How can I modify all existing <a> tags while keeping the urls themselves?

Question

I want to modify all current links to Amazon on my site, to add a rel="nofollower" tag — they currently have an existing rel="noopener" tag which, as I thought, was always placed at the beginning: <a rel="noopener" href="https://amzn.to/example">text</a>

I went into functions.php and added the following:

// add nofollow to Amazon
function add_noFollow($text) {
    $text = str_replace('rel="noopener" href="https://amzn.to', 'rel="noopener nofollow" href="https://amzn.to', $text);
    return $text;
}
add_filter('the_content', 'add_noFollow');

This worked as expected, keeping the full url (e.g. https://amaz.to/example). But then I realized that, for some reason, some links on my site were originally structured like this:

<a href="https://amzn.to/example" target="_blank" rel="noopener">text</a>

Since some links contained the rel="noopener" at the end, it means that I will have to modify the entire <a> tag, keeping the original url.

How can I modify my existing function to first detect if the <a> tag contains amzn.to and then replace the entire thing (adding the desired parameters, e.g. rel="nofollower noopener") but keeping the original url?

I thought some sort of wilcard function is needed, but I lack the necessary knowledge to go about it.

Answer 1

I solved the issue with help from this answer: https://wordpress.stackexchange.com/a/159570/176615

// add nofollow to Amazon
function add_nofollow_content($content) {
    $content = preg_replace_callback(
        '/<a[^>]*href=["|\']([^"|\']*)["|\'][^>]*>([^<]*)<\/a>/i',
    function($m) {
        if (strpos($m[1], "amzn.to") !== false)
            return '<a href="'.$m[1].'" rel="nofollow noopener" target="_blank">'.$m[2].'</a>';
        else
            return '<a href="'.$m[1].'" rel="noopener" target="_blank">'.$m[2].'</a>';
    },
    $content);
    return $content;
}
add_filter('the_content', 'add_nofollow_content');