code: public function getScriptFile()
      {
          if ($this->_scriptFile === null) {
              if (isset($_SERVER['SCRIPT_FILENAME'])) {
                  $this->setScriptFile($_SERVER['SCRIPT_FILENAME']);
              } else {
                  throw new InvalidConfigException('Unable to determine the entry script file path.');
              }
          }
  
          return $this->_scriptFile;
      }
docs: Returns entry script file path.
  @return string entry script file path (processed w/ realpath())
  @throws InvalidConfigException if the entry script file path cannot be determined automatically.