comm: compare two sorted text files

man comm:
  
Compare sorted files FILE1 and FILE2 line by line.

       With  no  options,  produce  three-column output.  Column one contains lines unique to FILE1, column two contains lines unique to FILE2, and column three contains lines common to both files.

       -1     suppress lines unique to FILE1

       -2     suppress lines unique to FILE2

       -3     suppress lines that appear in both files