pacakge MyProject::DBH;

use DBI;

my $DBH;    # lexical scope outside the constructor
            # makes it available to all calls to new().

sub get_dbh { 
    if ref($DBH) eq 'DBI::db') { 
        # dbh already created, so return it
        return $DBH;
    } else { 
        # connect to the DB and return the handle
        # (assume $user, $pass and $dsn come from somewhere)
        $DBH = DBI->connect($dsn, $user, $pass);
        return $DBH;
    }
}