knoppix@Microknoppix:~$ perl -E '
> $trilet = q{AGT};
> say $trilet;
> $ss02 = substr $trilet, 0, 2;
> say $ss02;
> $ss12 = substr $trilet, 1, 2;
> say $ss12;
> $ss22 = substr $trilet, 2, 2;
> say $ss22;'
AGT
AG
GT
T
knoppix@Microknoppix:~$