Intro to Regex

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Cheatsheet

Metacharacters

Char	Purpose
\	Escaping next character
^	Start of String or Negation in Character Class
$	End of String
.	Any Character (Except Newlines)
|	Alternation in Groups
?	Zero or One or Lazy Mode or Lookarounds & more
*	Zero or More
+	One or More
{}	Range Delimiters
()	Group Delimiters
[]	Character Class Delimiters

Note: Lazy Mode & Lookarounds are not discussed in this workshop

Repeating Characters

Pattern	Description	Matches
a?	Zero or One 'a'	'' 'a'
a*	Zero or More 'a'	'' 'a' 'aa' 'aaa' 'aaaa'...
a+	One or More 'a'	'a' 'aa' 'aaa' 'aaaa'...
a{3}	Exactly three 'a'	'aaa'
a{2,4}	Two to four 'a'	'aa' 'aaa' 'aaaa'
a{2,}	Two or more 'a'	'aa' 'aaa' 'aaaa' 'aaaaa'...
a{,3}	Three or fewer 'a'	'' 'a' 'aa' 'aaa'

Character Class

Pattern	Description	Matches
[abc]	One of 'a', 'b' or 'c'	'a' 'b' 'c'
[a-g]	Letters between a and g	'a' 'b' 'c' 'd' 'e' 'f' 'g'
[a-c1-3]	Letters a-c or number 1-3	'a' 'b' 'c' '1' '2' '3'
[ab]{2}	Two of 'a' or 'b'	'aa' 'bb' 'ab' 'ba'

Shorthand Character Class

Shorthand	Equivalent
[0-9]	[0123456789]
\d	[0-9]
\w	[A-Za-z\d_]
\s	[ \t\n\r]

Shorthand Negation

Shorthand	Equivalent
\D	[^\d]
\S	[^\s]
\W	[^\w]
.	[^\r\n]
[\w\W]	Anything

Literal Characters

Command	Matches
a	a
\?	?
\.	.
\\	\

Groups

const reg = /(na)+/

const isTheme = str => reg.test(str)

isTheme("nanananananana Batman!")
// true

isTheme("aaaaannnnnnnnn Batman!")
// false

Backreferences

const reg = /(\w+)-\1/

const strings = ["foo-foo", "foo-bar", "bar-bar"]
strings.filter(str => reg.test(str))
// [ "foo-foo", "bar-bar" ]

Note: Backreferences are 1-indexed

Flags

Command	Purpose
g	Global -- find all matches (default is 1st only)
i	Insensitive -- Case insensitive
m	Multi-line -- ^ and $ refer to line ends
s	Dotall -- . == [\w\W]