You can also use substitution to build the log filename.

   $logfile = $file;
   $logfile =~ s/\.asc$/.log/;
[download]

Or maybe you already have a regex to determine if you have a valid ascii filename:

   if ($file =~ m{(.*)\.asc}) {
      $logfile = "$1.log";
   }
[download]

YuckFoo