Re: substitution vs expansion in Makefile.am

[Ralf Wildenhues]

Hi John,

* John Calcote wrote on Tue, Mar 04, 2008 at 10:38:50PM CET:
> Newbie question here: Is it better to do this in a Makefile.am:
> 
>    install-exec-hook:
>            $(mkdir_p) $(DESTDIR)@syslogdir@
> 
> or this:
> 
>    install-exec-hook:
>           $(mkdir_p) $(DESTDIR)$(syslogdir)
> 
> assuming, of course, that I called AC_SUBST(syslogdir) in configure.ac?
> 
> The first will expand to $(prefix)/..., so you'd have the option of
> changing the resulting directory by passing prefix= on the make
> command line. The second will allow you to change the resulting
> directory with either prefix= or syslogdir= on the make command line.
> I guess you'd get a bit more flexibility by using the second option
> because you could change the syslogdir without changing the prefix.
> But, is there a conventional, or more correct approach?

Nice question.  You already deliver the answer, including full rationale
and all: the second form is preferable because it allows more override.

In general, there is one other bit of difference between @foo@ and
$(foo) in that automake may not be able to look into the former.
But for this case that makes little difference.

Cheers,
Ralf