LINK LEX & YACC

Lex & Yacc :-
Lex - A Lexical Analyzer Generator
Yacc - Yet Another Compiler - Compiler
A Compact Guide to Lex and Yacc
Lex and Yacc Primer/Howto
Debugging Lex, Yacc, etc..
Therobs Lex & Yacc Examples and Download Links
How to Write a Parser / Translator Using Lex / Yacc

FLex & Bison :-
FLex - A Scanner Generator
Bison - The Yacc Compatible Parser Generator
Flex Man Page
Compiler Construction Using FLex and Bison

Misc :: Online Books:-
Compilers and Compiler Generator :: An Introduction with C++
Implementing Functional Language :: A Tutorial
Let's Build A Compiler - Jack Crenshaw
Parsing Techniques A Practical Guide
Semantics with Applications
Partial Evaluation and Automatic Program Generation
Modern Compiler Design