COMM(1)
NAME
comm − select or reject lines common to two sorted files
USAGE
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. If a dash (−) is used in place of a filename, comm reads 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.