Regex Guide: Regular Expressions Cheat Sheet

Master regular expressions with our comprehensive guide and cheat sheet for pattern matching.

What is Regex?
Basic Syntax
Character Classes
Quantifiers
Anchors and Boundaries
Regex Flags
Common Examples

What is Regular Expression?

A regular expression (regex or regexp) is a sequence of characters that defines a search pattern. Regex is used for string matching, search-and-replace operations, and input validation.

Basic Syntax

Pattern	Description	Example
`.`	Any character	`a.c` matches "abc", "adc"
`\d`	Digit (0-9)	`\d+` matches "123"
`\w`	Word character	`\w+` matches "hello"
`\s`	Whitespace	`a\sb` matches "a b"
`[abc]`	Character set	`[abc]` matches "a", "b", or "c"
`[^abc]`	Negated set	`[^abc]` matches any except a,b,c

Quantifiers

Quantifier	Description	Example
`*`	0 or more	`ab*` matches "a", "ab", "abb"
`+`	1 or more	`ab+` matches "ab", "abb"
`?`	0 or 1	`ab?` matches "a", "ab"
`{n}`	Exactly n times	`a{3}` matches "aaa"
`{n,m}`	n to m times	`a{2,4}` matches "aa", "aaa", "aaaa"

Anchors and Boundaries

^ - Start of string/line
$ - End of string/line
\b - Word boundary
\B - Non-word boundary

Regex Flags

g - Global match (find all matches)
i - Case insensitive
m - Multiline mode
s - Dot matches newline
u - Unicode mode

Common Examples

Email Validation

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

Phone Number (US)

^\(?\d{3}\)?[-.\s]?\d{3}[-.\s]?\d{4}$

URL Matching

^https?://[^\s/$.?#].[^\s]*$

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