Regular Expressions Cheat Sheet 2026

Regular expressions are incredibly powerful but notoriously difficult to remember. Even experienced developers need to look up syntax frequently. This comprehensive cheat sheet covers all the most important regex patterns, from basic character classes to advanced lookahead assertions. Keep this guide open while learning regex, bookmark it for quick reference, and use it with ToolPilot's regex tester for hands-on practice.

Character Classes

Pattern	Meaning	Example
.	Any character except newline	a.c matches abc, adc, a1c
\d	Digit (0-9)	\d{3} matches 123
\D	Non-digit	\D+ matches abc
\w	Word character [a-zA-Z0-9_]	\w+ matches hello_world
\W	Non-word character	\W matches !, @, #
\s	Whitespace	\s+ matches spaces, tabs
\S	Non-whitespace	\S+ matches hello
[abc]	Character set	[abc] matches a, b, or c
[^abc]	Negated set	[^abc] matches any char except a, b, c
[a-z]	Range	[a-z] matches lowercase letters

Quantifiers

Pattern	Meaning	Example
*	Zero or more	a*b matches b, ab, aab
+	One or more	a+b matches ab, aab (not b)
?	Zero or one (optional)	a?b matches b, ab
{n}	Exactly n times	a{3} matches aaa
{n,}	n or more times	a{2,} matches aa, aaa
{n,m}	Between n and m times	a{2,4} matches aa, aaa, aaaa

Anchors and Assertions

Pattern	Meaning	Example
^	Start of string/line	^hello matches hello at start
$	End of string/line	world$ matches world at end
\b	Word boundary	\bword\b matches word (not sword)
\B	Non-word boundary	\Bword matches sword

Groups and Capture

Pattern	Meaning	Example
(abc)	Capture group	(\d{3}) captures 123
(?:abc)	Non-capturing group	(?:foo|bar) without capture
(?=...)	Positive lookahead	foo(?=bar) matches foo only if followed by bar
(?!...)	Negative lookahead	foo(?!bar) matches foo not followed by bar
(?<=...)	Positive lookbehind	(?<=foo)bar matches bar only if preceded by foo
(?<!...)	Negative lookbehind	(?<!foo)bar matches bar not preceded by foo

Alternation

Use the pipe symbol (|) for alternation—matching one of several options. The pattern cat|dog matches either cat or dog. In groups: (foo|bar|baz) matches any of the three options. Alternation is tried left-to-right, so order matters in some cases.

Common Patterns

Purpose	Pattern
Email	[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}
URL	https?://[^\s]+
Phone (US)	\d{3}-\d{3}-\d{4}
IP Address	\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}
Hex Color	#[0-9a-fA-F]{6}
Date (YYYY-MM-DD)	\d{4}-\d{2}-\d{2}
Positive Integer	[1-9]\d*
Negative Integer	-[1-9]\d*

Flags

Regex flags modify matching behavior. The 'i' flag enables case-insensitive matching so /hello/i matches HELLO. The 'g' flag enables global matching, finding all matches instead of just the first. The 'm' flag enables multiline mode where ^ and $ match line boundaries not just string boundaries. The 's' flag makes . match newlines. Different languages support different flags.