00.mk

foo = xxx
bar = $(foo) @ $(foo)
boo = [ $(bar) ]

# or
# foo := xxx
# bar := $(foo) @ $(foo)
# boo := [ $(bar) ]

$(info * $$(foo) is $(foo))
$(info * $$(bar) is $(bar))
$(info * $$(boo) is $(boo))

default:

01.mk

foo = $(shell python echo.py xxx)
bar = $(shell python echo.py $(foo) @ $(foo))
boo = $(shell python echo.py [ $(bar) ])

$(info $$(foo) is $(foo))
$(info $$(bar) is $(bar))
$(info $$(boo) is $(boo))

default:

02.mk

foo := $(shell python echo.py xxx)
bar := $(shell python echo.py $(foo) @ $(foo))
boo := $(shell python echo.py [ $(bar) ])

$(info $$(foo) is $(foo))
$(info $$(bar) is $(bar))
$(info $$(boo) is $(boo))

default:

echo.py

import shlex
import sys

print(shlex.join(sys.argv[1:]))
print("\t --", shlex.join(sys.argv), file=sys.stderr)

Makefile

FILE = $(shell echo $@*.mk)

00:
	make -f $(FILE) -s
01:
	make -f $(FILE) -s
02:
	make -f $(FILE) -s