replied to https://photogabble.co.uk/resources/snippets/bash-script-for-pruning-stale-local-git-branches/
I use this alias in my .gitconfig:
prune-br = "! git fetch --all --prune && git branch -vv | grep '\\(origin\\|fork\\|src\\)/.*: gone]' | awk '{print $1}' | xargs git branch -D"