use strict;
use warnings;

sub foo {
    my $bar if 0; # <--- HACK!
    $bar = @_ ? shift : 1;
    sub bar {
        my $foo = shift;
        return $foo * (++$bar);
    }
    my $result = bar($bar);
    $result;
}
warn "calling foo(1): 1 * 2 = " . foo(1) . "\n";
warn "calling foo():  1 * 2 = " . foo()  . "\n";
warn "calling foo():  1 * 2 = " . foo()  . "\n";
warn "calling bar(5): 3 * 5 = " . bar(5) . "\n";
warn "calling foo(3): 3 * 4 = " . foo(3) . "\n";
__END__
Variable "$bar" will not stay shared at bar.pl line 17.
calling foo(1): 1 * 2 = 2
calling foo():  1 * 2 = 2
calling foo():  1 * 2 = 2
calling bar(5): 3 * 5 = 15
calling foo(3): 3 * 4 = 12