What is Shell?
In the simplest terms, a shell is a program. It is responsible for taking commands and setting them up for execution. Basically, it acts as an interface between the user and the system hence allowing the user to input the commands, and for the system to execute them. Once the command is inputted, it is the shell’s job to validate the command and accept it or reject it accordingly. Once it accepts it, it will then send the command to another part of the command processor to be executed.
The shell is also known as the command interpreter. The shell is the outermost layer of the operating system, whereas the kernel is the innermost. UNIX has various shells, the most popular of them being the Cshell, the Bourne shell, and the Korn shell.