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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



Verified by

Verified on


Verified by

Janet Casey

Verified on

10 January 2003

Leaders and contributors

W. L. Estes Maintainer
Vern Paxson Contributor

Resources and communication

AudienceResource typeURI
DeveloperMailing List Info/Archivehttp://lists.sourceforge.net/mailman/listinfo/flex-announce
Debian (Ref)https://tracker.debian.org/pkg/flex
SupportMailing List Info/Archivehttp://lists.sourceforge.net/mailman/listinfo/flex-help
Python (Ref)https://pypi.org/project/flex
DeveloperVCS Repository Webviewhttps://github.com/westes/flex
Ruby (Ref)https://rubygems.org/gems/flex
DeveloperBug Trackinghttps://github.com/westes/flex/issues

Software prerequisites

Required to buildgcc
Required to usegettext for i18n support
Required to buildbash
Required to usehelp2man to generate the flex man page
Required to buildm4
Required to usetar, gzip, etc. for packaging of the source distribution
Required to usebison to generate parse.c from parse.y
Required to usetexinfo to build and test the flex manual
Required to useautoconf for handling the build system
Required to useindent for indenting the flex source the way we want it done
Required to useautomake for Makefile generation

This entry (in part or in whole) was last reviewed on 16 April 2018.


"History" is not in the list (General, Help, Bug Tracking, Support, Developer) of allowed values for the "Resource audience" property.

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.