How to find the Set - Subset of two files from the command line?

Question

I have two files with sorted lines. One file (B) is a subset of the other file (A). I would like to find all lines in A that ARE NOT in B. Ideally, I would like to create a file (C) that contains these lines. Is this possible in Unix? I'm looking for a one line command to do this instead of writing a script. I looked at the join and diff commands, but I could not find a command option to do this. Thanks for the help.

Answer 1

This will suppress common lines:

comm -3 a b

Answer 2

How about this:

grep -v -f B A > C