Uid switching in Perl

Yes, you can even use setuid/setgid in Perl.

  $uid = 10;  $gid = 100;

  #  setuid($uid);
  $< = $uid;        $UID = $uid;          $REAL_USER_ID = $uid;

  # seteuid($uid)
  $> = $uid;       $EUID = $uid;     $EFFECTIVE_USER_ID = $uid;
  
  # setgid($gid)
  $( = $gid;        $GID = $gid;          $REAL_GROUP_ID = $gid;

  # setegid($gid)
  $) = $gid;       $EGID = $gid;     $EFFECTIVE_GROUP_ID = $gid;

Make sure you check that $UID == $uid (etc) after setting it!