$text = 'howdoidoit';;

print for unpack '(a3X2)*', $text;;
how
owd
wdo
doi
oid
ido
doi
oit
it
it

print for unpack '(a4X3)*', $text;;
howd
owdo
wdoi
doid
oido
idoi
doit
oit
oit
oit