Clones only one subdirectory of a git repo. Preserves history, but removes all refs that don't contain the subdirectory

git-clone-subdir.sh

#! /bin/bash
# https://stackoverflow.com/questions/39956637/running-git-filter-branch-subdirectory-filter-to-also-remove-get-rid-of-other-su

repo=${1:?"Repo in first argument"}
subdir=${2:?"subdirectory name in second argument"}
temp_dir=$(mktemp -d)

function log {
    >&2 echo
    >&2 echo -e "\t $@"
    >&2 echo
}


log Using temporary directory ${temp_dir}

function rm_temp_dir {
       [[ ! -z ${temp_dir} ]] && [[ -z ${NO_TEMP_RM} ]] && rm -rf ${temp_dir}
}

trap rm_temp_dir EXIT

pushd . >/dev/null 2>&1

cd ${temp_dir}

git clone ${1} $(pwd) || exit 1

log Removing refs that don\'t reference ${subdir}

git for-each-ref --format='%(refname)' | \
while read ref; do
    if test "$(git rev-list --count "$ref" -- "${subdir}")" = 0; then
        log "delete $ref"
        echo "delete $ref"
    fi
done | git update-ref --stdin || exit 2

log "Making ${subdir} the root of the new repo"
git filter-branch -f --prune-empty --tag-name-filter cat --subdirectory-filter "${subdir}" -- --all || exit 3

log Checking out remaining remote branches

git for-each-ref --format="%(refname:lstrip=3)" refs/remotes | \
while read branch; do
    git checkout ${branch} || exit 4
done

log Removing ref backups
git for-each-ref --format="%(refname)" refs/original/ | xargs -n 1 git update-ref -d

log Done, moving back to original directory

popd >/dev/null 2>&1

NO_TEMP_RM=1
mv -nv $temp_dir $subdir || exit 5