Easy to follow Regular Expression Cheatsheet

Hi Everyone, We know regular expressions can be tricky to read and write. I prepared this Regular expression cheatsheet with the help of various resources. I hope this helps.

Basic Matching

Character	Meaning	Example	Matches
.	Any single character	h.t	"hat", "hot", "hit"
*	0 or more of previous character	go*gle	"ggle", "google", "gooogle"
+	1 or more of previous character	go+gle	"google", "gooogle"
?	0 or 1 of previous character	colou?r	"color", "colour"
^	Start of line	^Hello	"Hello world" (not "say Hello")
$	End of line	world$	"Hello world" (not "worldly")

Character Classes

Syntax	Meaning	Example	Matches
[abc]	Any single character in set	[aeiou]	Any vowel
[^abc]	Any single character NOT in set	[^0-9]	Any non-digit
[a-z]	Range of characters	[0-9]	Any single digit

Predefined Character Classes

Shorthand	Equivalent	Meaning
\d	[0-9]	Digit
\D	[^0-9]	Non-digit
\w	[a-zA-Z0-9_]	Word character
\W	[^\w]	Non-word character
\s	[ \t\n\r\f\v]	Whitespace
\S	[^\s]	Non-whitespace

Quantifiers

Syntax	Meaning	Example	Matches
{n}	Exactly n times	a{3}	"aaa"
{n,}	n or more times	a{2,}	"aa", "aaa", "aaaa"
{n,m}	Between n and m times	a{2,4}	"aa", "aaa", "aaaa"

Grouping & Capturing

Syntax	Meaning	Example	Matches
(...)	Capture group	(ab)+	"ab", "abab", "ababab"
(?:...)	Non-capturing group	(?:ab)+	Same as above
\1, \2	Backreference	(.)\1	"aa", "bb", "11"

Anchors & Boundaries

Syntax	Meaning	Example	Matches
\b	Word boundary	\bcat\b	"cat" (not "category")
\B	Non-word boundary	\Bcat\B	"category"

Advanced Assertions

Syntax	Meaning	Example	Matches
(?=...)	Positive lookahead	\d(?=px)	"5" in "5px"
(?!...)	Negative lookahead	\d(?!px)	"5" in "5em"
(?<=...)	Positive lookbehind	(?<=\$)\d+	"42" in "$42"
(?<!...)	Negative lookbehind	(?<!\$)\d+	"42" in "USD 42"

Common Use Case Patterns

Pattern	Description	Matches
`^[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+.[A-Z	a-z]{2,}$`	Email
^\d{3}-\d{3}-\d{4}$	US Phone Number	"123-456-7890"
^(?=.*[A-Za-z])(?=.*\d)[A-Za-z\d]{8,}$	Strong Password	Alphanumeric, 8+ chars

Regex Flags

Flag	Meaning	Example
i	Case-insensitive	/pattern/i
g	Global match	/pattern/g
m	Multiline mode	/pattern/m
s	Dot matches newline	/pattern/s

Performance Tips

• Use non-capturing groups (?:...) when possible
• Avoid backtracking
• Use character classes instead of OR |
• Be specific with quantifiers

Regex Test Tools

• regex101.com
• regexr.com
• debuggex.com

Language Support

• JavaScript: /pattern/flags
• Python: re module
• PHP: preg_ functions
• Java: Pattern class
• Ruby: // literals

Common Gotchas

• . doesn't match newline
• * and + are greedy
• Escape special chars with \
• Different syntax in different languages

Escape Special Characters

\ ^ $ . | ? * + ( ) [ ] { }

Pro Tip: Always test your regex with various inputs!

Please leave a like if you found this helpful. Thanks

Comments

[Miguel Neto]

Useful and straight to the point. Thank you.

[Lakh Bawa]

Thank you @miguelneto

[Jon Randy 🎖️]

Most useful image I ever downloaded: