: No
saving -- file unchanged The pack, pcat, and unpack commands
are marked to be withdrawn from the XPG4-UNIX standard.
The compress, uncompress, and zcat commands should
be used instead.
The following exit values are returned:
The pack command [Toc] [Back]
Successful completion. [Tru64 UNIX] The number of files
that could not be packed.
The pcat command [Toc] [Back]
Successful completion. [Tru64 UNIX] The number of files
that could not be unpacked.
The unpack command [Toc] [Back]
Successful completion. [Tru64 UNIX] The number of files
that could not be unpacked.
To compress files, enter: pack chap1 chap2
This compresses the files chap1 and chap2, replacing
them with files named chap1.z and chap2.z. The
pack command displays the percent decrease in size
for each file. To display statistics about the
amount of compression done, enter: pack - chap1
- chap2
This compresses the files chap1 and chap2 and displays
statistics about chap1, but not about chap2.
The first - (dash) turns on the statistic display,
and the second turns it off. To display compressed
files, enter: pcat chap1.z chap2 | more
This displays the compressed files chap1.z and
chap2.z on the screen in expanded form, a page at a
time (more). The pcat command added the to the end
of chap2, even though it was not entered. To use a
compressed file without expanding the copy stored
on disk, enter: pcat chap1.z | grep 'Greece'
This pipes the contents of chap1.z in its expanded
form to the grep command. To unpack packed files,
enter: unpack chap1.z chap2
This expands the packed files chap1.z and chap2.z,
replacing them with files named chap1 and chap2.
You can give unpack file names either with or without
the suffix.
ENVIRONMENT VARIABLES [Toc] [Back] The following environment variables affect the execution
of pack, pcat, and unpack: Provides a default value for
the internationalization variables that are unset or null.
If LANG is unset or null, the corresponding value from the
default locale is used. If any of the internationalization
variables contain an invalid setting, the utility
behaves as if none of the variables had been defined. If
set to a non-empty string value, overrides the values of
all the other internationalization variables. Determines
the locale for the interpretation of sequences of bytes of
text data as characters (for example, single-byte as
opposed to multi-byte characters in arguments). Determines
the locale for the format and contents of diagnostic
messages written to standard error. Determines the location
of message catalogues for the processing of LC_MESSAGES.
Commands: cat(1), compress(1), uncompress(1), zcat(1)
Standards: standards(5)
pack(1)
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