What is "shell"

This is a program that takes, interprets and executes user commands, appearing on the screen as a command line, represented by a command interpreter, which waits on the screen for user commands. " Shell" is also used to describe applications, including software that is "built around" a specific component, such as browsers and email clients that are themselves "shells" for HTML rendering engines. The term "shell" in computing, being the outer layer between the user and the kernal operating system, is synonymous with the general word "shell".

Generally, operating system shells use a command line interface (CLI) or graphical user interface (GUI). Mac OS xxx and Windows xxx are widely used operating systems with graphical interfaces.

The ideal choice of user interface depends on the function on the particular computer the operation. Clis allows some operations to be executed more quickly by reorganizing large blocks of data, for example. Clis may be better for servers that are managed by experts: administrators, while Guis offer simplicity and ease of use and would be more suitable for image editing, CADD and electronic publishing. In practice, many systems provide both user interfaces that can be called on a command-by-command basis. Windows xxx is the most obvious example, with its "command prompt" and in normal "windows" mode. It’s no exaggeration to say that both Apple Macintosh OS xxx and Microsoft Windows xxx revolutionized home computing by helping relatively inexperienced users with a PC interface using a GUI.

In specialist systems, a shell is a piece of software that is an "empty" expert system, without the knowledge base for any particular application.