如何以编程方式添加rel =" external"到一串HTML的外部链接？ [英] How do I programmatically add rel="external" to external links in a string of HTML?

问题描述

如何检查字符串变量中的链接是否为外部链接？此字符串是网站内容（如评论，文章等）。

How can I check if links from a string variable are external? This string is the site content (like comments, articles etc).

如果是，我如何追加外部值为 rel 属性？如果他们没有这个属性，请追加 rel =external？

And if they are, how do I append a external value to their rel attribute? And if they don't have this attribute, append rel="external" ?

推荐答案

HTML解析器适用于输入过滤，但是对于修改输出，您需要具有简单的正则表达式解决方案的性能。在这种情况下，回调正则表达式会这样做：

A HTML parser is appropriate for input filtering, but for modifying output you'll need the performance of a simpleminded regex solution. In this case a callback regex would do:

$html = preg_replace_callback("#<a\s[^>]*href="(http://[^"]+)"[^>]*>#",
     "cb_ext_url", $html);

function cb_ext_url($match) {
    list ($orig, $url) = $match;
    if (strstr($url, "http://localhost/")) {
        return $orig;
    }
    elseif (strstr($orig, "rel=")) {
        return $orig;
    }
    else {
        return rtrim($orig, ">") . ' rel="external">';
    }
}

您可能需要更细致的检查。但这是一般方法。

You'll probably need more fine-grained checks. But that's the general approach.

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