add shellcheck

Signed-off-by: Jess Frazelle <acidburn@microsoft.com>

Makefile

@@ -7,9 +7,28 @@ latest-versions: ## Checks all the latest versions of the Dockerfile contents.
 	./latest-versions.sh
 
 .PHONY: test
-test: ## Runs the tests on the repository.
+test: shellcheck dockerfiles ## Runs the tests on the repository.
+
+.PHONY: dockerfiles
+dockerfiles: ## Tests the changes to the Dockefiles build.
 	./test.sh
 
+# if this session isn't interactive, then we don't want to allocate a
+# TTY, which would fail, but if it is interactive, we do want to attach
+# so that the user can send e.g. ^C through.
+INTERACTIVE := $(shell [ -t 0 ] && echo 1 || echo 0)
+ifeq ($(INTERACTIVE), 1)
+        DOCKER_FLAGS += -t
+endif
+
+.PHONY: shellcheck
+shellcheck: ## Runs the shellcheck tests on the scripts.
+	docker run --rm -i $(DOCKER_FLAGS) \
+		--name df-shellcheck \
+		-v $(CURDIR):/usr/src:ro \
+		--workdir /usr/src \
+		r.j3ss.co/shellcheck ./shellcheck.sh
+
 .PHONY: help
 help:
 	@grep -E '^[a-zA-Z_-]+:.*?## .*$$' $(MAKEFILE_LIST) | sort | awk 'BEGIN {FS = ":.*?## "}; {printf "\033[36m%-30s\033[0m %s\n", $$1, $$2}'