如果链接链接到其他网站，我想在我网站的所有链接中添加rel="nofollow"。
例如，
$str = "<a href='www.linktoothersite.com'>I swear this isn't spam!</a><br><a href='www.mywebsite.com'>Hello World</a>";
输出应为
$str = "<a href='www.linktoothersite.com' rel="nofollow">I swear this isn't spam!</a><br><a href='www.mywebsite.com'>Hello World</a>";
我真的想要正则表达式，但不想要DDOMDocument。因为当我使用DOMDocument时，我总是会出错"警告：DOMDocument:：loadHTML（）[DOMDocument.loadHTML]：htmlParseEntityRef:应为"；"在实体"
使用DOM解析器并在所有链接上循环，检查其他站点的href属性。这是未经测试的，可能需要一些调整。
// assuming your html is in $HTMLstring
$dom = new DOMDocument();
$dom->loadHTML($HTMLstring);
// May need to disable error checking if the HTML isn't fully valid
$dom->strictErrorChecking = FALSE;
// Get all the links
$links = $dom->getElementsByTagName("a");
foreach($links as $link) {
$href = $link->getAttribute("href");
// Find out if the link points to a domain other than yours
// If your internal links are relative, you'll have to do something fancier to check
// their destinations than this simple strpos()
if (strpos("yourdomain.example.com", $href) == -1) {
// Add the attribute
$link->setAttribute("rel", "nofollow");
}
// Save the html
$output = $dom->saveHTML;