Frankly I prefer the name and interface of Filesys::DiskUsage. Sadly, despite the docs mentioning "blocks", this module doesn't really count block usage like the Unix "du" command, because it doesn't take multiple hard links into account.
Even more sadly, Filesys::DiskUsage doesn't either.
I guess I'll have to do with 'system "du $file"' command for now.
Not sure what "UNAUTHORIZED RELEASE" means; I couldn't install the module via cpan File::Size. However, module does what it is ment to do and does it fast. Documentation could be improved a bit as I had to run test codes to figure out what exactly some methods return, other than that I like this module.