use Log::StdLog { file => "$0.log" }; # OK
#use Log::StdLog { file => $filename }; # NOT OK

##</code><code>##

use Log::StdLog; # at compile time
my $file = "$config{dir}". basename($0) .".log.$$"; # at run time
my $level = 'warn';
# specify file at runtime (below).
Log::StdLog->import ({ level => $level, file => $file } ); # works, runtime