Check if host:port is up

port-check.sh

#!/bin/bash

# see https://securityreliks.wordpress.com/2010/08/20/devtcp-as-a-weapon/
echo "Waiting for ${HOST}:${PORT} to become available"
while :
do
  (echo > /dev/tcp/${HOST}/${PORT}) >/dev/null 2>&1
  available=$?
  if [[ $available -eq 0 ]]; then
    echo "Service on ${HOST}:${PORT}" is available
    break
  fi
  sleep 1
done