def _construct_cmdlines(self):
        """
        Top-level _construct_* method.

        From here, it will branch out to the different cases:
        _construct_sharded, _construct_replicaset, _construct_single. These can
        themselves call each other (for example sharded needs to create the
        shards with either replicaset or single node). At the lowest level, the
        construct_mongod, _mongos, _config will create the actual command line
        strings and store them in self.startup_info.
        """
        if self.args['sharded']:
            # construct startup string for sharded environments
            self._construct_sharded()

        elif self.args['single']:
            # construct startup string for single node environment
            self._construct_single(self.dir, self.args['port'])

        elif self.args['replicaset']:
            # construct startup strings for a non-sharded replica set
            self._construct_replset(self.dir, self.args['port'],
                                    self.args['name'],
                                    list(range(self.args['nodes'])),
                                    self.args['arbiter'])

        # discover current setup
        self.discover()