comm

Compare two sorted files line by line.

Synopsis

comm [OPTION]... FILE1 FILE2

Main Purpose

• Compare two sorted files line by line.
• Read from standard input when FILE1 or FILE2 is -.
• Without options, output three columns: lines unique to FILE1, lines unique to FILE2, and lines common to both.

Options

-1                        Suppress column 1 (lines unique to FILE1).
-2                        Suppress column 2 (lines unique to FILE2).
-3                        Suppress column 3 (lines common to both).
--check-order             Check that the input is correctly sorted, even if all input lines are paired.
--nocheck-order           Do not check that the input is correctly sorted.
--output-delimiter=STR    Use STR as the separator between output columns instead of the default TAB.
--total                   Output a fourth column containing a summary.
-z, --zero-terminated     Set line delimiter to NUL instead of newline.
--help                    Display help information and exit.
--version                 Display version information and exit.

Return Value

Returns 0 on success, and non-zero on failure.

Examples

Content of aaa.txt:

[root@localhost text]# cat aaa.txt 
aaa
bbb
ccc
ddd
eee
111
222

Content of bbb.txt:

[root@localhost text]# cat bbb.txt 
bbb
ccc
aaa
hhh
ttt
jjj

Comparison result:

[root@localhost text]# comm --nocheck-order aaa.txt bbb.txt 
aaa
                bbb
                ccc
        aaa
ddd
eee
111
222
        hhh
        ttt
        jjj

The first column contains lines only in aaa.txt, the second column contains lines only in bbb.txt, and the third column contains lines common to both. TAB (\t) is used as the default separator between columns.

Comparing Sorted Files

First, sort the file contents using sort:

[root@localhost ~]# sort aaa.txt > aaa1.txt
[root@localhost ~]# sort bbb.txt > bbb1.txt

Comparison result:

[root@localhost ~]# comm aaa1.txt bbb1.txt
111
222
		aaa
		bbb
		ccc
ddd
eee
	hhh
	jjj
	ttt

Intersection

To print the intersection of two files, suppress the first and second columns:

[root@localhost text]# comm aaa.txt bbb.txt -1 -2
bbb
ccc

Difference

By suppressing unwanted columns, you can obtain the difference between aaa.txt and bbb.txt:

Lines unique to aaa.txt:

[root@localhost text]# comm aaa.txt bbb.txt -2 -3
aaa
ddd
eee
111
222

Lines unique to bbb.txt:

[root@localhost text]# comm aaa.txt bbb.txt -1 -3
aaa
hhh
ttt
jjj

Note

1. This command is part of the GNU coreutils package. For more information, see man -s 1 comm or info coreutils 'comm invocation'. 观察