$ cat Foo.pm
print("Foo!\n");
1;

$ perl -e'use Foo'
Foo!

$ perl -T -e'use Foo'
Can't locate Foo.pm in @INC (@INC contains: ...) at -e line 1.
BEGIN failed--compilation aborted at -e line 1.

$ perl -T -I. -e'use Foo'
Foo!