@m=();

'abcdefghijklmnopqrstuvwxyz' =~ m[(?:(?=(..)(?{ push @m, $^N })).)+]; 

print for @m;;
ab
bc
cd
de
ef
fg
gh
hi
ij
jk
kl
lm
mn
no
op
pq
qr
rs
st
tu
uv
vw
wx
xy
yz