for (sort {$a <=> $b} keys %foo) {
    print "$_\n";
}

##</code><code>##

for my $k ( sort {%{ $ref_HoH{$a} } <=> %{ $ref_HoH{$b} }    }keys %$ref_HoH ) {

##</code><code>##

for my $k (sort {$a <=> $b } keys %$ref_HoH) {