There's no general solution for all types of loops and all data the loops may be iterating over. Could you explain what your data source is, and whether you're using a for/foreach loop, a while loop, or something else? I assume you're using a loop that looks like:

foreach my $element (@array) {...
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But that could be a mistaken assumption. Also, how different does that last element need to be treated? What populated the array, and what will you be doing with it afterwards?

This is probably a terrible idea but you could bless a reference to the last element and detect that blessing:

my @array = qw(a b c d e f g);

{
    local $array[-1] = $array[-1];
    bless \$array[-1], 'last';

    foreach my $element (@array) {
        if (ref(\$element) eq 'last') {
            print "This is the last element: ";
        }
        print "$element\n";
    }
}
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The straightforward approach of just counting elements is less opaque. And if you're going to do that, a C style loop is probably the logical conclusion. However, if we knew more about where the data is coming from and what is really needed we may be able to provide a more on-target solution.