The command line provides a keyboard-driven interface between a computer and the user. The user types in a command and the computer processes the appropriate instruction for that command, after which it displays a specified prompt indicating to the user that the system is ready for further commands.

MS-DOS was a command line driven system. Microsoft® Windows®, by contrast, offers a Graphical User Interface [GUI] and the means to input instructions using a mouse (in addition to command line access. Most Unix-based operating systems also offer both command line and GUI interfaces.