Regex Syntax

Regular expression tokens with descriptions and examples. JavaScript flavor.

anchorsAnchors4 tokens
^
Start of string (or line in multiline mode).
/^hello/→ matches hello at the start
$
End of string (or line in multiline mode).
/world$/→ matches world at the end
\b
Word boundary — position between a word character and a non-word character.
/\bcat\b/→ matches cat, not concatenate
\B
Non-word boundary — the inverse of \b.
/\Bcat\B/→ matches concatenate, not cat
classesCharacter Classes10 tokens
.
Any character except newline (unless s/dotAll flag is set).
/c.t/→ matches cat, cut, c3t
[abc]
Character set — matches any one of the listed characters.
/[aeiou]/→ matches any vowel
[^abc]
Negated character set — matches any character NOT in the set.
/[^aeiou]/→ matches any non-vowel
[a-z]
Character range — matches any character between a and z (inclusive).
/[a-z]/→ matches any lowercase letter
\d
Digit — equivalent to [0-9].
/\d+/→ matches 42, 007
\D
Non-digit — equivalent to [^0-9].
/\D+/→ matches abc, hello
\w
Word character — equivalent to [a-zA-Z0-9_].
/\w+/→ matches hello_world
\W
Non-word character — equivalent to [^a-zA-Z0-9_].
/\W+/→ matches spaces and punctuation
\s
Whitespace — space, tab, newline, carriage return, form feed.
/\s+/→ matches spaces and tabs
\S
Non-whitespace — any character that isn't whitespace.
/\S+/→ matches non-space tokens
quantifiersQuantifiers9 tokens
*
Zero or more — greedy, matches as many as possible.
/ab*/→ matches a, ab, abb, abbb
+
One or more — greedy.
/ab+/→ matches ab, abb (not a)
?
Zero or one — makes the preceding token optional.
/colou?r/→ matches color and colour
{n}
Exactly n repetitions.
/\d{4}/→ matches exactly 4 digits
{n,}
n or more repetitions.
/\d{2,}/→ matches 2 or more digits
{n,m}
Between n and m repetitions (inclusive).
/\d{2,4}/→ matches 2, 3, or 4 digits
*?
Lazy zero or more — matches as few as possible.
/<.*?>/s→ matches shortest tag
+?
Lazy one or more.
/\d+?/→ matches minimal digits
??
Lazy zero or one.
/colou??r/→ prefers color over colour
groupsGroups & Capturing6 tokens
(abc)
Capturing group — captures matched text and assigns a numbered backreference.
/(\w+)@(\w+)/→ captures username and domain separately
(?:abc)
Non-capturing group — groups without capturing. Useful for applying quantifiers without saving the match.
/(?:ab)+/→ matches ababab without capturing
(?<name>abc)
Named capturing group — like a capturing group but accessed by name.
/(?<year>\d{4})-(?<month>\d{2})/→ groups.year, groups.month
\1
Backreference — matches the same text captured by group 1.
/(\w+) \1/→ matches repeated words like the the
\k<name>
Named backreference — matches the text captured by the named group.
/(?<q>['"]).*?\k<q>/→ matches matching quote pairs
a|b
Alternation — matches either a or b.
/cat|dog/→ matches cat or dog
lookaroundLookahead & Lookbehind4 tokens
(?=abc)
Positive lookahead — asserts that what follows matches abc, without consuming it.
/\d+(?= dollars)/→ matches 100 in '100 dollars'
(?!abc)
Negative lookahead — asserts that what follows does NOT match abc.
/\d+(?! dollars)/→ matches numbers not followed by dollars
(?<=abc)
Positive lookbehind — asserts that what precedes matches abc.
/(?<=\$)\d+/→ matches digits after $
(?<!abc)
Negative lookbehind — asserts that what precedes does NOT match abc.
/(?<!\$)\d+/→ matches digits not preceded by $
flagsFlags6 tokens
g
Global — find all matches, not just the first.
/abc/g→ returns all matches
i
Case-insensitive — makes the pattern case-insensitive.
/hello/i→ matches Hello, HELLO, hello
m
Multiline — ^ and $ match start/end of each line, not just the string.
/^\w+/m→ matches first word of every line
s
DotAll — makes . match newline characters too.
/foo.bar/s→ matches across newlines
u
Unicode — enables full Unicode matching and disallows some ambiguous patterns.
/\u{1F600}/u→ correctly matches emoji code points
y
Sticky — anchors the match to lastIndex; only matches at that exact position.
/\d+/y→ matches only at current position
escapesEscape Sequences7 tokens
\n
Newline (line feed, LF).
/line1\nline2/→ matches across a newline
\r
Carriage return (CR). Windows line endings are \r\n.
/\r\n/→ matches Windows line ending
\t
Horizontal tab.
/\t/→ matches tab character
\0
Null character (NUL, U+0000).
/\0/→ matches null byte
\xhh
Hexadecimal escape — matches the character with hex code hh.
/\x41/→ matches A (0x41)
\uhhhh
Unicode escape — matches the character with the given 4-digit hex code point.
/\u00E9/→ matches é
\u{hhhh}
Extended Unicode escape (requires u flag) — supports code points above U+FFFF.
/\u{1F600}/u→ matches 😀