Small script to create multiple listeners with 'nc'

create-listener.sh

#!/bin/bash
#
# Small script to create multiple listeners with 'nc'
#
# Execute script with 'nohup' into the background and forward 
# output to /dev/null for minimal interference in console:
# nohup sudo ./create_listener.sh "4005 4006 4007 4008 4009" >/dev/null 2>&1 &
#
# Using quotes is only necessary for multiple listening ports!
#
# To terminate just force kill 'nohup' process and all 'nc' processes: 
# sudo pkill -9 -f listener.sh; sudo pkill -9 -f nc
#
# Üllar Seerme

# Use the following if you want hardcoded ports
# declare -a ports=(4005 4006 4007 4008 4009)

IFS=" " read -r -a ports <<< "$1"

# Keep running until killed manually
while true; do
	for i in "${ports[@]}"; do
		echo "Testing port: {$i}"

		if ! ss -tlp | grep -q :"$i"; then
			echo "No process listening on port ${i}; creating listener"
			nc -l -p "$i" &
		else
			echo "Process already listening on port ${i}; skipping"
		fi
	done
	# Adjust according to preference
	# Without this it will just needlessly load the CPU way too much
	sleep 5;
done