Regex Cheat Sheet and Online Tester Guide

Regular expressions (regex) are patterns used to match, search, and manipulate text. They appear in programming, command-line tools, text editors, and database queries. Here is a practical cheat sheet and how to test patterns instantly.

Regex Basics

• . — Matches any single character except newline.
• * — Matches 0 or more of the preceding element.
• + — Matches 1 or more of the preceding element.
• ? — Matches 0 or 1 of the preceding element (makes it optional).
• ^ — Matches start of string.
• $ — Matches end of string.
• [] — Character class. [abc] matches a, b or c.
• [^] — Negated class. [^abc] matches anything except a, b, c.
• {n,m} — Matches between n and m repetitions.
• | — Alternation (OR). cat|dog matches cat or dog.
• () — Capturing group.
• \d — Digit (0-9). \D is non-digit.
• \w — Word character (a-z, A-Z, 0-9, _). \W is non-word.
• \s — Whitespace. \S is non-whitespace.
• \b — Word boundary.

Common Regex Patterns

• Email: [a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}
• URL: https?:\/\/[^\s/$.?#].[^\s]*
• IP Address: \b(?:\d{1,3}\.){3}\d{1,3}\b
• Date (YYYY-MM-DD): \d{4}-\d{2}-\d{2}
• Phone (US): \(?\d{3}\)?[-.\s]?\d{3}[-.\s]?\d{4}
• Hex color: #?([a-fA-F0-9]{6}|[a-fA-F0-9]{3})

How to Test Regex Online

Use Anonymiz Regex Tester — paste your pattern and test string, and see matches highlighted in real time. Supports JavaScript regex syntax. Free, runs in your browser.

Regex Flags

• g — Global: find all matches, not just the first.
• i — Case-insensitive.
• m — Multiline: ^ and $ match start/end of each line.
• s — Dotall: . matches newlines too.