{
   package MyDB;
   my $DBH;
   sub dbh {
      if ($DBH) {
         print "found existing $DBH\n";
      } else {
         $DBH = 'dbh';
         print "Init $DBH\n";
      }
   }
}

MyDB->dbh();  # Init dbh
MyDB->dbh();  # Found existing dbh
MyDB->dbh();  # Found existing dbh