Irule to Run a tmsh command

Take a look at this post for information on setting up user_alert.conf to launch a shell process;

https://devcentral.f5.com/questions/clearing-machine-cache

I would add though, that launching the process on every CLIENT_ACCEPTED event (where there are at least two pool members) will very quickly eat all of your a system resources. If you're going to do this at all, you should limit it to something that happens rarely.