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

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 .