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Regex cheatsheet

Javascript Regex/Regular Expression cheatsheet

Normal characters

Expression	Description
`.` 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`
`\S`	inverse of `\s`

Whitespace characters

Expression	Description
	space
`\t`	tab
`\n`	newline
`\r`	carriage return
`\s`	space, tab, newline or carriage return

Character set

Expression	Description
`[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

Expression	Description
`\.`	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

Expression	Description
`\\`	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

Expression	Description
`{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

Expression	Description
`^`	start of string
`$`	end of string
`\b`	word 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

Expression	Description
`foo\|bar`	match either `foo` or `bar`
`foo(?=bar)`	match `foo` if it’s before `bar`
`foo(?!bar)`	match `foo` if it’s not before `bar`
`(?<=bar)foo`	match `foo` if it’s after `bar`
`(?<!bar)foo`	match `foo` if it’s not after `bar`

Grouping and capturing

Expression	Description
`(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