$ perl -E '
> @arr = qw{
>    abCdeFg
>    hIJklMn
>    OpqrsTu
>    };
> say join q{:}, @arr;
> $str = join q{:},
>    map { s{[A-Z]}{*}g } @arr;
> say $str;'
abCdeFg:hIJklMn:OpqrsTu
2:3:2
$

##</code><code>##

$ perl -E '
> @arr = qw{
>    abCdeFg
>    hIJklMn
>    OpqrsTu
>    };
> say join q{:}, @arr;
> $str = join q{:},
>    map { s{[A-Z]}{*}g; $_ } @arr;
> say $str;'
abCdeFg:hIJklMn:OpqrsTu
ab*de*g:h**kl*n:*pqrs*u
$