Sed and awk are classic examples of tools that, on one level, provide a simple means for accomplishing basic tasks, while on a deeper level have complex, powerful, and versatile feature sets. Their base concepts can quickly be understood by beginners, while one could spend years learning all the intracies they programs have to offer. This book is good in that it covers both areas. As an introductory text, the novice is walked through basic operations, introduced to regular expressions, etc. in a comprehensible step-by-step fashion. For experienced users, it offers a handy reference for those functions you don't use every day, but sure come in handy when you need them. For intermediates, it presents a solid review and plenty of new territory to cover. Excellent book! I reccomend it highly.