I think what chromatic was trying to say is:

print "\nDelete children of $test :\n";
foreach $key (keys %index) {
    ...
    delete $index{$key};
}
[download]

I suspect what is happening with your code:

foreach $key (%index) {
    delete $index{$key};
}
[download]

is the following. Remember that when you're dealing with foreach loops the item that you've got ($key in this case) is the item in the hash. That is, $key becomes an alias to the memory address within the hash.

So what is happening is that you're generating a list of all the keys and values in the hash, which is a list of aliases to those and then you're screwing it up. Remember that the list gets generated right at the very start of the for/foreach loop's execution.

You see, you delete a key, which means that your value gets deleted as well. Then you go onto a value and attempt to reference/delete that. All of a sudden you're attempting to delete something that you have a kind of reference to (from the generated list) but that has already been deleted from the hash! Hence, no doubt, the Attempt free unreferenced scalar at line 27. warning.

No wonder that makes Perl sad!

So, in conclusion, use keys. And remember that you should never fool around with the list you're interating over. I mentioned this recently over here too, although in a different case. I do accept that the best way to do what you need to do, is to iterate over your hash, just make sure that you're iterating over the keys of your hash, rather than the whole thing.

All the very best and I hope this helped

jarich

Update: Upon further thought and a little discussion I should probably mention that delete doesn't work on values and wouldn't normally cause this error. As far as I can tell the warning is caused because we're trying to use a scalar (the value of a deleted key) that no longer exists. This was the idea I was trying to convey above, but I suspect I wasn't very clear.

Update II: chromatic has corrected me by pointing out that he was merely pointing out that keys was missing from the original poster's loop in this case. Rather than showing where it should be used, which the original poster obviously would have known by using keys elsewhere.