Characters

Character	Legend	Example	Sample Match
\d	Most engines: one digit from 0 to 9	file_\d\d	file_25
\d	.NET, Python 3: one Unicode digit in any script	file_\d\d	file_9੩
\w	Most engines: "word character": ASCII letter, digit or underscore	\w-\w\w\w	A-b_1
\w	.Python 3: "word character": Unicode letter, ideogram, digit, or underscore	\w-\w\w\w	字-ま_۳
\w	.NET: "word character": Unicode letter, ideogram, digit, or connector	\w-\w\w\w	字-ま‿۳
\s	Most engines: "whitespace character": space, tab, newline, carriage return, vertical tab	a\sb\sc	a b c
\s	.NET, Python 3, JavaScript: "whitespace character": any Unicode separator	a\sb\sc	a b c
\D	One character that is not a digit as defined by your engine's \d	\D\D\D	ABC
\W	One character that is not a word character as defined by your engine's \w	\W\W\W\W\W	*-+=)
\S	One character that is not a whitespace character as defined by your engine's \s	\S\S\S\S	Yoyo

Quantifiers

Quantifier	Legend	Example	Sample Match
+	One or more	Version \w-\w+	Version A-b1_1
{3}	Exactly three times	\D{3}	ABC
{2,4}	Two to four times	\d{2,4}	156
{3,}	Three or more times	\w{3,}	regex_tutorial
*	Zero or more times	ABC*	AAACC
?	Once or none	plurals?	plural

Character	Legend	Example	Sample Match
`.`	Any character except line break	a.c	abc
`.`	Any character except line break	.*	whatever, man.
`\.`	A period (special character: needs to be escaped by a `\`)	a.c	a.c
`\`	Escapes a special character	`\.\*\+\? \$\^\/\\`	`.*+? $^/\`
`\`	Escapes a special character	`\[\{\}\]`	[{()}]