Quote

$a
$b Special package variables when using sort(), see "sort" in
perlfunc. Because of this specialness $a and $b don't need to be
declared (using use vars, or our()) even when using the "strict
'vars'" pragma. Don't lexicalize them with "my $a" or "my $b" if
you want to be able to use them in the sort() comparison block
or function.