We have some mail servers which occasionally get way behind on their mail queue. I wanted a good way to see the size of the queue in real time, without having to log into the web interface of the machine (it's a proprietary device). So I wrote this script which not only prints out the current value of the SNMP OID, but also tracks the value so you can see if it's increasing and if so, by how much. It could easily be adapted to any numeric SNMP variable.

watch-snmp.pl