{
package Common;

  my $dbh = 0;

  sub getDbh
  {
    if ($dbh == 0)
    {
      # do all the stuff you said above to connect ...
    }
    return $dbh;
  }

  sub END
  {
    # print "disconnecting ..";
    $dbh->disconnect();
  }
}

# other stuff ....

1;