Answer the following questions to describe your code submission. Please keep
all lines to a maximum of 80 characters wide.

1 - From the main() function, how did you distinguish if the shell was using
    a script or an interactive prompt?

    If the -b flag was passed we read in whatever file was passed, printing
    an error message if the input file was invalid. Otherwise, use stdin.


2 - How does the quit command exit the shell?

    It calls exit(0)