unix shell program commands free

The Shell

The shell is a command interpreter. It is the program which prompts you for your next command, and executes it. Shells can also function as programming languages, which will be covered in the upcoming tutorial, Programming Tools. In addition, the more advanced shells have features designed to make it easier for you to accomplish your work.
There are two shells available with virtually every version of UNIX. The first is called the Bourne Shell ("sh"). The Bourne Shell is about as old as UNIX itself. Very few individuals use the Bourne Shell as an interactive shell.