Seeing you ask this question to what executable to use, I suspect you are not very familiar with this anti-virus or even with handling files in Windows.
So, I very strongly suggest you first read the instructions and help files of Avira AntiVir Personal, specifically how to use the command line functions.
It might, or then again, it might not be as easy as simply selecting avscan.exe. It might involve all kinds of needed parameters etc... (if it even has them! It might well be that Avira does not even offer command line scanning).
I'm not familiar with it either. So either read the help files yourself, or wait for somebody who does know this anti-virus (and does not need to guess) and has used the command line scanning tool (if it exist).
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