unpack, as alluded to by zentara.

$ perl -le '
> $text = q{abcdefghij} x 15;
> print for unpack q{(a9)*}, $text;'
abcdefghi
jabcdefgh
ijabcdefg
hijabcdef
ghijabcde
fghijabcd
efghijabc
defghijab
cdefghija
bcdefghij
abcdefghi
jabcdefgh
ijabcdefg
hijabcdef
ghijabcde
fghijabcd
efghij
[download]

Cheers,

JohnGG