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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.

Flex was never part of the GNU Project , although the GNU Project helped distribute it and wrote its manual.



Verified by

Verified on


Verified by


Verified on

2 January 2019

Leaders and contributors

W. L. Estes Maintainer

Resources and communication

AudienceResource typeURI
Mailing Listhttps://lists.gnu.org/mailman/listinfo/help-flex/
Mailing Listhttps://lists.sourceforge.net/mailman/listinfo/flex-help
Debian (Ref) (R)https://tracker.debian.org/pkg/flex-old
VCS Repository Webviewhttps://github.com/westes/flex/
Debian (Ref)https://tracker.debian.org/pkg/flex
Mailing Listhttps://lists.gnu.org/mailman/listinfo/gnu-system-discuss/
Mailing Listhttps://lists.sourceforge.net/mailman/listinfo/flex-announce

Software prerequisites

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


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

"Debian (Ref)" 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.