Regular Expressions Cheat Sheet

Essential syntax, character classes, lookarounds, and common patterns

Anchors & Boundaries

Start of string / lineMatches the beginning of input

End of string / lineMatches the end of input

Word boundaryMatches a boundary between \w and \W

\b

Non-word boundary

\B

Any character (except newline)

Digit [0-9]Non-digit: \D

\d

Word character [a-zA-Z0-9_]Non-word: \W

\w

Whitespace [ \t\r\n\f]Non-whitespace: \S

\s

Custom character setNegated: [^a-z]

[a-z0-9_]

0 or more (greedy)

1 or more (greedy)

0 or 1 (optional)

Exact count {n}e.g. \d{4} matches 4 digits

{4}

Range {min, max}

{2,8}

Lazy / Non-greedyMatches shortest possible match

*? or +?

Capturing group

(abc)

Non-capturing group

(?:abc)

Named group

(?<userName>[a-z]+)

Positive lookaheadMatches 'foo' only if followed by 'bar'

foo(?=bar)

Negative lookaheadMatches 'foo' only if NOT followed by 'bar'

foo(?!bar)

Positive lookbehindMatches 'bar' only if preceded by 'foo'

(?<=foo)bar

Email Address

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

IPv4 Address

^(?:(?: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]?)$

URL (HTTP/HTTPS)

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

UUID (v4)

^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$