Regular Expressions Symbology

Regular Expressions Anchors
^	Start of string, or start of line in multi-line pattern
A	Start of string
$	End of string, or end of line in multi-line pattern
Z	End of string
b	Word boundary
B	Not word boundary
<	Start of word
>	End of word

Regular Expressions Character Classes
c	Control character
s	White space
S	Not white space
d	Digit
D	Not digit
w	Word
W	Not word
x	Hexade­cimal digit
O	Octal digit

Regular Expressions POSIX
[:upper:]	Upper case letters
[:lower:]	Lower case letters
[:alpha:]	All letters
[:alnum:]	Digits and letters
[:digit:]	Digits
[:xdigit:]	Hexade­cimal digits
[:punct:]	Punctu­ation
[:blank:]	Space and tab
[:space:]	Blank characters
[:cntrl:]	Control characters
[:graph:]	Printed characters
[:print:]	Printed characters and spaces
[:word:]	Digits, letters and underscore

Regular Expressions Assertions
?=	Lookahead assertion
?!	Negative lookahead
?<=	Lookbehind assertion
?!= or ?<!	Negative lookbehind
?>	Once-only Subexp­ression
?()	Condition [if then]
?()|	Condition [if then else]
?#	Comment

Regular Expressions Quantifiers
*	0 or more
+	1 or more
?	0 or 1
{3}	Exactly 3
{3,}	3 or more
{3,5}	3, 4 or 5
Add a ? to a quantifier to make it ungreedy.

Regular Expressions Escape Sequences
	Escape following character
Q	Begin literal sequence
E	End literal sequence
"­Esc­api­ng" is a way of treating characters which have a special meaning in regular expres­sions literally, rather than as special charac­ters.

Regular Expression Common Metacharacters
^	[	.
$	{	*
(		+
)	|	?
<	>
The escape character is usually the backslash - .

Regular Expressions Special Characters
n	New line
r	Carriage return
t	Tab
v	Vertical tab
f	Form feed
xxx	Octal character xxx
xhh	Hex character hh

Regular Expressions Groups and Ranges
.	Any character except new line (n)
(a|b)	a or b
(...)	Group
(?:...)	Passive (non-c­apt­uring) group
[abc]	Range (a or b or c)
[^abc]	Not a or b or c
[a-q]	Letter from a to q
[A-Q]	Upper case letter from A to Q
[0-7]	Digit from 0 to 7
n	nth group/­sub­pattern
Ranges are inclusive.

Regular Expressions Pattern Modifiers
g	Global match
i	Case-i­nse­nsitive
m	Multiple lines
s	Treat string as single line
x	Allow comments and white space in pattern
e	Evaluate replac­ement
U	Ungreedy pattern

Regular Expressions String Replacement
$n	nth non-pa­ssive group
$2	"­xyz­" in /^(abc­(xy­z))$/
$1	"­xyz­" in /^(?:a­bc)­(xyz)$/
$`	Before matched string
$'	After matched string
$+	Last matched string
$&	Entire matched string
Some regex implem­ent­ations use instead of $.