Using bash's `/dev/udp`, how would I know if the port was open?

I do not have access to netcat or nmap so I'm trying to use bash and the /dev/udp/ special files to test ports.

I could do something like:

echo "" > /dev/udp/example.com/8000

But $? is always 0 when using UDP. I'm assuming that's because that is the return value of the echo "" command correct?

I am basically trying to replicate with what I am able to do with nmap and netcat:

nmap -sU -p 8000 example.com | grep open >/dev/null && echo 'open'
nc -z -u example.com 8000 && echo 'open'

How would I do this with /dev/udp?