3.x  Show variables;
   4.x  Show variables;
   5.0  Show global variables
   5.1+ Select * from information_schema.global_variables order by 1;

 sub var
     {
       my $sgv = $dbh->prepare("show variables");
     $sgv->execute();
  while (my ($keyword, $value) = $sgv->fetchrow_array()) 
     {
       $variables{$keyword} = $value;
     }
        $sgv->finish();
 }