Regular Expressions cheat sheet

Cheat Sheet

Character	Meaning	Example
^	the beginning of the string
$	the end of the string
\b	whole word only	\babc\b matches 'abc', but not 'abcc '
\B	if the pattern is fully surrounded by word	\Babc\B mathes 'aabcc', but not 'abc'
.	anything
\d	single digit in 0-9
\D	single non-digit
\w	single word character
\W	single non-word
\s	white space(space, tab, return, new line)
\S	non-whitespace
\t	tab
\r	return
\n	new line
\g	global search, which means it doesn't stop at the first match
*	zero or more of the previous	abc* matches a string that has ab followed by zero or more c
+	one or more of the previous	abc+ matches a string that has ab followed by one or more c
?	zero or one of the previous	abc? matches a string that has ab followed by zero or one c
?:	non-capturing group
X{m}	number of X === m
X{m,}	m < number of X
X{m, n}	m < number of X < n
(X | Y)	X or Y
[...]	any of characters in the class	[abcd] matches a string that has one of the char (a, b, c, d)
-	range	[a-d] same as above

Key words from the cheat sheet

Anchor
Anchor is not a pattern, it is a position.
It matches a position before, after or between characters.
For example, ^ is the beginning of the string, and it is also a start of line anchor.

Boundaries
\b is a word boundary because \babc\b has to match the whole word abc.
\B is non-word-boundary because \Babc\B means any words that includes abc (abcc, eabc).

Quantifiers
Greedy: The optional item is included in the match if possible. ? is a typical example of greedy quantifiers. abc? can match either abc or ab.
Lazy: * The optional item is excluded in the match if possible. ?? is a typical one because abc?? only matches ab.

Non-capturing group
?: means the pattern doesn't capture to the group. It usually uses with .match(). So if you use ?:, then the pattern won't be included to the array.