Template for Makefiles with '.env' file, precondition check and automatic help.

Template Makefile

#!/usr/bin/env make

ENV_FILE:=./.env$(if $(FOO),_$(FOO),)

ifneq (,$(wildcard ${ENV_FILE}))
  include ${ENV_FILE}
  VARS:=$(shell sed -ne 's/ *\#.*$$//; /./ s/=.*$$// p' .env )
  $(foreach v,$(VARS),$(eval $(shell echo export $(v)="$(shell echo $($(v)) | sed "s/^'//")")))
else
  $(error Environment file '${ENV_FILE}' not found)
endif

.DEFAULT_GOAL:=help

.PHONY: .pre foobar help

.pre:
        @ls . > /dev/null 2>&1 || { echo "failure!"; exit 1; }

foobar: .pre       ## Do the main thing
        echo "Doing the main thing..."

help: .pre         ## Show this help
        @printf "\nUsage: make \033[36m<target>\033[0m\n"
        @awk 'BEGIN {FS = ":.*##"} /^[a-zA-Z_-]+:.*?##/ { printf "  \033[36m%-10s\033[0m %s\n", $$1, $$2 } /^##@/ { printf "\n\033[1m%s\033[0m\n", substr($$0, 5) } ' $(MAKEFILE_LIST)
        @printf "\nVariable \033[36mFOO\033[0m can be used to switch between environments, e.g.: FOO=dev make \033[36m<target>\033[0m\n"