Regular Expressions Cheat Sheet for Developers

Regular expressions (regex) are powerful patterns for matching, searching, and manipulating text. This cheat sheet covers the most commonly used regex features with practical examples.

Basic Syntax

PatternDescriptionExample

|---------|-------------|---------|

.Any character except newlinea.c matches "abc", "a1c" \dAny digit (0-9)\d{3} matches "123" \wWord character (a-z, A-Z, 0-9, _)\w+ matches "hello_123" \sWhitespace character\s+ matches spaces, tabs ^Start of string^Hello matches "Hello world" $End of stringworld$ matches "Hello world"

Quantifiers

PatternDescription

|---------|-------------|

*0 or more +1 or more ?0 or 1 (optional) {n}Exactly n times {n,m}Between n and m times {n,}n or more times

Common Patterns

Email Validation

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

URL Matching

https?:\/\/(www\.)?[-a-zA-Z0-9@:%._\+~#=]{1,256}\.[a-zA-Z0-9()]{1,6}\b([-a-zA-Z0-9()@:%_\+.~#?&//=]*)

Phone Number (US)

^\+?1?[-.\s]?\(?[0-9]{3}\)?[-.\s]?[0-9]{3}[-.\s]?[0-9]{4}$

IP Address (IPv4)

^((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]?)$

Date (YYYY-MM-DD)

^\d{4}-(0[1-9]|1[0-2])-(0[1-9]|[12][0-9]|3[01])$

Password Strength

At least 8 chars, one uppercase, one lowercase, one digit, one special:

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

Groups and Lookaheads

Capturing Groups

(\d{4})-(\d{2})-(\d{2})

// Captures year, month, day separately

Non-Capturing Groups

(?:https?|ftp)://

// Groups but doesn't capture

Lookahead and Lookbehind

(?=.*\d)      // Positive lookahead: followed by digit

(?!.*\d)      // Negative lookahead: NOT followed by digit
(?<=\$)\d+    // Positive lookbehind: preceded by $
(?

Flags

FlagDescription

|------|-------------|

gGlobal (find all matches) iCase insensitive mMultiline sDotall (. matches newline) uUnicode

Performance Tips

1. Be specific: [0-9] is faster than .*\d

2. Avoid catastrophic backtracking: Use atomic groups or possessive quantifiers

3. Anchor when possible: ^pattern$ is faster than unanchored pattern

4. Prefer character classes: [aeiou] over (a|e|i|o|u)

Test your regular expressions with our Regex Tester tool.