Tutorials
Regular Expressions: A Practical Developer Tutorial
Marcus Brennan··10 min read
Regular Expressions for Developers
Regular expressions (regex) are powerful pattern-matching tools used in nearly every programming language.
Basic Syntax
- . (dot) — Any character
- — 0 or more repetitions
- — 1 or more repetitions
- ? — 0 or 1 repetitions
- ^ — Start of string
- $ — End of string
- [] — Character class
- () — Capturing group
Common Patterns
Email: ^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+.[a-zA-Z]{2,}$ UUID v4: ^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$ IP Address: ^(\d{1,3}.){3}\d{1,3}$
Flags
- g — Global (find all matches)
- i — Case insensitive
- m — Multiline
- s — Dot matches newlines
Try Regex Tester
Use our free Regex Tester to test patterns with real-time match highlighting.
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Marcus Brennan writes for CodeUtilityKit, where the team builds free, privacy-first developer tools that run entirely in your browser. Every guide is written and reviewed by developers who use these tools daily.