use XML::Twig;
my $file = $ARGV[0];
$file =~ /(.+)\.xml/;
my $outfile = $1.".snp" ;
open my $out,'>',$outfile or die "Could not open file '$outfile' $!";
my $twig = XML::Twig->new
(
twig_handlers => 
    {
        'Rs/MergeHistory' => \&MergeHistory,
    }
);
 $twig -> parsefile( "$file");
sub MergeHistory 
    {
        my ($twig, $elt) = @_;
        print $out "\t";
        print $out "rs";
                print $out $elt->att('rsId'), ",";
        print $out "b";
        print $out $elt->att('buildId'), ",";
    }