Regex Cheat Sheet

Q: Does this apply to Python, PHP and Java too?

Nearly all of it. The table is written for JavaScript; rows marked “JS” behave differently or are missing in some other engines. Python uses (?P …) for named groups, for example.

Q: What is the difference between greedy and lazy?

Greedy quantifiers (*, +) take as much as they can and back off; lazy ones (*?, +?) take as little as possible. On x , matches the whole string while matches just .

Every piece of regular expression syntax you’re likely to need, with an example you can open in the tester in one click.

Character classes

Syntax	Meaning	Example	Try
`.`	Any character except newline	`/c.t/g`	Try
`\d`	Digit 0–9	`/\d+/g`	Try
`\D`	Not a digit	`/\D+/g`	Try
`\w`	Word character [A-Za-z0-9_]	`/\w+/g`	Try
`\W`	Not a word character	`/\W/g`	Try
`\s`	Whitespace	`/\s+/g`	Try
`\S`	Not whitespace	`/\S+/g`	Try
`[abc]`	Any one of a, b or c	`/gr[ae]y/g`	Try
`[^abc]`	Any character except a, b, c	`/[^aeiou\s]/g`	Try
`[a-z]`	A range	`/[A-F0-9]+/g`	Try
`\p{L}`	Any Unicode letter (u flag) JS	`/\p{L}+/gu`	Try

Anchors & boundaries

Syntax	Meaning	Example	Try
`^`	Start of string / line (m)	`/^\w+/gm`	Try
`$`	End of string / line (m)	`/\w+$/gm`	Try
`\b`	Word boundary	`/\bcat\b/g`	Try
`\B`	Not a word boundary	`/\Bcat/g`	Try

Quantifiers

Syntax	Meaning	Example	Try
`*`	0 or more	`/ab*c/g`	Try
`+`	1 or more	`/ab+c/g`	Try
`?`	0 or 1 (optional)	`/colou?r/g`	Try
`{3}`	Exactly 3	`/\d{3}/g`	Try
`{2,}`	2 or more	`/\d{2,}/g`	Try
`{2,4}`	Between 2 and 4	`/\d{2,4}/g`	Try
`*? +?`	Lazy: as few as possible	`/<.+?>/g`	Try

Groups & references

Syntax	Meaning	Example	Try
`(abc)`	Capture group	`/(\d{4})-(\d{2})/g`	Try
`(?:abc)`	Group without capturing	`/(?:ha)+/g`	Try
`(?<name>…)`	Named capture group	`/(?<year>\d{4})-(?<month>\d{2})/g`	Try
`\1`	Back-reference to group 1	`/\b(\w+) \1\b/g`	Try
`a\|b`	Alternation (or)	`/cat\|dog/g`	Try

Lookaround

Syntax	Meaning	Example	Try
`(?=…)`	Followed by	`/\d+(?=px)/g`	Try
`(?!…)`	Not followed by	`/\d+(?!px\|\d)/g`	Try
`(?<=…)`	Preceded by	`/(?<=\$)\d+/g`	Try
`(?<!…)`	Not preceded by	`/(?<!\$)\b\d+/g`	Try

Flags

Syntax	Meaning	Example	Try
`g`	Global: find all matches	`/o/g`	Try
`i`	Case-insensitive	`/json/gi`	Try
`m`	Multiline: ^ $ match per line	`/^-/gm`	Try
`s`	Dot matches newline	`/a.b/gs`	Try
`u`	Unicode mode	`/./gu`	Try
`y`	Sticky: match at lastIndex only JS	`/\d/gy`	Try

Common patterns

Pattern for	Regex	Try
Email (practical) Good enough for form checks; the full RFC 5322 grammar is not a sensible regex	`^[^\s@]+@[^\s@]+\.[^\s@]{2,}$`	Try
URL (http/https) Links in text	`https?:\/\/[^\s/$.?#].[^\s]*`	Try
IPv4 address Four octets 0–255	`\b(?:(?:25[0-5]\|2[0-4]\d\|1?\d?\d)\.){3}(?:25[0-5]\|2[0-4]\d\|1?\d?\d)\b`	Try
ISO date YYYY-MM-DD	`\b\d{4}-(0[1-9]\|1[0-2])-(0[1-9]\|[12]\d\|3[01])\b`	Try
Hex colour #rgb or #rrggbb	`#(?:[0-9a-fA-F]{3}){1,2}\b`	Try
UUID 8-4-4-4-12 hex	`\b[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}\b`	Try
Trailing whitespace Spaces at line ends	`[ \t]+$`	Try
Duplicate words the the	`\b(\w+)\s+\1\b`	Try
Semantic version major.minor.patch	`\bv?\d+\.\d+\.\d+(?:-[\w.]+)?\b`	Try

Questions

Does this apply to Python, PHP and Java too?

Nearly all of it. The table is written for JavaScript; rows marked “JS” behave differently or are missing in some other engines. Python uses (?P<name>…) for named groups, for example.

What is the difference between greedy and lazy?

Greedy quantifiers (*, +) take as much as they can and back off; lazy ones (*?, +?) take as little as possible. On <b>x</b>, <.+> matches the whole string while <.+?> matches just <b>.