1.\" Copyright (c) 1989, 1990, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" This code is derived from software contributed to Berkeley by 5.\" the Institute of Electrical and Electronics Engineers, Inc. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. Neither the name of the University nor the names of its contributors 16.\" may be used to endorse or promote products derived from this software 17.\" without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.Dd July 27, 2020 32.Dt COMM 1 33.Os 34.Sh NAME 35.Nm comm 36.Nd select or reject lines common to two files 37.Sh SYNOPSIS 38.Nm 39.Op Fl 123i 40.Ar file1 file2 41.Sh DESCRIPTION 42The 43.Nm 44utility reads 45.Ar file1 46and 47.Ar file2 , 48which should be 49sorted lexically, and produces three text 50columns as output: lines only in 51.Ar file1 ; 52lines only in 53.Ar file2 ; 54and lines in both files. 55.Pp 56The filename ``-'' means the standard input. 57.Pp 58The following options are available: 59.Bl -tag -width indent 60.It Fl 1 61Suppress printing of column 1, lines only in 62.Ar file1 . 63.It Fl 2 64Suppress printing of column 2, lines only in 65.Ar file2 . 66.It Fl 3 67Suppress printing of column 3, lines common to both. 68.It Fl i 69Case insensitive comparison of lines. 70.El 71.Pp 72Each column will have a number of tab characters prepended to it 73equal to the number of lower numbered columns that are being printed. 74For example, if column number two is being suppressed, lines printed 75in column number one will not have any tabs preceding them, and lines 76printed in column number three will have one. 77.Pp 78The 79.Nm 80utility assumes that the files are lexically sorted; all characters 81participate in line comparisons. 82.Sh ENVIRONMENT 83The 84.Ev LANG , 85.Ev LC_ALL , 86.Ev LC_COLLATE , 87and 88.Ev LC_CTYPE 89environment variables affect the execution of 90.Nm 91as described in 92.Xr environ 7 . 93.Sh EXIT STATUS 94.Ex -std 95.Sh EXAMPLES 96Assuming a file named 97.Pa example.txt 98with the following contents: 99.Bd -literal -offset indent 100a 101b 102c 103d 104.Ed 105.Pp 106Show lines only in 107.Pa example.txt , 108lines only in stdin and common lines: 109.Bd -literal -offset indent 110$ echo -e "B\enc" | comm example.txt - 111 B 112a 113b 114 c 115d 116.Ed 117.Pp 118Show only common lines doing case insensitive comparisons: 119.Bd -literal -offset indent 120$ echo -e "B\enc" | comm -1 -2 -i example.txt - 121b 122c 123.Ed 124.Sh SEE ALSO 125.Xr cmp 1 , 126.Xr diff 1 , 127.Xr sort 1 , 128.Xr uniq 1 129.Sh STANDARDS 130The 131.Nm 132utility conforms to 133.St -p1003.2-92 . 134.Pp 135The 136.Fl i 137option is an extension to the POSIX standard. 138.Sh HISTORY 139A 140.Nm 141command appeared in 142.At v4 . 143