split /(?<=..)/, $in;

I don't think that is going to do quite what you expected. It will split the string at every point that is preceded by two characters.

$ perl -le '
-> $str = q{abcdefg};
-> @bits = split m{(?<=..)}, $str;
-> print for @bits;'
ab
c
d
e
f
g
$
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It seems that split is not perhaps the handiest tool for this task.