compress(1) User Commands compress(1)
compress, uncompress, zcat - compress, uncompress files or display
compress [-fv] [-b bits] [file...]
compress [-cfv] [-b bits] [file]
uncompress [-cfv] [file...]
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 modifica-
tion 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 out-
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 cod-
ing (as used in pack(1)) and it 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
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 out-
This utility supports the uncompressing of any files produced by com-
press. For files produced by compress on other systems, uncompress sup-
ports 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 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 corre-
sponding file.Z file already exists. If the -f option is not
given, and the process is not running in the background,
prompts to verify whether an existing file.Z file should be
overwritten. When uncompressing, does not prompt for over-
writing files. If the -f option is not given, 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 given, writes a diagnostic mes-
sage to standard error and exits with a status greater than 0.
-v Verbose. Writes to standard error messages concerning the per-
centage 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
The following operand is supported:
file A path name of a file to be compressed by compress, uncom-
pressed by uncompress, or whose uncompressed form is written
to standard out by zcat. If file is -, or if no file is speci-
fied, the standard input will be used.
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).
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.
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.
See attributes(5) for descriptions of the following attributes:
tab() allbox; cw(2.750000i)| cw(2.750000i) lw(2.750000i)|
lw(2.750000i). ATTRIBUTE TYPEATTRIBUTE VALUE AvailabilitySUNWesu
CSIEnabled Interface StabilityStandard
ln(1), pack(1), attributes(5), environ(5), largefile(5), standards(5)
Usage: compress [-fvc] [-b maxbits] [file... ]
Invalid options were specified on the command line.
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
file: already has .Z suffix -- no change
The file is assumed to be already compressed. Rename the file and
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.
Percentage of the input saved by compression. (Relevant only for
- - 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
- - file unchanged
No savings are achieved by compression. The input remains uncom-
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.
SunOS 5.10 9 Sep 1999 compress(1)