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I am currently working on a project and I have implemented a simple chat application using the netcat libraries.

The client is prompted to enter port number and the command

nc -l -p xxxx

where xxxx is the port number entered by the client.

Similarly, the host is prompted for the same port number and a connection is established using

nc <ip_address> -p xxxx

However, this gives a blank chat experience as it does not show the username of the person typing the messages, something like

hey
hello
what's up
Nothing

Instead, I want it to be something like,

Foo : hey
Boo : hello
Foo : what's up
Boo : Nothing

Can I use netcat to achieve this functionality or is there anything else that does this?

Sachin S Kamath
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2 Answers2

36

You can do something like this.

Assume Alice is the server. She types:

mawk -W interactive '$0="Alice: "$0' | nc -l -p <port_number> <ip_of_alice>

Then Bob connects to that server. He types:

mawk -W interactive '$0="Bob: "$0' | nc <ip_of_alice> <port_number>

The mawk lines just adds the prepending name of the person to the "chat". We need -W interactive to set unbuffered writes to stdout and line buffered reads from stdin.

Now Alice types Hi Bob and sees:

Hi Bob

Bob sees:

Alice: Hi Bob

Bob types Hi Alice and sees:

Alice: Hi Bob
Hi Alice

Alice sees:

Hi Bob
Bob: Hi Alice
dessert
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chaos
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    nc cannot use -s and -l at the same time. the -s is not required. – Sachin S Kamath Aug 25 '15 at 11:03
  • I got awk: option `-W interactive' unrecognized, ignored – zt1983811 Jul 04 '16 at 16:03
  • @zt1983811 you need GNU awk, not mawk. – chaos Jul 04 '16 at 17:57
  • @chaos I did use awk awk -W interactive '$0="Alice: "$0' | nc -lvk ip port ; ls -al /usr/bin/awk lrwxrwxrwx 1 root root 21 Jun 27 06:48 /usr/bin/awk -> /etc/alternatives/awk – zt1983811 Jul 04 '16 at 20:03
  • @zt1983811 default is mawk, use apt-get install gawk to install GNU awk. awk will then point to GNU awk. – chaos Jul 04 '16 at 21:12
  • @chaos I do not think it is still working, I even tried following:

    gawk -W interactive '$0="Alice: "$0' | nc -lvk 10.0.5.30 4000 Listening on [10.0.5.30] (family 0, port 4000) gawk: option `-W interactive' unrecognized, ignored

     – zt1983811 Jul 05 '16 at 12:32
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    @zt1983811 This is a mawk option, not gawk. Did you try it using mawk explicitly? – dessert Sep 15 '17 at 06:59
0

A bit ago, I actually made one program that enables chatting (via IP address) on lan, there must be errors I didn't really had time to maintain it but it should give you something to start.

https://github.com/Aeres-u99/ncChat

PS: I had tried adding a file sharing support as well :P

Reitsu Y
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