|-1||Suppress printing of column 1, lines only in file1.|
|-2||Suppress printing of column 2, lines only in file2.|
|-3||Suppress printing of column 3, lines common to both.|
|-i||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 conforms to -p1003.2-92.
The -i option is an extension to the POSIX standard.
A comm command appeared in AT&T v4 .