Command lines are powerful. It was the only UI before the GUI. There is usually a learning curve, but once you master the commands, you can distil massively complex applications down to a few keystrokes. Command lines are unfortunately stigmatised, and considered "bad user experience". I disagree.
Lately I've been thinking about having a command line interface as the primary means of operating mobile devices. Almost all mobile devices have a "command line input" interface already: iOS has spotlight search input once you swipe left and Android phones have a search bar with an input on the homescreen. A quick demo (might take a minute to load the animation):