# bad: ternary in void context: 
exists($checked->{Group}{$GroupDN}) ? ($rc_OK=1) : ($rc_OK=check_group($GroupDN,0));

# good: 'if' in void context:
if (exists($checked->{Group}{$GroupDN})) {
   $rc_OK = 1
} else {
   $rc_OK=check_group($GroupDN,0)
}

# also good: ternary in scalar context:
$rc_OK = exists($checked->{Group}{$GroupDN}) ? 1 :  check_group($GroupDN,0)