Regular Expression

Regular Expression Cheat Sheet

Regular Expression Websites

https://regexone.com/ - Very nice and quick questions to learn more about regex

Basic Matching

Each symbol matches a single character

Syntax	Description
.	Anything
\d	Digit in 0,1,2,3,4,5,6,7,8,9
\D	Non-digit
\w	"Word" (letters and digits and _)
\W	Non-word
\c	Control Character
{SPACE_KEYPRESS}	space
\t	tab
\r	return
\n	new line
\s	whitespace
\S	non-whitespace
\x	Hexadecimal digit
\O	Octal digit

Character Classes

Regexp Tutorial - Character Classes or Character Sets

Character classes - JavaScript | MDN

Syntax	Description
[xyz]	[abcd] is the same as [a-d]. They match the "b" in "brisket", and the "c" in "chop".
[^xyz]	[^abc] is the same as [^a-c]. They initially match "o" in "bacon" and "h" in "chop".

Escape Sequences

"­Esc­api­ng" is a way of treating characters which have a special meaning in regular expres­sions literally, rather than as special charac­ters. The escape character is usually \

Syntax	Description
\	Escape following character
\Q	Begin literal sequence
\E	End literal sequence

Boundaries

Boundary characters are helpful in "anchoring" your pattern to some edge, but do not select any characters themselves

Syntax	Description
\b	word boundaries (as defined as any edge between a \w and \W)
\B	non-word boundaries
\A	Start of string
\Z	End of string
\<	Start of word
\>	End of word
^	the beginning of the line
$	The end of the line

Example: \bcat\b finds a match in "the cat in the hat" but not in "locate"

Quantifiers

By default quantifiers just apply to the one character. Use (...) to specify explicit quantifier "scope"

Syntax	Description
X*	0 or more repetitions of X
X+	1 or more repetitions of X
X?	0 or 1 instances of X
X{m}	Exactly m instances of X
X{m,}	At least m instances of X
X{m,n}	Between m and n (inclusive) instances of X

Disjunction

Syntax	Description
(X|Y)	X or Y

Example: \b(cat|dog)s\b matches cats and dogs.

Special Characters

The character {} [] ^ $ . | * + > \ (and - inside [...]) have special meaning in regex, so they must be "escaped" with \ to match them

Example: \. matches the period . and \\ matches the backslash \

Backreferences

Count your open parentheses ( from the left, starting with 1. Whatever is matched by parthesis number n can be refernced later by \n

Example: \b(\w+) \1\b matches two identical words with a space in between

Example 2: \b(\w+)er\b and replacing with more \1 will map "the taller man" -> "the more tall man" and "I am shorter" -> "I am more short"