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.
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
.
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.
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.
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
COMM (P)
2003
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