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

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

NAME
       comm - select or reject lines common to two files

SYNOPSIS
       comm [-123] file1 file2

DESCRIPTION
       The  comm  utility shall read file1 and file2, which should be ordered in the current col-
       lating sequence, and produce three text columns as output: lines only in file1, lines only
       in file2, and lines in both files.

       If the lines in both files are not ordered according to the collating sequence of the cur-
       rent locale, the results are unspecified.

OPTIONS
       The comm 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:

       -1     Suppress the output column of lines unique to file1.

       -2     Suppress the output column of lines unique to file2.

       -3     Suppress the output column of lines duplicated in file1 and file2.

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 to the same FIFO special, block spe-
       cial, or character special file, the results are undefined.

STDIN
       The standard input shall be used only if one of the file1  or  file2  operands  refers  to
       standard input. See the INPUT FILES section.

INPUT FILES
       The input files shall be text files.

ENVIRONMENT VARIABLES
       The following environment variables shall affect the execution of comm:

       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.

       LC_COLLATE

	      Determine the locale for the collating sequence comm expects to have been used when
	      the input files were sorted.

       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 argu-
	      ments and input files).

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

       NLSPATH
	      Determine the location of message catalogs for the processing of LC_MESSAGES .

ASYNCHRONOUS EVENTS
       Default.

STDOUT
       The  comm  utility  shall produce output depending on the options selected. If the -1, -2,
       and -3 options are all selected, comm shall write nothing to standard output.

       If the -1 option is not selected, lines contained only in file1 shall be written using the
       format:

	      "%s\n", <line in file1>

       If the -2 option is not selected, lines contained only in file2 are written using the for-
       mat:

	      "%s%s\n", <lead>, <line in file2>

       where the string <lead> is as follows:

       <tab>  The -1 option is not selected.

       null string
	      The -1 option is selected.

       If the -3 option is not selected, lines contained in both files shall be written using the
       format:

	      "%s%s\n", <lead>, <line in both>

       where the string <lead> is as follows:

       <tab><tab>
	      Neither the -1 nor the -2 option is selected.

       <tab>  Exactly one of the -1 and -2 options is selected.

       null string
	      Both the -1 and -2 options are selected.

       If the input files were ordered according to the collating sequence of the current locale,
       the lines written shall be in the collating sequence of the original lines.

STDERR
       The standard error shall be used only for diagnostic messages.

OUTPUT FILES
       None.

EXTENDED DESCRIPTION
       None.

EXIT STATUS
       The following exit values shall be returned:

	0     All input files were successfully output as specified.

       >0     An error occurred.

CONSEQUENCES OF ERRORS
       Default.

       The following sections are informative.

APPLICATION USAGE
       If the input files are not properly presorted, the output of comm might not be useful.

EXAMPLES
       If a file  named  xcu  contains	a  sorted  list  of  the  utilities  in  this  volume  of
       IEEE Std 1003.1-2001,  a file named xpg3 contains a sorted list of the utilities specified
       in the X/Open Portability Guide, Issue 3, and a file named svid89 contains a  sorted  list
       of the utilities in the System V Interface Definition Third Edition:

	      comm -23 xcu xpg3 | comm -23 - svid89

       would  print  a	list of utilities in this volume of IEEE Std 1003.1-2001 not specified by
       either of the other documents:

	      comm -12 xcu xpg3 | comm -12 - svid89

       would print a list of utilities specified by all three documents, and:

	      comm -12 xpg3 svid89 | comm -23 - xcu

       would print a list of utilities specified by both XPG3 and the SVID, but not specified  in
       this volume of IEEE Std 1003.1-2001.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       cmp , diff , sort , uniq

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

IEEE/The Open Group			       2003					  COMM(P)


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