#!/bin/sh
#
# Wait until a given host is down (determined by ping) then execute the
# given command
#
# Usage:
# ./when-down HOST COMMAND...
#
# Example
# ./when-down 1.2.3.4 ssh 1.2.3.4
#

# Ensure we received the correct number of arguments.
if [ "$#" -lt 2 ]; then
  echo "Usage: $0 HOST COMMAND..."
  exit 1
fi

wait_for_host_down()
{
  local host=$1

  echo "Waiting for $host to go down..."

  while ping -c 1 -W 1 "$host" > /dev/null 2>&1; do
    sleep 1
  done
}

main()
{
  local host=$1
  shift

  wait_for_host_down "$host"

  "$@"
}

main "$@"
