1COMPRESS(1P) POSIX Programmer's Manual COMPRESS(1P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
13 compress — compress data
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16 compress [−fv] [−b bits] [file...]
17 compress [−cfv] [−b bits] [file]
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21 The compress utility shall attempt to reduce the size of the named
22 files by using adaptive Lempel-Ziv coding algorithm.
23 Note: Lempel-Ziv is US Patent 4464650, issued to William Eastman,
25 Abraham Lempel, Jacob Ziv, Martin Cohn on August 7th, 1984,
26 and assigned to Sperry Corporation.
27 Lempel-Ziv-Welch compression is covered by US Patent 4558302,
29 issued to Terry A. Welch on December 10th, 1985, and assigned
30 to Sperry Corporation.
31 On systems not supporting adaptive Lempel-Ziv coding algorithm, the
33 input files shall not be changed and an error value greater than two
34 shall be returned. Except when the output is to the standard output,
35 each file shall be replaced by one with the extension .Z. If the
36 invoking process has appropriate privileges, the ownership, modes,
37 access time, and modification time of the original file are preserved.
38 If appending the .Z to the filename would make the name exceed
39 {NAME_MAX} bytes, the command shall fail. If no files are specified,
40 the standard input shall be compressed to the standard output.
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43 The compress utility shall conform to the Base Definitions volume of
44 POSIX.1‐2008, Section 12.2, Utility Syntax Guidelines.
45 The following options shall be supported:
47 −b bits Specify the maximum number of bits to use in a code. For a
49 conforming application, the bits argument shall be:
50 9 <= bits <= 14
52 The implementation may allow bits values of greater than 14.
54 The default is 14, 15, or 16.
55 −c Cause compress to write to the standard output; the input
57 file is not changed, and no .Z files are created.
58 −f Force compression of file, even if it does not actually
60 reduce the size of the file, or if the corresponding file.Z
61 file already exists. If the −f option is not given, and the
62 process is not running in the background, the user is
63 prompted as to whether an existing file.Z file should be
64 overwritten. If the response is affirmative, the existing
65 file will be overwritten.
66 −v Write the percentage reduction of each file to standard
68 error.
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71 The following operand shall be supported:
72 file A pathname of a file to be compressed.
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76 The standard input shall be used only if no file operands are speci‐
77 fied, or if a file operand is '−'.
78
80 If file operands are specified, the input files contain the data to be
81 compressed.
82
84 The following environment variables shall affect the execution of com‐
85 press:
86 LANG Provide a default value for the internationalization vari‐
88 ables that are unset or null. (See the Base Definitions vol‐
89 ume of POSIX.1‐2008, Section 8.2, Internationalization Vari‐
90 ables for the precedence of internationalization variables
91 used to determine the values of locale categories.)
92 LC_ALL If set to a non-empty string value, override the values of
94 all the other internationalization variables.
95 LC_COLLATE
97 Determine the locale for the behavior of ranges, equivalence
98 classes, and multi-character collating elements used in the
99 extended regular expression defined for the yesexpr locale
100 keyword in the LC_MESSAGES category.
101 LC_CTYPE Determine the locale for the interpretation of sequences of
103 bytes of text data as characters (for example, single-byte as
104 opposed to multi-byte characters in arguments), the behavior
105 of character classes used in the extended regular expression
106 defined for the yesexpr locale keyword in the LC_MESSAGES
107 category.
108 LC_MESSAGES
110 Determine the locale used to process affirmative responses,
111 and the locale used to affect the format and contents of
112 diagnostic messages, prompts, and the output from the −v
113 option written to standard error.
114 NLSPATH Determine the location of message catalogs for the processing
116 of LC_MESSAGES.
117
119 Default.
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122 If no file operands are specified, or if a file operand is '−', or if
123 the −c option is specified, the standard output contains the compressed
124 output.
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127 The standard error shall be used only for diagnostic and prompt mes‐
128 sages and the output from −v.
129
131 The output files shall contain the compressed output. The format of
132 compressed files is unspecified and interchange of such files between
133 implementations (including access via unspecified file sharing mecha‐
134 nisms) is not required by POSIX.1‐2008.
135
137 None.
138
140 The following exit values shall be returned:
141 0 Successful completion.
143 1 An error occurred.
145 2 One or more files were not compressed because they would have
147 increased in size (and the −f option was not specified).
148 >2 An error occurred.
150
152 The input file shall remain unmodified.
153 The following sections are informative.
155
157 The amount of compression obtained depends on the size of the input,
158 the number of bits per code, and the distribution of common substrings.
159 Typically, text such as source code or English is reduced by 50‐60%.
160 Compression is generally much better than that achieved by Huffman cod‐
161 ing or adaptive Huffman coding (compact), and takes less time to com‐
162 pute.
163 Although compress strictly follows the default actions upon receipt of
165 a signal or when an error occurs, some unexpected results may occur. In
166 some implementations it is likely that a partially compressed file is
167 left in place, alongside its uncompressed input file. Since the general
168 operation of compress is to delete the uncompressed file only after the
169 .Z file has been successfully filled, an application should always
170 carefully check the exit status of compress before arbitrarily deleting
171 files that have like-named neighbors with .Z suffixes.
172 The limit of 14 on the bits option-argument is to achieve portability
174 to all systems (within the restrictions imposed by the lack of an
175 explicit published file format). Some implementations based on 16-bit
176 architectures cannot support 15 or 16-bit uncompression.
177
179 None.
180
182 None.
183
185 None.
186
188 uncompress, zcat
189 The Base Definitions volume of POSIX.1‐2008, Chapter 8, Environment
191 Variables, Section 12.2, Utility Syntax Guidelines
192
194 Portions of this text are reprinted and reproduced in electronic form
195 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
196 -- Portable Operating System Interface (POSIX), The Open Group Base
197 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
198 cal and Electronics Engineers, Inc and The Open Group. (This is
199 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
200 event of any discrepancy between this version and the original IEEE and
201 The Open Group Standard, the original IEEE and The Open Group Standard
202 is the referee document. The original Standard can be obtained online
203 at http://www.unix.org/online.html .
204 Any typographical or formatting errors that appear in this page are
206 most likely to have been introduced during the conversion of the source
207 files to man page format. To report such errors, see https://www.ker‐
208 nel.org/doc/man-pages/reporting_bugs.html .
209IEEE/The Open Group 2013 COMPRESS(1P)