参考 - 这个正则表达式是什么意思？

Question

这是什么？

这是常见问答集。这也是一个社区 Wiki，因此邀请所有人参与维护它。

这是为什么？

regex 正在遭受 give me ze code 类型的问题和没有任何解释的糟糕答案。此参考旨在提供高质量问答的链接。

范围是多少？

此参考适用于以下语言：php、perl、javascript、python、ruby、java、.net。

这可能过于宽泛，但这些语言共享相同的语法。对于特定的功能，它背后有语言的标签，例如：

• 什么是正则表达式平衡组？ .net

Answer 1

堆栈溢出正则表达式常见问题解答

在regextag details page 上还可以查看很多一般提示和有用的链接。

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在线教程

• RegexOne ↪
• Regular Expressions Info ↪

量词

• 零个或多个：*:greedy、*?:reluctant、*+:possessive
• 一个或多个：+:greedy、+?:reluctant、++:possessive
• ?:optional (zero-or-one)
• 最小/最大范围（包括所有）：{n,m}:between n & m、{n,}:n-or-more、{n}:exactly n
• 贪婪、不情愿（又名“懒惰”、“不贪婪”）和所有格量词之间的区别：
  • Greedy vs. Reluctant vs. Possessive Quantifiers
  • In-depth discussion on the differences between greedy versus non-greedy
  • What's the difference between {n} and {n}?
  • Can someone explain Possessive Quantifiers to me? php, perl, java, ruby
  • Emulating possessive quantifiers.net
  • 非堆栈溢出参考：来自Oracle、regular-expressions.info

字符类

• What is the difference between square brackets and parentheses?
• [...]：任何一个字符，[^...]：否定/任何字符，但是
• [^] matches any one character including newlinesjavascript
• [\w-[\d]] / [a-z-[qz]]：设置减法.net，xml-schema，xpath，JGSoft
• [\w&&[^\d]]: set intersectionjava,ruby1.9+
• [[:alpha:]]:POSIX 字符类
• [[:<:]] 和 [[:>:]] 字边界
• Why do [^\\D2], [^[^0-9]2], [^2[^0-9]] get different results in Java?java
• 简写：
  • 数字：\d:digit，\D:non-digit
  • 单词字符（字母、数字、下划线）：\w:word character、\W:non-word character
  • 空白：\s:whitespace，\S:non-whitespace
• Unicode categories (\p{L}, \P{L}, etc.)

转义序列

• 水平空白：\h:space-or-tab, \t:tab
• 换行符：
  • \r, \n:carriage return and line feed
  • \R:generic newlinephpjava-8
• 否定的空白序列：\H:Non horizontal whitespace character, \V:Non vertical whitespace character, \N:Non line feed characterpcrephp5java-8
• 其他：\v:vertical tab、\e:the escape character

锚点

anchor	matches	flavors
^	Start of string	Common*
^	Start of line	Commonm
$	End of line	Commonm
$	End of text	Common*
$	The very end of string	phpD, javascript
\A	Start of string	Common except js
\Z	End of text	Common except js python
\Z	The very end of string	python
\z	The very end of string	Common except js python
\b	Word boundary	Common
\B	Not a word boundary	Common
\G	End of previous match	Common except js, python re

Term	Definition
Start of string	At the very start of the string.
Start of line	At the very start of the string, and after a non-terminal line terminator.
End of string	At the very end of the string.
End of text	At the very end of the string, and at a terminal line terminator.
End of line	At the very end of the string, and at a line terminator.
Word boundary	At a word character not preceded by a word character, and at a non-word character not preceded by a non-word character.
End of previous match	At a previously set position, usually where a previous match ended. At the very start of the string if no position was set.

“普通”指的是：icujavajs.netobjective-cpcreperlphpphpphppythonswiftswiftp>

* 默认| ^m 多行模式。 | ^D 美元结束模式。

群组

• (...):capture group, (?:):non-capture group
  • Why is my repeating capturing group only capturing the last match?
• \1:backreference and capture-group reference, $1:capture group reference
  • What's the meaning of a number after a backslash in a regular expression?
  • \g<1>123:How to follow a numbered capture group, such as \1, with a number?:python
• What does a subpattern (?i:regex) mean?
• What does the 'P' in (?P<group_name>regexp) mean?
• (?>):atomic group 或 independent group, (?|):branch reset
  • Equivalent of branch reset in .NET/C#.net
• 命名的捕获组：
  • General named capturing group reference at regular-expressions.info
  • java: (?<groupname>regex): Overview 和 naming rules （非堆栈溢出链接）
  • 其他语言：(?P<groupname>regex)python,(?<groupname>regex).net,(?<groupname>regex)perl,(?P<groupname>regex)和(?<groupname>regex)php

环顾四周

• 前瞻：(?=...):positive、(?!...):negative
• 向后看：(?<=...):positive、(?<!...):negative
• 后向限制：
  • Lookbehinds need to be constant-length php, perl, python, ruby
  • Lookarounds of limited length {0,n}java
  • Variable length lookbehinds are allowed.net
• 后视替代方案：
  • Using \Kphp,perl(Flavors that support \K)
  • Alternative regex module for Pythonpython
    • The hacky way
    • JavaScript negative lookbehind equivalents ^{External link}

修饰符

flag	modifier	flavors
a	ASCII	python
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	ruby
U	ungreedy	php r
u	unicode	most
x	whitespace-extended	most
y	sticky ↪	javascript

• How to convert preg_replace e to preg_replace_callback?
• What are inline modifiers?
• What is '?-mix' in a Ruby Regular Expression

其他：

• |:alternation (OR) operator, .:any character, [.]:literal dot character
• What special characters must be escaped?
• 控制动词（php 和 perl）：(*PRUNE)、(*SKIP)、(*FAIL) and (*F)
  • php 仅限：(*BSR_ANYCRLF)
• 递归（php 和 perl）：(?R)，(?0) and (?1)，(?-1)，(?&groupname)

常见任务

• Get a string between two curly braces: {...}
• Match (or replace) a pattern except in situations s1, s2, s3...
• How do I find all YouTube video ids in a string using a regex?
• 验证：
  • 互联网：email addresses、URLs（主机/端口：regex 和 non-regex 替代品）、passwords
  • 数字：a number、min-max ranges (such as 1-31)、phone numbers、date
  • 使用正则表达式解析 HTML：请参阅“一般信息 > 何时不使用正则表达式”

高级正则表达式-Fu

• 字符串和数字：
  • Regular expression to match a line that doesn't contain a word
  • How does this PCRE pattern detect palindromes?
  • Match strings whose length is a fourth power
  • How does this regex find triangular numbers?
  • How to determine if a number is a prime with regex?
  • How to match the middle character in a string with regex?
• 其他：
  • How can we match a^n b^n?
  • 匹配嵌套括号
    • Using a recursive patternphp,perl
    • Using balancing groups.net
  • “Vertical” regex matching in an ASCII “image”
  • List of highly up-voted regex questions on Code Golf
  • How to make two quantifiers repeat the same number of times?
  • An impossible-to-match regular expression: (?!a)a
  • Match/delete/replace this except in contexts A, B and C
  • Match nested brackets with regex without using recursion or balancing groups?

风味特定信息

（标有* 的除外，此部分包含非堆栈溢出链接。）

• Java
  • 官方文档：Pattern Javadoc ↪、Oracle's regular expressions tutorial ↪
  • java.util.regex.Matcher中函数的区别：
    • matches()): 匹配必须同时定位到 input-start 和 -end
    • find()): 匹配可能在输入字符串（子字符串）中的任何位置
    • lookingAt(): 匹配必须仅锚定到输入开始
    • （对于一般的锚点，请参阅“锚点”部分）
  • 唯一接受正则表达式的java.lang.String函数：matches(s)、replaceAll(s,s)、replaceFirst(s,s)、split(s)、split(s,i)
  • *An (opinionated and) detailed discussion of the disadvantages of and missing features in java.util.regex
• .NET
  • How to read a .NET regex with look-ahead, look-behind, capturing groups and back-references mixed together?
• 官方文档：
  • Boost 正则表达式引擎：General syntax、Perl syntax （由 TextPad、Sublime Text、UltraEdit 使用...？？？）
  • JavaScript general info 和 RegExp object
  • .NETMySQLOraclePerl5 version 18.2
  • PHP：pattern syntax，preg_match
  • Python：Regular expression operations、search vs match、how-to
  • 锈：crate regex，struct regex::Regex
  • Splunk：regex terminology and syntax 和 regex command
  • Tcl：regex syntax，manpage，regexp command
  • Visual Studio Find and Replace

一般信息

（标有* 的链接是非堆栈溢出链接。）

• 其他通用文档资源：Learning Regular Expressions、*Regular-expressions.info、*Wikipedia entry、*RexEgg、Open-Directory Project
• DFA versus NFA
• Generating Strings matching regex
• 书籍：Jeffrey Friedl 的 Mastering Regular Expressions
• 什么时候不使用正则表达式：
  • Some people, when confronted with a problem, think "I know, I'll use regular expressions." Now they have two problems.（Stack Overflow创始人写的博文）*
  • 不要使用正则表达式解析 HTML：
    • Don't。 Please, just don't
    • Well, maybe...if you're really determined（这个问题的其他答案也不错）

可能导致正则表达式引擎失败的正则表达式示例

• Why does this regular expression kill the Java regex engine?

工具：测试者和解释者

（此部分包含非 Stack Overflow 链接。）

• 在线（*包括更换测试仪，+包括拆分测试仪）：

  • Debuggex（还有一个有用的正则表达式存储库）javascript，python，pcre
  • *Regular Expressions 101 php, pcre, python, javascript
  • Regex Pal, regular-expressions.info javascript
  • RubularrubyRegExrRegex Herodotnet
  • *+ regexstorm.net .net
  • * RegexPlanet：Java 987654612 @，Go 987654614 @，Haskell 987654616 @，JavaScript 987654618 @，.NET 987654620 @，Perl 987654622 php PCRE php, Python python, Ruby ruby, XRegExp xregexp
  • freeformatter.comxregexp
  • *+regex.larsolavtorvik.com php PCRE 和 POSIX，javascript
  • Refiddle javascript ruby .net

• 离线：

  • Microsoft Windows：RegexBuddy（分析）、RegexMagic（创建）、Expresso（分析、创建、免费）