cmd-on-host-up-down.sh

#! /usr/bin/env sh

host=""
wait=10
max_tries=3

up_cmd=""
down_cmd=""

# --------------------

log="logger -t wg-if-up"
host_status="down"
try=1
err=""

[ -n "$host" ] || err="No host specified"
[ -n "$up_cmd" ] || err="No up command specified"
[ -n "$down_cmd" ] || err="No down command specified"
[ -z "$err" ] || { $log "$err"; exit 1; }

while :; do
  case $host_status in
    up)
      while ping -c 1 -W 1 $host > /dev/null; do
        try=1
        sleep $wait
      done

      $log "No connection to $host detected (try $try)"

      if [ $try -lt $max_tries ]; then
        try=$(( try + 1 ))
        continue
      fi

      host_status="down"
      $down_cmd
      ;;

    down)
      until ping -c 1 -W 1 $host > /dev/null; do
        sleep $wait
      done

      try=1
      host_status="up"
      $up_cmd
      ;;
  esac

  $log "Host $host $host_status"
  sleep $wait
done