Flex a tool for generating text scanners in C. The input file read by Flex specifies a set of rules (code to be executed when a pattern is found) which describe the scanner to be generated. The output of Flex is a C source file which can be compiled and linked with your sources, giving to your executable the scanning capabilities tailored to your needs.
Generally, Flex is used in combination with a parser generator, like Bison.
At one point, Open Hub analyzed source code for this project based on code location(s) available at that time. Since then, the code locations have been removed.