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Linux 2.6 - man page for cmp (linux section 1posix)

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

       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 out-
       put  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 IEEE Std 1003.1-2001, Sec-
       tion 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 IEEE Std 1003.1-2001, Section 8.2, Inter-
	      nationalization 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 interna-
	      tionalization variables.

	      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 argu-

	      Determine the locale that should be used to affect the format and contents of diag-
	      nostic messages written to standard error and informative messages written to stan-
	      dard output.

	      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 sec-
       ond 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 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



       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 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  <new-
       line>, without any implication that the file is organized into lines.


       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

       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 file-
       name  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

       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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003					   CMP(P)

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