Netcat UDP command not working?
You seem to have accidentially reversed which one is the listener and which one is not. I.e. you'll need to change the commands to the following:

Open the listener first:

nc -u -l 127.0.0.1 10000


Then the sender:

echo "test" | nc -u 127.0.0.1 10000


Then you'll see that the listener outputs "test" on the console.

You can stop the nc program by pressing Ctrl-c.