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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  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 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
       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 <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


       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 .