Regex.md

Regex 101

Find

/cool/

• looks for the first instance of cool

Flags

/cool/gi

Global /g

• looks for all matches

Insensitive /i

• case insensitive

Character sets []

/[cp]ool/

• matches cool and pool

Exclude ^

/[^1]000/

• Match everything except for 1 in the first position
• 2000, 3000 . . .

Ranges

/[a-g]/

• instead of writing [abcdefg] we can specify a range

/[a-zA-Z0-9]/

• lowercase, uppercase, and numbers

Repeating Characters

/[0-9]+/

• match unlimited times, but at least 1

/[0-9]{10}/

• match 10 times

/[0-9]{8,11}/

• match between 8 to 11 times

/[0-9]{8,}/

• match at least 8 times

Metacharacters

\d

• match any digit character [0-9]

\w

• match any word character [a-zA-Z0-9_]

\s

• match any whitespace character (spaces, tabs)

\t

• match tab character only

Special Characters

+ one or more

\ escape

[] character set

[^] negate in set

? zero or one (optional)

/hey?/

• he is a match
• hey is a match

. any character (except newline)

.+

• matches all characters

* zero or more

Start/End patterns

/^[a-z]{5}$/

• Only find a 5 letter word
• ^ ensures front
• $ ensures back - line end

Alternate Characters

/cool|pool/
/(c|p)ool/

() groups up Regex

JavaScript

let reg = /[a-z]/ig
let reg = new RegExp(/[a-z]/, 'ig');

HTML

<input pattern="[a-z]">