Building a shortcode to display categories

Hello,

I’m trying to create a shortcode to output a formatted list of categories associated with the post the shortcode is called into. The problem i’m having is that its only displaying 1 category and not all of the categories associated with each post.

//[categories-list]
function categories_list_func( $atts ){
 $categories = get_the_category();

	 if($categories) {
 	 	foreach($categories as $category) {
    		$output = '<li class="cat-' . $category->cat_ID . '"><a href="'.get_category_link( $category->term_id ).'" title="' . esc_attr( sprintf( __( "Read more posts from : %s" ), $category->name ) ) . '">'.$category->cat_name.'</a></li>';
        }
		$second_output = trim($output);
      }
	  $return_string = '<h4>'.__( "Categories :", "my_site").'</h4><div class="overflow"><ul class="post-categories">' . $second_output . '</ul></div>';

 return $return_string;

} // END Categories
add_shortcode( 'categories-list', 'categories_list_func' );

Does anyone know what i’m doing wrong?

Thanks,

Cyril