Pack is a legacy
Unix shell
A Unix shell is a command-line Interpreter (computing), interpreter or shell (computing), shell that provides a command line user interface for Unix-like operating systems. The shell is both an interactive command language and a scripting langua ...
compression program based on
Huffman coding
In computer science and information theory, a Huffman code is a particular type of optimal prefix code that is commonly used for lossless data compression. The process of finding or using such a code proceeds by means of Huffman coding, an algori ...
.
The unpack utility will restore files to their original state after they have been compressed using the ''pack'' utility. If no files are specified, the
standard input
In computer programming, standard streams are interconnected input and output communication channels between a computer program and its environment when it begins execution. The three input/output (I/O) connections are called standard input (stdin ...
will be uncompressed to the standard output.
Although obsolete, support for packed files exists in modern compression tools such as
gzip
gzip is a file format and a software application used for file compression and decompression. The program was created by Jean-loup Gailly and Mark Adler as a free software replacement for the compress program used in early Unix systems, and in ...
and
7-zip
7-Zip is a free and open-source file archiver, a utility used to place groups of files within compressed containers known as "archives". It is developed by Igor Pavlov and was first released in 1999. 7-Zip has its own archive format called 7z, ...
.
Description of program
Files compressed by ''pack'' are typically given the
extension
Extension, extend or extended may refer to:
Mathematics
Logic or set theory
* Axiom of extensionality
* Extensible cardinal
* Extension (model theory)
* Extension (predicate logic), the set of tuples of values that satisfy the predicate
* E ...
".z" (not to be confused with the ".Z" of
compress
compress is a Unix shell compression program based on the LZW compression algorithm. Compared to more modern compression utilities such as gzip and bzip2, compress performs faster and with less memory usage, at the cost of a significantly l ...
). Files can be returned to their original state using ''unpack''. In addition, there may also be a ''pcat'' command which reads in a compressed file and sends its output to
stdout
In computer programming, standard streams are interconnected input and output communication channels between a computer program and its environment when it begins execution. The three input/output (I/O) connections are called standard input (stdin ...
.
See also
*
Data compression
In information theory, data compression, source coding, or bit-rate reduction is the process of encoding information using fewer bits than the original representation. Any particular compression is either lossy or lossless. Lossless compression ...
*
Image compression
Image compression is a type of data compression applied to digital images, to reduce their cost for storage or transmission. Algorithms may take advantage of visual perception and the statistical properties of image data to provide superior r ...
*
List of Unix commands
This is a list of Unix commands as specified by IEEE Std 1003.1-2008, which is part of the Single UNIX Specification (SUS). These commands can be found on Unix operating systems and most Unix-like operating systems.
List
See also
* List of G ...
References
External links
pack(1)in The Single UNIX Specification, Version 2, 1997, opengroup.org
in The Open Group Base Specifications Issue 6, opengroup.org – indicates pack as excluded
*
*
Pack command Manual
{{Compression Software Implementations
Data compression software
Unix archivers and compression-related utilities