Command-line Interface - Operating System Command-line Interfaces

Operating System Command-line Interfaces

Operating system (OS) command line interfaces are usually distinct programs supplied with the operating system.

A program that implements such a text interface is often called a command-line interpreter, command processor or shell. The term 'shell', often used to describe a command-line interpreter, can be in principle any program that constitutes the user-interface, including fully graphically oriented ones—for example, the default Windows GUI is created by a shell program named EXPLORER.EXE, as defined in the SHELL=EXPLORER.EXE line in the WIN.INI configuration file.

Examples of command-line interpreters include the various Unix shells (sh, ksh, csh, tcsh, bash, etc.), the historical CP/M CCP, and MS-DOS/IBM-DOS/DR-DOS's COMMAND.COM, as well as the OS/2 and the Windows CMD.EXE programs, the latter groups being based heavily on DEC's RSX and RSTS CLIs. Under most operating systems, it is possible to replace the default shell program by more specialized or powerful alternatives; some widespread examples include 4DOS for DOS, 4OS2 for OS/2, and 4NT or Take Command for Windows.

The general pattern of an OS command line interface is:

prompt command param1 param2 param3 ... paramN

• Prompt - generated by the program to provide context for the client.
• Command - provided by the client. Commands are usually one of three classes:
  1. Internal - recognized and processed by the command line interpreter itself and not dependent upon any external executable file.
  2. Included - A separate executable file generally considered part of the operating environment and always included with the OS.
  3. External - External executable files not part of the basic OS, but added by other parties for specific purposes and applications.
• param1 ...paramN - Optional parameters provided by the client. The format and meaning of the parameters depends upon the command issued. In the case of Included or External commands, the values of the parameters are delivered to the process (specified by the Command) as it is launched by the OS. Parameters may be either Arguments or Options.