my $mask=/_(\d\d)_/;

sub  sorter ($$){
    my ($am,$bm);
    $_[0] =~ /$mask/;
    $am=$1;

    '' =~ /()/; # A match that always succeeds

    $_[1] =~ /$mask/;
    $bm=$1;

    $am <=> $bm || $am cmp $bm;
}

@result = sort sorter @f;