Re: Variable assignment that depends on a generated target

[Paul Smith]

On Wed, 2007-04-25 at 21:25 +0300, Eli Zaretskii wrote:
> > From: Paul Smith <address@hidden>
> > Cc: David Wuertele <address@hidden>, address@hidden
> > Date: Wed, 25 Apr 2007 09:12:34 -0400
> > 
> > >  VERSION := $(shell make /path/to/some/file && grep VERSION 
> > > /path/to/some/file)
> > 
> > This will work, but I prefer the include version I mentioned earlier.
> 
> Can you explain why you prefer that method?

Well, firstly because as written your method will recurse infinitely :).
You'd need something like:

        VERSION := $(shell $(MAKE) VERSION= /path/to/some/file && grep VERSION 
/path/to/some/file)

to avoid that.

Secondly, in your method the invocation of the sub-make will happen
every time this makefile is parsed, while with the include method the
version.mk is only rebuilt (and make re-invoked) if /path/to/some/file
has actually changed.  Also you could avoid re-invoking make by having
the script to build version.mk smart enough to not change the file if
the version string didn't change (even if /path/to/some/file did).

But beyond that, I just think it's cleaner and nicer to use make's
builtin capabilities in this area, rather than force it with
$(shell ...)

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