Where can I learn the basics of writing a lexer?

Question

I want to learn how to write a lexer. My university course had an assignment where we had to write a parser (and a lexer to go along with it) but this was given to us with no in

Answer 1

The Dragon Book is probably the definitive guide on the subject, although it can be a bit overwhelming. Language Implementation Patterns and Programming Language Pragmatics are great resources as well.