So far we have seen how an operating system provides resources and services to processes. We will now study how an operating system provides resources and services to users.
An operating system provides services to users through one or more programs which
may be invoked by users.
Some of these,
called command interpreters,
provide a command language which is used to express a user's request.
We shall study these in detail.
Others,
invoked usually through a command interpreter,
provide services such as manipulation of files and processes.
(eg: `ls', `chmod', `rm', `ps' and `kill' in Unix).
We shall discuss only command interpreters.