Folder Defaults AppFolder with current date

Hello,

I need to manipulate the default folder AppFolder to %ProgramFilesFolder%\%ProductName%_yyyymmdd

with yyyymmdd is the current date.

I tried it with a custom variable but I'm not able to set it to the current date with "system.getdate(date_fmt_year) + system.getdate(date_fmt_month)+ system.getdate(date_fmt_day)".
It seem that the variable is not "solved", so i get the string "system.getdate(date_fmt_year) ... " in my default folder.

Any ideas?

Thanks
Stephan