Re: Can make restart b/c of generated include while a target is running?

[Victor Sergienko]

Thank you!
Shame on me. For some reason, I never figured that r.e. variables are
expanded each time, but believed they are just lazily evaluated.


On Wed, 20 May 2020 at 21:57, Paul Smith <address@hidden> wrote:

> On Wed, 2020-05-20 at 17:45 -0700, Victor Sergienko wrote:
> > DIRNAME = dir-$(shell date +%Y-%m-%dT%H-%M-%S)
> > first_target:
> >     mkdir -p $(DIRNAME)
> >     ( do something; echo "done" > $(DIRNAME)/.done ) | tee
> > $(DIRNAME)/build.log
> >
> > Now I have a log where $(DIRNAME) in the "mkdir -p" line is different
> > from $(DIRNAME) used in the following line.
>
> Of course that's easily possible.  The rule expands to this:
>
>   first_target:
>           mkdir -p dir-$(shell date +%Y-%m-%dT%H-%M-%S)
>           ( do something; echo "done" > \
>                 dir-$(shell date +%Y-%m-%dT%H-%M-%S)/.done ) | \
>             tee dir-$(shell date +%Y-%m-%dT%H-%M-%S)/build.log
>
> Since you are invoking the date function three times, it's not strange
> at all that they would not all have identical output, if the clock
> changed in between two of them.
>
> You should use simple variable assignment:
>
>   DIRNAME := dir-$(shell date +%Y-%m-%dT%H-%M-%S)
>
> so that the contents of the variable are expanded exactly once, when
> the variable is assigned, and henceforth will have the same value
> always.
>
> See https://www.gnu.org/software/make/manual/html_node/Flavors.html
>
>