
for REPO in $(curl -s --header "PRIVATE-TOKEN: <TOKEN>" "https://<YOURGITLAB>/api/v4/groups/<GROUPID>/projects?include_subgroups=true&per_page=20000000" | ./jq -r ".[] | .ssh_url_to_repo");
do git clone $REPO;
done;
&per_page=20000000 (or any high number) is needed to get all projects (default seems to be around 20 project/page)