Howdy!

...or, you could do something like the following:

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";
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which printed:

b knob1
SCALAR(0x10062530)
SCALAR(0x10065230)
[download]

showing that the two variables are each a name for the same location.