Quick hack to check a remote host is accepting connections on a tcp port (useful when doing dangerous things, like kernel updates!)

checkhost.sh

#!/bin/bash

if [ "$1" == "" ] || [ "$2" == "" ]; then
  echo "usage: $0 [options] <host> <port>"
  echo
  echo "options:"
  echo "   -i <interval>   Number of seconds between checks [default: 5]"
  exit 1
fi

interval=5
getopts ":i:" opt
if [ "$opt" == "i" ]; then
  interval=$OPTARG
fi
shift $((OPTIND-1))

while true; do
  output=`nc -z -G 5 $1 $2 2>&1`
  echo `date +%H:%M:%S` $output
  sleep $interval
done