MY_MODULE.module

<?php
/**
 * Returns the node identifier should the path be a node viewing path.
 *
 * Note: This function returns FALSE for all node action or local task paths
 * such as node/[nid]/edit.
 *
 * Furthermore, a node alias may be specified as $path which will perform a path
 * normalization allowing for the node system path to be retrieved and parsed.
 *
 * @param string $path
 *   The path to attempt to retrieve the node id for.
 *
 * @return mixed
 *   Returns the node id as an integer, otherwise FALSE.
 */
function MY_MODULE_path_is_node_view($path) {
  $path = drupal_get_normal_path($path);
  if (preg_match('|node/([0-9]+)?|', $path, $matches)) {
    return isset($matches[1]) && is_numeric($matches[1]) ? intval($matches[1]) : FALSE;
  }
  return FALSE;
}

For a complex usage and multiple variations, see http://github.com/amcgowanca/drupal_uuid_menu_links.