I’ve highlighted the only line that I think really needs further explanation. The “$if_snmp_descr” is a variable that exists in the MRTG script. That field is shown with the label Description when you click to the port’s page. The “=~” immediately after that signals to Perl that it needs to use a regular expression match. After that is the string to match. Within a regular expression, the pipe character ( | ) means “or”. So, I’m just looking inside the description for any of those items. If it’s found, I tell MRTG to do nothing — this means that the item is not displayed. For anything else, I pass it along to the default handler, which will set up the graphs and index pages and so on. I can keep editing this line or use “elsif”s to add further conditions.