Appending text to a subgroup

[lambertjosh]

It does not appear possible to append text directly to a subgroup, without introducing characters in between.

I have a metric that outputs the exact HTTP return codes, and I'd like to instead view these as their groups. (e.g. 2xx, 4xx, 5xx)

I can do this with some very ugly nested label_replace's:
sum(label_replace(label_replace(label_replace(label_replace(rate(nginx_ingress_controller_requests[2m]), "status_code", "5xx", "status", "5.*"), "status_code", "4xx", "status", "4.*"), "status_code", "3xx", "status", "3.*"), "status_code", "2xx", "status", "2.*")) by (status_code)

But I would much prefer to use a regex subgroup to grab the group code, then append xx onto it. For example:
label_replace(rate(nginx_ingress_controller_requests[2m]), "status_code", "$1xx", "status", "(.)..")

However this has the weird behavior of actually doing nothing. If you put a space or any symbol between $1 and the trailing text, it works, but it would be nice for there to be some method to do this cleanly.

[brian-brazil]

Try ${1}.

It makes more sense to ask questions like this on the prometheus-users mailing list rather than in a GitHub issue. On the mailing list, more people are available to potentially respond to your question, and the whole community can benefit from the answers provided.

[lambertjosh]

Thanks, for anyone searching this does resolve the problem I was having.