Update: The above was well intentioned, but bleary-eyed /me carelessly missed the typo in prop's OP, in which

find{ sub $total_size += -s if -f}, '.');
    should be
find (sub { $total_size += -s if -f}, '.');.

mea culpa and apologies.

But sentence 2 amount to a direct and gratuitous negative implication about props' integrity (or, I suppose, ability to copy code from a book)... and it is wrong.

The intial code fragment comes from p71 of Intermediate Perl, 2nd edition. It is verbatim, save for the book's inclusion of a use File::Find above. And it's available, on line, for your ease of checking these assertions, at http://safari.oreilly.com/ (more precisely, and as a link, 7.4 . Closures)