What you need is eval, BUT 'command $foo' is unlikely to be valid perl so the eval will fail. This regex method works because we capture the scalar and perform the required (double) eval (first eval gets you $var out of $1, second gets you 'value' out of $var). You may wish to add more than \w in the capture after the $ for things like $foo->{bar} if you are getting that weird.

%hash = ( 'command' => 'command_name -n $var1 -p $var2' );
$var1 = 'foo';
$var2 = 'bar';
$command = $hash{'command'};
$command =~ s/(\$\w+)/$1/gee;
print $command;
# system ($command);
__DATA__
command_name -n foo -p bar
[download]

This is almost certainly a bad way to do it BTW.