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

my $length=10;

while (<DATA>) {
    my @bits=split; # defaults to splitng $_ on whitespace
    foreach (@bits) {
         while ((length $_) > $length) {
              print "long one\n";
              # here we substitute an empty string for the
              # first $length characters and printing the
              # ones replaced 
              print ((substr $_, 0, $length, "")."\n");
         }
         print "$_\n";
    }
}

__DATA__

This one is fine

ThisOneIsNotReallySoGood

Here is a mixedbagoflongbits and then reasonably shortishbutnotshortenough