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PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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COMPRESS(1P) POSIX Programmer's Manual COMPRESS(1P)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
compress — compress data
compress [-fv] [-b bits] [file...]
compress [-cfv] [-b bits] [file]
The compress utility shall attempt to reduce the size of the named
files by using adaptive Lempel-Ziv coding algorithm.
Note: Lempel-Ziv is US Patent 4464650, issued to William Eastman,
Abraham Lempel, Jacob Ziv, Martin Cohn on August 7th, 1984,
and assigned to Sperry Corporation.
Lempel-Ziv-Welch compression is covered by US Patent
4558302, issued to Terry A. Welch on December 10th,
1985, and assigned to Sperry Corporation.
On systems not supporting adaptive Lempel-Ziv coding algorithm,
the input files shall not be changed and an error value greater
than two shall be returned. Except when the output is to the
standard output, each file shall be replaced by one with the
extension .Z. If the invoking process has appropriate privileges,
the ownership, modes, access time, and modification time of the
original file are preserved. If appending the .Z to the filename
would make the name exceed {NAME_MAX} bytes, the command shall
fail. If no files are specified, the standard input shall be
compressed to the standard output.
The compress utility shall conform to the Base Definitions volume
of POSIX.1‐2017, Section 12.2, Utility Syntax Guidelines.
The following options shall be supported:
-b bits Specify the maximum number of bits to use in a code. For
a conforming application, the bits argument shall be:
9 <= bits <= 14
The implementation may allow bits values of greater than
14. The default is 14, 15, or 16.
-c Cause compress to write to the standard output; the
input file is not changed, and no .Z files are created.
-f 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,
the user is prompted as to whether an existing file.Z
file should be overwritten. If the response is
affirmative, the existing file will be overwritten.
-v Write the percentage reduction of each file to standard
error.
The following operand shall be supported:
file A pathname of a file to be compressed.
The standard input shall be used only if no file operands are
specified, or if a file operand is '-'.
If file operands are specified, the input files contain the data
to be compressed.
The following environment variables shall affect the execution of
compress:
LANG Provide a default value for the internationalization
variables that are unset or null. (See the Base
Definitions volume of POSIX.1‐2017, Section 8.2,
Internationalization Variables for the precedence of
internationalization variables used to determine the
values of locale categories.)
LC_ALL If set to a non-empty string value, override the values
of all the other internationalization variables.
LC_COLLATE
Determine the locale for the behavior of ranges,
equivalence classes, and multi-character collating
elements used in the extended regular expression defined
for the yesexpr locale keyword in the LC_MESSAGES
category.
LC_CTYPE Determine the locale for the interpretation of sequences
of bytes of text data as characters (for example,
single-byte as opposed to multi-byte characters in
arguments), the behavior of character classes used in
the extended regular expression defined for the yesexpr
locale keyword in the LC_MESSAGES category.
LC_MESSAGES
Determine the locale used to process affirmative
responses, and the locale used to affect the format and
contents of diagnostic messages, prompts, and the output
from the -v option written to standard error.
NLSPATH Determine the location of message catalogs for the
processing of LC_MESSAGES.
Default.
If no file operands are specified, or if a file operand is '-', or
if the -c option is specified, the standard output contains the
compressed output.
The standard error shall be used only for diagnostic and prompt
messages and the output from -v.
The output files shall contain the compressed output. The format
of compressed files is unspecified and interchange of such files
between implementations (including access via unspecified file
sharing mechanisms) is not required by POSIX.1‐2008.
None.
The following exit values shall be 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.
The input file shall remain unmodified.
The following sections are informative.
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 or adaptive Huffman coding (compact),
and takes less time to compute.
Although compress strictly follows the default actions upon
receipt of a signal or when an error occurs, some unexpected
results may occur. In some implementations it is likely that a
partially compressed file is left in place, alongside its
uncompressed input file. Since the general operation of compress
is to delete the uncompressed file only after the .Z file has been
successfully filled, an application should always carefully check
the exit status of compress before arbitrarily deleting files that
have like-named neighbors with .Z suffixes.
The limit of 14 on the bits option-argument is to achieve
portability to all systems (within the restrictions imposed by the
lack of an explicit published file format). Some implementations
based on 16-bit architectures cannot support 15 or 16-bit
uncompression.
None.
None.
None.
uncompress(1p), zcat(1p)
The Base Definitions volume of POSIX.1‐2017, Chapter 8,
Environment Variables, Section 12.2, Utility Syntax Guidelines
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 by the Institute of Electrical and Electronics Engineers,
Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard,
the original IEEE and The Open Group Standard is the referee
document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page
are most likely to have been introduced during the conversion of
the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 COMPRESS(1P)
Pages that refer to this page: uncompress(1p), zcat(1p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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