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



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may dif-
       fer (consult the corresponding Linux manual page for details of Linux behavior), or the interface  may  not  be
       implemented on Linux.

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 collating 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  current  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 special, or  character  spe-
       cial 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, Internationalization Variables for the prece-
              dence 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_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  exam-
              ple, single-byte as opposed to multi-byte characters in arguments and input files).

       LC_MESSAGES
              Determine  the locale that should be used to affect the format and contents of diagnostic messages writ-
              ten 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 format:


              "%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, Stan-
       dard  for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifica-
       tions 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 Stan-
       dard, the original IEEE and The Open Group Standard is the referee  document.  The  original  Standard  can  be
       obtained online at http://www.opengroup.org/unix/online.html .



IEEE/The Open Group                  2003                             COMM(1P)