#! perl -w
use strict;

package This::Module;
use CONSTANT _Filename => __FILE__;

#        ...

package main;
#print "$This::Module::_Filename\n";
#Use of uninitialized value in concatenation (.) at getfilename1.pl line 10.

print " @{[ This::Module::_Filename ]}\n";
#Bareword "This::Module::_Filename" not allowed while "strict subs" in use at getfilename1.pl line 13.