s{
    \G(
        [^",]+
    |
        "((?:
            [^"]+
        |   ""
        |   "[^",][^"]*"
        ))*"
    )(,|$)
}{
    if(  ! $2  ) {
        $1.$3;
    } else {
        my $f= $2;
        $f =~ s/"/""/g;
        '"'.$f.'"'.$2;
    }
}gx;