Re: $@ documentation

[Henning Makholm]

Scripsit "Albert D. Cahalan" <address@hidden>

> -------- this didn't work --------
> $(BINFILES) : $(notdir $@)
>         $(install) --mode a=rx --strip $(notdir $@) $@
> ---------------------------------

> It seems make doesn't set $@ where I want it set.

No. That's one of the things you just have to know: automatic
variables work *only* in commands, not in dependency list or
elsewhere. This doesn't seem to be said explicitly in the manual, but
I'm sure that Paul would welcome an actual patch for it, if you care
enough to learn Texinfo and figure out where to add what language.

The technical reason for this is that variables in the entire
dependencies line are only onfolded once, namely to read the
dependency information info make's database. On the other hand,
variables (and function applications) in *command* lines are only
expanded hen the command is actually about to be launched, at which
point the automatic variables have been set.

> ------ also didn't work -------
> $(BINFILES) : % : $(notdir %)
>         $(install) --mode a=rx --strip $(notdir $@) $@
> ------------------------------

> That won't do it either, for some really strange reason.

The reason is the same: When the dependency line is read in, the
following happens *in order*:

1. Variables and function calls are expanded. The function call
   "$(notdir %)" expands to "%" because the notdir function does not
   assign any special mening to the % character, and the non-directory
   part of a file called "%" is indeed "%".

2. Then the line is parsed as a static pattern rule, and the targets
   and patterns are stored in the database. Now "%" does have a
   special significanse, but "$" has lost _its_ special significanse.

3. Then one of the $(BINFILES) are to be remade, its name is matched
   against the "%" target pattern and root thus found is inserted in
   the dependency pattern "%".

> It'd be mighty nice if somebody could fix my code too. :-)

If your $(BINFILES) live in different directories, I dont think
there's any way to get around writing separate rules for each
directory (save for some kind of clever abuse of the new $(eval ...)
function in 3.80 which I have not investigate in detail). If they are
in the same directory, I would try something like

$(BINFILES) : $(exec_prefix)/% : %
        <do stuff>

It would indeed be convenient from time to time to have variables in
the dependency list of a (static) pattern rule be unfolded only after
the target has been selected. However, this would lead to parsing
problems: The colons that seperate different parts of the rule can
*themself* arise from variable expansions - so how would poor make
know when to defer further expansion until the target is known?

It wouldn't do to redefine the rules such that the colons must be
explicitly given in the rule, because someone, somewhere, is sure to
have a Makefile that depend on getting the rule punctuation from
variables - and they would have a right to expect it to work, because
all other make implementation I know works that way.


[Disclaimer: I am not a GNU make developer, much less the maintainer.
I just try to relieve the guys who do the real work by answering
questions that I feel competent to answer.]

-- 
Henning Makholm         "Khanivore is climbing out of its life-support pod."