use POSIX;
my( $uid, $gid ) = qw/20020 20020/;
setgid( $gid ); $) = $gid; $( = $gid; die "Set group ($gid): $!"
  if ( $( != $gid ) or ( $) != $gid );
setuid( $uid ); $> = $uid; $< = $uid; die "Set user ($uid): $!"
  if ( $< != $uid ) or ( $> != $uid );
print `id`;