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functionmakefileexport

Export a function in Makefile

I'd like to use a function in a recursive call of make.

I have the following in the principal Makefile:

define my_func
Hello $(1) from $(2)
endef
export my_func

And further, in another one called later, I have :

$(error my_func is $(call my_func,StackOverFlow,Me))

It gives me this output Makefile_rec.mk:1: *** my_func is Hello from . Stop.

But what I'd like is Makefile_rec.mk:1: *** my_func is Hello StackOverFlow from Me. Stop.

Is there a way using make to export such a variable/function and get it to work when using call function ?

Thanks !

-- EDIT --

As pointed by @Renaud Pacalet here, I would like also to use this kind of macro either in the current Makefile and in sub-makes.

If possible, not by including a file each time I need the macro

Solution

  • If you want this to work you must double the $ signs in your definition:

    define my_func
Hello $$(1) from $$(2)
endef
export my_func

    From the manual:

    To pass down, or export, a variable, make adds the variable and its value to the environment for running each line of the recipe. The sub-make, in turn, uses the environment to initialize its table of variable values.

    You must protect the $ from one extra expansion.

    Of course, you cannot use the same macro in the top Makefile. If it is a problem, you must define a macro for the top Makefile and another one for the sub-make Makefile:

    host> cat Makefile
define my_func
Hello $(1) from $(2)
endef
my_func_1 := $(call my_func,$$(1),$$(2))
export my_func_1

all:
    $(MAKE) -f Makefile_rec.mk
    $(info TOP: $(call my_func,StackOverFlow,Me))

host> cat Makefile_rec.mk
all:
    $(info BOT: $(call my_func_1,StackOverFlow,Me))

host> make --no-print-directory 
TOP: Hello StackOverFlow from Me
make -f Makefile_rec.mk
BOT: Hello StackOverFlow from Me
make[1]: 'all' is up to date.