Makefile

Makefile

ifeq ($(strip $(shell git status --porcelain 2>/dev/null)),)
	GIT_TREE_STATE=clean
else
	GIT_TREE_STATE=dirty
endif

all: build

build: 
	@echo "==> Building the project"

release: check
	@echo "==> Releasing the project"

check:
ifeq ($(GIT_TREE_STATE),dirty)
    $(error git state is not clean)
endif

.PHONY: all build release

Just came up with this one-liner, what do you think?

GIT_TREE_STATE=$(shell (git status --porcelain | grep -q .) && echo dirty || echo clean)

Wow, just saw this gist here :D Thanks @broady. I think you're one liner is much better than what I have.