comm
Compare two sorted files line by line. 
SYNTAX
      comm [-123] file1 file2
Options
     -1      Suppress printing of column 1.
     -2      Suppress printing of column 2.
     -3      Suppress printing of column 3.
Notes
  The comm utility reads file1 and file2, which should be sorted lexically, 
  and produces three text columns as output:
lines only in file1; lines only in file2; lines in both files.
The filename ``-'' means the standard input.
If printing of a column is suppressed, the output will be padded with TAB characters.
"You don't sew with a fork, so I see no reason to eat with knitting needles" - Miss Piggy, on eating Chinese Food
Related commands:
  
  cmp - Compare two files 
  diff - Display the differences between two files
  diff3 - Show differences among three files
  sdiff - merge two files interactively
  sort - Sort text files 
  
  Equivalent BASH command:
  
  comm - Compare two sorted files line by line