A nicer way to do it that's not as obtuse, since 5.6 is to do

  use IO::Handle;
  *STDOUT->autoflush(1);

This ends up far clearer than either example, and the idiom even extends easily to all file handles, lexical or otherwise.

EDIT: That being said,

  system("sleep 0.02") == 0 or last

is even worse. There is no need to go out to a shell or even an external program for that.

  use Time::HiRes;
  ...
  sleep(0.02);
  ...

Not only will that work on far more systems, it will use less resources and is available to all perl's since 5.7.3 (development release from March 2002, first in stable release from July 2002).