in reply to
What I Most Recently Learned in Perl, But Should Have Already Known
I've discovered that an excellent way to dust off those less-than-oft remembered features of Perl is to try to interpret the obfuscated JAPH programs. You wind up looking up deprecated and seldom-used operators and functions in the course of trying to decipher what those things do.
The advantage to this is that it sometimes gets your creative juices flowing in a new way, and suddenly study might be your newest old toy.
"Perl. There is no substitute."