gistfile1.txt

    static public function link_shortcode_handler($arguments, $content = null, $parser = null) {
        if (!isset($arguments['id']) || !is_numeric($arguments['id']))
            return;

        if (
                !($page = DataObject::get_by_id('SiteTree', $arguments['id']))         // Get the current page by ID.
                && !($page = Versioned::get_latest_version('SiteTree', $arguments['id'])) // Attempt link to old version.
                && !($page = DataObject::get_one('ErrorPage', '"ErrorPage"."ErrorCode" = \'404\'')) // Link to 404 page.
        ) {
            return; // There were no suitable matches at all.
        }

        $link = Convert::raw2att($page->Link());
        if ($content) {
            return sprintf('<a href="%s">%s</a>', $link, $parser->parse($content));
        } else {
            return $link;
        }

    }

/* _config.php */
ShortcodeParser::get('default')->register('sitetree_link', array('Block_HTMLArea', 'link_shortcode_handler'));