Article·
Regular Expressions: A Practical Guide for Developers
From basic patterns to lookaheads, understand the regex features you actually need day to day.
The Basics
A regex is a pattern that matches text. /hello/ matches the literal string "hello". Add flags: i (case-insensitive), g (global), m (multiline).
Character Classes
\d— digit,\w— word char,\s— whitespace[a-z]— range,[^abc]— negation
Quantifiers
*zero or more,+one or more,?optional{3}exactly 3,{2,5}between 2 and 5
Groups and Lookaheads
(abc)— capturing group(?:abc)— non-capturing group(?=abc)— positive lookahead (match if followed by)(?!abc)— negative lookahead
Practical Patterns
Email: /^[^\s@]+@[^\s@]+\.[^\s@]+$/
UUID: /^[0-9a-f]{8}-([0-9a-f]{4}-){3}[0-9a-f]{12}$/i
Slug: /^[a-z0-9]+(?:-[a-z0-9]+)*$/
Test patterns live with the Regex Tester.