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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 differ (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 dif-
       fer, 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 differ-
              ing 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 Vari-
              ables 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 .

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 <newline>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 special 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 orga-
       nized 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 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 <addi-
       tional 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, Standard for Information Technology
       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
       Specifications 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 Standard, 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)