#!/bin/bash

RESULTS=(OK WARNING CRITICAL UNKNOWN)

perror() {
	echo "$@"
} >&2

fail() {
	local RET=$1
	shift
	perror "$@"
	exit $RET
}

result() {
	local RET=$1
	shift
	echo "SNMP IF ${RESULTS[$RET]}: $@"
	exit $RET
}

while getopts ":H:c:i:" opt; do
	case $opt in
		H)
			HOSTNAME="$OPTARG"
			;;
		c)
			COMMUNITY="$OPTARG"
			;;
		i)
			INTERFACE="$OPTARG"
			;;
		:)
			fail 3 "$OPTARG requires Argument."
			;;
		*)
			fail 3 "Invalid option $OPTARG"
	esac
done

SNMPWALK_RESULT=$(snmpwalk -c "$COMMUNITY" -v 2c "$HOSTNAME" 1.3.6.1.2.1.2.2.1.8.$INTERFACE; exit $?)
RET=$?

[ $RET -ne 0 ] && result 3 "snmpwalk failed with code $RET: $SNMPWALK_RESULT"
[ -z "$SNMPWALK_RESULT" ] && result 2 "No matching entry found."

IFS='=' LINE=($SNMPWALK_RESULT)

sed -n 's/.*=\(.*\)/\1/p' <<< "$SNMPWALK_RESULT" | grep "up\|1" > /dev/null && result 0 "Interface $INTERFACE is up."

result 2 "Interface $INTERFACE is not up: $SNMPWALK_RESULT"