for ( grep /^default_option_/, keys %def ) {

   $s{ (split /_/, $_, 2)[-1] } = $def{ $_ };
}

##</code><code>##

foreach (map { /^default_option_(.*)/ ? $1 : () } keys %def) {
    $s{"option_$_"} = $def{"default_option_$_"};
}

##</code><code>##

for (grep /^default_option_(.*)/, keys %def) {
    $s{"option_$1"} = $def{$_};
}

##</code><code>##

$s{"option_$1"} = $def{$_} for (grep /^default_option_(.*)/, keys %def);