Open System Services Shell and Utilities Reference Manual (G06.27+, H06.04+)

User Commands (c) compress(1)
NAME
compress - Compresses or decompresses data
SYNOPSIS
compress [-CdfFnqvV][-b maxbits][file ...]
compress [-cCdfFnqvV][-b maxbits][file]
FLAGS
-b maxbits
Specifies the maximum number of bits to use to replace common substrings in the file.
The default value for the maxbits argument is 16, with values of 9 through 16 accept-
able. First, the algorithm uses 9-bit codes 257 through 512. Then it uses 10-bit codes,
continuing until the maxbits limit is reached. (This action is not permitted with the
uncompress command.)
After the maxbits limit is reached, the compress command periodically checks the
compression ratio. If the ratio increases, compress continues to use the existing code
dictionary. However, if the compression ratio decreases, compress discards the table
of substrings and rebuilds it from the beginning. This strategy allows the algorithm to
adapt to the next block of the file.
-c Makes the compress command write to the standard output file; no input files are
changed and no .Z file is created. The nondestructive behavior of the zcat command is
identical to that of compress -cd.
-C Produces output compatible with BSD compress revision 2.0.
-d Specifies decompression (uncompressing) the specified file.
-f or -F For both compressing and decompressing files (except when this command is run in the
background under the /usr/bin/sh file), this flag suppresses the prompt as to whether an
existing file given by the file operand should be overwritten. For compressing files
only, this flag forces the compression of file even if the file does not actually get
smaller or the corresponding file.Z already exists.
-n Specifies that no header is added or expected. This flag might be useful for
decompressing old files.
-q Specifies a quiet operation. This flag is the default action; diagnostics are displayed
only if the -v flag is specified.
-v For a compression operation, prints the percentage reduction of each file. For a
decompression operation, this flag prints the percentage expansion of each file.
-V Displays the version number and any options with which the program was compiled.
DESCRIPTION
The compress command reduces the size of the specified files using adaptive Lempel-Ziv cod-
ing.
For compress, whenever possible, each file is replaced by one with the extension .Z that has the
same ownership modes, access, and modification times. Note that the filename extension used by
compress is different from that used by pack command compression (.z extension). If no files
are specified or if the file operand is a - (dash), the standard input file is compressed and written
to the standard output file. If appending the .Z extension to the filename would make the name
exceed NAME_MAX bytes, the compress command fails.
Compressed files can be restored to their original form using the uncompress or zcat command
or using the compress command with the -d flag.
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