Help target for self-documentation of a Makefile

Makefile

.PHONY: # add tasks here to avoid timestamp checks
default: help

# Based on https://gist.github.com/prwhite/8168133#comment-1313022

## Another dummy task
dummy-task:
	echo dummy

## This help screen
help:
	@printf "Available targets\n\n"
	@awk '/^[a-zA-Z\-\_0-9]+:/ { \
		helpMessage = match(lastLine, /^## (.*)/); \
		if (helpMessage) { \
			helpCommand = substr($$1, 0, index($$1, ":")-1); \
			helpMessage = substr(lastLine, RSTART + 3, RLENGTH); \
			printf "%-30s %s\n", helpCommand, helpMessage; \
		} \
	} \
	{ lastLine = $$0 }' $(MAKEFILE_LIST)

helpCommand = substr($$1, 0, index($$1, ":")-1); truncated last letter of my command, need to remove -1 on my debian 9