open STUB, "stub.c" or die "Cannot open stub.c : $!\n";
  while (<STUB>) {
    chomp;
    # $_ is now a line from stub.c,
    # and we have to decide whether to print it or not.
    # If it's a key in %hash1 we don't want to print it;
    # otherwise, we do:
    print "$_\n" if not exists $hash1{$_};
  }