Yes: of course this does not take care of the case when the given string has a length that is not a multiple of 5.

If you want to catch that, you can change the regex to /.{1,5}/g.

perl -le 'print for "ABCDEFGHIJKLMNOPQRSTUVWXYZ" =~ /.{1,5}/g'
ABCDE
FGHIJ
KLMNO
PQRST
UVWXY
Z
[download]

Of course, depending on what it's used for, simply discarding it can be a better idea, and /.{5}/g works just fine for that.