### 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









### 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









### QUANTIFIERS ###
* 			0 or more
{3}			Exactly 3
+			1 or more
{3,}			3 or more
?			0 or 1
{3,5}			3, 4 or 5









### 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]		Lower case letter from a to q
[A-Q]		Upper case letter from A to Q
[0-7]		Digit from 0 to 7
\x		Group/subpattern number "x"









### SPECIAL CHARACTERS ###

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








### PATTERN MODIFIERS ###

g			Global match
i *			Case-insensitive
m *			Multiple lines
s *			Treat string as single line
x *			Allow comments and whitespace in pattern
e *			Evaluate replacement
U *			Ungreedy pattern









### 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








### 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