cmp(1p) — Linux manual page


CMP(1P)                   POSIX Programmer's Manual                  CMP(1P)

PROLOG         top

       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.

NAME         top

       cmp — compare two files

SYNOPSIS         top

       cmp [−l|−s] file1 file2

DESCRIPTION         top

       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.

OPTIONS         top

       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.

OPERANDS         top

       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.

STDIN         top

       The standard input shall be used only if the file1 or file2 operand
       refers to standard input. See the INPUT FILES section.

INPUT FILES         top

       The input files can be any file type.


       The following environment variables shall affect the execution of

       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

       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).

                 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

       NLSPATH   Determine the location of message catalogs for the
                 processing of LC_MESSAGES.



STDOUT         top

       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

STDERR         top

       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.

OUTPUT FILES         top




EXIT STATUS         top

       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.



       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.

EXAMPLES         top


RATIONALE         top

       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.



SEE ALSO         top

       comm(1p), diff(1p)

       The Base Definitions volume of POSIX.1‐2008, Chapter 8, Environment
       Variables, Section 12.2, Utility Syntax Guidelines

COPYRIGHT         top

       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 .

       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 .

IEEE/The Open Group                 2013                             CMP(1P)

Pages that refer to this page: comm(1p)diff(1p)