Check if mac-adress is online, call with ./check-mac.sh 11:11:11:11:11:11

check-mac.sh

#!/usr/bin/env bash
(
set -f # turn of globbing, the file contains probably an *

MAC_TO_CHECK=$1
ARP_FILE=/proc/net/arp
STATUS=unreachable

# try to find the host based on existing arp cache entries
# return values are:
# 0 = mac is online
# 1 = mac is in arp but seems offline
# 2 = mac is not in arp
# 3 = should not happen
check_arp_file ()
{
   local was_in_arp=false
   local is_online=false
   while read line
   do
     was_in_arp=true
     ping -n -q -c 1 `echo $line | cut -d" " -f 1` > /dev/null 2>&1
     if [ $? -eq 0 ]; then
       is_online=true
       break
     fi
   done < <(cat $1 | grep -i $2)

   if [ "$was_in_arp" = true ] && [ "$is_online" = true ]; then
     return 0
   elif [ "$was_in_arp" = true ] && [ "$is_online" = false ]; then
     return 1
   elif [ "$was_in_arp" = false ]; then
     return 2
   fi
   return 3
}

if [ ! -e "$ARP_FILE" ] # check if the arp file exists
then
  exit 1
fi

if [ ! -r "$ARP_FILE" ] # check if the arp file is user readable
then
  exit 1
fi

if ! check_arp_file $ARP_FILE $MAC_TO_CHECK; then
  # was not online, ping all hosts in subnet
  ip_base=`hostname --all-ip-addresses | cut -d. -f1,2,3`
  for i in `seq 1 255`; do
    ping -n -q -W 2 -c 1 $ip_base.$i > /dev/null 2>&1 &
    pids="$pids $!"
  done
  wait $pids
  check_arp_file $ARP_FILE $MAC_TO_CHECK
  if [ $? -eq 0 ]; then
   STATUS=reachable
  fi
else
  STATUS=reachable
fi

echo -n "{\"mac\":\"$MAC_TO_CHECK\",\"status\":\"$STATUS\",\"timestamp:\"`date +%s`\"}"
)