(not necessarily to 2teez) Be aware that (see perlop's precedence table) the use of not here means that the entire clause on the right side is negated. You can also use ! to just negate the next closest term.

I often give the advice to use (and, or, not) for flow control, and (&&, ||, !) for logic. In this case I am not taking the position that this use of not is incorrect, just that it is important for the OP to be aware of what it is actually saying.

Update: As ambrus stated in the CB: "How about unless".