compress(1) manual page
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compress, uncompress, zcat - compress, uncompress files or display
expanded files
compress [-fv] [-b bits] [file...]
compress [-cfv] [-b bits] [file]
uncompress [-cfv] [ file...]
zcat [ file...]
SUNWesu
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 name would make the
name exceed {NAME_MAX}
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 takes less time to compute. The bits parameter 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.
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 produced by compress. For files produced by compress on other
systems, uncompress supports 9- to 16-bit compression (see -b).
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.
The following options are supported:
- -c
- Write 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, force 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 process is not running in the background,
prompt to verify whether an existing file.Z file should be overwritten. When
uncompressing, do not prompt for overwriting files. If the -f option is not
given, and the process is not running in the background, prompt to verify
whether an existing file should be overwritten. If the standard input is
not a terminal and -f is not given, write a diagnostic message to standard
error and exit with a status greater than 0.
- -v
- Verbose. Write to standard
error messages concerning the percentage reduction or expansion of each
file.
- -b bits
- Set 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.
The following operands
are supported:
- file
- A path name of a file to be compressed. If file is
-, or if no file is specified, the standard input will be used.
See
environ(5)
for descriptions of the following environment variables that
affect the execution of compress, uncompress, and zcat: LC_CTYPE,
LC_MESSAGES,
and NLSPATH.
The following error values are returned:
- Successful
completion.
- An error occurred.
- 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.
ln(1)
, pack(1)
- 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%
- 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.
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.
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