SOA Update Monitor

dns-soa-mon.sh

#!/bin/sh

usage() {
	printf "%s\n" "
$0 Usage:

Mandatory params:

  --serial=X            set SOA serial to watch for
  --nameserver=NS       set nameserver to query
  --domain=X		set domain to query SOA for

Optional params:

  --delay=s             seconds to delay for, default=300 (5 minutes)
  --logfail=y/n         y/n value to log failures
"
        exit 99
}
die() {
	printf "%s\n" "Fatal: $1"
	exit ${2:-1}
}

# defaults:
DELAY=300
LOGFAIL=n

while [ -n "$1" ]; do
	cmd="${1%=*}"
	v="${1#*=}"
	case "$cmd" in
	--help|-h|help|-help) usage ;;
	--serial) SERIAL="$v" ;;
	--nameserver) NS="$v" ;;
	--domain) DOMAIN="$v" ;;
	--delay) DELAY="$v" ;;
	--logfail)
		case "$v" in
			y) LOGFAIL=y ;;
			n) LOGFAIL=n ;;
			*) die "Invalid value for --logfail: $v (needs y or n)" ;;
		esac
	esac
	shift
done

[ -n "$SERIAL" ] || die "Missing serial"
[ -n "$NS" ] || die "Missing nameserver"
[ -n "$DOMAIN" ] || die "Missing domain"

check_output() {
	if grep -Eq ".*SOA.* $SERIAL .*"; then
		printf "%s\n" "$(date) SUCCESS: SOA matched $SERIAL"
		return 0
	fi
	[ "$LOGFAIL" = "y" ] && \
		printf "%s\n" "$(date) NO MATCH"
	return 1
}

# Main loop
printf "%s\n\n" \
	"Starting up watching $DOMAIN for $SERIAL at $NS with delay $DELAY"
while :; do
	dig "@$NS" SOA "$DOMAIN" 2>/dev/null | check_output && exit 0
	sleep $DELAY
done