That only wraps a line if it ends at a multiple of the boundary, it doesn't prevent a word from going past it (you need to check if the current word is going to go past the boundary before printing it). On a $str of 'George Washington was the first president of these United States' it won't insert a <br> despite there being significantly more than 10 chars in it. This loop should do it:

foreach (split(/\s/, $str))
 {
   if($len + 1 + length > POS && $len)
    {
      $len = 0;
      print "\n";
    }
   elsif($len)
    {
      print ' ';
      $len++;
    }
   print;
   $len += length;
 }
[download]