$ perl -E '
    #use strict;
    use warnings;

    {
        my $i;

        for $i (1,2,3) {
            say $i;
        }

        say $i // "undefined";
    }

    {
        for my $i (1,2,3) {
            say $i;
        }

        say $i // "undefined";
    }

    {
        for $i (1,2,3) {
            say $i;
        }

        say $i // "undefined";
    }

    {
        my $i = q{completely different $i};

        for $i (1,2,3) {
            say $i;
        }

        say $i // "undefined";
    }
'
1
2
3
undefined
1
2
3
undefined
1
2
3
undefined
1
2
3
completely different $i