use strict; behaviour not working as expected in Perl wrt $a and $b

问题

I have written a sample perl code:

use strict;
use warnings;
$a=1;
$b=2;
if($b==2) {
    $a=3;
}
print $a;

Ideally, when I run this code, it should give an error as 'Global symbol "$a" requires explicit package name...' But it is not giving any error. It gives the output as '3'. Why so? As far as I know, if we use strict, then we need to define the scope of the variable otherwise it gives an error. Is my understanding wrong?

回答1:

$a and $b are special variables, and thus are not rising error when used with strict.

From perldoc strict,

Because of their special use by sort(), the variables $a and $b are exempted from this check.

来源：https://stackoverflow.com/questions/24646689/use-strict-behaviour-not-working-as-expected-in-perl-wrt-a-and-b