Regular Expressions Explained — A Beginner's Guide with Examples

Regular expressions look scary but they're incredibly useful. Learn the basics with practical examples you can try right now.

Regular expressions (regex) are one of those things that look like your cat walked across the keyboard. But once you understand the basics, they become one of the most powerful tools in your toolkit. They let you search, match, and manipulate text patterns in ways that would take dozens of lines of code otherwise.

What regex actually does

At its simplest, regex is a pattern that describes text. The pattern cat matches the literal text "cat." Not very exciting. But c.t matches "cat," "cot," "cut," and any three-letter word starting with c and ending with t. That dot is a wildcard — it matches any character.

The essential building blocks

. — Matches any single character. h.t matches "hat," "hit," "hot."

* — Matches zero or more of the previous character. ab*c matches "ac," "abc," "abbc," "abbbc."

+ — Matches one or more of the previous character. ab+c matches "abc," "abbc" but NOT "ac."

? — Makes the previous character optional. colou?r matches both "color" and "colour."

[abc] — Matches any one of the characters inside. [aeiou] matches any vowel.

\d — Matches any digit (0-9). \d{3} matches any three digits.

^ and $ — Match the start and end of a line. ^Hello matches "Hello" only at the beginning.

Real-world examples

Email validation: [a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}

Phone numbers: \(?\d{3}\)?[-.\s]?\d{3}[-.\s]?\d{4}

URLs: https?://[\w.-]+\.[a-zA-Z]{2,}(/\S*)?

These patterns look complex, but they're just combinations of the basic building blocks.

Testing your patterns

The best way to learn regex is to experiment. Toolozo's Regex Tester lets you type a pattern and test text, seeing matches highlighted in real-time. It's invaluable when you're trying to get a pattern right before using it in your code.