LOTS of theory, may not be the best place to begin
If you're trying to learn REGEX, this book may not be the place to start. Friedl's book is generally recognized as *the* single most authoritative book on REGEX *theory*. But the book's excruciating and labyrinthine discussion of every possible detail of REGEX theory, including corner-cases, may simply overwhelm you.
I began with a much shorter book titled "Regular Expressions in 10 Minutes". That book, along with the regex101 online tool, enabled me to get started using REGEX. Only after I'd used that book to help me work and experiment with REGEX for a few months did "Mastering Regular Expressions" begin to make some sense.
If you really want to work with REGEX's most complex capabilities, "Mastering" will be a great complement to your other REGEX learning resources and tools. But unless you're a computer science major who learns by digesting a large body of theory before setting to work, this book might not be all that helpful, at least initially...
