package My::DB;
use strict;
use DBI;

use vars qw( $dbname );
$dbname = 'dbi:mysql:production_db';

{ my $dbh;

sub dbh {
  $dbh ||= DBI->new($dbname);
  $dbh;
};

  sub disconnect {
    $dbh->disconnect
      if $dbh;
  };
};

package main;
use My::DB;

my $dbh = My::DB::dbh;

# ... do stuff