++ For the review.

I would also like to add that the module Smart::Comments also supports progress bars, like so:

use Smart::Comments;
foreach (@array) { ### Evaluating...           done
    # do something...
}
[download]

When the program enters the loop, it will show the comment and the dots will add until they reach the "done" word. It also supports many other formats.

I've read somewhere that its use was not recommended because, unlike the approach reviewed in the root node, it does source filtering. Although it might not be a guarantee of anything, I personally used it for my "progress bar" needs without a problem.