CL-PPCRE is a portable regular expression library for Common Lisp which has the following features:

• It is compatible with Perl (especially when used in conjunction with cl-interpol, to allow compatible parsing of regexp strings).
• It is pretty fast.
• It is portable between ANSI-compliant Common Lisp implementations.
• It is thread-safe.
• In addition to specifying regular expressions as strings like in Perl you can also use S-expressions.
• It comes with a BSD-style license so you can basically do with it whatever you want.

CL-PPCRE has been used successfully in various applications like BioBike, clutu, LoGS, CafeSpot, Eboy, or The Regex Coach.

Further documentation can be found in doc/index.html, or on the cl-ppcre homepage.