I want to send only one short value in a UDP packet, but running the command
echo -n "hello" | nc -4u localhost 8000 I can see that the server is getting the hello stuff but I have to press Ctrl+c to quit the netcat command.
How can I make it quit after sending hello?
Sorry, for the noise, I re-read the man page and found the -q option.
echo -n "hello" | nc -4u -q1 localhost 8000 works (it quits after 1 second).
For some reason it does not work with -q0.
If you are using bash, you might as well write
echo -n "hello" >/dev/udp/localhost/8000 and avoid all the idiosyncrasies and incompatibilities of netcat.
This also works sending to other hosts, ex:
echo -n "hello" >/dev/udp/remotehost/8000 These are not "real" devices on the file system, but bash "special" aliases. There is additional information in the Bash Manual.
127.0.0.1 instead on localhost on Ubuntu 14.04. (Yes, I do have localhost in /etc/hosts.)
/dev/udp/ is not a real file. It's only a file name interpreted specially by bash.I did not find the -q1 option on my netcat. Instead I used the -w1 option. Below is the bash script I did to send an udp packet to any host and port:
#!/bin/bash def_host=localhost def_port=43211 HOST=${2:-$def_host} PORT=${3:-$def_port} echo -n "$1" | nc -4u -w1 $HOST $PORT 
On a current netcat (v0.7.1) you have a -c switch:
-c, --close close connection on EOF from stdin Hence,
echo "hi" | nc -cu localhost 8000 should do the trick.
I had the same problem but I use -w 0 option to send only one packet and quit. You should use this command :
echo -n "hello" | nc -4u -w0 localhost 8000 Unfortunately nc is not a unique name for a single tool. To find out which nc you have, look at the first line of output from nc -h. To send a single UDP packet and exit immediately, use the appropriate arguments for your specific nc.
nc -uc localhost 8000 <<<hellonc -uq0 localhost 8000 <<<hellonc -uq0 localhost 8000 <<<helloRelated but thankfully not calling themselves nc:
ncat -u --send-only localhost 8000 <<<helloecho hello >/dev/udp/localhost/8000socat - UDP:localhost:8000 <<<hellosendip -p ipv4 -p udp -ud 8000 -d $'hello\n' localhostpacketsender -ua localhost 8000 $'hello\n'If you want a portable nc wrapper for sending a single UDP packet, try this as nc-udp-oneshot.sh:
#!/bin/sh helpword=$(nc -h 2>&1 | awk '{print$1;exit}') case $helpword in *GNU*) args=-uc ;; *) args=-uq0 ;; esac exec nc $args "$@" Now you can run echo -n hello | ./nc-udp-oneshot.sh with whichever nc happens to be installed. Or xxd -r -p <<<68656c6c6f | ./nc-udp-oneshot.sh for sending more complicated binary data, represented in hex.
Netcat sends one packet per newline. So you're fine. If you do anything more complex then you might need something else.
I was fooling around with Wireshark when I realized this. Don't know if it helps.
echo -n "hello\nworld" >/dev/udp/localhost/514 and you'll get 2 lines
Use -w0
echo -n "hello" | nc -4u -w0 localhost 8000
From @simon-unsworth 's answer below.
-q seconds: after EOF on stdin, wait the specified number of seconds and then quit. If seconds is negative, wait forever.