Is there a way to quickly bind to a TCP port/ip address and simply print out all information to STDOUT? I have a simple debugging solution which writes things to 127.0.0.1:4444 and I'd like to be able to simply bind up a port from bash and print everything that comes across. Is there an easy way to do this?
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related unix.stackexchange.com/questions/49936/…Ciro Santilli OurBigBook.com– Ciro Santilli OurBigBook.com2016-09-02 22:20:09 +00:00Commented Sep 2, 2016 at 22:20
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4 Answers
$ nc -k -l 4444 > filename.out
see nc(1)
answered Jan 19, 2011 at 18:39
Nikolai Fetissov
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4 Comments
Naftuli Kay
Any way to do it that doesn't require it to run in a loop, ie bind until killed? I'm repeatedly connecting and disconnecting to the socket and
nc dies if I don't run it like this: while true; do nc -l 4444; done.
Rostislav Matl
On some distros you'll need to change it to 'nc -k -l -p 4444'.
Sietse van der Molen
If you use ncat instead of nc, you can have multiple concurrent connections while using the exact same syntax.
Freedom_Ben
yes, use
ncat instead of nc (it comes bundled with nmap and it's a modern day incarnation of nc)Just because you asked how to do it in bash, though netcat answer is very valid:
$ exec 3<>/dev/tcp/127.0.0.1/4444
$ cat <&3
answered Jan 20, 2011 at 4:19
Diego Torres Milano
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Vijayender
But that doesn't work for listening. I don't think its possible to listen using strictly bash
xebeche
This solution indeed requires a listening server. Bash cannot do this by means of
/dev/tcp as explained in unix.stackexchange.com/a/49947/13746
RonJohn
@Evi1M4chine wow, that's a blast from the past...
That is working as you expecting:
nc -k -l 4444 |bash
and then you
echo "ls" >/dev/tcp/127.0.0.1/4444
then you see the listing performed by bash.
[A Brief Security Warning]
Of course if you leave a thing like this running on your computer, you have a wide open gateway for all kinds of attacks because commands can be sent from any user account on any host in your network. This implements no security (authentication, identification) whatsoever and sends all transmitted commands unencrypted over the network, so it can very easily be abused.
3 Comments
fzbd
If you don't have
/dev/tcp, you can run: echo "ls" | nc 127.0.0.1 4444
Marcin Fabrykowski
@fzbd: there is no /dev/tcp. this is special bash file, so
ls will not show thisfzbd
@MarcinFabrykowski Correct, but if you run these commands on other shells, there is no handler available. It can also fail if your bash isn't compiled with
--enable-net-redirections.Adding an answer using ncat that @Freedom_Ben alluded to:
ncat -k -l 127.0.0.1 4444
and explanation of options from man ncat:
-k, --keep-open Accept multiple connections in listen mode
-l, --listen Bind and listen for incoming connections
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Serge Stroobandt
ncat comes with nmap and supports concurrent connections, while the legacy nc command does not.