I have directory a and directory b. They are big. b is almost identical to a. "almost" means that 4-5 files differ, and I don't know which they are. I want to copy b over a, but only the files that differ. i'm in bash.
(no, I can't simply delete a and replace it with b, because 1) a is version-controlled 2) a full copy (or a mv) would take too much. I want to copy only the files that differ).