I forgot to mention that I tried it but either I am doing something wrong or ...: 
$str =~ s/(?=hello kitty )(\d+)/sprintf "%d", $1/e;

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does not do anything. it is probably me but I don't see it.

In reply to Re^2: regexp: non-capturing grouping in replacement possible? by diweooy
in thread regexp: non-capturing grouping in replacement possible? by diweooy

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