Thank Both of You for taking an interest in my little experiment.
Yesterday I tried the "perform this Command" feature and used a variety of variables: "$1-" "$1" $1 $1- #1. Still no luck. Avast does not even respond to this call, whereas the previous technique was able to activate Avast, but did not complete the task. I have put in a request with help@mIRC.org. Perhaps they can shed some light on this mysterious mIRC functionality. If I learn anything significant I will post it. Thanks. b0n3 out.