#include <unistd.h>

int
main (int argc, char *argv[])
{
  int real_id = getgid ();
  int eff_id = getegid ();

  printf ("Startup: Real ID %i, Effective ID %i.\n", getgid (), getegid());

  if (argc > 1)
    {
      int old_saved_id = atoi (argv[1]);

      setegid (old_saved_id);
      printf ("Seteuid: Real ID %i, Effective ID %i.\n", getgid (), getegid());
    }
  else
    {
      char *args[] = { 0, 0, 0 };

      asprintf (&args[0], "%s-nogid", argv[0]);
      asprintf (&args[1], "%i", eff_id);
      setgid (real_id);
      printf ("Preexec: Real ID %i, Effective ID %i.\n", getgid (), getegid());
      execvp (args[0], args);
    }
  return 0;
}