Nagios with custom Finger Commands


i m new to nagios, would like some help with creating a custom command for nagios to check with finger. i am using nagios version 3.2.0 on ubuntu server.
This is the command i would like to run " finger @$hostname | grep PPP -c " and compare output with a value and nagios to email a warning if the value is greater. i.e. using finger command to monitor my cisco 2600 dial in router with 16 dial in lines. would like nagios to email me if more than 14 users are connected at the same time.

thank you


it’s probably better to get the value from SNMP if available…