正则表达式中的大于和小于符号 [英] Greater than and less than symbol in regular expressions
问题描述
我是正则表达式的新手，我只是因为真正研究了所有正则表达式字符而感到疲倦.我需要知道正则表达式中大于符号的目的是什么，例如:
I am new to regular expressions, and I am just tired by really studying all of the regex charatcer and all. I need to know what is the purpose of greater than symbol in regex for eg:
preg_match('/(?<=<).*?(?=>)/', 'sadfas<email@email.com>', $email);
请告诉我正则表达式中大于号和小于号的用法.
Please tell me the use of greater than symbo and less than symbol in regex.
推荐答案
大于号只是匹配目标字符串末尾的文字 >.
The greater than symbol simply matches the literal > at the end of your target string.
小于符号不是那么简单.首先让我们回顾一下环视语法:
The less than symbol is not so simple. First let's review the lookaround syntax:
模式 (?<={pattern}) 是一个肯定的后视断言，它测试当前匹配的字符串前面是否有匹配 {pattern} 的字符串.
The pattern (?<={pattern}) is a positive lookbehind assertion, it tests whether the currently matched string is preceded by a string matching {pattern}.
模式 (?={pattern}) 是一个积极的前瞻断言，它测试当前匹配的字符串后面是否跟有匹配 {pattern} 的字符串.
The pattern (?={pattern}) is a positive lookahead assertion, it tests whether the currently matched string is followed by a string matching {pattern}.
所以打破你的表达
(?<=<)断言当前匹配的字符串前面是文字<.*?匹配任何东西零次或多次，懒惰(?=>)断言当前匹配的字符串后跟文字>
(?<=<)assert that the currently matched string is preceded by a literal<.*?match anything zero or more times, lazily(?=>)assert than the currently matched string is followed by a literal>
将它们放在一起，模式将从您提供的输入字符串中提取 email@email.com.
Putting it all together the pattern will extract email@email.com from the input string you have given it.
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