get file extension

/*
  * get the extension of file
  * @param : String file name
  * @return : String file extension
  */
 
function get_extension($file) {
    if (function_exists("pathinfo")) {
        $extension = pathinfo($file, PATHINFO_EXTENSION);
    } else {
        $extension = end(explode(".", $file));
    }
    return trim(strtolower($extension));
}