Here's another method if you're running perl 5.8.0 or better:

$str = "this is just a test\nthis is another test\nthis is yet another
+ test\n";
open F, "<", \$str or die;  # open a handle to our string
$/ = \5;                    # Read 5 characters at a time
while (<F>) {               # Read 'em!
   print "$_\n";
}
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