Some minor clarification to the http://docs.mongodb.org/manual/reference/program/mongo/ page

Unfortunately, the shell doesn't quite agree with all the other tools
about how it processes command line arguments and options.
Specifically:

the shell parses its first non-option argument as [hostname[:port]/]dbname.

The other tools take a --host, --port, and --db option, which are
the only way to point these tools at a MongoDB deployment. The --host
must either parse as an IP address or else resolve as a hostname, the
port must parse as a port number, and the db must be a valid database
name.

The shell also takes the --host and --port options, but if you
supply them, then you can't use the hostname and port number as part
of the non-optional argument, but can only specify a database name.

The shell does not take a --db option.