Regex for Beginners: How to Use Regular Expressions

A regular expression (regex) is a pattern that describes a set of strings. Instead of searching for an exact word, you write a pattern that matches any text fitting a certain shape — for example, any string of digits, any email address, or any word starting with a capital letter.

Regex is built into almost every programming language and text editor. Once you learn the basics, you can use the same patterns in JavaScript, Python, Go, VS Code find-and-replace, grep, and many other tools.

The essential syntax

Most regex patterns are combinations of literal characters and special metacharacters. Literal characters match themselves — the pattern cat matches the string "cat". Metacharacters have special meaning:

• . (dot) — matches any single character except a newline
• * — matches the previous item zero or more times
• + — matches the previous item one or more times
• ? — matches the previous item zero or one time (makes it optional)
• [abc] — matches any one character inside the brackets (a, b, or c)
• [a-z] — matches any lowercase letter (a character range)
• ^ — matches the start of the string
• $ — matches the end of the string
• \d — matches any digit (0–9)
• \w — matches any word character (letters, digits, underscore)
• \s — matches any whitespace character (space, tab, newline)

Practical examples

A pattern like \d+ matches one or more digits — it would match "42", "2026", or "100" inside any string. The pattern [A-Z][a-z]+ matches a capital letter followed by one or more lowercase letters — useful for finding proper nouns. The pattern \b\w+@\w+\.\w+\b is a basic email pattern, though real email validation requires something more complete.

Flags change how the pattern works

Most regex engines support flags that modify matching behaviour. The g (global) flag finds all matches instead of stopping at the first one. The i (case-insensitive) flag makes [a-z] also match [A-Z]. The m (multiline) flag makes ^ and $ match the start and end of each line rather than the whole string.

Common mistakes

• Forgetting to escape special characters — a literal dot should be \. not . (which matches any character)
• Using .* greedily when you want a minimal match — use .*? for non-greedy matching
• Not anchoring patterns — without ^ and $, a pattern can match anywhere inside a longer string

The best way to learn regex

The fastest way to learn regex is to write a pattern, test it against real text, and see what it matches and misses. An interactive regex tester lets you see matches highlighted in real time as you type the pattern, which makes the feedback loop immediate.