use v5.10;
use strict;
use warnings;

BEGIN {
	package Some::Module;
	no thanks;
	our $LOGFILE;
	
	sub what_is_logfile {
		say "logfile is $LOGFILE";
	}
};

package main;
use Some::Module; 

my $log = 'foo.txt';
$Some::Module::LOGFILE = $log;

Some::Module->what_is_logfile;