the last two sentences look wrong to me. tried this:

D:\>perl -MData::Dumper -e "sub x{1 for 1..5};@y=x();print 'ha' if def
+ined @y"
ha
[download]

There's a few things to note:

• It's said that If the last statement is a loop control structure like a foreach or a while, the returned value is unspecified. "Unspecified" is not equal to "undefined", it means Perl can't guarantee what such subs would return. But in your case, it returns a list with a single empty element.

  $ perl -MData::Dumper -e 'sub x{1 for 1..5};@y=x();print Dumper(\@y)'
  $VAR1 = [
            ''
          ];
  [download]

• You don't use defined function for aggregate variables such as arrays and hashes because, Use of "defined" on aggregates (hashes and arrays) is deprecated. It used to report whether memory for that aggregate has ever been allocated. This behavior may disappear in future versions of Perl. So, it prints "ha" when you check the defined-ness of the array @y because it has been allocated some memory.
• Most (if not all) of the time you want to check whether an array or a hash have element, thus say ... if @y; instead of ... if defined @y;. Eventhough, it would still print "ha" because the array has, indeed, an element which is empty (see point 1).

Finally, consider the following snippets:

$ perl -wle 'sub x{};@y=x(); print "array" if @y'
(nothing)
$ perl -wle 'sub x{};%y=x();print "hash" if %y'
(nothing)
$ perl -wle 'sub x{1..3};@y=x(); print "array" if @y'
array
$ perl -wle 'sub x{a => 1};%y=x();print "hash" if %y'
hash
[download]

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