invoke start script from our entrypoint

rather than replacing our entrypoint

repo2docker/buildpacks/base.py

@@ -154,12 +154,12 @@ RUN ./{{ s }}
 
 # Add start script
 {% if start_script is not none -%}
-RUN chmod +x "{{ start_script }}"
-ENTRYPOINT ["{{ start_script }}"]
-{% else %}
+ENV R2D_ENTRYPOINT "{{ start_script }}"
+{% endif -%}
+
+# Add entrypoint
 COPY /repo2docker-entrypoint /usr/local/bin/repo2docker-entrypoint
 ENTRYPOINT ["/usr/local/bin/repo2docker-entrypoint"]
-{% endif -%}
 
 # Specify the default command to run
 CMD ["jupyter", "notebook", "--ip", "0.0.0.0"]

repo2docker/buildpacks/repo2docker-entrypoint

@@ -2,4 +2,8 @@
 # lightest possible entrypoint that ensures that
 # we use a login shell to get a fully configured shell environment
 # (e.g. sourcing /etc/profile.d, ~/.bashrc, and friends)
-exec "$@"
+if [[ ! -z "${R2D_ENTRYPOINT:-}" ]]; then
+    exec "$R2D_ENTRYPOINT" "$@"
+else
+    exec "$@"
+fi