1CMP(1P) POSIX Programmer's Manual CMP(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
12 cmp — compare two files
13
15 cmp [-l|-s] file1 file2
16
18 The cmp utility shall compare two files. The cmp utility shall write no
19 output if the files are the same. Under default options, if they dif‐
20 fer, it shall write to standard output the byte and line number at
21 which the first difference occurred. Bytes and lines shall be numbered
22 beginning with 1.
23
25 The cmp utility shall conform to the Base Definitions volume of
26 POSIX.1‐2017, Section 12.2, Utility Syntax Guidelines.
27 The following options shall be supported:
29 -l (Lowercase ell.) Write the byte number (decimal) and the dif‐
31 fering bytes (octal) for each difference.
32 -s Write nothing to standard output or standard error when files
34 differ; indicate differing files through exit status only.
35 It is unspecified whether a diagnostic message is written to
36 standard error when an error is encountered; if a message is
37 not written, the error is indicated through exit status only.
38
40 The following operands shall be supported:
41 file1 A pathname of the first file to be compared. If file1 is '-',
43 the standard input shall be used.
44 file2 A pathname of the second file to be compared. If file2 is
46 '-', the standard input shall be used.
47 If both file1 and file2 refer to standard input or refer to the same
49 FIFO special, block special, or character special file, the results are
50 undefined.
51
53 The standard input shall be used only if the file1 or file2 operand
54 refers to standard input. See the INPUT FILES section.
55
57 The input files can be any file type.
58
60 The following environment variables shall affect the execution of cmp:
61 LANG Provide a default value for the internationalization vari‐
63 ables that are unset or null. (See the Base Definitions vol‐
64 ume of POSIX.1‐2017, Section 8.2, Internationalization Vari‐
65 ables for the precedence of internationalization variables
66 used to determine the values of locale categories.)
67 LC_ALL If set to a non-empty string value, override the values of
69 all the other internationalization variables.
70 LC_CTYPE Determine the locale for the interpretation of sequences of
72 bytes of text data as characters (for example, single-byte as
73 opposed to multi-byte characters in arguments).
74 LC_MESSAGES
76 Determine the locale that should be used to affect the format
77 and contents of diagnostic messages written to standard error
78 and informative messages written to standard output.
79 NLSPATH Determine the location of message catalogs for the processing
81 of LC_MESSAGES.
82
84 Default.
85
87 In the POSIX locale, results of the comparison shall be written to
88 standard output. When no options are used, the format shall be:
89 "%s %s differ: char %d, line %d\n", file1, file2,
92 <byte number>, <line number>
93 When the -l option is used, the format shall be:
95 "%d %o %o\n", <byte number>, <differing byte>,
98 <differing byte>
99 for each byte that differs. The first <differing byte> number is from
101 file1 while the second is from file2. In both cases, <byte number>
102 shall be relative to the beginning of the file, beginning with 1.
103 No output shall be written to standard output when the -s option is
105 used.
106
108 The standard error shall be used only for diagnostic messages. If the
109 -l option is used and file1 and file2 differ in length, or if the -s
110 option is not used and file1 and file2 are identical for the entire
111 length of the shorter file, in the POSIX locale the following diagnos‐
112 tic message shall be written:
113 "cmp: EOF on %s%s\n", <name of shorter file>, <additional info>
116 The <additional info> field shall either be null or a string that
118 starts with a <blank> and contains no <newline> characters. Some imple‐
119 mentations report on the number of lines in this case.
120 If the -s option is used and an error occurs, it is unspecified whether
122 a diagnostic message is written to standard error.
123
125 None.
126
128 None.
129
131 The following exit values shall be returned:
132 0 The files are identical.
134 1 The files are different; this includes the case where one file is
136 identical to the first part of the other.
137 >1 An error occurred.
139
141 Default.
142 The following sections are informative.
144
146 Although input files to cmp can be any type, the results might not be
147 what would be expected on character special device files or on file
148 types not described by the System Interfaces volume of POSIX.1‐2017.
149 Since this volume of POSIX.1‐2017 does not specify the block size used
150 when doing input, comparisons of character special files need not com‐
151 pare all of the data in those files.
152 For files which are not text files, line numbers simply reflect the
154 presence of a <newline>, without any implication that the file is orga‐
155 nized into lines.
156 Since the behavior of -s differs between implementations as to whether
158 error messages are written, the only way to ensure consistent behavior
159 of cmp when -s is used is to redirect standard error to /dev/null.
160 If error messages are wanted, instead of using -s standard output
162 should be redirected to /dev/null, and anything written to standard
163 error should be discarded if the exit status is 1. For example:
164 silent_cmp() {
167 # compare files with no output except error messages
168 message=$(cmp "$@" 2>&1 >/dev/null)
169 status=$?
170 case $status in
171 (0|1) ;;
172 (*) printf '%s\n' "$message" ;;
173 esac
174 return $status
175 }
176
178 None.
179
181 The global language in Section 1.4, Utility Description Defaults indi‐
182 cates that using two mutually-exclusive options together produces
183 unspecified results. Some System V implementations consider the option
184 usage:
185 cmp -l -s ...
188 to be an error. They also treat:
190 cmp -s -l ...
193 as if no options were specified. Both of these behaviors are considered
195 bugs, but are allowed.
196 The word char in the standard output format comes from historical
198 usage, even though it is actually a byte number. When cmp is supported
199 in other locales, implementations are encouraged to use the word byte
200 or its equivalent in another language. Users should not interpret this
201 difference to indicate that the functionality of the utility changed
202 between locales.
203 Some implementations report on the number of lines in the identical-
205 but-shorter file case. This is allowed by the inclusion of the <addi‐
206 tional info> fields in the output format. The restriction on having a
207 leading <blank> and no <newline> characters is to make parsing for the
208 filename easier. It is recognized that some filenames containing white-
209 space characters make parsing difficult anyway, but the restriction
210 does aid programs used on systems where the names are predominantly
211 well behaved.
212
214 Future versions of this standard may require that diagnostic messages
215 are written to standard error when the -s option is specified.
216
218 comm, diff
219 The Base Definitions volume of POSIX.1‐2017, Chapter 8, Environment
221 Variables, Section 12.2, Utility Syntax Guidelines
222
224 Portions of this text are reprinted and reproduced in electronic form
225 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
226 table Operating System Interface (POSIX), The Open Group Base Specifi‐
227 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
228 Electrical and Electronics Engineers, Inc and The Open Group. In the
229 event of any discrepancy between this version and the original IEEE and
230 The Open Group Standard, the original IEEE and The Open Group Standard
231 is the referee document. The original Standard can be obtained online
232 at http://www.opengroup.org/unix/online.html .
233 Any typographical or formatting errors that appear in this page are
235 most likely to have been introduced during the conversion of the source
236 files to man page format. To report such errors, see https://www.ker‐
237 nel.org/doc/man-pages/reporting_bugs.html .
238IEEE/The Open Group 2017 CMP(1P)