参考 - 这个正则表达式意味着什么？

Question

这是什么？

这是常见问答的集合。这也是社区Wiki，因此邀请每个人参与维护。

为什么是这样？

regex正在遭受给我代码类型的问题和糟糕的答案，没有任何解释。此参考旨在提供质量问答的链接。

范围是什么？

本参考文献适用于以下语言：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。对于特定功能，它背后的语言标签，例如：

• 什么是正则表达式平衡组？ .net

Answer 1

Stack Overflow正则表达式常见问题解答

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在线教程

• RegexOne
• Regular Expressions Info

量词

• 零或多：*:greedy，*?:reluctant，*+:possessive
• 一个或多个：+:greedy，+?:reluctant，++:possessive
• ?:optional (zero-or-one)
• 最小/最大范围（全包）：{n,m}:between n & m，{n,}:n-or-more，{n}:exactly n
• 贪婪，不情愿（a.k.a。“lazy”，“ungreedy”）和占有量词之间的差异： 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Stack Overflow参考：来自Oracle，regular-expressions.info

角色类

• What is the difference between square brackets and parentheses?
• [...]：任何一个角色，[^...]：否定/任何角色但是
• [^] matches any one character including newlines javascript
• [\w-[\d]] / [a-z-[qz]]：设置减法.net，xml-schema，xpath，JGSoft
• [\w&&[^\d]]: set intersection java，ruby 1.9+
• [[:alpha:]]：POSIX字符类
• Why do [^\\D2], [^[^0-9]2], [^2[^0-9]] get different results in Java? java
• 速记： 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： \r, \n:carriage return and line feed \R:generic newline php
• 否定的空白序列：\H:Non horizontal whitespace character, \V:Non vertical whitespace character, \N:Non line feed character pcre php5 java-8
• 其他：\v:vertical tab，\e:the escape character

锚

• ^: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（Python中的\Z）.net，php，pcre，java，ruby，icu，swift，objective-c
• \G:start of match php，perl，ruby

（另请参阅“风味特定信息→Java→Matcher中的功能”）

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
• 命名捕获组： General named capturing group reference at regular-expressions.info java：(?<groupname>regex)：Overview和naming rules（非Stack Overflow链接） 其他语言：(?P<groupname>regex) python，(?<groupname>regex) .net，(?<groupname>regex) perl，(?P<groupname>regex)和(?<groupname>regex) php

Lokaraunds

• 前瞻：(?=...):positive，(?!...):negative
• Lookbehinds：(?<=...):positive，(?<!...):negative（不支持javascript）
• Lookbehind限制在： Lookbehinds need to be constant-length php，perl，python，ruby Lookarounds of limited length {0,n} java Variable length lookbehinds are allowed .net
• Lookbehind替代品： Using \K php，perl（Flavors that support \K） Alternative regex module for Python python The hacky way JavaScript negative lookbehind equivalents External link

修饰符

• 大多数口味：qazxsw poi，qazxsw poi，qazxsw poi，qazxsw poi
• g:global i:case-insensitive u:unicode x:whitespace-extended c:current position perl e:expression
• php perl o:once ruby m:multiline php perl，python javascript
• .net（不支持java或m:(non)multiline），ruby s:single line
• javascript ruby s workaround javascript S:study
• php
• U:ungreedy
• php

其他：

• r，How to convert preg_replace e to preg_replace_callback?，What are inline modifiers?
• What is '?-mix' in a Ruby Regular Expression
• 控制动词（|:alternation (OR) operator和.:any character）：[.]:literal dot character，What special characters must be escaped?，php 仅限perl：(*PRUNE)
• 递归（qazxsw poi和qazxsw poi）：qazxsw poi，(*SKIP)，(*FAIL) and (*F)，php

常见任务

• (*BSR_ANYCRLF)
• php
• perl
• 验证： 互联网：(?R)，(?0) and (?1)（主机/港口：(?-1)和(?&groupname)替代品），Get a string between two curly braces: {...} 数字：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?，email addresses，URLs 使用正则表达式解析HTML：请参阅“常规信息>何时不使用正则表达式”

高级正则表达式

• 字符串和数字： regex non-regex passwords a number min-max ranges (such as 1-31) phone numbers
• 其他： qazxsw poi 匹配嵌套括号 qazxsw poi qazxsw poi，date 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? How can we match a^n b^n with Java regex? Using a recursive pattern

风味特定信息

（除了那些标有php的内容外，此部分包含非Stack Overflow链接。）

• Java的 官方文件：perl，Using balancing groups .net中函数之间的差异： “Vertical” regex matching in an ASCII “image”）：匹配必须锚定到input-start和-end List of highly up-voted regex questions on Code Golf）：匹配可以在输入字符串中的任何位置（子串） How to make two quantifiers repeat the same number of times?：匹配必须仅限于输入 - 开始 （一般情况下，锚点见“锚点”一节） 唯一接受正则表达式的An impossible-to-match regular expression: (?!a)a函数：Match/delete/replace this except in contexts A, B and C，Match nested brackets with regex without using recursion or balancing groups?，*，Pattern Javadoc，Oracle's regular expressions tutorial * java.util.regex.Matcher
• 。净 matches()
• 官方文件： 提升正则表达式引擎：find()，lookingAt()（由TextPad使用，Sublime Text，UltraEdit，...... ???） JavaScript 1.5 java.lang.String和matches(s) replaceAll(s,s) replaceFirst(s,s) split(s) split(s,i) PHP：An (opinionated and) detailed discussion of the disadvantages of and missing features in java.util.regex，How to read a .NET regex with look-ahead, look-behind, capturing groups and back-references mixed together? Python：General syntax，Perl syntax，general info Splunk：RegExp object和.NET Tcl：MySQL，Oracle，Perl5 version 18.2 pattern syntax

一般信息

（标记为preg_match的链接是非Stack Overflow链接。）

• 其他一般文献资源：Regular expression operations，* search vs match，* how-to，* regex terminology and syntax，regex command
• regex syntax
• manpage
• 书籍：Jeffrey Friedl的regexp command
• 何时不使用正则表达式： Visual Studio Find and Replace（由*创始人撰写的博文）* 不要使用正则表达式来解析HTML： Learning Regular Expressions。 Regular-expressions.info Wikipedia entry（这个问题的其他答案也很好）

可能导致正则表达式引擎失败的正则表达式示例

• RexEgg

工具：测试人员和解说员

（此部分包含非Stack Overflow链接。）

• 在线（*包括更换测试仪，+包括分体测试仪）： Open-Directory Project（也有一个有用的正则表达式的存储库）DFA versus NFA，Generating Strings matching regex，Mastering Regular Expressions * Some people, when confronted with a problem, think "I know, I'll use regular expressions." Now they have two problems. Stack Overflow，Don't，Please, just don't，Well, maybe...if you're really determined Why does this regular expression kill the Java regex engine?，Debuggex javascript python pcre Regular Expressions 101 php pcre * + python javascript * RegexPlanet：Regex Pal regular-expressions.info，javascript Rubular，ruby RegExr，Regex Hero dotnet，regexstorm.net .net，Java java Go go Haskell，haskell JavaScript，javascript .NET，dotnet Perl perl php * + PCRE php PCRE和POSIX，Python python Ruby ruby XRegExp
• 离线： Microsoft Windows：xregexp（分析），freeformatter.com（创作），xregexp（分析，创作，免费）