print "What Book would you like to borrow? ";
my $book_to_borrow =<STDIN>;
chomp $book_to_borrow;
if (exists($borrowed_DB{$book_to_borrow})) {
    if (defined($borrowed_DB{$book_to_borrow})) {
	print "This book is not available for checkout\n";
    } else {
        print "This book is available for checkout.
                  \nPlease type your name: ";
	my $borrower = <STDIN>;
	$borrowed_DB{$book_to_borrow} = $borrower;
    }
} else {
    print "Sorry. Not Available.\n";
}