use IPC::Open2;

my @ldapsearch = qw(ldapsearch -r);
my @userdncmd = (@ldapsearch,
                 -h => $ldapserver,
                 -b => 'dc=xxx,dc=com',
                 'employeenumber=' . $id,
                 'dn');
my ($rdrfh, $wtrfh);
my $pid = open2($rdrfh, $wtrfh, @usrdncmd);
close $wtrfh; # don't need to write to the stdin of ldapsearch
my $userdn = do { local $/ = undef; <$rdrfh> };
chomp $userdn;