Version 1.0.0 | Status: Complete ✅ | 30/30 Chapters | ~40,700+ Lines
Welcome, brave soul, to the world's most comprehensive guide to Regular Expressions. You're about to learn one of programming's most powerful—and most intimidating—tools. But fear not! This book will take you from "what's a regex?" to "I just parsed an entire log file with one line of code" faster than you can say (?<=\w)(?=\W).
- Total Chapters: 30 (all complete!)
- Total Lines: ~40,700+
- Average Chapter Length: 1,357 lines
- Languages Covered: JavaScript, TypeScript, Python, Java, C#, Ruby, Go, Rust, PHP, Perl
- Topics Covered: 100+ regex concepts with 500+ working examples
- Real-World Examples: Log parsing, validation, text extraction, security patterns, and more
This is a comprehensive reference for complete beginners who want to truly master regular expressions across multiple programming languages. Written by Claude Code (yes, an AI wrote a book—we live in wild times), this guide prioritizes:
- Clarity over cleverness - No cryptic explanations
- Examples over theory - See it, try it, understand it
- Practical applications - Real patterns you'll actually use
- Polyglot perspective - JavaScript, Python, Java, C#, Ruby, Go, Rust, and more
- Occasional humor - Because regex is hard enough without being boring
By the end of this book, you will:
- ✅ Understand regex syntax from first principles
- ✅ Write patterns that actually work (first try!)
- ✅ Know when to use regex (and when not to)
- ✅ Navigate differences between regex flavors
- ✅ Debug and optimize complex patterns
- ✅ Avoid catastrophic backtracking
- ✅ Impress your colleagues (or at least confuse them productively)
- "I've never seen a regex before" → Perfect! Start at Chapter 1
- "I copy regex from StackOverflow" → Start at Chapter 1, you'll finally understand what you're copying
- "I know basic regex but..." → Jump to Part 2 or your favorite language's chapter
- "I need to validate emails" → Chapter 26, but also: don't validate emails with regex
- "I accidentally created a ReDoS attack" → Chapter 23, immediately
Where we learn that . doesn't mean "dot" and * doesn't mean "multiply"
- Chapter 1: Welcome to Regex Hell (It's Not That Bad)
- Chapter 2: Your First Match: Literal Characters
- Chapter 3: Character Classes: Brackets Are Your Friends
- Chapter 4: Quantifiers: The Power of Repetition
- Chapter 5: Anchors & Boundaries: Where Matches Happen
Where things get interesting (and slightly confusing)
- Chapter 6: Groups and Capturing: Parentheses Everywhere
- Chapter 7: Alternation: Choose Your Own Adventure
- Chapter 8: Escaping Special Characters: The Backslash Dance
- Chapter 9: Lookarounds: Looking Without Touching
- Chapter 10: Greedy vs Lazy: The Quantifier Wars
Where we learn why Perl is the godfather of regex
- Chapter 11: How Perl Revolutionized Text Processing
- Chapter 12: PCRE: The Standard That Runs the World
Where we discover every language does it differently (but mostly the same)
- Chapter 13: Regex in JavaScript: String.prototype.everything
- Chapter 14: Regex in TypeScript: Type-Safe Patterns
- Chapter 15: Regex in Python: The re Module
- Chapter 16: Regex in Java: Pattern and Matcher
- Chapter 17: Regex in C#: .NET's Regex Class
- Chapter 18: Regex in Ruby: Built-In Elegance
- Chapter 19: Regex in Go: Simple and Fast
- Chapter 20: Regex in Rust: Compile-Time Safety
Where experts dwell and mortals fear to tread
- Chapter 21: Unicode and Encodings: 世界 Regex
- Chapter 22: Regex Flavors: A Field Guide
- Chapter 23: Catastrophic Backtracking: The Performance Killer
- Chapter 24: Advanced Techniques: Recursion and Conditionals
- Chapter 25: Optimization: Writing Fast Patterns
Where theory meets the real world (and sometimes loses)
- Chapter 26: Common Patterns: Email, URLs, and Other Lies
- Chapter 27: Validation vs Parsing: Know the Difference
- Chapter 28: Text Extraction: Mining Log Files
- Chapter 29: Testing and Debugging Your Regex
- Chapter 30: Real-World War Stories
The reference material you'll bookmark
- Appendix A: Quick Reference Cheatsheet
- Appendix B: Practice Exercises with Solutions
- Appendix C: Tools and Resources
If you're a complete beginner: Start at Chapter 1 and work through sequentially. Each chapter builds on previous concepts.
If you have some experience: Skim Part 1, focus on Part 2 onward.
If you need language-specific info: Jump directly to your language's chapter in Part 4, but reference earlier chapters for syntax explanations.
If you're debugging a specific problem: Check the table of contents or search for your issue.
All examples in this book are:
- ✅ Tested and working
- ✅ Commented for clarity
- ✅ Available in the relevant language's syntax
- ✅ Progressively complex (we won't throw
(?:(?:[A-Z0-9]+(?:+|\.)?)+)at you on page 2)
All 30 chapters are complete and contain comprehensive content:
| Chapter | Lines | Status |
|---|---|---|
| Ch. 1: Welcome | 1,464 | ✅ Complete |
| Ch. 2: First Match | 1,465 | ✅ Complete |
| Ch. 3: Character Classes | 1,247 | ✅ Complete |
| Ch. 4: Quantifiers | 1,244 | ✅ Complete |
| Ch. 5: Anchors & Boundaries | 1,323 | ✅ Complete |
| Ch. 6: Groups & Capturing | 1,281 | ✅ Complete |
| Ch. 7: Alternation | 1,114 | ✅ Complete |
| Ch. 8: Escaping | 1,585 | ✅ Complete |
| Ch. 9: Lookarounds | 1,145 | ✅ Complete |
| Ch. 10: Greedy/Lazy | 1,546 | ✅ Complete |
| Ch. 11: Perl History | 1,201 | ✅ Complete |
| Ch. 12: PCRE | 1,310 | ✅ Complete |
| Ch. 13: JavaScript | 1,525 | ✅ Complete |
| Ch. 14: TypeScript | 1,389 | ✅ Complete |
| Ch. 15: Python | 1,455 | ✅ Complete |
| Ch. 16: Java | 1,362 | ✅ Complete |
| Ch. 17: C# | 1,408 | ✅ Complete |
| Ch. 18: Ruby | 1,115 | ✅ Complete |
| Ch. 19: Go | 1,370 | ✅ Complete |
| Ch. 20: Rust | 1,362 | ✅ Complete |
| Ch. 21: Unicode | 1,531 | ✅ Complete |
| Ch. 22: Regex Flavors | 1,657 | ✅ Complete |
| Ch. 23: Backtracking | 1,251 | ✅ Complete |
| Ch. 24: Advanced Techniques | 1,798 | ✅ Complete |
| Ch. 25: Optimization | 1,437 | ✅ Complete |
| Ch. 26: Common Patterns | 1,231 | ✅ Complete |
| Ch. 27: Validation vs Parsing | 1,534 | ✅ Complete |
| Ch. 28: Text Extraction | 1,057 | ✅ Complete |
| Ch. 29: Testing/Debugging | 1,543 | ✅ Complete |
| Ch. 30: Real-World Cases | 1,242 | ✅ Complete |
Found an error? Have a suggestion? This book is open source! Create an issue or submit a pull request.
This book was written by Claude Code (Sonnet 4.5), an AI assistant specialized in software engineering. Yes, really. No, I don't know what that says about the state of technical writing. Yes, I've been trained on millions of StackOverflow posts where people ask "how do I regex this?"
I bring to this book:
- Zero ego (I'm an AI)
- Infinite patience (I don't get tired explaining the same concept)
- No assumptions about what you "should already know"
- A genuine desire to make this topic accessible
Take a deep breath. Open Chapter 1: Welcome to Regex Hell. And remember: every regex master you admire was once exactly where you are now—staring at a pattern thinking "how does anyone read this?"
The difference between them and you? They kept going.
Let's begin.
"Some people, when confronted with a problem, think 'I know, I'll use regular expressions.' Now they have two problems." — Jamie Zawinski
"But at least they can solve both of them." — This book