Regular Expressions Cheat Sheet for Developers

Regular expressions are the Swiss Army knife of text processing. They are also notoriously hard to remember. This cheat sheet covers the syntax you will use 95% of the time, with examples you can test in your browser.

Character Classes

• . — Any character except newline
• \d — Digit (0-9)
• \w — Word character (a-z, A-Z, 0-9, _)
• \s — Whitespace (space, tab, newline)
• [abc] — Any of a, b, or c
• [^abc] — Anything except a, b, or c
• [a-z] — Range: lowercase letters

Quantifiers

• * — Zero or more
• + — One or more
• ? — Zero or one (also makes quantifiers lazy)
• {n} — Exactly n times
• {n,m} — Between n and m times

Anchors

• ^ — Start of string (or line in multiline mode)
• $ — End of string (or line in multiline mode)
• \b — Word boundary

Groups and Capturing

• (abc) — Capturing group
• (?:abc) — Non-capturing group
• (?<name>abc) — Named group
• \1 — Back-reference to group 1

Lookarounds

• (?=abc) — Positive lookahead: match only if followed by abc
• (?!abc) — Negative lookahead: match only if NOT followed by abc
• (?<=abc) — Positive lookbehind
• (?<!abc) — Negative lookbehind

Real-World Examples

• Email (simple): ^\w+@\w+\.\w+$
• URL: https?://[^\s]+
• Phone (US): ^\(?\d{3}\)?[-.\s]?\d{3}[-.\s]?\d{4}$
• Hex color: ^#?([a-fA-F0-9]{6}|[a-fA-F0-9]{3})$
• Slug: ^[a-z0-9]+(?:-[a-z0-9]+)*$

Flags

• i — Case insensitive
• g — Global (find all matches)
• m — Multiline (^ and $ match line boundaries)
• s — Dotall (. matches newline)

Test Your Patterns

Open the Regex Tester, paste a pattern, and type test text. Matches highlight in real time. Toggle flags with the checkboxes above the input.