...
print "PARENT($$): Before multi_dir() call";

my $multi_dir_return = multi_dir();

if ($multi_dir_return) { 
    print "CHILD($multi_dir_return): exiting";
    exit;
}

print "PARENT($$): After multi_dir() call";

sub multi_dir {
    ...
            print "CHILD($$): system() finished";
            return $$;
        }
    }

    return 0;
}