常用表达.在两个词之间匹配特定词 [英] Regular expressions. Match specific word between two words

问题描述

我使用C#.我有一个字符串:

I use C#. I have a string:

wordA wordB wordC wordB wordD

我需要匹配wordA和wordD之间所有出现的wordB.我使用lookahead和lookbehind来匹配wordA和worD之间的所有内容，如下所示:

I need to match all occurrences of wordB between wordA and wordD. I use lookahead and lookbehind to match everything between wordA and worD like this:

(?<=wordA)(.*?)(?=wordD)

但是类似

(?<=wordA)(wordB)(?=wordD) 

不匹配任何内容.匹配单词A和单词D之间所有出现的单词B的最佳方法是什么?

matches nothing. What would be the best way to match all occurrences of wordB between wordA and wordD?

推荐答案

将.*?放入环顾四周:

(?<=wordA.*?)wordB(?=.*?wordD)

请参见现在，该模式表示:

• (?< = wordA.*?)-(积极地向后看)要求存在 wordA ，后跟任意0+个字符(尽可能少)紧接...
• wordB -单词B
• (?=.*?wordD)-(正向查找)要求存在任何0+个字符(尽可能少)，后跟一个 wordD 它们(因此，可以紧接在 wordB 之后或某些字符之后).

• (?<=wordA.*?) - (a positive lookbehind) requires the presence of wordA followed with any 0+ chars (as few as possible) immediately before...
• wordB - word B
• (?=.*?wordD) - (a positive lookahead) requires the presence of any 0+ chars (as few as possible) followed with a wordD after them (so, it can be right after wordB or after some chars).

如果您需要考虑多行输入，请使用 RegexOptions.Singleline 标志编译正则表达式，以便.可以与换行符匹配(或在模式前加上(?s)内联修饰符选项-(?s)(?< = wordA.*?)wordB(?=.*?wordD)).

If you need to account for multiline input, compile the regex with RegexOptions.Singleline flag so that . could match a newline symbol (or prepend the pattern with (?s) inline modifier option - (?s)(?<=wordA.*?)wordB(?=.*?wordD)).

如果单词"由字母/数字/下划线组成，并且您需要将它们作为整个单词进行匹配，请不要忘记将 wordA ， wordB 和带有 \ b (单词边界)的 wordD .

If the "words" consist of letters/digits/underscores, and you need to match them as whole words, do not forget to wrap the wordA, wordB and wordD with \bs (word boundaries).

始终在目标环境中测试您的正则表达式:

Always test your regexes in the target environment:

var s = "wordA wordB wordC wordB \n wordD";
var pattern = @"(?<=wordA.*?)wordB(?=.*?wordD)";
var result = Regex.Replace(s, pattern, "<<<$&>>>", RegexOptions.Singleline);
Console.WriteLine(result);
// => wordA <<<wordB>>> wordC <<<wordB>>> 
//    wordD

请参见 C#演示.

这篇关于常用表达.在两个词之间匹配特定词的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！