How to build a simple chat using netcat?

command-line networking c++ netcat

19,946

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

19,946

Sachin S Kamath

Security researcher. Red Teamer. Open Source Sorcerer. He/Him.

Updated on September 18, 2022

Comments

Sachin S Kamath almost 2 years
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?
- 2707974 almost 9 years
  
  nc don't known username and can not send it. Only can do is to type message in format Bob: hello.
- Sachin S Kamath almost 9 years
  
  I want to avoid that exact thing . I am also open to alternate programs that can achieve the same functionality.
- 2707974 almost 9 years
  
  Try to find solution in this answer
Sachin S Kamath almost 9 years

nc cannot use -s and -l at the same time. the -s is not required.
zt1983811 almost 8 years

I got awk: option `-W interactive' unrecognized, ignored
chaos almost 8 years

@zt1983811 you need GNU awk, not mawk.
zt1983811 almost 8 years

@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
chaos almost 8 years

@zt1983811 default is mawk, use apt-get install gawk to install GNU awk. awk will then point to GNU awk.
zt1983811 almost 8 years

@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
dessert almost 7 years

@zt1983811 This is a mawk option, not gawk. Did you try it using mawk explicitly?