protected function processOperation()
    {
        if ($this->_operation!==null) {
            $value = $this->_operationArgument ? $this->_operationArgument : null;
            if ($value instanceof TmpFile) {
                $value = (string) $value;
            }
            $this->addArg($this->_operation, $value, $this->_escapeOperationArgument);
        }
    }