comm(1) -23 %3C%28cat source %7C cut -d%27 %27 -f 1 %7C sort -u%29 %3C%28cat output %7C cut -d%27 %27 -f 2 %7C sort -u%29
compare two sorted files line by line
-2     suppress column 2 (lines unique to FILE2)
-3     suppress column 3 (lines that appear in both files)
source manpages: comm