comm.1

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.\"     From: @(#)comm.1	8.1 (Berkeley) 6/6/93
.\" $FreeBSD$
.\"
.Dd July 27, 2020
.Dt COMM 1
.Os
.Sh NAME
.Nm comm
.Nd select or reject lines common to two files
.Sh SYNOPSIS
.Nm
.Op Fl 123i
.Ar file1 file2
.Sh DESCRIPTION
The
.Nm
utility reads
.Ar file1
and
.Ar file2 ,
which should be
sorted lexically, and produces three text
columns as output: lines only in
.Ar file1 ;
lines only in
.Ar file2 ;
and lines in both files.
.Pp
The filename ``-'' means the standard input.
.Pp
The following options are available:
.Bl -tag -width indent
.It Fl 1
Suppress printing of column 1, lines only in
.Ar file1 .
.It Fl 2
Suppress printing of column 2, lines only in
.Ar file2 .
.It Fl 3
Suppress printing of column 3, lines common to both.
.It Fl i
Case insensitive comparison of lines.
.El
.Pp
Each column will have a number of tab characters prepended to it
equal to the number of lower numbered columns that are being printed.
For example, if column number two is being suppressed, lines printed
in column number one will not have any tabs preceding them, and lines
printed in column number three will have one.
.Pp
The
.Nm
utility assumes that the files are lexically sorted; all characters
participate in line comparisons.
.Sh ENVIRONMENT
The
.Ev LANG ,
.Ev LC_ALL ,
.Ev LC_COLLATE ,
and
.Ev LC_CTYPE
environment variables affect the execution of
.Nm
as described in
.Xr environ 7 .
.Sh EXIT STATUS
.Ex -std
.Sh EXAMPLES
Assuming a file named
.Pa example.txt
with the following contents:
.Bd -literal -offset indent
a
b
c
d
.Ed
.Pp
Show lines only in
.Pa example.txt ,
lines only in stdin and common lines:
.Bd -literal -offset indent
$ echo -e "B\enc" | comm example.txt -
        B
a
b
                c
d
.Ed
.Pp
Show only common lines doing case insensitive comparisons:
.Bd -literal -offset indent
$ echo -e "B\enc" | comm -1 -2 -i example.txt -
b
c
.Ed
.Sh SEE ALSO
.Xr cmp 1 ,
.Xr diff 1 ,
.Xr sort 1 ,
.Xr uniq 1
.Sh STANDARDS
The
.Nm
utility conforms to
.St -p1003.2-92 .
.Pp
The
.Fl i
option is an extension to the POSIX standard.
.Sh HISTORY
A
.Nm
command appeared in
.At v4 .