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       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.


       cmp — compare two files


       cmp [−l|−s] file1 file2


       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.


       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.


       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.


       The  standard  input  shall  be used only if the file1 or file2 operand refers to standard
       input. See the INPUT FILES section.


       The input files can be any file type.


       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

                 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.




       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.


       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.






       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.



       The following sections are informative.


       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.




       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

       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.




       comm, diff

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


       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 .

       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
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