I have installed CPAN modules some time ago. After I open a folder of module
The documentation for the
dir_target target in ExtUtils::MM_Any says this:
Because depending on a directory to just ensure it exists doesn't work too well (the modified time changes too often) dir_target() creates a .exists file in the created directory. It is this you should depend on.
So it's part of the mechanisms used by the CPAN module installation toolchain.