A good double-tab auto-completion in a CLI gives explicit boundaries and flattens learning curve almost to the GUI level, while letting you retain full flexibil

A good double-tab auto-completion in a CLI gives explicit boundaries and flattens learning curve almost to the GUI level, while letting you retain full flexibility and expressive power of a CLI. This work wonders in systems where complete set of commands is (semi-)fixed, like Cisco IOS CLI. *nix CLI is somewhat behind on this front, unfortunately.