Dear monks,

I have been writing a regexp that would transform this:

$s = 'aaaabababbbbaaaccccbbbbbbaadddd';
[download]

into

$s = '4ababa4b3a3a4c6b2a4d';
[download]

Basicly it is something similar to mathematical series test (ummm... not sure if this is the correct translation from Lithuanian) where subsequent occurrences of the same character are counted (except no number would be inserted if there is only one character).

I have been trying to come up with a regexp that would do this transformation and I got to the point where everything works:

$s = 'aaaabababbbbaaaccccbbbbbbaadddd';
$s =~ s"($_{2,})"length($1).$_"ge for ('a'..'d');
print $s;
[download]

However I am not very happy with the for loop. I wonder if the same can be achieved in one regexp, without the need to scan the line for each character. Can character classes be somehow involved in the regexp to avoid looping?

Thanks for any help in advance.