$shape="square";

(stuff deleted)

foreach ('square  ', 'circle ', 'polygon'){
         $frame2->Radiobutton(
                              -bg=>COLOR,
                              -activebackground=>COLOR,
                              -text=>$_,
                              -font=>'code14',
                              -value=>$_,
                              -variable=>\$shape,
                              )->pack(-anchor=>'w');
         }