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 IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
27 The following options shall be supported:
29 -l (Lowercase ell.) Write the byte number (decimal) and the differ‐
31 ing bytes (octal) for each difference.
32 -s Write nothing for differing files; return exit status only.
34
37 The following operands shall be supported:
38 file1 A pathname of the first file to be compared. If file1 is '-',
40 the standard input shall be used.
41 file2 A pathname of the second file to be compared. If file2 is '-',
43 the standard input shall be used.
44 If both file1 and file2 refer to standard input or refer to the same
47 FIFO special, block special, or character special file, the results are
48 undefined.
49
51 The standard input shall be used only if the file1 or file2 operand
52 refers to standard input. See the INPUT FILES section.
53
55 The input files can be any file type.
56
58 The following environment variables shall affect the execution of cmp:
59 LANG Provide a default value for the internationalization variables
61 that are unset or null. (See the Base Definitions volume of
62 IEEE Std 1003.1-2001, Section 8.2, Internationalization Vari‐
63 ables for the precedence of internationalization variables used
64 to determine the values of locale categories.)
65 LC_ALL If set to a non-empty string value, override the values of all
67 the other internationalization variables.
68 LC_CTYPE
70 Determine the locale for the interpretation of sequences of
71 bytes of text data as characters (for example, single-byte as
72 opposed to multi-byte characters in arguments).
73 LC_MESSAGES
75 Determine the locale that should be used to affect the format
76 and contents of diagnostic messages written to standard error
77 and informative messages written to standard output.
78 NLSPATH
80 Determine the location of message catalogs for the processing of
81 LC_MESSAGES .
82
85 Default.
86
88 In the POSIX locale, results of the comparison shall be written to
89 standard output. When no options are used, the format shall be:
90 "%s %s differ: char %d, line %d\n", file1, file2,
93 <byte number>, <line number>
94 When the -l option is used, the format shall be:
96 "%d %o %o\n", <byte number>, <differing byte>,
99 <differing byte>
100 for each byte that differs. The first <differing byte> number is from
102 file1 while the second is from file2. In both cases, <byte number>
103 shall be relative to the beginning of the file, beginning with 1.
104 No output shall be written to standard output when the -s option is
106 used.
107
109 The standard error shall be used only for diagnostic messages. If file1
110 and file2 are identical for the entire length of the shorter file, in
111 the POSIX locale the following diagnostic message shall be written,
112 unless the -s option is specified:
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>s. Some implementations
119 report on the number of lines in this case.
120
122 None.
123
125 None.
126
128 The following exit values shall be returned:
129 0 The files are identical.
131 1 The files are different; this includes the case where one file
133 is identical to the first part of the other.
134 >1 An error occurred.
136
139 Default.
140 The following sections are informative.
142
144 Although input files to cmp can be any type, the results might not be
145 what would be expected on character special device files or on file
146 types not described by the System Interfaces volume of
147 IEEE Std 1003.1-2001. Since this volume of IEEE Std 1003.1-2001 does
148 not specify the block size used when doing input, comparisons of char‐
149 acter special files need not compare all of the data in those files.
150 For files which are not text files, line numbers simply reflect the
152 presence of a <newline>, without any implication that the file is orga‐
153 nized into lines.
154
156 None.
157
159 The global language in Utility Description Defaults indicates that
160 using two mutually-exclusive options together produces unspecified
161 results. Some System V implementations consider the option usage:
162 cmp -l -s ...
165 to be an error. They also treat:
167 cmp -s -l ...
170 as if no options were specified. Both of these behaviors are considered
172 bugs, but are allowed.
173 The word char in the standard output format comes from historical
175 usage, even though it is actually a byte number. When cmp is supported
176 in other locales, implementations are encouraged to use the word byte
177 or its equivalent in another language. Users should not interpret this
178 difference to indicate that the functionality of the utility changed
179 between locales.
180 Some implementations report on the number of lines in the identical-
182 but-shorter file case. This is allowed by the inclusion of the <addi‐
183 tional info> fields in the output format. The restriction on having a
184 leading <blank> and no <newline>s is to make parsing for the filename
185 easier. It is recognized that some filenames containing white-space
186 characters make parsing difficult anyway, but the restriction does aid
187 programs used on systems where the names are predominantly well
188 behaved.
189
191 None.
192
194 comm, diff
195
197 Portions of this text are reprinted and reproduced in electronic form
198 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
199 -- Portable Operating System Interface (POSIX), The Open Group Base
200 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
201 Electrical and Electronics Engineers, Inc and The Open Group. In the
202 event of any discrepancy between this version and the original IEEE and
203 The Open Group Standard, the original IEEE and The Open Group Standard
204 is the referee document. The original Standard can be obtained online
205 at http://www.opengroup.org/unix/online.html .
206IEEE/The Open Group 2003 CMP(1P)