Regex Cheatsheet

Essential regular expression syntax, patterns, and common use cases for pattern matching.

Useful Regex Resources

Regex101 - Online regex tester with explanation
Regexr - Learn, build, and test regex
RegexOne - Interactive regex tutorial
Regular-Expressions.info - Comprehensive reference

Basic Patterns

abc

Match exact string "abc"

Match any single character (except newline)

\.

Match literal dot (escape special character)

\d

Match any digit (0-9)

\D

Match any non-digit

\w

Match any word character (a-z, A-Z, 0-9, _)

\W

Match any non-word character

\s

Match any whitespace (space, tab, newline)

\S

Match any non-whitespace

Anchors

Match start of string/line

Match end of string/line

\b

Match word boundary

\B

Match non-word boundary

^hello$

Match exact string "hello" only

\bhello\b

Match "hello" as a whole word

Quantifiers

Match 0 or more times (greedy)

Match 1 or more times (greedy)

Match 0 or 1 time (optional)

{n}

Match exactly n times

{n,}

Match n or more times

{n,m}

Match between n and m times

*?

Match 0 or more times (lazy/non-greedy)

+?

Match 1 or more times (lazy/non-greedy)

Character Classes

[abc]

Match any character in set (a, b, or c)

[^abc]

Match any character NOT in set

[a-z]

Match any lowercase letter

[A-Z]

Match any uppercase letter

[0-9]

Match any digit

[a-zA-Z]

Match any letter

[a-zA-Z0-9]

Match any alphanumeric character

[^0-9]

Match any non-digit

Groups & Alternation

(abc)

Capturing group - match and capture "abc"

(?:abc)

Non-capturing group - match but don't capture

a|b

Alternation - match "a" or "b"

(cat|dog)

Match "cat" or "dog"

(?<name>pattern)

Named capturing group

\1

Backreference - match same text as group 1

(\w+)\s+\1

Match repeated word (e.g., "the the")

Lookahead & Lookbehind

(?=pattern)

Positive lookahead - match if followed by pattern

(?!pattern)

Negative lookahead - match if NOT followed by pattern

(?<=pattern)

Positive lookbehind - match if preceded by pattern

(?<!pattern)

Negative lookbehind - match if NOT preceded by pattern

\d+(?=px)

Match digits followed by "px" (e.g., "100" in "100px")

(?<=\$)\d+

Match digits preceded by "$" (e.g., "50" in "$50")

Common Patterns

Email Address

^[\w.-]+@[\w.-]+\.[a-zA-Z]{2,}$

URL

https?:\/\/[\w.-]+(?:\/[\w.-]*)*\/?

Phone Number (US)

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

Date (YYYY-MM-DD)

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

Time (HH:MM:SS)

^(?:[01]\d|2[0-3]):[0-5]\d:[0-5]\d$

IP Address (IPv4)

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

Hex Color

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

Username (alphanumeric, 3-16 chars)

^[a-zA-Z0-9_]{3,16}$

Password (8+ chars, upper, lower, number)

^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)[a-zA-Z\d]{8,}$

Slug (URL-friendly)

^[a-z0-9]+(?:-[a-z0-9]+)*$

Flags / Modifiers

Case-insensitive matching

Global - match all occurrences

Multiline - ^ and $ match line boundaries

Dotall - . matches newlines too

/pattern/gi

Example: case-insensitive, global match

Escape Sequences

\\

Match backslash

\/

Match forward slash

\.

Match dot

\*

Match asterisk

\+

Match plus

\?

Match question mark

\^

Match caret

\$

Match dollar sign

\[

Match opening bracket

\]

Match closing bracket

\(

Match opening parenthesis

\)

Match closing parenthesis

\{

Match opening brace

\}

Match closing brace

\|

Match pipe

Usage Examples

JavaScript

const regex = /\d+/g;
const text = "I have 3 apples and 5 oranges";
const matches = text.match(regex); // ["3", "5"]

Python

import re
pattern = r'\d+'
text = "I have 3 apples and 5 oranges"
matches = re.findall(pattern, text)  # ['3', '5']

Validation Example

const emailRegex = /^[\w.-]+@[\w.-]+\.[a-zA-Z]{2,}$/;
const isValid = emailRegex.test("user@example.com"); // true

Replace Example

const text = "Hello World";
const result = text.replace(/world/i, "Regex"); // "Hello Regex"

Regex Cheatsheet: Regular Expression Patterns