RE: simply expanded variable getting overwritten

[Paul Smith]

On Mon, 2007-08-20 at 22:12 -0700, micron_make wrote:

>        $(loc_mod)_CLCMD := Module/$(loc_mod)/*.bak
>         
>         $(loc_mod)_clean:
>               @echo $($(@:_clean=)_CLCMD)
> This worked for me. It was difficult to find any specific documentation  for
> this kind (($(@: )of usage of automatic variables in the GNU Make pdf. Could
> you please point me to some documentation stressing on usage with some
> examples.

Look at the section on "Substitution References", in "Advanced Features
for Reference to Variables", in the "How to Use Variables" chapter.
This is just shorthand for:

        $(loc_mod)_clean:
                @echo $($(@:%_clean=%)_CLCMD)

which itself is just syntactic sugar for:

        $(loc_mod)_clean:
                @echo $($(patsubst %_clean,%,$@)_CLCMD)

> I couldn't get  eval method working
> > To get it expanded earlier, you need an eval:
> > 
> > define clean_rule
> > $(loc_mod)_clean:
> >         @echo $$($(loc_mod)_CLCMD)
> > endef
> > 
> > $(eval $(call clean_rule))

It's useless to use $(call ...) here, because you're not passing any
arguments.  There's no difference between $(call clean_rule) and just
using $(clean_rule) directly.

Call is only useful for parametrized functions.

> I get "prerequisites cannot be defined in command scripts. Stop"
> 
> The way I am using eval is
> define clean_rule
>  $(loc_mod)_clean:
>          @echo $$($(loc_mod)_CLCMD)
>  endef
>  
> $(loc_mod)_clean:
>     $(eval $(call clean_rule))

> Am I doing something wrong here? Just curious to know since I want to
> explore the eval function in detail.

Yes, you're doing something wrong: that's nothing like what was
recommended to you (as quoted above).

You can't put the eval INSIDE the command script, because you can't
create new rules inside a command script.  What you're writing is
basically this (which is completely illegal in make):

        $(loc_mod)_clean:
                $(loc_mod)_clean:
                        @echo $(foo_CLCMD)

In other words, a rule where the target is only evaluated when the
target is run; this doesn't even make sense.

-- 
-------------------------------------------------------------------------------
 Paul D. Smith <address@hidden>          Find some GNU make tips at:
 http://www.gnu.org                      http://make.paulandlesley.org
 "Please remain calm...I may be mad, but I am a professional." --Mad Scientist