1. The shell must support the following internal commands:
i. cd - Change the current default directory to
. If the argument is not present, report
the current directory. If the directory does not exist an appropriate
error should be reported. This command should also change the PWD
environment variable.
ii. clr - Clear the screen.
iii. dir - List the contents of directory .
iv. environ - List all the environment strings.
v. echo - Display on the display followed by a
new line (multiple spaces/tabs may be reduced to a single space).
vi. help - Display the user manual using the more filter.
vii. pause - Pause operation of the shell until ''Enter'' is pressed.
viii. quit - Quit the shell.
ix. The shell environment should contain shell=/myshell
where /myshell is the full path for the shell executable
(not a hardwired path back to your directory, but the one from which
it was executed).