分隔符之间的匹配文本:贪婪还是懒惰的正则表达式? [英] Matching text between delimiters: greedy or lazy regular expression?

问题描述

对于在分隔符(例如<和>)之间匹配文本的常见问题，有两种常见的模式:

For the common problem of matching text between delimiters (e.g. < and >), there's two common patterns:

• 使用格式为START [^END]* END的贪婪的*或+量词，例如<[^>]*>或
• 使用形式为START .*? END的惰性*?或+?量词，例如<.*?>.

• using the greedy * or + quantifier in the form START [^END]* END, e.g. <[^>]*>, or
• using the lazy *? or +? quantifier in the form START .*? END, e.g. <.*?>.

是否有一个特定的理由要一个人胜于另一个人?

Is there a particular reason to favour one over the other?

推荐答案

一些优点:

[^>]*:

• 更具表现力.
• 捕获换行符而与/s标志无关.
• 考虑更快，因为引擎不必回溯即可找到成功的匹配项(使用[^>]引擎不会做出选择-我们仅提供一种将模式与字符串进行匹配的方法).

• More expressive.
• Captures newlines regardless of /s flag.
• Considered quicker, because the engine doesn't have to backtracks to find a successful match (with [^>] the engine doesn't make choices - we give it only one way to match the pattern against the string).

.*?

• 没有代码重复"-结束字符仅出现一次.
• 在结束定界符超过一个字符长的情况下更简单. (在这种情况下，字符类将不起作用)常见的替代方法是(?:(?!END).)*.如果END分隔符是另一种模式，则情况更糟.

• No "code duplication" - the end character only appears once.
• Simpler in cases the end delimiter is more than a character long. (a character class would not work in this case) A common alternative is (?:(?!END).)*. This is even worse if the END delimiter is another pattern.

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