The NuttShell (
nsh) is an embedded equivalent to bash and similar Unix shells (command lines). It understands a reasonable set of shell commands. It is used to start all on-board applications. NSH interacts with the user over a serial port: either on the FMU system's UARTs or on USB.
See this page for details on how to connect to nsh over a serial connection.
See the official NuttShell documentation for information about its features.