PHP: Use WordPress blog tags to find related posts

A simple script that can be used to pull related-type posts for a WordPress blog post. The related aspect is based on the fist tag assigned to the post. The script will return at most 5 other posts from the site that also include the first tag.

<?php

$tags = wp_get_post_tags($post->ID);

if ($tags) {
    
    $first_tag = $tags[0]->term_id;
    
    $select = array(
       'tag__in'          => array($tags[0]->term_id),
       'post__not_in'     => array($post->ID),
       'posts_per_page'   => 5,
       'caller_get_posts' => 1
    );
    
    $tag = get_tag($first_tag);
   
    $tag_query = new WP_Query($select);
   
    if( $tag_query->have_posts() ) {
        echo "<ul>";
        while ($tag_query->have_posts()) : $tag_query->the_post(); ?>
            <li>
                <a href="<?php the_permalink() ?>">
                   <?php the_title(); ?>
                </a>
            </li>

        <?php endwhile;
        echo "</ul>";
    }
    
    wp_reset_query();
}

?>