%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