Background

What you need to know when you finish this document

This technology may seem archaic, but it hasn’t gone away.

We need to be able to work at the command prompt for some tasks, in Windows, Unix of any form, or on appliances and communications equipment.

In DOS, we have a command processor. It may be a little more complex under Windows, but in pure DOS we have a programme called COMMAND.COM which interprets many of the basic commands. In Windows, we open a special command window to access the prompt.

In UNIX we call this the Shell. The shell acts as an interface between the user and the kernel. When a user logs in, the login program checks the username and password, and then starts another program called the shell. The shell is a command line interpreter (CLI). It interprets the commands the user types in and arranges for them to be carried out.

In our UNIX examples, we use the bash shell, however there are many others in common use including the Bourne Shell and the C Shell. Each command at the command prompt refers to a programme or routine within the operating system. With some commands it is possible to include parameters after the command, these are referred to as arguments.

When you type a command, you run that programme and when it terminates, the shell gives the user another prompt. A user can customise their own shell, and users can use different shells on the same machine. The shell keeps a list of the commands you have typed in. If you need to repeat a command, use the cursor keys to scroll up and down the list or type history for a list of previous commands.