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Regex cheatsheet

Javascript Regex/Regular Expression cheatsheet

Normal characters

ExpressionDescription
. or [^\n\r]any character excluding a newline or carriage return
[A-Za-z]alphabet
[a-z]lowercase alphabet
[A-Z]uppercase alphabet
\d or [0-9]digit
\D or [^0-9]non-digit
_underscore
\w or [A-Za-z0-9_]alphabet, digit or underscore
\W or [^A-Za-z0-9_]inverse of \w
\Sinverse of \s

Whitespace characters

ExpressionDescription
space
\ttab
\nnewline
\rcarriage return
\sspace, tab, newline or carriage return

Character set

ExpressionDescription
[xyz]either x, y or z
[^xyz]neither x, y nor z
[1-3]either 1, 2 or 3
[^1-3]neither 1, 2 nor 3
  • Think of a character set as an OR operation on the single characters that are enclosed between the square brackets.
  • Use ^ after the opening [ to “negate” the character set.
  • Within a character set, . means a literal period.

Characters that require escaping

Outside a character set

ExpressionDescription
\.period
\^caret
\$dollar sign
|pipe
\\back slash
\/forward slash
\(opening bracket
\)closing bracket
\[opening square bracket
\]closing square bracket
\{opening curly bracket
\}closing curly bracket

Inside a character set

ExpressionDescription
\\back slash
\]closing square bracket
  • A ^ must be escaped only if it occurs immediately after the opening [ of the character set.
  • A - must be escaped only if it occurs between two alphabets or two digits.

Quantifiers

ExpressionDescription
{2}exactly 2
{2,}at least 2
{2,7}at least 2 but no more than 7
*0 or more
+1 or more
?exactly 0 or 1
  • The quantifier goes after the expression to be quantified.

Boundaries

ExpressionDescription
^start of string
$end of string
\bword boundary
  • How word boundary matching works:
    • At the beginning of the string if the first character is \w.
    • Between two adjacent characters within the string, if the first character is \w and the second character is \W.
    • At the end of the string if the last character is \w.

Matching

ExpressionDescription
foo|barmatch either foo or bar
foo(?=bar)match foo if it’s before bar
foo(?!bar)match foo if it’s not before bar
(?<=bar)foomatch foo if it’s after bar
(?<!bar)foomatch foo if it’s not after bar

Grouping and capturing

ExpressionDescription
(foo)capturing group; match and capture foo
(?:foo)non-capturing group; match foo but without capturing foo
(foo)bar\1\1 is a backreference to the 1st capturing group; match foobarfoo
  • Capturing groups are only relevant in the following methods:
    • string.match(regexp)
    • string.matchAll(regexp)
    • string.replace(regexp, callback)
  • \N is a backreference to the Nth capturing group. Capturing groups are numbered starting from 1.

References and tools