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Re: $(info ...) in variable, with expansion in recipes
From: |
Yann Droneaud |
Subject: |
Re: $(info ...) in variable, with expansion in recipes |
Date: |
Fri, 04 Jul 2014 19:01:39 +0200 |
Le vendredi 04 juillet 2014 à 18:24 +0200, Yann Droneaud a écrit :
> Hi,
>
> I'm a bit puzzled regarding the behavor of make: I don't understand why
> a make function is executed twice when stored in a variable which is
> expanded as part of a recipe.
>
> See the following Makefile fragment, as info.mk:
>
> ifeq ($(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:
>
I've found a workaround, but such workaround so counter-intuitive that's
demonstrate there's really something wrong about having $(info ...) in
a variable which is expanded as part of a recipe. See this new makefile
fragment, info-empty.mk, which use $(if ...):
ifeq ($(V),1)
Q :=
else
Q ?= @
endif
empty :=
all:
$(Q) : $(info 1)
$(Q)$(if $(empty),$(RECIPE))
$(Q) : $(info 3)
$(if ...) is said to not expand one of its arguments, so my variable
RECIPE containing $(info ...) should not be expanded, as $(empty) is
always false.
Let's try:
$ ./make -f ./info-empty.mk RECIPE=': $(info 2)'
1
3
2
And with V=1:
$ ./make -f ./info-empty.mk V=1 RECIPE=': $(info 2)'
1
3
:
2
:
$(info 2) is only evaluated once ... but it should never be evaluated as
far as I understand how make proceed to variable expansion and function
execution.
What do you think of this ?
Regards.
--
Yann Droneaud
OPTEYA
- $(info ...) in variable, with expansion in recipes, Yann Droneaud, 2014/07/04
- Re: $(info ...) in variable, with expansion in recipes,
Yann Droneaud <=
- Re: $(info ...) in variable, with expansion in recipes, Etan Reisner, 2014/07/04
- Re: $(info ...) in variable, with expansion in recipes, Yann Droneaud, 2014/07/04
- Re: $(info ...) in variable, with expansion in recipes, Philip Guenther, 2014/07/04
- Re: $(info ...) in variable, with expansion in recipes, Etan Reisner, 2014/07/04
- Re: $(info ...) in variable, with expansion in recipes, Yann Droneaud, 2014/07/08
- Re: $(info ...) in variable, with expansion in recipes, Philip Guenther, 2014/07/08
- Re: $(info ...) in variable, with expansion in recipes, Yann Droneaud, 2014/07/15
- Re: $(info ...) in variable, with expansion in recipes, Etan Reisner, 2014/07/04