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Regex Cheat Sheet

A searchable reference of regular-expression syntax, grouped by category. Filter live and copy any token with one click.

Tokens

Character classes

.
Any single character except a line break (unless the s flag is set).
Examplea.c matches abc, axc
[abc]
Any one of the listed characters (a, b, or c).
Example[aeiou] matches a single vowel
[^abc]
Any single character that is NOT one of the listed characters.
Example[^0-9] matches a non-digit
[a-z]
Any character in the given range (here, a lowercase letter).
Example[A-Fa-f0-9] matches a hex digit
\d
Any digit. Equivalent to [0-9].
Example\d\d matches 42
\D
Any non-digit character. Equivalent to [^0-9].
\w
Any word character: a letter, digit, or underscore. Same as [A-Za-z0-9_].
Example\w+ matches snake_case_99
\W
Any non-word character. Equivalent to [^A-Za-z0-9_].
\s
Any whitespace character: space, tab, newline, carriage return, form feed.
Example\s+ collapses runs of spaces
\S
Any non-whitespace character.
\.
A literal dot. Backslash-escape any metacharacter to match it literally.
Example\d+\.\d+ matches 3.14
\t
A literal tab character. Likewise \n (newline) and \r (carriage return).

Anchors & boundaries

^
Start of the string (or start of a line with the m flag).
Example^Error matches lines beginning with Error
$
End of the string (or end of a line with the m flag).
Example\.csv$ matches a filename ending in .csv
\b
A word boundary: the position between a word and a non-word character.
Example\bcat\b matches cat but not category
\B
A non-word boundary: any position that is not a word boundary.
Example\Bend matches the end in weekend
\A
Start of the string only, never a line start (PCRE; not in JavaScript).
\z
Very end of the string only (PCRE; not in JavaScript).

Quantifiers

*
Zero or more of the preceding token (greedy).
Exampleab*c matches ac, abc, abbbc
+
One or more of the preceding token (greedy).
Example\d+ matches one or more digits
?
Zero or one of the preceding token (makes it optional).
Examplecolou?r matches color and colour
{n}
Exactly n of the preceding token.
Example\d{4} matches a four-digit year
{n,}
At least n of the preceding token.
Example\d{2,} matches two or more digits
{n,m}
Between n and m of the preceding token, inclusive.
Examplea{1,3} matches a, aa, or aaa
*?
Lazy (non-greedy) match: as few repetitions as possible. Also +?, ??, {n,m}?.
Example<.*?> matches one tag, not the whole line
*+
Possessive match: like greedy but never backtracks (PCRE). Also ++, ?+.

Groups & alternation

(abc)
A capturing group; remembers the match for back-references and replacement.
Example(ab)+ matches abab and captures ab
(?:abc)
A non-capturing group: groups tokens without allocating a capture slot.
Example(?:https?)://
(?<name>abc)
A named capturing group, referenced later by its name.
Example(?<year>\d{4})-(?<month>\d{2})
a|b
Alternation: match the expression on the left OR the one on the right.
Examplecat|dog matches cat or dog
\1
A back-reference: matches the same text the first capturing group matched.
Example(['"]).*?\1 matches a quoted string
\k<name>
A back-reference to a named capturing group.
Example(?<q>['"]).*?\k<q>

Lookaround

(?=abc)
Positive lookahead: asserts what follows, without consuming it.
Example\d+(?= USD) matches digits before USD
(?!abc)
Negative lookahead: asserts that what follows is NOT the pattern.
Examplefoo(?!bar) matches foo not before bar
(?<=abc)
Positive lookbehind: asserts what precedes, without consuming it.
Example(?<=\$)\d+ matches digits after a $
(?<!abc)
Negative lookbehind: asserts that what precedes is NOT the pattern.
Example(?<!\d)\.\d+ matches a leading decimal

Flags & modifiers

g
Global: find all matches rather than stopping at the first.
Example/a/g replaces every a
i
Case-insensitive matching.
Example/error/i matches Error and ERROR
m
Multiline: ^ and $ match at the start and end of each line.
s
Dotall (single line): . also matches newline characters.
u
Unicode: treat the pattern as a sequence of Unicode code points.
Example/\u{1F600}/u matches an emoji
y
Sticky: match only from the regex's lastIndex position (JavaScript).
(?i)
Inline flag: enable case-insensitivity from this point on (PCRE).

Common patterns

^[\w.+-]+@[\w-]+\.[\w.-]+$
A pragmatic email address. Good enough for form validation, not RFC 5322.
Examplematches [email protected]
^https?:\/\/[^\s/$.?#].[^\s]*$
A http(s) URL, requiring a scheme and a non-empty host.
Examplematches https://example.com/path
^(25[0-5]|2[0-4]\d|1?\d?\d)(\.(25[0-5]|2[0-4]\d|1?\d?\d)){3}$
An IPv4 address with each octet bounded to 0-255.
Examplematches 192.168.0.1
^#?([\da-fA-F]{3}|[\da-fA-F]{6})$
A 3- or 6-digit hexadecimal color, with an optional leading hash.
Examplematches #1a2b3c and fff
^\d{4}-\d{2}-\d{2}$
An ISO-8601 calendar date (YYYY-MM-DD).
Examplematches 2026-05-30
^[a-z0-9]+(?:-[a-z0-9]+)*$
A URL slug: lowercase words joined by single hyphens.
Examplematches my-blog-post
^\+?[1-9]\d{7,14}$
An E.164 international phone number (digits with an optional leading +).
Examplematches +14155552671
[0-9a-fA-F]{8}-(?:[0-9a-fA-F]{4}-){3}[0-9a-fA-F]{12}
A UUID / GUID in its canonical 8-4-4-4-12 hyphenated form.
Examplematches 550e8400-e29b-41d4-a716-446655440000

About this cheat sheet

Tokens follow the PCRE and JavaScript (ECMAScript) flavors, which cover the vast majority of everyday matching. Engine-specific notes are called out in the explanations. The common patterns are practical, validation-grade starting points — not exhaustive specifications — so test them against your own data before shipping.