makefile to see if it's possible to detect source of shell invocation with the make run

Makefile

# use a bash as sh is sh*#
.SHELL = /bin/bash -e

# Turn off make's legacy cruft
.SUFFIXES:

# Unless otherwise stated
.DEFAULT_GOAL := diff

# TOOLS
## diff returns 1 for there is a difference but we don't want make to fail to prefix -
DIFF := -diff
## -f = force
RM := rm -f
## -fs = force symbolic
LN := ln -fs
## -e = extended
ECHO := echo -e
## set
SET := set

# TESTS
FROM_SHELL := from_shell
FROM_RECIPE := from_recipe
NEXT_LEVEL := next_level

# OUTPUTS
OP_FROM_SHELL := $(FROM_SHELL)_$(MAKELEVEL).txt
OP_FROM_RECIPE := $(FROM_RECIPE)_$(MAKELEVEL).txt
OP_NEXT_LEVEL := $(NEXT_LEVEL).txt

# using the shell keyword
$(info make is using shell)
$(shell $(SET) > $(OP_FROM_SHELL))


all: $(OP_FROM_RECIPE) $(NEXT_LEVEL) | $(info make all)


# Using a recipe
$(OP_FROM_RECIPE):
	$(info make is using recipe)
	$(SET) > $(OP_FROM_RECIPE)

# Stepping up a level
.PHONY: $(NEXT_LEVEL)
next_level:
	$(info make next_level from $(MAKELEVEL))
	$(MAKE) $(NEXT_LEVEL)_$(MAKELEVEL).txt

# Hander for next level
$(NEXT_LEVEL)%.txt:
	$(info make $@)
	$(SET) > $@


# Shiney Shiney
.PHONY: clean
clean:
	$(info -> make clean)
	$(RM) $(NEXT_LEVEL)*.txt
	$(RM) $(FROM_RECIPE)*.txt
	$(RM) $(FROM_SHELL)*.txt
	$(RM) diff*.txt


# Collect the results
.PHONY: diff
diff: all
	$(info -> make diff)
	$(ECHO) "$(FROM_SHELL)_0.txt <-> $(OP_FROM_RECIPE)"
	$(DIFF)  $(FROM_SHELL)_0.txt $(OP_FROM_RECIPE) > diff_shell0_recipe.txt

	$(ECHO) "$(FROM_SHELL)_0.txt <-> $(NEXT_LEVEL)_0.txt"
	$(DIFF)  $(FROM_SHELL)_0.txt $(NEXT_LEVEL)_0.txt > diff_shell0_level0.txt

	$(ECHO) "$(FROM_SHELL)_0.txt <-> $(NEXT_LEVEL)_1.txt"
	$(DIFF)  $(FROM_SHELL)_0.txt $(NEXT_LEVEL)_1.txt > diff_shell0_level1.txt

	$(ECHO) "$(FROM_SHELL)_1.txt <-> $(OP_FROM_RECIPE)"
	$(DIFF)  $(FROM_SHELL)_1.txt $(OP_FROM_RECIPE) > diff_shell1_recipe.txt

	$(ECHO) "$(FROM_SHELL)_1.txt <-> $(NEXT_LEVEL)_0.txt"
	$(DIFF)  $(FROM_SHELL)_1.txt $(NEXT_LEVEL)_0.txt > diff_shell1_level0.txt

	$(ECHO) "$(FROM_SHELL)_1.txt <-> $(NEXT_LEVEL)_1.txt"
	$(DIFF)  $(FROM_SHELL)_1.txt $(NEXT_LEVEL)_1.txt > diff_shell1_level1.txt

	$(ECHO) "$(FROM_SHELL)_0.txt <-> $(FROM_SHELL)_1.txt"
	$(DIFF)  $(FROM_SHELL)_0.txt $(FROM_SHELL)_1.txt > diff_shell0_shell1.txt

	$(ECHO) "$(OP_FROM_RECIPE) <-> $(NEXT_LEVEL)_0.txt"
	$(DIFF)  $(OP_FROM_RECIPE) $(NEXT_LEVEL)_0.txt > diff_recipe_level0.txt

	$(ECHO) "$(OP_FROM_RECIPE) <-> $(NEXT_LEVEL)_1.txt"
	$(DIFF)  $(OP_FROM_RECIPE) $(NEXT_LEVEL)_1.txt > diff_recipe_level1.txt