Last checked against version &flex-contversion;. flex is a tool for generating programs which recognize patterns in text. Pattern recognition is very useful in many applications. A user sets up rules about what to look for and flex will make a program that looks for those patterns. The reason people use flex is that it is much easier to set up rules for what to look for than to write the actual program which finds the text. flex++ invokes a version of flex which is used exclusively for C++ scanners. We create a bash script called lex which calls flex using the -l option. This is for compatibility purposes for programs which use lex instead of flex. libfl is the flex library.