Regex Cheat Sheet: Complete Regular Expression Guide

Regular expressions (regex) are powerful tools for pattern matching in strings. While they can seem intimidating at first, once you understand the basics, they become invaluable for text processing, validation, and data extraction.

Basic Syntax

Pattern	Description	Example
.	Any character except newline	a.c matches "abc", "a1c"
^	Start of string	^Hello matches "Hello world"
$	End of string	world$ matches "Hello world"
\d	Any digit (0-9)	\d+ matches "123"
\w	Word character (a-z, A-Z, 0-9, _)	\w+ matches "hello_123"
\s	Whitespace (space, tab, newline)	\s+ matches spaces

Quantifiers

Pattern	Description	Example
*	0 or more	ab*c matches "ac", "abc", "abbc"
+	1 or more	ab+c matches "abc", "abbc"
?	0 or 1	colou?r matches "color", "colour"
{n}	Exactly n times	\d{3} matches "123"
{n,}	n or more times	\d{2,} matches "12", "123"
{n,m}	Between n and m times	\d{2,4} matches "12", "1234"

Character Classes

Pattern	Description	Example
[abc]	Any of a, b, or c	[aeiou] matches vowels
[^abc]	Not a, b, or c	[^0-9] matches non-digits
[a-z]	Range: a to z	[A-Za-z] matches letters
\D	Non-digit	\D+ matches "abc"
\W	Non-word character	\W matches "@", "#"
\S	Non-whitespace	\S+ matches words

Groups and Lookahead

Pattern	Description
(abc)	Capturing group
(?:abc)	Non-capturing group
(?=abc)	Positive lookahead
(?!abc)	Negative lookahead
(?<=abc)	Positive lookbehind
(?<!abc)	Negative lookbehind

Common Regex Patterns

Email Validation

^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$

URL Validation

^(https?:\/\/)?([\da-z\.-]+)\.([a-z\.]{2,6})([\/\w \.-]*)*\/?$

Phone Number (US)

^\(?([0-9]{3})\)?[-. ]?([0-9]{3})[-. ]?([0-9]{4})$

Password (Strong)

^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[@$!%*?&])[A-Za-z\d@$!%*?&]{8,}$

IPv4 Address

^(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$

Hex Color Code

^#?([a-fA-F0-9]{6}|[a-fA-F0-9]{3})$

Regex Tips

• Start simple: Build your regex piece by piece
• Use non-greedy quantifiers: Add ? after * or + for minimal matching
• Escape special characters: Use \ before . * + ? ^ $ { } [ ] \ | ( )
• Test incrementally: Test parts of your regex as you build it
• Use comments: In verbose mode, add # comments for clarity

Conclusion

Regular expressions are a powerful tool every developer should know. Bookmark this cheat sheet and practice with our Regex Tester to master pattern matching.