If I want to see a list of files which contain the word 'FOO' I can use
fgrep -l 'FOO' *
but what if I want to see all of the files which do not contain the word FOO?
I can't use
fgrep -vl 'FOO' *
because that will show me every file (unless there's a file which only) contains the word 'FOO'.
(It seems like I knew of a way to do this, but now I can't remember it.)