Linux daemon waiting for a socket connection

Question

I would like to create a simple Linux daemon which will...

• open a tcp/ip server socket on localhost and specified port
• wait for a connection
• after someone connects, it will read the first line from the client's socket (ended by \n)
• if the line is foo, it will run command bar
• after the bar command is finished (or if the line wasn't foo), the daemon will wait for another connection and do the same (in infinite loop)...

Is it possible to write this in bash? (And how?)

Also, I would like to be able to start and stop the script with service my-foobar-daemon start / stop (on Ubuntu), how can I do that?

Thanks :)

Answer 1

#! /bin/bash
coproc nc -l -p 8080
while true; do
    if read -u "${COPROC[0]}" line; then
        case "$line" in
            foo)
                bar
                break
                ;;
            *)
                echo "$line: unknown command" >&2
                ;;
        esac
    fi
done
kill "$COPROC_PID"

Answer 2

The following snippet uses bash and nc to implement the requirements:

#! /bin/bash
while true; do
    coproc nc -l -p 8080
    if read -u "${COPROC[0]}" line; then
        case "$line" in
            foo)
                bar
                ;;
            *)
                echo "$line: unknown command" >&2
                ;;
        esac
    fi
    kill "$COPROC_PID"
    wait "$COPROC_PID"
done