Regular Expression Reference

Character Classes

Pattern	Matches / Meaning	Example
`.`	Any character except newline	`he.llo`
`\d`	Any digit (0-9)	`\d{3}`
`\D`	Any non-digit	`\D{3}`
`\w`	Any word character (a-z, A-Z, 0-9, _)	`\w{3}`
`\W`	Any non-word character	`\W{3}`
`\s`	Any whitespace character	`\s{3}`
`\S`	Any non-whitespace character	`\S{3}`
`[abc]`	Any character in the set	`[abc]{3}`
`[^abc]`	Any character not in the set	`[^abc]{3}`
`[a-z]`	Any lowercase letter	`[a-z]{3}`
`[A-Z]`	Any uppercase letter	`[A-Z]{3}`
`[0-9]`	Any digit	`[0-9]{3}`
`[a-zA-Z]`	Any letter	`[a-zA-Z]{3}`
`[^a-zA-Z]`	Any non-letter	`[^a-zA-Z]{3}`
`[0-9a-fA-F]`	Any hexadecimal digit	`[0-9a-fA-F]{3}`

Anchors

Pattern	Matches / Meaning	Example
`^`	Start of string	`^hello`
`$`	End of string	`hello$`
`\b`	Word boundary	`\bhello\b`
`\B`	Non-word boundary	`\Bhello\B`
`\A`	Start of string (multiline)	`\Ahello`
`\Z`	End of string (multiline)	`hello\Z`
`\z`	End of string (strict)	`hello\z`

Quantifiers

Pattern	Matches / Meaning	Example
`*`	Zero or more of the preceding element	`he*llo`
`+`	One or more of the preceding element	`he+llo`
`?`	Zero or one of the preceding element	`he?llo`
`{n}`	Exactly n occurrences of the preceding element	`he{2}llo`
`{n,}`	n or more occurrences of the preceding element	`he{2,}llo`
`{n,m}`	Between n and m occurrences of the preceding element	`he{2,4}llo`
`*?`	Zero or more of the preceding element (lazy)	`he*?llo`
`+?`	One or more of the preceding element (lazy)	`he+?llo`
`??`	Zero or one of the preceding element (lazy)	`he??llo`
`{n,m}?`	Between n and m occurrences (lazy)	`he{2,4}?llo`

Groups & Backreferences

Pattern	Matches / Meaning	Example
`(group)`	Grouping	`(he){2}llo`
`(?:non-capturing)`	Non-capturing group	`(?:he){2}llo`
`\1`	Backreference to the first group	`(he)\1llo`
`\2`	Backreference to the second group	`(he)(wo)\2llo`
`(?)`	Named group	`(?he)\gllo`
`\k<name>`	Backreference by name	`(?he)\kllo`
`(?:...)`	Non-capturing group	`(?:he){2}llo`
`(?=...)`	Positive lookahead	`he(?=llo)`
`(?!...)`	Negative lookahead	`he(?!llo)`
`(?<=...)`	Positive lookbehind	`(?<=he)llo`
`(?<!...)`	Negative lookbehind	`(?`

Lookarounds

Pattern	Matches / Meaning	Example
`(?=)`	Positive lookahead	`he(?=llo)`
`(?!)`	Negative lookahead	`he(?!llo)`
`(?<=)`	Positive lookbehind	`(?<=he)llo`
`(?`	Negative lookbehind	`(?`
`(?=(?=...))`	Nested lookahead	`he(?=(?=llo))`
`(?=(?!...))`	Nested negative lookahead	`he(?=(?!llo))`
`(?<=...)(?=...)`	Combined lookbehind and lookahead	`(?<=he)(?=llo)`

Flags

Pattern	Matches / Meaning	Example
`g`	Global search	`he/g`
`i`	Case-insensitive search	`he/i`
`m`	Multiline search	`he/m`
`s`	Dot matches newline	`he/s`
`x`	Ignore whitespace and comments	`he/x`
`u`	Unicode mode	`he/u`
`y`	Sticky search	`he/y`
`gi`	Global and case-insensitive	`he/gi`
`gm`	Global and multiline	`he/gm`

Common Patterns

Pattern	Matches / Meaning	Example
`\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Z\|a-z]{2,}\b`	Email address	`example@example.com`
`https?://[^\s/$.?#].[^\s]*`	URL	`http://example.com`
`\b(?:25[0-5]\|2[0-4][0-9]\|[01]?[0-9][0-9]?)\.(?:25[0-5]\|2[0-4][0-9]\|[01]?[0-9][0-9]?)\.(?:25[0-5]\|2[0-4][0-9]\|[01]?[0-9][0-9]?)\.(?:25[0-5]\|2[0-4][0-9]\|[01]?[0-9][0-9]?)\b`	IPv4 address	`192.168.1.1`
`#([A-Fa-f0-9]{6}\|[A-Fa-f0-9]{3})`	Hex color	`#ff0000`
`\d{4}-\d{2}-\d{2}`	ISO date	`2023-10-05`
`\d{2}\/\d{2}\/\d{4}`	MM/DD/YYYY date	`10/05/2023`
`\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}`	IPv4 address (simplified)	`192.168.1.1`
`^0x[0-9a-fA-F]+$`	Hexadecimal number	`0xFF`
`^\d{3}-\d{2}-\d{4}$`	US SSN	`123-45-6789`
`^\+?[1-9]\d{0,15}$`	Phone number	`+1234567890`
`^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$`	Basic email	`user@domain.com`
`^([0-9]{4})-([0-9]{2})-([0-9]{2})$`	ISO date with groups	`2023-10-05`
`^([0-9]{1,3}\.){3}[0-9]{1,3}$`	IPv4 with groups	`192.168.1.1`
`^#([A-Fa-f0-9]{3}\|[A-Fa-f0-9]{6})$`	Hex color with groups	`#ff0000`
`^https?:\/\/[^\s\/$.?#].[^\s]*$`	URL with groups	`http://example.com`