protected function getCredentials()
    {
        // Database credentials.
        $credentialArgs = [
            '--host=%s --port=%s --user=%s --password=%s %s',
            escapeshellarg($this->config['host']),
            escapeshellarg($this->config['port']),
            escapeshellarg($this->config['user']),
            escapeshellarg($this->config['pass']),
            escapeshellarg($this->config['database']),
        ];
        return call_user_func_array('sprintf', $credentialArgs);
    }