$ perl -Mdiagnostics -e 'my %keys={A=>"b"};my ($a,$b); while (($a,$b)=
+each %keys) { print "$a $b\n"; }'
Reference found where even-sized list expected at -e line 1 (#1)
    (W misc) You gave a single reference where Perl was expecting a li
+st
    with an even number of elements (for assignment to a hash). This u
+sually
    means that you used the anon hash constructor when you meant to us
+e
    parens. In any case, a hash requires key/value pairs.

        %hash = { one => 1, two => 2, };        # WRONG
        %hash = [ qw/ an anon array / ];        # WRONG
        %hash = ( one => 1, two => 2, );        # right
        %hash = qw( one 1 two 2 );                      # also fine

Use of uninitialized value in concatenation (.) or string at -e line 1
+ (#2)
    (W uninitialized) An undefined value was used as if it were alread
+y
    defined.  It was interpreted as a "" or a 0, but maybe it was a mi
+stake.
    To suppress this warning assign a defined value to your variables.

    To help you figure out what was undefined, perl tells you what ope
+ration
    you used the undefined value in.  Note, however, that perl optimiz
+es your
    program and the operation displayed in the warning may not necessa
+rily
    appear literally in your program.  For example, "that $foo" is
    usually optimized into "that " . $foo, and the warning will refer 
+to
    the concatenation (.) operator, even though there is no . in your
    program.

HASH(0x60b220)
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