As much as I would like it to be, Perl is not the answer to everything. I personally would stick with the shell commands.

I've not used File::Sort, but lets assume it sorts the file... I'd do something like

open(FILE, "sorted.file");

while (<FILE>) {


if($_ != $previous) {

   print $current;
   $count++;

}

$previous = $_;

}

print "There are $count unique records";
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Code is untested and not well formated, but hopefully you'll get the idea.