Running lex and yacc on Linux systems

Student accounts

An account has been created for all CS315 students on As soon as possible, you should login into your account with your initial password and change it by using the passwd command. You should be able to use any ssh client from Windows or Linux machines available in student labs.

Editing files

emacs and vi editors are available on dijkstra and can be used to edit your lex and yacc source files. If you have your own Linux machine or another environment within which you have lex and yacc installed, you can use your favorite text editor to work on your project.

Compiling Standalone lex programs

Normally, lex and yacc are used together. However, it is possible to use only lex and create programs that just do lexical analysis. There are two ways of doing this:
  1. If you do not need to include your own custom main() in your code, put the following line at the beginning of your lex specification file:
        %option main
    This makes sure that a default main() and yywrap() are created for you.
    Suppose you have a lex specification file called example.l. You can use the following commands to obtain an executable and run it:
        lex example.l
        gcc -o example lex.yy.c
  2. If you want to define a more complex main function, you will also need to define yywrap() in your code. In the simplest case, your lex specification file should look like the following:
        ...additional user code...
        main() {
        int yywrap() { return 1; }
    You can compile your specification file with the same method as before.

Using lex and yacc together

Once again, there are a number of different ways you can build your lex and yacc specification files with a varying degree of customization. Here are a few notes: