正则表达式将匹配字符串中最后出现的点 [英] RegEx that will match the last occurrence of dot in a string

问题描述

我有一个文件名，其中可以包含多个点，并且可以以任何扩展名结尾:

I have a filename that can have multiple dots in it and could end with any extension:

tro.lo.lo.lo.lo.lo.png

我需要使用正则表达式将点的最后一次出现替换为另一个字符串，例如@2x，然后再次点(非常类似于视网膜图像文件名)，即:

I need to use a regex to replace the last occurrence of the dot with another string like @2x and then the dot again (very much like a retina image filename) i.e.:

tro.lo.png -> [e-mail]

这是我到目前为止所拥有的，但与任何内容都不匹配...

Here's what I have so far but it won't match anything...

str = "http://example.com/image.png";
str.replace(/.([^.]*)$/, " @2x.");

有什么建议吗?

推荐答案

您不需要正则表达式. String.lastIndexOf 即可.

You do not need a regex for this. String.lastIndexOf will do.

var str = 'tro.lo.lo.lo.lo.lo.zip';
var i = str.lastIndexOf('.');
if (i != -1) {
    str = str.substr(0, i) + "@2x" + str.substr(i);
}

查看实际效果 .

See it in action.

更新:正则表达式解决方案，仅出于乐趣:

Update: A regex solution, just for the fun of it:

str = str.replace(/\.(?=[^.]*$)/, "@2x.");

匹配文字点，然后断言((?=)是正向超前)字符串末尾没有其他字符是点.替换项应包括一个匹配的点，除非您要删除它.

Matches a literal dot and then asserts ((?=) is positive lookahead) that no other character up to the end of the string is a dot. The replacement should include the one dot that was matched, unless you want to remove it.

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