custom_excerpt.php

function custom_excerpt($limit, $post_id=NULL) {
  if($post_id == NULL) { $the_excerpt = get_the_excerpt(); } 
  else { $the_excerpt = get_the_excerpt($post_id); }

  $excerpt = explode(' ', $the_excerpt, $limit);     

  if (count($excerpt)>=$limit) {
    array_pop($excerpt);
    $excerpt = implode(" ",$excerpt).'...';
  } else {
    $excerpt = implode(" ",$excerpt);
  } 
  $excerpt = preg_replace('`\[[^\]]*\]`','',$excerpt);
  return $excerpt;
}