The implementation was built for educational purposes, so it doesn't provide support for literal tokens (and many other things).
After running make, you should be able to test the example file, which is
based on the Pig Latin question in the Dragon Book:
./lex examples/lex.l
cc lex.yy.c
./a.out 'the quick brown fox jumps over the lazy dog'
he tay uick qay rown bay ox fay umps jay overay he tay azy lay ogdayI've detailed my experience in building this project here.