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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 differ (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 out-
       put: 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
       POSIX.1-2008, 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  special  file,  the  results  are
       undefined.
STDIN
       The  standard input shall be used only if one of the file1 or file2 op-
       erands 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  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_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  arguments  and  input
                 files).
       LC_MESSAGES
                 Determine the locale that should be used to affect the format
                 and contents  of  diagnostic  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 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 POSIX.1-2008, 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  POSIX.1-2008  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 POSIX.1-2008.
RATIONALE
       None.
FUTURE DIRECTIONS
       None.
SEE ALSO
       cmp, diff, sort, uniq
       The Base Definitions volume of  POSIX.1-2008,  Chapter  8,  Environment
       Variables, Section 12.2, Utility Syntax Guidelines
COPYRIGHT
       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 http://www.unix.org/online.html .
       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-
       nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group                  2013                             COMM(1P)