Someone seems intent on repeating this particular piece of misinformation, so perhaps it's worth repeating (just this once) that it's incorrect.

I do agree that $|++ is unnecessarily clever, since it might confuse an ignorant maintenenance programmer, and that $| = 1 is clearer. But it's simply wrong to say that it could “bite you if $| doesn't happen to have the value you assume”. It couldn't, for reasons that will be obvious to anyone who has understood this thread.