in reply to print a backspace in nph-"HTML"?

I don't know enough about textareas to answer your main question, but the canonical way to do the $count thing is with modulo arithmetic:

print "\b\b\b\b" if ++$count % 4 == 0;
Or you may want to use == 1 or == 3, depending on what effect you want to achieve. You can read about %, the modulus operator, in perlop.