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



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may dif-
       fer (consult the corresponding Linux manual page for details of Linux behavior), or the interface  may  not  be
       implemented on Linux.

NAME
       cmp - compare two files

SYNOPSIS
       cmp [ -l | -s ] file1 file2

DESCRIPTION
       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
       The  cmp  utility  shall  conform to the Base Definitions volume of IEEE Std 1003.1-2001, 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
       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
       The  standard  input  shall  be used only if the file1 or file2 operand refers to standard input. See the INPUT
       FILES section.

INPUT FILES
       The input files can be any file type.

ENVIRONMENT VARIABLES
       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 IEEE Std 1003.1-2001, Section 8.2, Internationalization Variables for the prece-
              dence 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 exam-
              ple, 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  writ-
              ten to standard error and informative messages written to standard output.

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


ASYNCHRONOUS EVENTS
       Default.

STDOUT
       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.

STDERR
       The  standard error shall be used only for diagnostic messages. If file1 and file2 are identical for the entire
       length of the shorter file, in the POSIX locale the following diagnostic message shall be written,  unless  the
       -s option is specified:


              "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 <new-
       line>s. Some implementations report on the number of lines in this case.

OUTPUT FILES
       None.

EXTENDED DESCRIPTION
       None.

EXIT STATUS
       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.


CONSEQUENCES OF ERRORS
       Default.

       The following sections are informative.

APPLICATION USAGE
       Although  input files to cmp can be any type, the results might not be what would be expected on character spe-
       cial device files or on file types not described by the System Interfaces volume of IEEE Std 1003.1-2001. Since
       this volume of IEEE Std 1003.1-2001 does not specify the block size used when doing input, comparisons of char-
       acter 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
       None.

RATIONALE
       The  global  language  in  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 num-
       ber. When cmp is supported in other locales, implementations are encouraged to use the word byte or its equiva-
       lent 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>s 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.

FUTURE DIRECTIONS
       None.

SEE ALSO
       comm, diff

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Stan-
       dard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base  Specifica-
       tions  Issue  6,  Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The
       Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Stan-
       dard,  the  original  IEEE  and  The  Open Group Standard is the referee document. The original Standard can be
       obtained online at http://www.opengroup.org/unix/online.html .



IEEE/The Open Group                  2003                              CMP(1P)