The operating system is the layer of software that drives the
hardware of a computer and provides the user with a comfortable work
environment. Operating systems vary, but most have a shell, or
text interface. You use the GNU shell every time you type in a command
that launches an email program or text editor under GNU.
In the following sections of this chapter, we will explore how to create
a C program from the GNU shell, and what might go wrong when you do.