One of the things that `use strict` does is enable `use strict "vars"`.

    use strict;

    no strict qw(vars);
    $foo = $bar;

That's part of the reason `use strict` is recommended.

---

The other major reason is `"refs"`, which disable symbolic refs. Honestly this is *THE* main reason I recommend `use strict`.

Symbolic refs are how you did arrays of arrays prior to Perl5. (Among other uses.)

    use 4.0;

    @a = 'b','c';
    @b = (1, 2);
    @c = (3, 4);

    print $a[1]->[1], "\n"; # 4

That can be a security risk if an attacker can insert or change strings in `@a`.

It isn't (generally) needed anymore of course.

    use 5.0;
    my @a = ( \[1,2], \[3,4] );

    print $a[1]->[1], "\n"; # 4

(The only reason `@b` and `@c` existed was to symbolically reference them.)