#!/bin/bash

export LC_ALL=C
export PATH=/bin:/sbin:/usr/bin:/usr/sbin
declare -A state
declare -A state_changed

state_dir=/dev/shm/nmap_state
hosts=(192.168.12.2 192.168.12.6 192.168.12.9 192.168.12.10 192.168.12.125 192.168.12.200 192.168.12.203 192.168.12.204 192.168.12.205 192.168.12.206 192.168.12.207 192.168.12.208 192.168.12.209 192.168.12.211 192.168.12.212 192.168.12.213 192.168.12.215 192.168.12.225 192.168.12.226 192.168.12.230)
tcp_port=502
state_name[0]=UP
state_name[1]=DOWN

declare -x state hosts tcp_port PATH LC_ALL state_changed state_dir

check_port() {
        local host="$1"
        local port="$2"
        nmap -p$port $host 2>&1 | grep -q "$tcp_port/tcp open"
        echo $? >$state_dir/$host
}

mylog() {
        echo "$(date) : $1"
}

mkdir -p $state_dir
while :;do
        for host in ${hosts[@]}; do
                {
                state_changed[$host]=0
                check_port $host $tcp_port
                } &
        done
        wait
        for host in ${hosts[@]};do
                new_state="$(cat $state_dir/$host)"
                if [ "${state[$host]}" != "$new_state" ]; then
                        state_text=${state_name[$new_state]}
                        mylog "new state for host $host: $state_text"
                        state[$host]=$new_state
                fi
        done
        sleep 1
done