That command created a logged-in process on the modem device that Lenny was connected to in the context of the operator’s account. As soon as the operator typed in the command, a "$" prompt appeared on Lenny’s terminal. That meant he was logged in with the full privileges of the operator. When the "$" showed up, Lenny was so excited that he started shouting into the phone, "I’ve got a prompt! I’ve got a prompt!"