Which documentation are you talking about and where ?
As far as I'm aware this is an element of the Pro version.
What version of avast are you using home or pro ?
home, open search... do a search for ashcmd.exe... 6 instances... which if I had bothered to read #6, clearly states that it only comes in the pro version...
too bad, since the other free scanners mostly have them:
C:\Program Files\AntiVir PersonalEdition Classic\avcmd.exe
C:\Program Files\a-squared Free\a2cmd.exe
C:\Program Files\Grisoft\AVG7\avgscan.exe
and of course
McAfee and F-Prot
I was gathering up a pile of freeware command-line scanners so that I could batch them all together....