--- поменяй
 
use DBI();
 --- на
 
use DBI;

use strict;
use DBI;

my $dbh = DBI->connect( 'dbi:Oracle:orcl',
                        'jeffrey',
                        'jeffspassword',
                        {
                          RaiseError =>  1 ,
                          AutoCommit =>  0 
                        }
                      ) || die  "Database connection not made: $DBI::errstr" ;

my $sql = qq{ SELECT * FROM employees };
my $sth = $dbh->prepare( $sql );
$sth->execute();

$dbh->disconnect();