Clone a GitHub repo and, if it's a fork, setup the upstream as remote

ghclone

#!/bin/sh

if [ "$#" -ne 1 ]; then
    echo "Usage: $0 <git-repo-url>"
    exit 1
fi

url=$1
repo=$url

case "$url" in
https://*)
	repo=${repo#https://github.com/*}
	repo=${repo%*.git}
	;;
[email protected]:*)
	repo=${repo#[email protected]:*}
	repo=${repo%*.git}
	;;
*)
	echo "$url is not a GitHub repo"
	;;
esac

dir=${repo#*/}

[email protected]:$repo.git
api_url=https://api.github.com/repos/$repo
json=/tmp/ghclone-$$

curl -s "$api_url" >$json

fork=$(jq -r .fork <"$json")

[ "$fork" = true ] &&
	upstream=$(jq -r .source.clone_url <"$json")

rm -f "$json"

git clone "$downstream" || exit

# Repo is not a fork
[ -z "$upstream" ] && exit 0

cd "$dir"

exec git remote add -f upstream "$upstream"