transfer.sh/hooks/post_checkout

#!/usr/bin/env bash
set -eu

echo "post_checkout"
source hooks/.config

echo "Install qemu + binfmt support"
echo "⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯"
# it's an Ubuntu VM and you can install stuff.
apt-get update
apt-get install -y curl qemu-user-static binfmt-support jq moreutils

# Sadly docker itself uses Docker EE 17.06 on Dockerhub which does not support
# manifests.
echo "Install a fresh docker cli binary"
echo "⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯"

curl https://download.docker.com/linux/static/stable/x86_64/docker-19.03.9.tgz | \
  tar xvz docker/docker

echo "Build a usable config.json file"
echo "⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯"
# Manifests are still experimental and enabled by a config file flag.
# Interestingly, there is no config file and the credential parts to push
# images is available in an environment variable. Let's create a config file to
# combine the two things:
#
mkdir -p ~/.docker
jq --null-input --argjson auths "$DOCKERCFG" '. + {auths: $auths}' | \
jq --arg experimental enabled '. + {experimental: $experimental}' | \
sponge ~/.docker/config.json

echo "copy qemu binaries into docker build context"
echo "⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯"
# The current setup copies the qemu binary into the image (see Dockerfile)
# Pro:
#      - it's easy to run non-amd64 images on amd64 systems for debugging
# Contra:
#      - it's dead weight in the "destination" architecture and consumes space
# Alternative:
#      - use a multistage Dockerfile (no RUN in the last stage possible of course)
#      - wait for https://github.com/moby/moby/issues/14080
#
for arch in ${build_architectures[@]}; do
  cp /usr/bin/qemu-${docker_qemu_arch_map[${arch}]}-static qemu-${arch}-static
done

ls -la