How to connect to a udp port command line?

This is what I tried,but seems not working :

[root@ ~]# netstat -a|grep 48772
udp        0      0 *:48772                     *:*                                     
[root@ ~]# telnet localhost 48772
Trying 127.0.0.1...
telnet: connect to address 127.0.0.1: Connection refused
telnet: Unable to connect to remote host: Connection refused

You can use netcat instead:

nc -u localhost 48772

You need to use netcat instead, telnet only supports tcp. Something like this will work:

$ nc -u localhost 48772

netcat is installed by default on most modern linux machines (assuming that's what you have).

Also for completeness sake I want to point out that there's another tool called socat which describes itself as 'netcat++'. Might be a good thing to check out. In general however netcat will do what you need just fine.

Another option is to use socat:

$ socat - UDP:localhost:48772

which connects its standard input to port 48772 on localhost.

Conversely, to set up a server listening on UDP port 48772 that outputs to standard output:

$ socat UDP-RECV:48772 STDOUT

If the port is below 1024 then you need to run the listener as root or use sudo. socat can act as a relay (actually its primary purpose) where it accepts input on one port and outputs to another. Definately netcat++.