Hi,
I'm a bit puzzled regarding the behavor of make: I don't understand why
a make function is executed twice when stored in a variable which is
expanded as part of a recipe.
See the following Makefile fragment, as info.mk:
ifeq ($(V),1)
Q :=
else
Q ?= @
endif
all:
$(Q) : $(info 1)
$(Q)$(RECIPE)
$(Q) : $(info 3)
When make is invoked with
$ $ ./make -f ./info.mk
1
3
Now, let's put some shell in RECIPE variable:
$ make -f ./info.mk RECIPE='echo 2'
1
3
2
Having 2 printed after 3 is OK here: $(info ...) in the recipe were
expanded before each command were feed to the shell for execution.
Now, try to get 2 printed between 1 and 3:
$ ./make -f ./info.mk RECIPE=': $(info 2)'
1
2
3
2
This way, 2 is printed twice. The second times seems to happen just
before passing to the shell the line where the variable is expanded.
That can be checked with
$ ./make -f ./info.mk V=1 RECIPE=': $(info 2)'
1
2
3
:
2
:
:
So the second 2 (!) seems to be reported after recipe line
$(Q) : $(info 1)
is executed by the shell, but before this recipe line
$(Q)$(RECIPE)
is executed by the shell.
As I haven't done my homework, I don't know if it's an expected
documented behavor. But it's a pity it behave this way.
Is there any workaround to have 2 printed only one ?
BTW, it seems to happen only with $(info ...), as it would be very bad
if other functions having side effect would be called twice. See for
example:
$ ./make -f ./info.mk V=1 RECIPE=': $(shell mktemp info.XXXXXXXXX)'
1
3
:
: info.vB12nZmM7
:
As you can see, hopefully, $(shell ...) is expanded once.
Regards.
--
Yann Droneaud
OPTEYA
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