Question

why do operating systems provide shells?

Answer 1

1.The outermost layer of a program. Shell is another term for user interface. Operating systems and applications sometimes provide an alternative shell to make interaction with the program easier. For example, if the application is usually command driven, the shell might be a menu-driven system that translates the user's selections into the appropriate commands.
2. Sometimes called command shell, a shell is the command processor interface. The command processor is the program that executes operating system commands. The shell, therefore, is the part of the command processor that accepts commands. After verifying that the commands are valid, the shell sends them to another part of the command processor to be executed.
UNIX systems offer a choice between several different shells, the most popular being the Cshell, the Bourne shell, and the Korn shell. Each offers a somewhat different command language.The programming language through which a user communicates with the operating system or an application. For example, the DOS command language includes the commands DIR, COPY, and DEL, to name a few. The part of an operating system that responds to operating system commands is called the command processor.
With graphical user interfaces, the command language consists of operations you perform with a mouse or similar input device.

Answer 2

In computing, a shell is a user interface for access to an operating system's services. In general, operating system shells use either a command-line interface (CLI) or graphical user interface (GUI), depending on a computer's role and particular operation.

The design of a shell is guided by cognitive ergonomics and the goal is to achieve the best workflow possible for the intended tasks; the design can be constricted by the available computing power (for example, of the GPU) or the available amount of graphics memory. The design of a shell is also dictated by the employed computer periphery, such as computer keyboard, pointing device (a mouse with one button, or one with five buttons, or a 3D mouse) or touchscreen, which is the direct human–machine interface.

CLI shells allow some operations to be performed faster, for example rearranging large blocks of data. However, they require the user to memorize all commands and their calling syntax, and also to learn the shell-specific scripting language, for example bash script. CLIs are also easier to be operated via refreshable braille display and provide certain advantages to screen readers.

Graphical shells have a low burden to start using a computer, and they are characterized as being simple and easy to use. With the widespread adoption of programs with GUIs, the use of graphical shells has gained greater adoption. Since graphical shells come with certain disadvantages (for example, lack of support for easy automation of operation sequences), most GUI-enabled operating systems also provide additional CLI shells.