protected function readEnvironmentVariable($line)
    {
        list($key, $value) = explode(':', substr($line, 4), 2);
        if (strncmp($key, 'arg_', 4) === 0) {
            $this->arguments[substr($key, 4)] = $value;
        } else {
            $this->variables[$key] = $value;
        }
    }