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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
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, Internationalization 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 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 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
original Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 COMM(P)