Re: How to create "re-entrant" makefiles?

[Paul Smith]

On Wed, 2007-01-03 at 01:48 +0000, David Wuertele wrote:

> MY_VAR := one
> include variabletest.mk
> 
> MY_VAR := two
> include variabletest.mk
> 
> variabletest.mk
> ---------------
> $(MY_VAR):
>       echo $(MY_VAR) > $(MY_VAR)
> 
> all: $(MY_VAR)

As Mike points out, target-specific variables are the new fancy way to
do what you want.  But, there are other ways as well... that I actually
prefer (althoug target-specific variables have more power so sometimes
you need them).

First, note that the situation above was _exactly_ why automatic
variables were created: use $@ in your rule and you're done:

  variabletest.mk
  ---------------
  $(MY_VAR):
          echo $@ > $@

  all: $(MY_VAR)

Other useful automatic variables are $< and $*; see the GNU make manual.
Of course, sometimes the value you want isn't directly derivable from
the target or prerequisites; in that case you can use constructed
variable names:

  variabletest.mk
  ---------------
  $(MY_VAR)_VALUE := foobar

  $(MY_VAR):
          echo $(address@hidden) > $@

  all: $(MY_VAR)

Of course, you can use other automatic variables as necessary.

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