my $dbh = DBI->connect(
   qw(DBI:Oracle: user pass),
   {RaiseError => 1},
);

# with RaiseError turned on, no need for die and errstr

$dbh->do("truncate table directory_data");

my $sth = $dbh->prepare(q{
    INSERT INTO directory_data(
       dn, cn, surname, given_name, initials, 
       generational_qualifier, building, room_number,
       mailstop, telephone, fax, mail, tfs_id, uid
    ) VALUES (?,?,?,?,?,?,?,?,?,?,?,?,?,?)
});
 
$sth->execute($employee{$_},.,....) for keys %employee;

##</code><code>##

my @field = qw(
   dn cn surname given_name initials
   generational_qualifier building room_number
   mailstop telephone fax mail tfs_id uid
);

my $table = 'directory_data';

my $sql = "insert into $table (" 
   . join(',', @field)
   . ') values (' 
   . join(',', map '?', @field) 
   . ')'
;