A B D EFile B
A B C DI want the command to just output 'C' By default comm compares two files and produces 3 columns of text - lines that are only in file A, lines that are only in file B and lines that are in both. So with these two files I get:
$ comm tmp_A tmp_B A B C D EUgly, and not what I want... But then you can suppress the output of one or more of these columns using -1, -2, -3 options and combinations of those. I want to suppress lines that are only in file A and those in common:
$ comm -13 tmp_A tmp_B CSimple - does exactly what I need - can't believe I didn't know about it...