How to add nofollow for external link in wordpress automatically

I guess you know what we are going to talk about ? Yes you are right we are going to know how to add rel=”noflollow” in WordPress automatically.We use rel=”nofollow” to tell spider not to follow the link.When spider like googlebot crawl our site they follow the link they find in our site and go to that page.And that page linked from our site get benefit from that link.Usually WordPress doesn’t add rel=”nofollow” to the external links automatically.You have to add it manually.Like below you have to edit the source code of your post.

<a title="wordpress the blogging tool" href="http://wordpress.org/" target="_blank" rel="nofollow">WordPress</a>

Here we added rel=”nofollow” within tag which is used for creating link in HTMl.Every time you put an external link in your post, you have to edit the source code and put the rel=”nofollow” code.It’s annoying isn’t it ? Now here comes the trick you can put a little code snippet in you theme function.php file to get rid of this problem.So go to your theme folder and open function.php file and put these line from bellow.You can put these line at the bottom as well as at the top.But never forget that you have to put this after

add_filter('the_content', 'auto_nofollow');

function auto_nofollow($content) {
    return stripslashes(wp_rel_nofollow($content));

    return preg_replace_callback('/<a>]+/', 'auto_nofollow_callback', $content);
}

function auto_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;
}

And save this file.That’s hit from now all of your external link will be modified automatically and rel=”nofollow” will be added automatically to all external link.

Thanks goes to OnextraPixel for this hack.