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

Just in case anyone stumbled upon putting the condition in the rule itself. below how I did it, thought it might help others.

In Makefile, suppose we have the following rule with check target and we need to check whether var was passed.

check:
    @[ "${var}" ] && echo "all good" || ( echo "var is not set"; exit 1 )

To test this out, run the following commands

$ make check 
  var is not set
  make: *** [check] Error 1  

$ make check var=test
  all good 

So, Now we can pass the variable value or a default value in case it was not passed to a bash script that will be responsible to do the logic. something like the following:

@[ "${var}" ] && ./b.sh ${var} || ./b.sh 'ss'

Here's below what b.sh might look like, though you can add more logic to it.

#!/bin/sh
echo $1