NAME
comm - select or reject lines common to two sorted files

SYNOPSIS
comm [ - [ 123 ] ] file1 file2

DESCRIPTION
Comm reads file1 and file2, which should be ordered in ASCII
collating sequence, and produces a three column output: lines only
in file1; lines only in file2; and lines in both files. The
filename ‘-’ means the standard input.

Flags 1, 2, or 3 suppress printing of the corresponding column.
Thus comm -12 prints only the lines common to the two files; comm
-23 prints only lines in the first file but not in the second; comm
-123 is a no-op.

SEE ALSO
cmp(1), diff(1), uniq(1)