/**
 * Search content for shortcodes and filter shortcodes through their hooks.
 *
 * If there are no shortcode tags defined, then the content will be returned
 * without any filtering. This might cause issues when plugins are disabled but
 * the shortcode will still show up in the post or content.
 *
 * @since 2.5
 * @uses $shortcode_tags
 * @uses get_shortcode_regex() Gets the search pattern for searching shortcodes.
 *
 * @param string $content Content to search for shortcodes
 * @return string Content with shortcodes filtered out.
 */
function do_shortcode($content) {
	global $shortcode_tags;

	if (empty($shortcode_tags) || !is_array($shortcode_tags))
		return $content;

	$pattern = get_shortcode_regex();
	return preg_replace_callback('/'.$pattern.'/s', 'do_shortcode_tag', $content);
}

/**
 * Retrieve the shortcode regular expression for searching.
 *
 * The regular expression combines the shortcode tags in the regular expression
 * in a regex class.
 *
 * @since 2.5
 * @uses $shortcode_tags
 *
 * @return string The shortcode search regular expression
 */
function get_shortcode_regex() {
	global $shortcode_tags;
	$tagnames = array_keys($shortcode_tags);
	$tagregexp = join( '|', array_map('preg_quote', $tagnames) );

	return '\[('.$tagregexp.')\b(.*?)(?:(\/))?\](?:(.+?)\[\/\1\])?';
}