Re: Rule producing several targets at once?

[David Boyce]

This is actually a very old and well known issue. It's not a deliberate
feature, more a missing capability which no one has ever filled in. There's
no way to tell make that one recipe makes multiple *explicit* targets;
however the same flaw does not affect pattern rules. This is discussed in
the manual in various places such as
https://www.gnu.org/software/make/manual/make.html#Pattern-Intro :

"Pattern rules may have more than one target. Unlike normal rules, this
does not act as many different rules with the same prerequisites and
recipe. If a pattern rule has multiple targets, make knows that the rule’s
recipe is responsible for making all of the targets. The recipe is executed
only once to make all the targets...."

Multiple workarounds have been published; google around and you should find
them. However the most robust solution, where possible, is to use pattern
rules instead. Sometimes it's possible to pretend an explicit rule is
implicit by appending a %. For instance this use of explicit rules does the
wrong thing:

% cat Makefile
.PHONY: all
all: axx bxx

axx bxx: cxx dxx
touch $@
touch bxx

% make -j
touch axx
touch bxx
touch bxx
touch bxx

But when converted to a fake pattern rule it works correctly:

% cat Makefile
.PHONY: all
all: axx bxx

ax% bx%: cxx dxx
touch $@
touch bxx

% make -j
touch axx
touch bxx

David

On Wed, Feb 28, 2018 at 6:52 AM, Alberto Luaces <address@hidden> wrote:

> Sébastien Hinderer writes:
>
> > Dear Alberto,
> >
> > Many thanks for your response.
> >
> > The comand was jsut an example, the real world one si different. Sorry
> > for the confusion it may have introduced.
> >
>
> Hi Sébastien.  No problem!
>
> Just post an example of what are you trying to do exactly, and we will
> manage to help you.
>
> Regards,
>
> --
> Alberto
>
>
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