Also note that looping over a lexical variable declaration does not 're-declare' that variable. It just gets marked as uninitialized.

I was reading the Monk tutorial "Coping with Scoping", and I found an example which is relevant to this discussion:

Every time control reaches a my declaration, Perl creates a new, fresh variable. For example, this code prints x=1 fifty times:

        for (1 .. 50) {
          my $x;
          $x++;
          print "x=$x\n";
        }
[download]

You get a new $x, initialized to undef, every time through the loop.

If the declaration were outside the loop, control would only pass by it once, so there would only be one variable:

        { my $x;
          for (1 .. 50) {
            $x++;
            print "x=$x\n";
          }     
        }
[download]

This prints x=1, x=2, x=3, ... x=50.

That seems at odds with what you are saying. In any case, there are situations where declaring a my variable inside a loop can cause problems.