User Commands compress(1)
NAME
compress, uncompress, zcat - compress, uncompress files or
display expanded filesSYNOPSIS
compress [-fv/] [-b bits] [file]...
compress -c [-fv] [-b bits] [file]
uncompress [-fv] [-c | -/] [file]...
zcat [file]...DESCRIPTION
compress
The compress utility attempts to reduce the size of the
named files by using adaptive Lempel-Ziv coding. Except when
the output is to the standard output, each file is replacedby one with the extension .Z, while keeping the same owner-
ship modes, change times and modification times, ACLs, andextended attributes. The compress utility also attempt to
set the owner and group of file.z to the owner and group of file, but does not fail if this cannot be done. If appending the .Z to the file pathname would make the pathname exceed 1023 bytes, the command fails. If no files are specified,the standard input is compressed to the standard output.
The amount of compression obtained depends on the size of
the input, the number of bits per code, and the distribution of common substrings. Typically, text such as source code orEnglish is reduced by 50-60%. Compression is generally much
better than that achieved by Huffman coding (as used inpack(1)) and it takes less time to compute. The bits parame-
ter specified during compression is encoded within the
compressed file, along with a magic number to ensure that
neither decompression of random data nor recompression of
compressed data is subsequently allowed.
uncompress
The uncompress utility restores files to their original
state after they have been compressed using the compress
utility. If no files are specified, the standard input isuncompressed to the standard output.
This utility supports the uncompressing of any files pro-
duced by compress. For files produced by compress on other
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User Commands compress(1)
systems, uncompress supports 9- to 16-bit compression (see
-b).
zcatThe zcat utility writes to standard output the uncompressed
form of files that have been compressed using compress. It
is the equivalent of uncompress-c. Input files are not
affected. OPTIONS The following options are supported:-b bits Sets the upper limit (in bits) for common sub-
string codes. bits must be between 9 and 16 (16 is the default). Lowering the number of bitsresult in larger, less compressed files.
-c Writes to the standard output; no files are
changed and no .Z files are created. The behaviorof zcat is identical to that of `uncompress -c'.
-f When compressing, forces compression of file,
even if it does not actually reduce the size of the file, or if the corresponding file.Z file already exists.If the -f option is not specified, and the pro-
cess is not running in the background, prompts to verify whether an existing file should be overwritten. If the response is affirmative, theexisting file is overwritten. When uncompressing,
does not prompt for overwriting files. If the -f
option is not specified, and the process is not running in the background, prompts to verify whether an existing file should be overwritten.If the standard input is not a terminal and -f is
not specified, writes a diagnostic message to standard error and exits with a status greater than 0.-v Verbose. Writes to standard error messages con-
cerning the percentage reduction or expansion of each file.-/ When compressing or decompressing, copies any
extended system attributes associated with the source file to the target file and copies any extended system attributes associated withSunOS 5.11 Last change: 13 Mar 2008 2
User Commands compress(1)
extended attributes of the source file to the corresponding extended attributes associated withthe target file. If any extended system attri-
butes cannot be copied, the original file is retained, a diagnostic is written to stderr, andthe final exit status is non-zero.
OPERANDS The following operand is supported:file A path name of a file to be compressed by compress,
uncompressed by uncompress, or whose uncompressed
form is written to standard out by zcat. If file is-, or if no file is specified, the standard input is
used.USAGE
See largefile(5) for the description of the behavior ofcompress, uncompress, and zcat when encountering files
greater than or equal to 2 Gbyte ( 2^31 bytes). ENVIRONMENT VARIABLES See environ(5) for descriptions of the following environmentvariables that affect the execution of compress, uncompress,
and zcat: LANG, LC_ALL, LC_COLLATE, LC_CTYPE, LC_MESSAGES,
and NLSPATH.Affirmative responses are processed using the extended regu-
lar expression defined for the yesexpr keyword in theLC_MESSAGES category of the user's locale. The locale speci-
fied in the LC_COLLATE category defines the behavior of
ranges, equivalence classes, and multi-character collating
elements used in the expression defined for yesexpr. Thelocale specified in LC_CTYPE determines the locale for
interpretation of sequences of bytes of text data a charac-
ters, the behavior of character classes used in the expres-
sion defined for the yesexpr. See locale(5). EXIT STATUS The following error values are returned: 0 Successful completion. 1 An error occurred.2 One or more files were not compressed because they
would have increased in size (and the -f option was
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User Commands compress(1)
not specified). >2 An error occurred.ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:________________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_________________________________|
| Availability | system/extended-system-utilities|
|_____________________________|_________________________________|
| CSI | Enabled ||_____________________________|_________________________________|
| Interface Stability | Committed ||_____________________________|_________________________________|
| Standard | See standards(5). ||_____________________________|_________________________________|
SEE ALSO
ln(1), pack(1), fgetattr(3C), fsetattr(3C), attributes(5), environ(5), largefile(5), locale(5), standards(5) DIAGNOSTICSUsage: compress [-fv/] [-b bits] [file... ]
compress c [-fv] [-b bits] [file... ]
Invalid options were specified on the command line.Usage: uncompress [-fv] [-c | -/] [file]...
Invalid options were specified on the command line. Missing maxbitsMaxbits must follow -b, or invalid maxbits, not a
numeric value.file: not in compressed format
The file specified to uncompress has not been
compressed.
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User Commands compress(1)
file: compressed with xxbits, can only handle yybits
file was compressed by a program that could deal with
more bits than the compress code on this machine.
Recompress the file with smaller bits.
file: already has .Z suffix -- no change
The file is assumed to be already compressed. Rename the
file and try again. file: already exists; do you wish to overwrite (y or n)? Respond y if you want the output file to be replaced; n if not.uncompress: corrupt input
A SIGSEGV violation was detected, which usually means that the input file is corrupted.Compression:xx.xx%
Percentage of the input saved by compression. (Relevant
only for -v.)
- - not a regular file: unchanged
When the input file is not a regular file, (such as a directory), it is left unaltered.- - has xx other links: unchanged
The input file has links; it is left unchanged. See ln(1) for more information.- - file unchanged
No savings are achieved by compression. The input
remains uncompressed.
- -filename too long to tack on .Z
The path name is too long to append the .Z suffix.SunOS 5.11 Last change: 13 Mar 2008 5
User Commands compress(1)
- -cannot preserve extended attributes. file unchanged
Extended system attributes could not be copied. NOTESAlthough compressed files are compatible between machines
with large memory, -b 12 should be used for file transfer to
architectures with a small process data space (64KB or less).compress should be more flexible about the existence of the
.Z suffix.SunOS 5.11 Last change: 13 Mar 2008 6