Just for kicks, and with extended character classes (5.005 or later? Not sure.):
my $str = "AbcDefGhiJkl";
$str = join "::", split(/(?<=[[:lower:]])(?=[[:upper:]])/, $str);
print "$str\n";

[download]
Update: Ok, it is slower, but interesting nonetheless and still maybe worthwhile to use the [:lower:] and [:upper:] character classes even on blakem's answer.

In reply to Re: Finding lowercase letters next to uppercase letters by runrig
in thread Finding lowercase letters next to uppercase letters by dsalada

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