COMM(1) FreeBSD General Commands Manual COMM(1)


commselect or reject lines common to two files


comm [ -123i] file1 file2


The comm utility reads file1 and file2, which should be sorted lexically, and produces three text columns as output: lines only in file1; lines only in file2; and lines in both files.

The filename ``-'' means the standard input.

The following options are available:

Suppress printing of column 1, lines only in file1.
Suppress printing of column 2, lines only in file2.
Suppress printing of column 3, lines common to both.
Case insensitive comparison of lines.

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.

The comm utility assumes that the files are lexically sorted; all characters participate in line comparisons.


The LANG, LC_ALL, LC_COLLATE, and LC_CTYPE environment variables affect the execution of comm as described in environ(7).


The comm utility exits 0 on success, and >0 if an error occurs.


The comm utility conforms to IEEE Std 1003.2-1992 (“POSIX.2”).

The -i option is an extension to the POSIX standard.


A comm command appeared in Version 4 AT&T UNIX.
December 12, 2009 FreeBSD