Re: Can I generate multiple recipe commands dynamically in makefile

[Chen Jun (陈军)]

Thank you Paul, your first two method is surely workable and I have
thought about them, but I am also aware of some drawback of them(just I
think). See my comment below. So I'd like to heard about the ultimate
$(eval ) method. I've been using GNU make intensively for five years and
Paul had kindly answer some real-world $(eval ) questions for me, so I'm
sure I'm quite versed in $(eval ), (ugh, except the very question today).

On 2011-05-15 23:22, Paul Smith wrote:
> On Sun, 2011-05-15 at 18:06 +0800, Chen(陈) Jun(军) wrote:
>> Please check my makefile:
>>
>> ================
>> define show
>>     echo "[$1]"
>> endef
>>
>> filelist = 1.c 2.c 3.c
>>
>> all:
>>     @$(call show,1.c)
>>     @$(call show,2.c)
>>     @$(call show,3.c)
>>
>> # That code below cannot work!
>> #all2:
>> #    @$(foreach f,$(filelist),$(call show,$p))
>> ================
>>
>> I'd like to dynamically generate N shell commands under "all" targets when
>> filelist has N words. How can I do it? Without the ultimate solution,
>> everytime I add a word to filelist, I have to manually add one command line
>> under "all".
> There are a number of ways to do this, some more portable/easier to
> understand than others.
>
> The most portable and simplest way is to use shell loops, not make
> loops, like this:
>
>       all:
>               @for f in $(filelist); do echo "[$$f]"; done
>

Assume this method1(M1). What if I want to generate dynamic shell
command with multiple factors, For example, for each word in
filelist($w), I will call a make function to get a parameter($p) and use
$p in shell command. $p is easy to get from makefile, but very hard from
shell script execution. That's the problem.

> Alternatively you can use make commands to generate a list of shell
> commands, similar to your attempt above, BUT you have to add a semicolon
> between them so the shell will interpret them as different commands,
> like this:
>
>       all:
>               @$(foreach f,$(filelist),$(call show,$p);)
>
> This is relatively straightforward but relies on GNU make features
> (foreach, call, etc.)
Assume this method2(M2). I'm afraid there's a problem here: If filelist
contains lots of words and each command-let is quite long, then the
single command(passed to ``sh -c'') can be very long, perhaps >32KB(that
will exceed Windows CreateProcess limit).
> The final method is to use $(eval ...); this is GNU make-specific AND
> complicated to understand.
>
So, I'm looking forward to $(eval ), just call it method3(M3), but
cannot figure it out myself. I'll be very grateful if you can exhibit
this great technique.