# foo.pl
use strict;
use warnings;
use Log::Log4perl;

my $conf = qq(
  log4perl.category.Script                 = INFO, ScreenAppender
  log4perl.appender.ScreenAppender         = Log::Log4perl::Appender::Screen
  log4perl.appender.ScreenAppender.layout  = PatternLayout
  log4perl.appender.ScreenAppender.layout.ConversionPattern=[%p] %d %M %F:%L - %m%n
);

Log::Log4perl::init( \$conf );
my $log = Log::Log4perl::->get_logger(q(Script));

# Add two numbers, no larger than 32 each
sub add {
  my ($i, $j) = @_;
  $log->logdie("type error") unless ($i and $j and $i =~ m/^\d+/ and $j =~ m/^\d+/);
  $log->warn("possible overflow") unless ($i < 2**5 and $j < 2**5);
  return $i + $j;
}

# When testing: Disable all logging,
# When not testing: call add()
caller() ? Log::Log4perl->appender_thresholds_adjust(7) : print add(@ARGV);

1;
__END__