package A;
use vars qw/$knob1/;

package B;
@ISA=('A');
*knob1 = *A::knob1;

package main;

$A::knob1 = 'a knob1';
$B::knob1 = 'b knob1';
print $A::knob1, "\n";
print \$A::knob1, "\n";
print \$B::knob1, "\n";