Command-line Interface - Application Command-line Interfaces

Application Command-line Interfaces

Application programs (as opposed to operating systems) may also have command line interfaces.

An application program may support none, any, or all of these three major types of command line interface mechanisms:

1. Commands are specified as parameters upon invocation of the program.
   • Most operating systems support a means to pass additional information to a program when it is launched. When a program is launched from an OS command line shell, additional text provided at the shell command line along with the program name is passed to the launched program via command line arguments.
2. Commands are entered via an interactive command line session controlled by the application.
   • After launch, a program may provide an operator with an independent means to enter commands in the form of text.
3. Commands are entered via the operating system STDIN/STDOUT mechanism.

Some applications provide both a CLI and a GUI. In some cases, the GUI is a wrapper around a CLI application; other times, there is a CLI to control a GUI application. The engineering/scientific numerical computation package MATLAB provides no GUI for some calculations, but the CLI can handle any calculation. The three-dimensional-modelling program Rhinoceros 3D provides a CLI as well as a distinct scripting language. In some computing environments, such as the Oberon or Smalltalk user interface, most of the text which appears on the screen may be used for giving commands.

There are command-line interpreters for editing text files like ED and EDLIN, DEBUG, for disk management DISKPART, DFSEE, calculators (PC-DOS ACALC), all of which present a usable command prompt.

Some programs have the command line separate from the action window (where the output would appear). The early Sierra games, like the first three King's Quest games (1984-1986), use commands from an internal command line to move the character around in the graphic window. Editors like Vi and IBM PC DOS E Editor use commands typed on the command line, switching back and forth to edit mode, a kind of graphical ED or EDLIN, as it were. (ED and EDLIN are pure teletype programs).

The Command-Line Interface continues to co-evolve with GUIs like those provided by Microsoft Windows, Mac OS and the X Window System. Programs that make use of external helper programs, often make use of command lines embedded in the GUI interface or configuration. In some applications, such as MATLAB, AutoCAD or EAGLE, a CLI is integrated with the GUI, with some benefits of both.