Content-type: text/html Man page of pack

pack

Section: User Commands (1)
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NAME

pack, pcat, unpack - Compresses and expands files  

SYNOPSIS

pack [-f] [-] file[.z]...

unpack file[.z]...

pcat file[.z]...


 

STANDARDS

Interfaces documented on this reference page conform to industry standards as follows:

pack:  XPG4, XPG4-UNIX

pcat:  XPG4, XPG4-UNIX

unpack:  XPG4, XPG4-UNIX

Refer to the standards(5) reference page for more information about industry standards and associated tags.
 

OPTIONS

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.


 

OPERANDS

A pathname of a file to be compressed or uncompressed.

If the .z suffix is included on the pack command, pack searches for files without that suffix. If the .z suffix is not included, the files created have the original name with .z appended.
If the .z suffix is included on a pcat or unpack command, the command processes files with that name. If the .z suffix is not included, the command appends .z to the file name.
Files created by the unpack command will not have the .z suffix.
 

DESCRIPTION


 

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 same access modes, access and modification dates, and owner as the original file.

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 .z 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 .z file cannot be created. An I/O error occurs during processing. The file name has more than NAME_MAX-2 bytes. The file is empty.
 

The pcat command

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. [Compaq]  The file name (exclusive of the .z) has more than 12 bytes and it resides on a System V file system.
 

The unpack command

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 .z 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 file name has more than NAME_MAX-2 bytes.
 

NOTES

Both pcat and unpack operate only on files ending in .z. As a result, when you specify a file name that does not end in .z, pcat and unpack add the suffix and search the directory for a file name with that suffix. [Compaq]  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. [Compaq]  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 .z extension. [Compaq]  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.
 

EXIT STATUS

The following exit values are returned:
 

The pack command

Successful completion. [Compaq]  The number of files that could not be packed.
 

The pcat command

Successful completion. [Compaq]  The number of files that could not be unpacked.
 

The unpack command

Successful completion. [Compaq]  The number of files that could not be unpacked.
 

EXAMPLES

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 .z 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 .z suffix.
 

ENVIRONMENT VARIABLES

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.
 

SEE ALSO

Commands:  cat(1), compress(1), uncompress(1), zcat(1)

Standards:  standards(5)


 

Index

NAME
SYNOPSIS
STANDARDS
OPTIONS
OPERANDS
DESCRIPTION
The pack command
The pcat command
The unpack command
NOTES
EXIT STATUS
The pack command
The pcat command
The unpack command
EXAMPLES
ENVIRONMENT VARIABLES
SEE ALSO

This document was created by man2html, using the manual pages.
Time: 02:42:51 GMT, October 02, 2010