use Data::Dumper;
print Dumper(\%INC);

##</code><code>##

$VAR1 = {
          [...]
          'subclass1.pm' => 'subclass1.pm',
          [...]
          'Subclass1.pm' => 'Subclass1.pm',
          [...]
        };

##</code><code>##

use fIlE::SpEc qw(catfile); # note the wrong case

$x = File::Spec->catfile('a', 'b', 'c'); # this works
$x = catfile('a', 'b', 'c'); # this croaks