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User Commands compress(1)
NAME
compress, uncompress, zcat - compress, uncompress files or
display expanded files
SYNOPSIS
compress [-fv] [-b bits] [file...]
compress [-cfv] [-b bits] [file]
uncompress [-cfv] [file...]
zcat [file...]
DESCRIPTION
compress
The compress utility will attempt 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 will be
replaced by one with the extension .Z, while keeping the
same ownership modes, change times and modification times.
If appending the .Z to the file pathname would make the
pathname exceed 1023 bytes, the command will fail. If no
files are specified, the standard input will be 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 or
English is reduced by 50-60%. Compression is generally much
better than that achieved by Huffman coding (as used in
pack(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 will restore files to their original
state after they have been compressed using the compress
utility. If no files are specified, the standard input will
be uncompressed to the standard output.
This utility supports the uncompressing of any files pro-
duced by compress. For files produced by compress on other
systems, uncompress supports 9- to 16-bit compression (see
-b).
zcat
The zcat utility will write 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.
SunOS 5.10 Last change: 9 Sep 1999 1
User Commands compress(1)
OPTIONS
The following options are supported:
-c Writes to the standard output; no files are changed
and no .Z files are created. The behavior of 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 given, and the pro-
cess is not running in the background, prompts to
verify whether an existing file.Z file should be
overwritten. When uncompressing, does not prompt
for overwriting files. If the -f option is not
given, and the process is not running in the back-
ground, prompts to verify whether an existing file
should be overwritten. If the standard input is not
a terminal and -f is not given, writes a diagnostic
message to standard error and exits with a status
greater than 0.
-v Verbose. Writes to standard error messages concern-
ing the percentage reduction or expansion of each
file.
-b bits Sets the upper limit (in bits) for common substring
codes. bits must be between 9 and 16 (16 is the
default). Lowering the number of bits will result
in larger, less compressed files.
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
will be used.
SunOS 5.10 Last change: 9 Sep 1999 2
User Commands compress(1)
USAGE
See largefile(5) for the description of the behavior of
compress, 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 environment
variables that affect the execution of compress, uncompress,
and zcat: LANG, LC_ALL, LC_CTYPE, LC_MESSAGES, and
NLSPATH.
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
not specified).
>2 An error occurred.
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Availability | SUNWesu |
|_____________________________|_____________________________|
| CSI | Enabled |
|_____________________________|_____________________________|
| Interface Stability | Standard |
|_____________________________|_____________________________|
SEE ALSO
ln(1), pack(1), attributes(5), environ(5), largefile(5),
standards(5)
SunOS 5.10 Last change: 9 Sep 1999 3
User Commands compress(1)
DIAGNOSTICS
Usage: compress [-fvc] [-b maxbits] [file... ]
Invalid options were specified on the command line.
Missing maxbits
Maxbits must follow -b, or invalid maxbits, not a
numeric value.
file: not in compressed format
The file specified to uncompress has not been
compressed.
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%
SunOS 5.10 Last change: 9 Sep 1999 4
User Commands compress(1)
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.
NOTES
Although 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 5.10 Last change: 9 Sep 1999 5
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This page was generated on Wed Sep 12 11:24:31 GMT 2007
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