May 10, 2011
We have today another exercise in our continuing series of Unix V7 commands:
comm — select or reject lines common to two sorted files
comm [ - ] file1 file2
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.