After cloning a GitHub fork, set 'upstream' remote to the original parent repo. Tiny, no gh repo set-default needed.

gh-set-upstream.sh

#!/usr/bin/env bash
set -euo pipefail

slug=$(git remote get-url origin | sed -E 's#^.*[/:]([^/]+/[^/.]+)(\.git)?$#\1#')
url=$(gh api "repos/$slug" --template '{{if .fork}}{{.parent.ssh_url}}{{end}}' 2>/dev/null || true)

[[ -z $url ]] && { echo "not a fork"; exit 0; }

git remote add upstream "$url" 2>/dev/null || git remote set-url upstream "$url"
git fetch upstream --prune
echo "upstream → $url"