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.TH COMM "1P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual"

.SH 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.

.SH NAME

comm

\(em select or reject lines common to two files

.SH SYNOPSIS

.LP

.nf

comm \fB[\fR\(mi123\fB] \fIfile1 file2\fR

.fi

.SH DESCRIPTION

The

.IR comm

utility shall read

.IR file1

and

.IR file2 ,

which should be ordered in the current collating sequence, and produce

three text columns as output: lines only in

.IR file1 ,

lines only in

.IR file2 ,

and lines in both files.

.P

If the lines in both files are not ordered according to the collating

sequence of the current locale, the results are unspecified.

.SH OPTIONS

The

.IR comm

utility shall conform to the Base Definitions volume of POSIX.1\(hy2008,

.IR "Section 12.2" ", " "Utility Syntax Guidelines".

.P

The following options shall be supported:

.IP "\fB\(mi1\fP" 10

Suppress the output column of lines unique to

.IR file1 .

.IP "\fB\(mi2\fP" 10

Suppress the output column of lines unique to

.IR file2 .

.IP "\fB\(mi3\fP" 10

Suppress the output column of lines duplicated in

.IR file1

and

.IR file2 .

.SH OPERANDS

The following operands shall be supported:

.IP "\fIfile1\fR" 10

A pathname of the first file to be compared. If

.IR file1

is

.BR '\(mi' ,

the standard input shall be used.

.IP "\fIfile2\fR" 10

A pathname of the second file to be compared. If

.IR file2

is

.BR '\(mi' ,

the standard input shall be used.

.P

If both

.IR file1

and

.IR file2

refer to standard input or to the same FIFO special, block special, or

character special file, the results are undefined.

.SH STDIN

The standard input shall be used only if one of the

.IR file1

or

.IR file2

operands refers to standard input. See the INPUT FILES section.

.SH "INPUT FILES"

The input files shall be text files.

.SH "ENVIRONMENT VARIABLES"

The following environment variables shall affect the execution of

.IR comm :

.IP "\fILANG\fP" 10

Provide a default value for the internationalization variables that are

unset or null. (See the Base Definitions volume of POSIX.1\(hy2008,

.IR "Section 8.2" ", " "Internationalization Variables"

for the precedence of internationalization variables used to determine

the values of locale categories.)

.IP "\fILC_ALL\fP" 10

If set to a non-empty string value, override the values of all the

other internationalization variables.

.IP "\fILC_COLLATE\fP" 10

.br

Determine the locale for the collating sequence

.IR comm

expects to have been used when the input files were sorted.

.IP "\fILC_CTYPE\fP" 10

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).

.IP "\fILC_MESSAGES\fP" 10

.br

Determine the locale that should be used to affect the format and

contents of diagnostic messages written to standard error.

.IP "\fINLSPATH\fP" 10

Determine the location of message catalogs for the processing of

.IR LC_MESSAGES .

.SH "ASYNCHRONOUS EVENTS"

Default.

.SH STDOUT

The

.IR comm

utility shall produce output depending on the options selected. If the

.BR \(mi1 ,

.BR \(mi2 ,

and

.BR \(mi3

options are all selected,

.IR comm

shall write nothing to standard output.

.P

If the

.BR \(mi1

option is not selected, lines contained only in

.IR file1

shall be written using the format:

.sp

.RS 4

.nf

\fB

"%s\en", <\fIline in file1\fR>

.fi \fR

.P

.RE

.P

If the

.BR \(mi2

option is not selected, lines contained only in

.IR file2

are written using the format:

.sp

.RS 4

.nf

\fB

"%s%s\en", <\fIlead\fR>, <\fIline in file2\fR>

.fi \fR

.P

.RE

.P

where the string <\fIlead\fP> is as follows:

.IP <tab> 10

The

.BR \(mi1

option is not selected.

.IP "null\ string" 10

The

.BR \(mi1

option is selected.

.P

If the

.BR \(mi3

option is not selected, lines contained in both files shall be written

using the format:

.sp

.RS 4

.nf

\fB

"%s%s\en", <\fIlead\fR>, <\fIline in both\fR>

.fi \fR

.P

.RE

.P

where the string <\fIlead\fP> is as follows:

.IP <tab><tab> 10

Neither the

.BR \(mi1

nor the

.BR \(mi2

option is selected.

.IP <tab> 10

Exactly one of the

.BR \(mi1

and

.BR \(mi2

options is selected.

.IP "null\ string" 10

Both the

.BR \(mi1

and

.BR \(mi2

options are selected.

.P

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.

.SH STDERR

The standard error shall be used only for diagnostic messages.

.SH "OUTPUT FILES"

None.

.SH "EXTENDED DESCRIPTION"

None.

.SH "EXIT STATUS"

The following exit values shall be returned:

.IP "\00" 6

All input files were successfully output as specified.

.IP >0 6

An error occurred.

.SH "CONSEQUENCES OF ERRORS"

Default.

.LP

.IR "The following sections are informative."

.SH "APPLICATION USAGE"

If the input files are not properly presorted, the output of

.IR comm

might not be useful.

.SH EXAMPLES

If a file named

.BR xcu

contains a sorted list of the utilities in this volume of POSIX.1\(hy2008, a file named

.BR xpg3

contains a sorted list of the utilities specified in the X/Open

Portability Guide, Issue 3, and a file named

.BR svid89

contains a sorted list of the utilities in the System V Interface

Definition Third Edition:

.sp

.RS 4

.nf

\fB

comm \(mi23 xcu xpg3 | comm \(mi23 \(mi svid89

.fi \fR

.P

.RE

.P

would print a list of utilities in this volume of POSIX.1\(hy2008 not specified by either of the

other documents:

.sp

.RS 4

.nf

\fB

comm \(mi12 xcu xpg3 | comm \(mi12 \(mi svid89

.fi \fR

.P

.RE

.P

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

.sp

.RS 4

.nf

\fB

comm \(mi12 xpg3 svid89 | comm \(mi23 \(mi xcu

.fi \fR

.P

.RE

.P

would print a list of utilities specified by both XPG3 and the SVID,

but not specified in this volume of POSIX.1\(hy2008.

.SH RATIONALE

None.

.SH "FUTURE DIRECTIONS"

None.

.SH "SEE ALSO"

.IR "\fIcmp\fR\^",

.IR "\fIdiff\fR\^",

.IR "\fIsort\fR\^",

.IR "\fIuniq\fR\^"

.P

The Base Definitions volume of POSIX.1\(hy2008,

.IR "Chapter 8" ", " "Environment Variables",

.IR "Section 12.2" ", " "Utility Syntax Guidelines"

.SH 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

Electrical 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.kernel.org/doc/man-pages/reporting_bugs.html .