# config file
log4perl.logger.ClassA = DEBUG, ClassA
log4perl.appender.ClassA = Log::Log4perl::Appender::File
log4perl.appender.ClassA.filename = sub { log_filename() }

# in the main code
use POSIX 'strftime';

sub log_filename {
    return strftime( "/tmp/ClassA%Y%m%d.log", localtime );
}

Log::Log4perl::init_and_watch('/etc/log4perl.conf',5);
my $mylog = Log::Log4perl->get_logger();