Javascript RegEx非捕获前缀 [英] Javascript RegEx non-capturing prefix

问题描述

我正在尝试使用Javascript中的RegEx进行一些字符串替换。该场景是一个单行字符串，包含长逗号分隔的数字列表，其中可能存在重复项。

I am trying to do some string replacement with RegEx in Javascript. The scenario is a single line string containing long comma-delimited list of numbers, in which duplicates are possible.

示例字符串为： 272， 2725,2726,272,2727,297,272 （结尾可能以逗号结尾也可能不以逗号结尾）

An example string is: 272,2725,2726,272,2727,297,272 (The end may or may not end in a comma)

在这个例子中，我正在尝试匹配整数272的每次出现。（预期3个匹配）
我试图使用的示例正则表达式是：（？：^ |，）272（？= $ |， ）

In this example, I am trying to match each occurrence of the whole number 272. (3 matches expected) The example regex I'm trying to use is: (?:^|,)272(?=$|,)

我遇到的问题是第二和第三场比赛包括我不想要的主要逗号。我很困惑，因为我认为（？：^ |，）会匹配，但不会捕获。有人可以为我阐明这个吗？有趣的是，尾随的逗号被排除在结果之外，这就是我想要的。

The problem I am having is that the second and third matches are including the leading comma, which I do not want. I am confused because I thought (?:^|,) would match, but not capture. Can someone shed light on this for me? An interesting bit is that the trailing comma is excluded from the result, which is what I want.

对于它的价值，如果我使用C＃，则有语法执行我想要的前缀匹配：（？< = ^ |，）
但是，它似乎在JavaScript中不受支持。

For what it is worth, if I were using C# there is syntax for prefix matching that does what I want: (?<=^|,) However, it appears to be unsupported in JavaScript.

最后，我知道我可以使用字符串拆分，数组操作和重新加入来解决它，但我想学习。

Lastly, I know I could workaround it using string splitting, array manipulation and rejoining, but I want to learn.

推荐答案

请改用字边界：

\b272\b

确保只有 272 匹配，但不是 2725 。

ensures that only 272 matches, but not 2725.

（？：...）匹配并且不捕获 - 但它匹配的任何内容都将成为整体匹配的一部分。

(?:...) matches and doesn't capture - but whatever it matches will be part of the overall match.

外观断言 （？= ...）是不同的：它只检查是否有可能（或不可能）匹配当前点的封闭正则表达式，但它不会添加整体比赛。

A lookaround assertion like (?=...) is different: It only checks if it is possible (or impossible) to match the enclosed regex at the current point, but it doesn't add to the overall match.

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