Show lines that only exist in file a: (i.e. what was deleted from a)
comm -23 a b
Show lines that only exist in file b: (i.e. what was added to b)
comm -13 a b
Show lines that only exist in one file or the other: (but not both)
comm -3 a b | sed 's/^\t//'
(Warning: If file a has lines that start with TAB, it (the first TAB) will be removed from the output.)
NOTE: Both files need to be sorted for “comm” to work properly. If they aren’t already sorted, you should sort them:
sort <a >a.sorted
sort <b >b.sorted
comm -12 a.sorted b.sorted