jfruhlinger writes "If you first went on line in the '90s, you probably remember a time when every e-mail you received was exciting, or at least relevant, and was worthy of your personal attention. One brave writer decided to take that approach to his present-day overflowing inbox. He read every email he received and dealt with them all, either by replying, filing, or unsubscribing. He even scanned his spam filter for false positives. It was a lot harder than he thought it would be."
egrep patterns are full regular expressions; it uses a fast deterministic
algorithm that sometimes needs exponential space.
-- unix manuals