<?php
//for use in the loop, list 5 post titles related to first tag on current post
$tags = wp_get_post_tags($post->ID);
if ($tags) { echo 'Related Posts'; $first_tag = $tags[0]->term_id; $args=array( 'tag__in' => array($first_tag), 'post__not_in' => array($post->ID), 'showposts'=>5, 'caller_get_posts'=>1 ); $my_query = new WP_Query($args); if( $my_query->have_posts() ) { while ($my_query->have_posts()) : $my_query->the_post(); ?> <p><a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title_attribute(); ?>"><?php the_title(); ?></a></p> <?php endwhile; }
}
?>

function related_posts_shortcode( $atts ) { extract(shortcode_atts(array( 'limit' => '5', ), $atts));
  global $wpdb, $post, $table_prefix;
  if ($post->ID) { $retval = '<ul>'; // Get tags $tags = wp_get_post_tags($post->ID); $tagsarray = array(); foreach ($tags as $tag) { $tagsarray[] = $tag->term_id; } $tagslist = implode(',', $tagsarray);
  // Do the query $q = "SELECT p.*, count(tr.object_id) as count FROM $wpdb->term_taxonomy AS tt, $wpdb->term_relationships AS tr, $wpdb->posts AS p WHERE tt.taxonomy ='post_tag' AND tt.term_taxonomy_id = tr.term_taxonomy_id AND tr.object_id = p.ID AND tt.term_id IN ($tagslist) AND p.ID != $post->ID AND p.post_status = 'publish' AND p.post_date_gmt < NOW() GROUP BY tr.object_id ORDER BY count DESC, p.post_date_gmt DESC LIMIT $limit;";
  $related = $wpdb->get_results($q); if ( $related ) { foreach($related as $r) { $retval .= ' <li><a title="'.wptexturize($r->post_title).'" href="'.get_permalink($r->ID).'">'.wptexturize($r->post_title).'</a></li>
'; } } else { $retval .= ' <li>No related posts found</li>
'; } $retval .= '</ul>
'; return $retval; } return;
}
add_shortcode('related_posts', 'related_posts_shortcode');

[related_posts]

/** * related post with category * @param: int $limit limit of posts * @param: bool $catName echo category name * @param: string $title string before all entries * Example: echo fb_cat_related_posts(); */
if ( !function_exists('fb_get_cat_related_posts') ) { function fb_get_cat_related_posts( $limit = 5, $catName = TRUE, $title = '<h3>Recent Pages</h3>' ) {
  if ( !is_single() ) return;
  $limit = (int) $limit; $output = ''; $output .= $title;
  $category = get_the_category(); $category = (int) $category[0]->cat_ID;
  if ( $catName ) $output .= __( 'Kategorie: ' ) . get_cat_name($category) . ' ';
  $output .= '<ul>';
  $args = array( 'numberposts' => $limit, 'category' => $category, );
  $recentposts = get_posts( $args ); foreach($recentposts as $post) { setup_postdata($post); $output .= '<li><a href="' . get_permalink($post->ID) . '">' . get_the_title($post->ID) . '</a></li>'; }
  $output .= '</ul>';
  return $output; }
}