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Figure 1. A computer system is composed of layers of hardware and software

+----------------+-------------------------------------------------+
|                |                                                 |
|       Shell    |               Application Programs              |
|                |                                                 |
|----------------+-------------------------------------------------+
|                                                                  | 
|                     Operating Sytem Kernel                       |
|                                                                  |
+------------------------------------------------------------------+
|                                                                  |
|                             Hardware                             |
|                (CPU, Memory, and Peripheral Devices)             |
|                                                                  |
+------------------------------------------------------------------+

Listing 1. Resetting the shell prompt

A. Reset the Bourne shell prompt by changing the PS1 shell variable:

$ PS1 = "Yes, Master? "
            
Yes, Master?  []

B. Reset the C shell by resetting the prompt variable:

$ set prompt = Yes, Master? "
Yes, Master? []

Listing 2. A general format for a UNIX system command

$ command_name [ option... ] [ filename... ]

Listing 3. Some Bourne shell error messages

A. Mistype a command name:

$ pws
pws: not found
$ []

B. Attempt to run a restricted command:

$ /etc/shutdown
/etc/shutdown: cannot execute
$ []

Listing 4. Equivalent C shell error messages

A. Mistype a command name:

% pws
pws: Command not found.
% []

B. Attempt to run a restricted command:

% /etc/shutdown
/etc/shutdown: Permission denied.
% []

Listing 5. Use the & directive to run a command in the background.

$ nroff -mm text.mm >text.fmt &