It works on the AIX system where I run it. I get 0s from du -kh for empty directories. I was going to ask if it was unreasonable to assume that posted code works, but then I remembered about a million cases where that wasn't the case, so I can't fault you for asking.
You can talk about the hardcoded directory, if you want. I'm pretty sure you can even change it or rewrite it without it.
But God demonstrates His own love toward us, in that while we were yet sinners, Christ died for us. Romans 5:8 (NASB)