How to make an Echo server with Bash?

Question

How to write a echo server bash script using tools like nc, echo, xargs, etc capable of simultaneously processing requests from multiple clients each with durable connection

Answer 1

Here are some examples. ncat simple services

TCP echo server

ncat -l 2000 --keep-open --exec "/bin/cat"

UDP echo server

ncat -l 2000 --keep-open --udp --exec "/bin/cat"