Wrapping a function in html tag and return?

Question

I am creating a shortcode. The shortcode will output a list of pages with the wp_list_pages() function. I am using the ('title_li') parameter and the list headline will be removed, because it is left empty and the "ul tag" will be removed as well, which is not desired.

http://codex.wordpress.org/Function_Reference/wp_list_pages#Hiding_or_Changing_the_List_Heading

Now I am trying to wrap it in ul tag again. This is what I am trying but it will return list of pages in "li" with out the "ul tag".

function sitemap_function() {
  $return_string .= "<ul>";
  $return_string .= wp_list_pages('sort_column=menu_order&title_li=');
  $return_string .= "</ul>";

  return $return_string;
}

function register_shortcodes() {
  add_shortcode('sitemap', 'sitemap_function');
}

add_action('init', 'register_shortcodes');

Hope someone can help me out here. Thanks in Advance.

Answer 1

you need to sert the 'echo' parameter of wp_list_pages() to 0 (zero):

$return_string .= wp_list_pages('sort_column=menu_order&title_li=&echo=0');