Regex for Beginners: Learn Regular Expressions with 10 Practical Examples

What Is a Regex?

A regular expression (regex) is a pattern that describes a set of strings. Instead of searching for an exact word, you describe its shape: "three digits, a dash, four digits", "a word that starts with a capital letter", "anything between two quotes".

Regex are everywhere: form validation, search and replace in code editors, log analysis, data cleaning, routing in web frameworks. They look cryptic at first, but a small number of symbols covers most uses.

The Basic Building Blocks

Characters and Classes

Symbol	Matches	Example
`abc`	The exact text "abc"	`cat` finds "cat" in "concatenate"
`.`	Any character (except line break)	`c.t` → cat, cut, c9t
`\d`	A digit (0–9)	`\d\d` → 42
`\w`	A letter, digit or underscore	`\w+` → a word
`\s`	A space, tab or line break	`a\sb` → "a b"
`[abc]`	One of the listed characters	`gr[ae]y` → gray, grey
`[a-z]`	A character in the range	`[A-Z]` → a capital letter
`[^abc]`	Any character except those	`[^0-9]` → not a digit

Quantifiers

Symbol	Meaning	Example
`*`	0 or more times	`ab*c` → ac, abc, abbbc
`+`	1 or more times	`\d+` → 7, 42, 2026
`?`	0 or 1 time (optional)	`colou?r` → color, colour
`{3}`	Exactly 3 times	`\d{3}` → 123
`{2,4}`	Between 2 and 4 times	`\d{2,4}` → 12, 123, 1234

Anchors and Groups

Symbol	Meaning
`^`	Start of the text (or of the line with the `m` flag)
`$`	End of the text (or of the line)
`\b`	Word boundary
`( )`	Capture group: extracts a part of the match

The vertical bar means "or": cat|dog matches "cat" or "dog".

Test Your Regex Live

The regex tester highlights matches as you type, shows capture groups and includes a cheat sheet. It uses the JavaScript engine, the same as your browser and Node.js. Your patterns run in a separate worker with a time limit, so a badly written regex can't freeze the page.

Regex Tester

Test your regular expressions in real time, groups included.

Try it for free

10 Practical Examples

A whole number: ^\d+$
A decimal number (with a dot or comma): ^\d+([.,]\d+)?$
A simple email check: ^[^\s@]+@[^\s@]+\.[^\s@]+$
A US ZIP code: ^\d{5}(-\d{4})?$
A date in YYYY-MM-DD format: ^\d{4}-\d{2}-\d{2}$
A time in 24h format: ^([01]\d|2[0-3]):[0-5]\d$
A hex color: ^#([0-9a-fA-F]{3}){1,2}$
A URL starting with http or https: ^https?://\S+$
Double spaces to clean up: \s{2,} (replace with a single space)
Words in capitals (acronyms): \b[A-Z]{2,}\b

Don't validate everything with regex

A regex can check the shape of an email, not that the address exists. For dates, a regex accepts "2026-02-31": check the actual value in code. Regex are a first filter, not a full validation.

The Flags

Flags change how the whole pattern behaves:

g (global): finds all matches, not just the first.
i (case-insensitive): ignores uppercase/lowercase.
m (multiline): ^ and $ match the start and end of each line.
s (dotAll): the dot also matches line breaks.

Common Beginner Mistakes

Forgetting to escape special characters: to search for a literal dot, write \., not ..
Forgetting the anchors: \d{5} also matches inside "123456789". Use ^\d{5}$ to validate a whole field.
Greedy quantifiers: ".*" on "a" and "b" captures everything from the first to the last quote. Use the lazy version ".*?".
Nested quantifiers like (a+)+: they can take an exponential time on some texts (catastrophic backtracking).

Use Regex Without Writing Code

Many AwesomeToolkit text tools accept regex: find and replace to transform a text in bulk (with capture groups in the replacement), and text search to find and count all occurrences.

Conclusion

You don't need to memorize the whole syntax: classes (\d, \w, [...]), quantifiers (+, *, ?, {n}) and anchors (^, $) cover the vast majority of needs. Write the pattern, test it live on real examples, and adjust until every case is right.