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  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  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

       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 POSIX.1‐2008, 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 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

       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  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

       None.

RATIONALE

       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.

FUTURE DIRECTIONS

       None.

SEE ALSO

       comm, diff

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

COPYRIGHT

       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
       http://www.unix.org/online.html .

       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
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                                   2013                                           CMP(1POSIX)