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

In case ncat is not an option, socat will also work:

socat TCP4-LISTEN:2000,fork EXEC:cat

The fork is necessary so multiple connections can be accepted. Adding reuseaddr to TCP4-LISTEN may be convenient.