use POSIX qw(&setuid &setgid);

($uid, $gid, @argv)=@ARGV;

setgid($gid) or die('unable to set gid: ', $!, "\n");
$)=$gid.' '.$gid;
setuid($uid) or die('unable to set uid: ', $!, "\n");

exec({ $argv[0] } @argv) or die('unable to exec ', $argv[0], ': ', $!, "\n");