(1 => 2, 3 => $x{1} )

##</code><code>##

(1, 2, 3, undef)

##</code><code>##

%x{1} = "old x sub 1";
%x = 
  ( 1 => 2, 
    3 => $x{1} 
  ); 

##</code><code>##

@a = (2, @a)

##</code><code>##

@a = reverse sort @a;