RegularExpression

Anchors
^    Start of string
\A    Start of string
$    End of string
\Z    End of string
\b    Word boundary
\B    Not word boundary
\<    Start of word
\>    End of word

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

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

Escape Character
\    Escape Character

Metacharacters (must be escaped)
^    [    .
$    {    *
(    \    +
)    |    ?
<    >

Quantifier Modifiers
"x"    below represents a quantifier
x?    Ungreedy version of "x"

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

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

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 white space in pattern
e    Evaluate replacement
U    Ungreedy pattern

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

String Replacement (Backreferences)
$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

Sample Patterns
Pattern    Will Match
([A-Za-z0-9-]+)    Letters, numbers and hyphens
(\d{1,2}\/\d{1,2}\/\d{4})    Date (e.g. 21/3/2006)
([^\s]+(?=\.(jpg|gif|png))\.\2)    jpg, gif or png image
(^[1-9]{1}$|^[1-4]{1}[0-9]{1}$|^50$)    Any number from 1 to 50 inclusive
(#?([A-Fa-f0-9]){3}(([A-Fa-f0-9]){3})?)    Valid hexadecimal colour code
((?=.*\d)(?=.*[a-z])(?=.*[A-Z]).{8,15})    String with at least one upper case letter, one lower case letter, and one digit (useful for passwords).
(\w+@[a-zA-Z_]+?\.[a-zA-Z]{2,6})    Email addresses
(\<(/?[^\>]+)\>)    HTML Tags
Note: These patterns are intended for reference purposes and have not been
extensively tested. Please use with caution and test thoroughly before use.

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