my %ext_map = ( '.tst' => '.test' );

open(FHA, ">renamebatch");
foreach my $file (@orderlist) {
(old_filename, undef, $ext) = fileparse($file,qr{\..*});
      my $new_ext = $ext_map{$ext} || $ext;
      my $new_filename = $old_filename;
print(FHA "$new_filename$new_ext");
}