Command line interface

A command line interface or CLI is a method of interacting with a computer by giving it lines of text commands in written form either from keyboard input or from a script. The computer then generally responds with text output to the display or to a file. It contrasts with graphical user interfaces (GUIs).

Examples of programs which use command line interfaces include the Unix shell, VMS DCL, and related follow-on designs like /A> and MS-DOS's command.com. These programs are often called command line interpreters.

There are other programs which use CLIs as well. The CAD program AutoCAD has one. In some computing environments like Oberon or Smalltalk, most of the text which appears on the screen may be used for giving commands.

The commands given on a command line interface often are of the form

  doSomething how toAFile

or

 doSomething how toAnInputFile > outputFile

doSomething corresponds to a verb, how to an adverb (it describes how the command should be performend) and toAFile to a direct object.

Advantages of a command line interface

Even though new users seem to learn GUIs more quickly to perform common operations, carefully developed CLIs have several advantages:

• All options and operations are invoked in consistent form, while with GUIs similar operations often appear on different menus with different interfaces and different applications have different approaches.

• All options and operations are documented (or should be), meaning that it is no more difficult to perform a rare operation than a common one.

• CLIs double as scripting languages (see shell script) and can perform operations in a batch processing mode without user interaction. That means that once an operation is analyzed, it can be saved in a script and consistently performed without further effort. With GUIs, users must start over at the beginning every time, as GUI scripting is more limited (and often nonexistent). Simple commands do not even need a script, as the completed command can usually be assigned a name and executed simply by typing that name into the CLI.

External Links

• "In the Beginning, was the Command Line" By Neal Stephenson (longish and not up to the point but may contain some useful information, which could be brought in here in a rewritten form)