Bootstrap: scratch

%setup
    alpine_minirootfs_url='http://dl-cdn.alpinelinux.org/alpine/v3.8/releases/x86_64/alpine-minirootfs-3.8.1-x86_64.tar.gz'

    # Download and extract alpine minirootfs.
    curl "${alpine_minirootfs_url}" \
       | tar xz -C "${SINGULARITY_ROOTFS}" --exclude=./dev --exclude=./etc/hosts
