Extract a docker image into a directory, does not require a container

extract-image.sh

set -e

# you need to run `docker save <image> -o <file>.tar
# then run this script like `extrat-image.sh <file>.tar`
# it will create a directoyr `<file>.tar-root` which containers
# all files from the image extracted

input=$1
if [ ! -f "${input}" ]; then
    echo "file does not exist"
    exit 1
fi

tmpdir=".${input}"
rootfs="${input}-root"
rm -rf $tmpdir || true
rm -rf $tmpdir || true

function finish {
    rm -rf ${tmpdir} || true
}

trap finish EXIT

mkdir -p ${rootfs}
mkdir -p ${tmpdir}

tar -xf $input -C $tmpdir
mf=${tmpdir}/manifest.json
if [ ! -f "${mf}" ]; then
    echo "invalid tar archive (no manifest.json file)"
    exit 1
fi

for layer in $(jq '.[0].Layers[]' $mf); do
    layer=${layer//\"/}
    tar -xf "${tmpdir}/${layer}" -C $rootfs
done

echo "done"