perl 中的$a和$b
这两个变量是为sort函数准备的内置变量，所以声明的时候可以不加 my即使打开了strict和warnings选项也无妨，下面代码并无错误和警告。
use strict;
use warnings;
sub test {
$a = 1;
$b = 2;
print $a, "\n";
print $b, "\n";
}
test();
1;
from perldoc perlvar
perldoc perlvar
$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.
==
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