# set debugging switch to OFF
my $debug_switch = 0;

# go through the argument evaluation at compile time
BEGIN
{
	# check each argument
	foreach $_ (@ARGV)
	{
		# is the debug switch submitted?
		if (/^-d$/i)
		{
			# yup. set debugging switch to ON
			$debug_switch = 1;
		}
	}
}
# set DEBUGGING to the debug_switch value
use constant DEBUGGING => $debug_switch;