flex  2.6.4
About: Flex ("Fast Lexical Analyzer") is a tool for generating scanners/tokenizers.
  Fossies Dox: flex-2.6.4.tar.gz  ("inofficial" and yet experimental doxygen-generated source code documentation)  

flex Documentation

Some Fossies usage hints in advance:

  1. To see the Doxygen generated documentation please click on one of the items in the steelblue colored "quick index" bar above or use the side panel at the left which displays a hierarchical tree-like index structure and is adjustable in width.
  2. If you want to search for something by keyword rather than browse for it you can use the client side search facility (using Javascript and DHTML) that provides live searching, i.e. the search results are presented and adapted as you type in the Search input field at the top right.
  3. Doxygen doesn't incorporate all member files but just a definable subset (basically the main project source code files that are written in a supported language). So to search and browse all member files you may visit the Fossies flex-2.6.4.tar.gz contents page and use the Fossies standard member browsing features (also with source code highlighting and additionally with optional code folding).

This is flex, the fast lexical analyzer generator.

flex is a tool for generating scanners: programs which recognize lexical patterns in text.

The flex codebase is kept in Git on GitHub.

Use GitHub's issues and pull request features to file bugs and submit patches.

There are several mailing lists available as well:

Find information on subscribing to the mailing lists at:


The flex distribution contains the following files which may be of interest:

  • README - This file.
  • NEWS - current version number and list of user-visible changes.
  • INSTALL - basic installation information.
  • ABOUT-NLS - description of internationalization support in flex.
  • COPYING - flex's copyright and license.
  • doc/ - user documentation.
  • examples/ - containing examples of some possible flex scanners and a few other things. See the file examples/README for more details.
  • tests/ - regression tests. See TESTS/README for details.
  • po/ - internationalization support files.

You need the following tools to build flex from the maintainer's repository:

  • compiler suite - flex is built with gcc
  • bash, or a good Bourne-style shell
  • m4 - m4 -p needs to work; GNU m4 and a few others are suitable
  • GNU bison; to generate parse.c from parse.y
  • autoconf; for handling the build system
  • automake; for Makefile generation
  • gettext; for i18n support
  • help2man; to generate the flex man page
  • tar, gzip, lzip, etc.; for packaging of the source distribution
  • GNU texinfo; to build and test the flex manual. Note that if you want to build the dvi/ps/pdf versions of the documentation you will need texi2dvi and related programs, along with a sufficiently powerful implementation of TeX to process them. See your operating system documentation for how to achieve this. The printable versions of the manual are not built unless specifically requested, but the targets are included by automake.
  • GNU indent; for indenting the flex source the way we want it done

In cases where the versions of the above tools matter, the file configure.ac will specify the minimum required versions.

Once you have all the necessary tools installed, life becomes simple. To prepare the flex tree for building, run the script:


in the top level of the flex source tree.

This script calls the various tools needed to get flex ready for the GNU-style configure script to be able to work.

From this point on, building flex follows the usual routine:

configure && make && make install

This file is part of flex.

This code is derived from software contributed to Berkeley by Vern Paxson.

The United States Government has rights in this work pursuant to contract no. DE-AC03-76SF00098 between the United States Department of Energy and the University of California.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

  1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
  2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

Neither the name of the University nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.