A quick reference guide for regular expressions (regex), including symbols, ranges, grouping, assertions and some sample patterns to get you started.

^Start of string, or start of line in multi-line pattern
\AStart of string
$End of string, or end of line in multi-line pattern
\ZEnd of string
\bWord boundary
\BNot word boundary
\<Start of word
\>End of word
\cControl character
\sWhite space
\SNot white space
\DNot digit
\WNot word
\xHexade­cimal digit
\OOctal digit
Character Classes
[:upper:]Upper case letters
[:lower:]Lower case letters
[:alpha:]All letters
[:alnum:]Digits and letters
[:xdigit:]Hexade­cimal digits
[:blank:]Space and tab
[:space:]Blank characters
[:cntrl:]Control characters
[:graph:]Printed characters
[:print:]Printed characters and spaces
[:word:]Digits, letters and underscore
?=Lookahead assertion
?!Negative lookahead
?<=Lookbehind assertion
?!= or ?<!Negative lookbehind
?>Once-only Subexp­ression
?()Condition [if then]
?()|Condition [if then else]
*0 or more
{3}Exactly 3
+1 or more
{3,}3 or more
?0 or 1
{3,5}3, 4 or 5
?Add a ? to a quantifier to make it ungreedy.
\Escape following character
\QBegin literal sequence
\EEnd literal sequence
„­Esc­api­ng“ is a way of treating characters which have a special meaning in regular expres­sions literally, rather than as special charac­ters.
Escape Sequences
Common Metach­ara­cters
\nNew line
\rCarriage return
\vVertical tab
\fForm feed
\xxxOctal character xxx
\xhhHex character hh
Special Characters
.Any character except new line (\n)
(a|b)a or b
(?:…)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
\xGroup/­sub­pattern number „­x“
Ranges are inclusive.
Groups and Ranges
gGlobal 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
* PCRE modifier
Pattern Modifiers
$nnth 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 $.
String Replac­ement

Source: davechild