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CMP(1P)			   POSIX Programmer's Manual		       CMP(1P)

       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 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.

       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 dif‐
		 fering 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

       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 vari‐
		 ables that are unset or null. (See the Base Definitions  vol‐
		 ume  of POSIX.1‐2008, 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).

		 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


       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

       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  diagnos‐
       tic 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 imple‐
       mentations 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  com‐
       pare 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.


       The  global language in Section 1.4, Utility Description Defaults indi‐
       cates that  using  two  mutually-exclusive  options  together  produces
       unspecified  results. Some System V implementations consider the option

	   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> 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 Electri‐
       cal 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 such errors, see https://www.ker‐ .

IEEE/The Open Group		     2013			       CMP(1P)

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