ANSWER:

Try it like this:

nc -u -l 7777 > newfile.jpg #on the destination machine
cat file.jpg | nc -u 192.168.x.x 7777 #on the source machine

Usually you want the machine getting the file to “listen” (run that first), and when it’s listening, send the data over udp. UDP does not have a ‘handshake’ sequence, and packets are sent immediately, even if noone is listening*.

*sometimes you get an ICMP packet, that the port is closed (unreachable), but you cannot depend on that (firewalls etc.)

by mulaz from http://serverfault.com/questions/386406