Flex Flex (The Fast Lexical Analyzer) Flex is a fast lexical analyser generator. It is a tool for generating programs that perform pattern-matching on text. Flex is a free (but non-GNU) implementation of the original Unix lex program. The project repository is now hosted at github: https://github.com/westes/flex. Releases can be found at https://github.com/westes/flex/releases. - View it on GitHub