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Reference - What does this regex mean?

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regex is suffering from give me ze code type of questions and poor answers with no explanation. This reference is meant to provide links to quality Q&A.

give me ze code

This reference is meant for the following languages: php, perl, javascript, python, ruby, java, .net.

This might be too broad, but these languages share the same syntax. For specific features there's the tag of the language behind it, example:

This question's answers are a collaborative effort: if you see something that can be improved, just edit the answer to improve it! No additional answers can be added here

1 Answer
1

Online tutorials

Quantifiers

*

*?

*+

+

+?

++

?

{n,m}

{n,}

{n}

{n}

{n}?

Character Classes

[...]

[^...]

[^]

[w-[d]]

[a-z-[qz]]

[w&&[^d]]

[[:alpha:]]

[^D2]

[^[^0-9]2]

[^2[^0-9]]

d

D

w

W

s

S

p{L}, P{L}

Escape Sequences

h

t

r

n

R

H

V

N

v

e

Anchors

^

b

B

$

A

Z

z

Z

G

(Also see "Flavor-Specific Information → Java → The functions in Matcher")

Matcher

Groups

(...)

(?:)

1

$1

g<1>123

1

(?i:regex)

(?P<group_name>regexp)

(?>)

(?|)

regular-expressions.info

(?<groupname>regex)

(?P<groupname>regex)

(?<groupname>regex)

(?<groupname>regex)

(?P<groupname>regex)

(?<groupname>regex)

Lookarounds

(?=...)

(?!...)

(?<=...)

(?<!...)

{0,n}

K

K

Modifiers

g

i

u

x

c

e

o

m

m

s

s

S

U

Other:

|

.

[.]

(*PRUNE)

(*SKIP)

(*FAIL)

(*F)

(*BSR_ANYCRLF)

(?R)

(?0)

(?1)

(?-1)

(?&groupname)

Common Tasks

{...}

Advanced Regex-Fu

(?!a)a

this

Flavor-Specific Information

(Except for those marked with *, this section contains non-Stack Overflow links.)

*

java.util.regex.Matcher

matches()

find()

lookingAt()

java.lang.String

matches(s)

replaceAll(s,s)

replaceFirst(s,s)

split(s)

split(s,i)

java.util.regex

preg_match

search

match

regexp

General information

(Links marked with * are non-Stack Overflow links.)

*

Examples of regex that can cause regex engine to fail

Tools: Testers and Explainers

(This section contains non-Stack Overflow links.)

Online (* includes replacement tester, + includes split tester):

freeformatter.com

regex.larsolavtorvik.com

Offline:

Reference - What does this regex mean?