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pack(1)
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: XCU5.0
pcat: XCU5.0
unpack: XCU5.0
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.
-f Forces compaction of input files.
Note
These options are applicable to the pack command only.
OPERANDS
file[.z]
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 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 .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 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.
· [Tru64 UNIX] 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.
NOTES
The pack, pcat and unpack utilities are marked LEGACY in XCU Issue 5.
1. 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.
2. [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.
3. [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 .z extension.
4. [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
5. 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
0 Successful completion.
>0 [Tru64 UNIX] The number of files that could not be packed.
The pcat command
0 Successful completion.
>0 [Tru64 UNIX] The number of files that could not be unpacked.
The unpack command
0 Successful completion.
>0 [Tru64 UNIX] The number of files that could not be unpacked.
EXAMPLES
1. 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.
2. 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.
3. 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.
4. 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.
5. 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:
LANG
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.
LC_ALL
If set to a non-empty string value, overrides the values of all the
other internationalization variables.
LC_CTYPE
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).
LC_MESSAGES
Determines the locale for the format and contents of diagnostic
messages written to standard error.
NLSPATH
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)
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