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Regular Expressions Cheat Sheet by 

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

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

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

Assertions

?=

Lookahead assertion

?!

Negative lookahead

?<=

Lookbehind assertion

?!= or ?<!

Negative lookbehind

?>

Once-only Subexp­ression

?()

Condition [if then]

?()|

Condition [if then else]

?#

Comment

 

Quanti­fiers

*

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 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.

Common Metach­ara­cters

^

[

.

$

{

*

(

\

+

)

|

?

<

>

The escape character is usually \

Special Characters

\n

New line

\r

Carriage return

\t

Tab

\v

Vertical tab

\f

Form feed

\xxx

Octal character xxx

\xhh

Hex character hh

 

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"

Ranges are inclusive.

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

* PCRE modifier

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 $.

 

 

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