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Fast lexical analyser generator

Flex (The Fast Lexical Analyzer) is a tool for generating programs that recognize lexical patterns in text. There are many applications for Flex, including writing compilers in conjunction with GNU Bison. Flex is a free implementation of the well known Lex program. It features a Lex compatibility mode, and also provides several new features such as exclusive start conditions.


Can be generated in various formats using the GNU documentation system.

Use help2man to generate the man page.

Related Projects


LicenseVerified byVerified onNotes
BSD AdClauseJanet Casey10 January 2003

Leaders and contributors

Vern Paxson Contributor
W. L. Estes Maintainer

Resources and communication

Audience Resource type URI
Developer VCS Repository Webview
Developer Bug Tracking
Developer Download
History Homepage
Developer Mailing List Info/Archive
Support Mailing List Info/Archive

Software prerequisites

Kind Description
Required to use help2man to generate the flex man page
Required to build m4
Required to use tar, gzip, etc. for packaging of the source distribution
Required to use bison to generate parse.c from parse.y
Required to use texinfo to build and test the flex manual
Required to use autoconf for handling the build system
Required to use indent for indenting the flex source the way we want it done
Required to use automake for Makefile generation
Required to build gcc
Required to use gettext for i18n support
Required to build bash

This entry (in part or in whole) was last reviewed on 2 January 2017.


Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the page “GNU Free Documentation License”.

The copyright and license notices on this page only apply to the text on this page. Any software or copyright-licenses or other similar notices described in this text has its own copyright notice and license, which can usually be found in the distribution or license text itself.

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