Add rel="nofollow" and target="_blank" for external links permanently

Question

I would like to add rel="nofollow" and target="_blank" for all external links in my Wordpress posts and pages permanently. I am aware, that there are plugins, which do the same, but as soon as they get disabled, all changes will be reversed and the articles are the same as from the beginning.

I do not know how to differ between internal or external links nor how to check if there is already a rel="nofollow" or target="_blank" attribute.

I guess the best way of doing this would be using PHP instead of MySQL. I already searched the web for guides, tutorials or plugins, without success.

May someone help me? I appreciate your support.

Answer 1

I have got a solution for applying nofollow to all existing and new external links. Copy the code into your functions.php of your activated theme

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

You can also call the function home_url() instead of "YOUR_DOMAIN_ADDRESS" in the space provided to avoid hard coding of the domain name.

The code is tested and it works. Hope this one helps.

Answer 2

You can use following snippet: http://wpsnipp.com/index.php/functions-php/nofollow-external-links-only-the_content-and-the_excerpt/

This great little snippet that will add rel=”nofollow” to external links within both the_content and the_excerpt. Add this snippet to the functions.php of your wordpress theme to enable nofollow external links.

add_filter('the_content', 'my_nofollow');
add_filter('the_excerpt', 'my_nofollow');
function my_nofollow($content) {
    return preg_replace_callback('/<a[^>]+/', 'my_nofollow_callback', $content);
}
function my_nofollow_callback($matches) {
    $link = $matches[0];
    $site_link = get_bloginfo('url');
    if (strpos($link, 'rel') === false) {
        $link = preg_replace("%(href=\S(?!$site_link))%i", 'rel="nofollow" $1', $link);
    } elseif (preg_match("%href=\S(?!$site_link)%i", $link)) {
        $link = preg_replace('/rel=\S(?!nofollow)\S*/i', 'rel="nofollow"', $link);
    }
    return $link;
}