Well, it's perfectly possible and reasonable to do it with eval:

%hash = ( 'command' => '"command_name -n $var1 -p $var2"' );
$var1 = 'foo';
$var2 = 'bar';
$command = eval $hash{'command'};
print $command;
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Just changed it so that what's being eval'd is a valid perl expression that evaluates to what he wants.