This is a collection of common Q&A. This is also a Community Wiki, so everyone is invited to participate in maintaining it.
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.
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 is related to
regex
See also a lot of general hints and useful links at the regex tag details page.
Online tutorials
Quantifiers
*
:greedy, *?
:reluctant, *+
:possessive+
:greedy, +?
:reluctant, ++
:possessive?
:optional (zero-or-one){n,m}
:between n & m, {n,}
:n-or-more, {n}
:exactly n{n}
and {n}?
Character Classes
[...]
: any one character, [^...]
: negated/any character but[^]
matches any one character including newlines javascript[\w-[\d]]
/ [a-z-[qz]]
: set subtraction .net, xml-schema, xpath, JGSoft[\w&&[^\d]]
: set intersection java, ruby 1.9+[[:alpha:]]
:POSIX character classes[^\\D2]
, [^[^0-9]2]
, [^2[^0-9]]
get different results in Java? java\d
:digit, \D
:non-digit\w
:word character, \W
:non-word character\s
:whitespace, \S
:non-whitespace\p{L}, \P{L}
, etc.)Escape Sequences
\h
:space-or-tab, \t
:tab\H
:Non horizontal whitespace character, \V
:Non vertical whitespace character, \N
:Non line feed character pcre php5 java-8\v
:vertical tab, \e
:the escape characterAnchors
^
:start of line/input, \b
:word boundary, and \B
:non-word boundary, $
:end of line/input\A
:start of input, \Z
:end of input php, perl, ruby\z
:the very end of input (\Z
in Python) .net, php, pcre, java, ruby, icu, swift, objective-c\G
:start of match php, perl, ruby(Also see "Flavor-Specific Information ? Java ? The functions in Matcher
")
Groups
(...)
:capture group, (?:)
:non-capture group
\1
:backreference and capture-group reference, $1
:capture group reference
(?i:regex)
mean?(?P<group_name>regexp)
mean?(?>)
:atomic group or independent group, (?|)
:branch reset
regular-expressions.info
(?<groupname>regex)
: Overview and naming rules (Non-Stack Overflow links)(?P<groupname>regex)
python, (?<groupname>regex)
.net, (?<groupname>regex)
perl, (?P<groupname>regex)
and (?<groupname>regex)
phpLookarounds
(?=...)
:positive, (?!...)
:negative(?<=...)
:positive, (?<!...)
:negative (not supported by javascript)Modifiers
flag | modifier | flavors |
---|---|---|
c |
current position | perl |
e |
expression | php perl |
g |
global | most |
i |
case-insensitive | most |
m |
multiline | php perl python javascript .net java |
m |
(non)multiline | ruby |
o |
once | perl ruby |
S |
study | php |
s |
single line | unsupported: javascript (workaround) | ruby |
U |
ungreedy | php r |
u |
unicode | most |
x |
whitespace-extended | most |
y |
sticky ? | javascript |
Other:
|
:alternation (OR) operator, .
:any character, [.]
:literal dot character(*PRUNE)
, (*SKIP)
, (*FAIL)
and (*F)
(*BSR_ANYCRLF)
(?R)
, (?0)
and (?1)
, (?-1)
, (?&groupname)
Common Tasks
{...}
Advanced Regex-Fu
(?!a)a
this
except in contexts A, B and CFlavor-Specific Information
(Except for those marked with *
, this section contains non-Stack Overflow links.)
java.util.regex.Matcher
:
matches()
): The match must be anchored to both input-start and -endfind()
): A match may be anywhere in the input string (substrings)lookingAt()
: The match must be anchored to input-start onlyjava.lang.String
functions that accept regular expressions: matches(s)
, replaceAll(s,s)
, replaceFirst(s,s)
, split(s)
, split(s,i)
java.util.regex
preg_match
search
vs match
, how-toregex
, struct regex::Regex
regexp
commandGeneral 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.)
Source: Stackoverflow.com