One tool for this is the 'comm' utility: given two files containing sorted lines, it can output one or more of (1) lines only in file 1, (2) lines only in file

One tool for this is the 'comm' utility: given two files containing sorted lines, it can output one or more of (1) lines only in file 1, (2) lines only in file 2, and (3) lines common to both files.