While pelagic's answer is probably the best way to go here is some script to do it too.

#!/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 shortishbutnotshorten
+ough
[download]

Cheers,
R.

Carpe diem my dear!

Update:
I just realise "Pereant, qui ante nos nostra dixerunt" being your standard "disclaimer" ;)

pelagic

A crude way of doing this without a module would be:

my $foo = '12345678901 23456789012345678901234567890123456789012345678
+901234567890123456789012345678901234567890';
                                                                      
+          
my $n = 15;
                                                                      
+          
my @chunks = ($foo =~ /(\S{0,$n})\s?/g);
                                                                      
+          
print join "\n",@chunks;
[download]

/J\