Presence detection service on Asus Merlin (should work on DD-WRT as well)

presence.sh

#!/bin/sh

### CONFIG
INTERFACES="eth1 eth2"

### DO NOT EDIT BELOW

LAST_MACS=""

assoclist()
{
	{ for i in $INTERFACES; do wl -i $i assoclist; done; } | awk '{print tolower($2)}' | sort -u
}

list_diff()
{
	list_1=$1
	list_2=$2

	for i in $list_1; do
		found=
		for j in $list_2; do
			[[ $i == $j ]] && { found=1; break; }
		done
		[[ -z $found ]] && echo $i
	done
}

run()
{
	CURRENT_MACS=$( assoclist )

	WENT_ONLINE_MACS=$( list_diff "$CURRENT_MACS" "$LAST_MACS" )
	WENT_OFFLINE_MACS=$( list_diff "$LAST_MACS" "$CURRENT_MACS" )
	[[ -n "$WENT_ONLINE_MACS" ]] && echo "Went online:" $WENT_ONLINE_MACS
	[[ -n "$WENT_OFFLINE_MACS" ]] && echo "Went offline:" $WENT_OFFLINE_MACS

	LAST_MACS="$CURRENT_MACS"
}

loop()
{
	while [ 1 ]; do
		run
		sleep 5
	done
}

loop | logger

Logs to syslog of the router:

Went online: 3c:a7:c3:73:67:1d 5c:c7:d3:9a:67:1d
Went offline: 3c:a7:c3:73:67:1d

can i use this script on an fritzbox aswell?