Simple script to expose /dev/ttyUSB* on a TCP socket using socat with some hacks

ser2sock.sh

#!/bin/ash

trap "trap - SIGTERM && kill -- -$$" SIGINT SIGTERM EXIT

while sleep 1; do 
	# search for a sutiable device

	# this is a bit lame match, it tries to find the last device, 
	# but if that last device is not suitable, it will not step back to the previous ones

	echo "Found devices:"
	for dev in /dev/ttyUSB?; do
		if [[ "${dev}" != "/dev/ttyUSB\?" ]] && [[ -c "${dev}" ]]; then # ash has no nullglob support
			echo "- $dev"
		else
			dev=""
		fi
	done

	if [[ -z "${dev}" ]]; then
		echo "nothing :("
		continue # restart loop if nothing found
	fi
	echo "selecting ${dev}"

	# start socat

	socat -d -d GOPEN:$dev,b9600,rawer,echo=0,creat=0 TCP4-LISTEN:3333,keepalive &
	socatpid=$!

	echo "socat pid: ${socatpid}"

	sleep 0.5 # make sure socat starts up (or fails) before we start checking stuff

	# monitor for device presence

	while [ -d "/proc/${socatpid}" ]; do
		if ! [ -c "${dev}" ]; then
			echo "device disappeared, restarting socat..."
			kill "${socatpid}"
			wait ${socatpid}
		else
			sleep 1
		fi
	done
done