Re: Conditionally executing a script and using return value

[Kaz Kylheku (gmake)]

On 2019-04-11 03:04, Thomas Nyberg wrote:
> Hello,
>
> I would like my Makefile to:
>
> 1. Check if a variable is set to specific value,
> 2. If it is, execute a script and get its return value,
> 3. Stop executing Makefile depending upon return value.
>
> Here is the Makefile I have:
>
> `Makefile`
> -------------------------------------------------------------
>     FORCE=true

Missing:

.PHONY: all check_force

so that make doesn't probe the filesystem looking for
targets named "all" and "check_force" (and refuse to build anything if 
they both exist and "all" is newer).

>     all: check_force
>         @echo "success"
>
>     check_force:
>         ifeq ($(FORCE),true)

ifeq lines cannot be indented with a tab. Tabbed lines
are strictly recipe lines.

>         $(shell sh ./prompt.sh)

This should just be: ./prompt.sh   since it's just a step
in the recipe; $(shell ...) is usually used outside of recipes for 
obtaining the effect of executing a shell command while Makefile syntax 
is being read, and substituting its output.

In a recipe line if we do  $(shell echo foo),  make will execute "echo 
foo" during the expansion of the recipe line and capture the "foo" 
output which will then be integrated into the expanded recipe line. Your 
recipe line here is saying, "take the output of sh ./prompt.sh and 
execute it as a command, failing the recipe if that command fails".

>         endif

we need an unconditionally successful recipe if the
variable isn't "true", rather than a blank recipe:

else
        exit 1
endif


Cheers ...