Makefile set if variable is empty

Question

I want to set a variable if it is empty. I tried in this way:

....
TEST := $(something)
...
TEST ?= $(something else)

The first $(somethi

Answer 1

Any elegant solution to set the variable if empty?

GNU make is hardly known for elegant solutions. Unless you find trapdoors and minefields to be elegant. I know only of the two ways to accomplish what you want:

1. The standard ifeq/endif solution:

   ifeq ($(TEST),)
   TEST := $(something else)
   endif
   

2. Use the $(if) function:

   TEST := $(if $(TEST),$(TEST),$(something else))
   

   One can try to package that construct into a function too, but that is inadvisable. The function would have the hidden pitfall of occasionally breaking the $(something else) if it contains the , (for which there are only wayward workarounds). (The built-in functions like $(if) are immune to the , bug.)

Elegance test is up to you.