How can one write a perl script in such a way that the code can report on itself?

If you have a __DATA__ section at the end, you can seek on the DATA filehandle, and read the source of your current program. Note that without the __DATA__ section, it will not work. Here's a quick example:

#!/usr/bin/perl
use strict;
use warnings;

my %chars;

seek DATA, 0, 0;
while (<DATA>) {
    chomp;
    $chars{$_}++ for split //;
}

for (sort keys %chars) {
    printf "%s => %2d\n", $_, $chars{$_};
}

__DATA__
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