How to add rel=“nofollow” to links with preg_replace()

Question

The function below is designed to apply rel=\"nofollow\" attributes to all external links and no internal links unless the path matches a predefined root URL de

Answer 1

Try to make it more readable first, and only afterwards make your if rules more complex:

function save_rseo_nofollow($content) {
    $content["post_content"] =
    preg_replace_callback('~<(a\s[^>]+)>~isU', "cb2", $content["post_content"]);
    return $content;
}

function cb2($match) { 
    list($original, $tag) = $match;   // regex match groups

    $my_folder =  "/hostgator";       // re-add quirky config here
    $blog_url = "http://localhost/";

    if (strpos($tag, "nofollow")) {
        return $original;
    }
    elseif (strpos($tag, $blog_url) && (!$my_folder || !strpos($tag, $my_folder))) {
        return $original;
    }
    else {
        return "<$tag rel='nofollow'>";
    }
}

Gives following output:

[post_content] =>
  internal
  internal cloaked link    
  external

The problem in your original code might have been $rseo which wasn't declared anywhere.