package Kale_1990::Database;

use strict;
use warnings;
use DBI;
use base qw(Exporter);

our @EXPORT = qw($dbh);

my ($user,$pass,$db,$host) = ("username","password","datenbank","host");
our $dbh = DBI->connect("DBI:mysql:$db:$host",$user,$pass) or die $DBI::errstr;

use Kale_1990::Database;

my $sth = $dbh->prepare('...');

package Kale_1990::Database;

use strict;
use warnings;
use DBI;
use DBD::mysql;

sub connect {
   my $class = shift;
   my ($user,$pass,$db,$host) = @_;
   my $dbh = DBI->connect("DBI:mysql:$db:$host",$user,$pass) or die $DBI::errstr;
   return $dbh;
}

use Kale_1990::Database;

my $dbh = connect Kale_1990::Database;
my $sth = $dbh->prepare('...');