tcp-route-probe

#!/bin/sh

add () {
	[ -z "$(ip route show $ADDR dev $DEV scope link)" ] \
			&& ip route add $ADDR dev $DEV

	return 0
}

del () {
	[ -n "$(ip route show $ADDR dev $DEV scope link)" ] \
			&& ip route del $ADDR dev $DEV

	return 0
}

stop () {
	del

	kill -STOP $PROCS
}

quit () {
	del

	exit 0
}

check () {
	WORKING=1

        for PORT in $@; do
		nc -z -w 1 $ADDR $PORT 2> /dev/null

		[ $? -ne 0 ] && { WORKING=0; break; }
	done

	[ $WORKING -eq 1 ] && add || del
}

go () {
	trap quit TERM
	trap stop TSTP

	while true; do
		check $@

		sleep 10
	done
}

SELF=$(basename "$0")
PROCS=$(pgrep -f "^/bin/sh $0 $*\$")
RC=$?
if [ $RC -gt 0 ]; then
	echo "unexpected pgrep results (ret=$RC)" >&2
	exit 70
fi
if [ "$PROCS" != "$$" ]; then
	echo "'$SELF $*' is already running" >&2
	exit 69
fi

if [ ! "$3" ]; then
	echo -e "Usage:\n\t$SELF dev address tcp-port0 [tcp-port1 [...]]" >&2
	exit 64
fi
DEV=$1
ADDR=$2
shift 2

0<&- 1<&- 2<&- go $@ &

exit 0