while (($_) = sort keys %data){ 
 
 print "while: $data{$_}\n"; 
 delete $data{$_}; 
}
[download]

This is a pretty expensive loop. You'd be much better doing:

while (my ($k, $v) = each %data) {
  print "key is $k, value is $v\n";
}
[download]

Without those parens around $_, I would expect it to try to pass '5' into the block (which it would do) if you took away the sort function, but it doesn't do that. I suppose that might qualify as an insignificant bug.

No, sort in a scalar context always returns undef. Maybe someday, it'll return something useful. But not yet. No bug, except in perhaps your understanding. {grin}

-- Randal L. Schwartz, Perl hacker