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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 |
CMP(1P) POSIX Programmer's Manual CMP(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.
cmp — compare two files
cmp [−l|−s] file1 file2
The cmp utility shall compare two files. The cmp utility shall write
no output if the files are the same. Under default options, if they
differ, it shall write to standard output the byte and line number at
which the first difference occurred. Bytes and lines shall be
numbered beginning with 1.
The cmp utility shall conform to the Base Definitions volume of
POSIX.1‐2008, Section 12.2, Utility Syntax Guidelines.
The following options shall be supported:
−l (Lowercase ell.) Write the byte number (decimal) and the
differing bytes (octal) for each difference.
−s Write nothing for differing files; return exit status only.
The following operands shall be supported:
file1 A pathname of the first file to be compared. If file1 is
'−', the standard input shall be used.
file2 A pathname of the second file to be compared. If file2 is
'−', the standard input shall be used.
If both file1 and file2 refer to standard input or refer to the same
FIFO special, block special, or character special file, the results
are undefined.
The standard input shall be used only if the file1 or file2 operand
refers to standard input. See the INPUT FILES section.
The input files can be any file type.
The following environment variables shall affect the execution of
cmp:
LANG Provide a default value for the internationalization
variables that are unset or null. (See the Base Definitions
volume of POSIX.1‐2008, 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_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).
LC_MESSAGES
Determine the locale that should be used to affect the
format and contents of diagnostic messages written to
standard error and informative messages written to standard
output.
NLSPATH Determine the location of message catalogs for the
processing of LC_MESSAGES.
Default.
In the POSIX locale, results of the comparison shall be written to
standard output. When no options are used, the format shall be:
"%s %s differ: char %d, line %d\n", file1, file2,
<byte number>, <line number>
When the −l option is used, the format shall be:
"%d %o %o\n", <byte number>, <differing byte>,
<differing byte>
for each byte that differs. The first <differing byte> number is from
file1 while the second is from file2. In both cases, <byte number>
shall be relative to the beginning of the file, beginning with 1.
No output shall be written to standard output when the −s option is
used.
The standard error shall be used only for diagnostic messages. If the
−l option is used and file1 and file2 differ in length, or if the −s
option is not used and file1 and file2 are identical for the entire
length of the shorter file, in the POSIX locale the following
diagnostic message shall be written:
"cmp: EOF on %s%s\n", <name of shorter file>, <additional info>
The <additional info> field shall either be null or a string that
starts with a <blank> and contains no <newline> characters. Some
implementations report on the number of lines in this case.
None.
None.
The following exit values shall be returned:
0 The files are identical.
1 The files are different; this includes the case where one file
is identical to the first part of the other.
>1 An error occurred.
Default.
The following sections are informative.
Although input files to cmp can be any type, the results might not be
what would be expected on character special device files or on file
types not described by the System Interfaces volume of POSIX.1‐2008.
Since this volume of POSIX.1‐2008 does not specify the block size
used when doing input, comparisons of character special files need
not compare all of the data in those files.
For files which are not text files, line numbers simply reflect the
presence of a <newline>, without any implication that the file is
organized into lines.
None.
The global language in Section 1.4, Utility Description Defaults
indicates that using two mutually-exclusive options together produces
unspecified results. Some System V implementations consider the
option usage:
cmp −l −s ...
to be an error. They also treat:
cmp −s −l ...
as if no options were specified. Both of these behaviors are
considered bugs, but are allowed.
The word char in the standard output format comes from historical
usage, even though it is actually a byte number. When cmp is
supported in other locales, implementations are encouraged to use the
word byte or its equivalent in another language. Users should not
interpret this difference to indicate that the functionality of the
utility changed between locales.
Some implementations report on the number of lines in the identical-
but-shorter file case. This is allowed by the inclusion of the
<additional info> fields in the output format. The restriction on
having a leading <blank> and no <newline> characters is to make
parsing for the filename easier. It is recognized that some filenames
containing white-space characters make parsing difficult anyway, but
the restriction does aid programs used on systems where the names are
predominantly well behaved.
None.
comm(1p), diff(1p)
The Base Definitions volume of POSIX.1‐2008, 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, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) 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.unix.org/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 2013 CMP(1P)
Pages that refer to this page: comm(1p), diff(1p)