Copyright Sams Teach Yourself Shell Programming in 24 Hours

Interactive mode means that the shell expects to read input from you and execute the commands
that you specify. This mode is called interactive because the shell is interacting with a user. This is usually
the mode of the shell that most users are familiar with: you log in, execute some commands, and log out.
When you log out using the exit command, the shell exits.
The shell can be run in another mode, called noninteractive mode . In this mode, the shell does
not interact with you; instead it reads commands stored in a file and executes them. When it reaches the
end of the file, the shell exits.
How login Starts a Shell
When the login program starts a shell, it basically executes the following command:
/bin/sh
By issuing this command, it puts the shell into interactive mode. You can start a shell in interactive mode by
issuing the same command at the prompt:
$ /bin/sh
$
The first prompt $ is displayed by the shell that login started; the second one is displayed by the shell you
started. To exit from this shell, use the exit command:
$ exit
$
The prompt that is displayed now is from the original shell started by login. Typing exit at this prompt
logs you out.
How to Start the Shell Noninteractively
You can start the shell noninteractively as follows:
$ /bin/sh filename
Here filename is the name of a file that contains commands to execute. As an example, consider the
compound command:
$ date ; who
Put these commands into a file called logins. First open a file called logins in an editor and type the
command shown previously. Assuming that the file is located in the current directory, after the file is saved,
the command can run as
$ /bin/sh logins