CL-PPCRE is a portable regular expression library for Common Lisp. It is compatible with Perl, and it's fast, portable (strictly ANSI-compliant), and thread-safe. It comes with convenient features like a SPLIT function, a couple of DO-like loop constructs, and a regex-based APROPOS feature similar to the one found in Emacs. In addition to specifying regular expressions as strings like in Perl, you can also use S-expressions which are more Lisp-y.
