Regex Cheatsheet

Any character except newline

a.c matches abc

Any digit (0-9)

\d+ matches 123

Any non-digit

\D+ matches abc

Word character (letter, digit, underscore)

\w+ matches hello_1

Non-word character

\W matches !

Whitespace character

a\sb matches 'a b'

Non-whitespace character

\S+ matches abc

Any of a, b, or c

[abc]+ matches cab

Any character except a, b, c

[^abc] matches d

Any lowercase letter

[a-z]+ matches hello

Start of string/line

^Hello matches 'Hello world'

End of string/line

world$ matches 'Hello world'

Word boundary

\bcat\b matches 'a cat sat'

Non-word boundary

\Bcat matches 'concatenate'

0 or more of the previous token

ab*c matches ac, abc, abbc

1 or more of the previous token

ab+c matches abc, abbc

0 or 1 of the previous token (optional)

colou?r matches color, colour

Exactly n repetitions

\d{3} matches 123

n or more repetitions

\d{2,} matches 12, 123

Between n and m repetitions

\d{2,4} matches 12, 123, 1234

Lazy (non-greedy) 0 or more

<.*?> matches '<a>' first, not '<a><b>'

Capturing group

(ab)+ captures repeated 'ab'

Non-capturing group

(?:ab)+ groups without capturing

Named capturing group

(?<year>\d{4})

Alternation — a or b

cat|dog matches cat or dog

Positive lookahead

\d(?=px) matches digit before 'px'

Negative lookahead

\d(?!px) matches digit not before 'px'

Positive lookbehind

(?<=\$)\d+ matches digits after $

Negative lookbehind

(?<!\$)\d+ matches digits not after $

Global flag — find all matches

/a/g

Case-insensitive flag

/abc/i matches ABC

Multiline flag — ^ and $ match line boundaries

/^a/m

Dotall flag — . matches newlines too

/a.b/s

Unicode flag

/\u{1F600}/u