CODEWITHSUNDEEP
makefilegnu
xian
xian

Reputation: 323

make, variables depend on target

Makefile

abc:
TEST=$@ /* TEST=abc */

def:
TEST=$@ /* TEST=def */

xxx:
        @echo $(TEST)

If I run make abc xxx, I expect output abc.

If I run make def xxx, I expect output def.

But it doesn't work like that. It seems like make won't let me define a variable in target. My question is how could I define a variable and its value which depend on which target is built?

Upvotes: 2

Views: 3669

Answers (1)

laindir
laindir

Reputation: 1710

Using GNU Make, you can duplicate the intended result of your Makefile as follows:

echo.%:
    @echo $*

or simply:

%:
    @echo $*

These would allow you to specify make echo.abc or make abc, respectively, and see abc as output.

That's all well and good, but it sounds like you would be more interested in target-specific variables. If the variable value is dependent on, but not a substring of, the target name, you can do something like this:

%:
    @echo $(TEST)

abc: TEST=xyzzy

def: TEST=plugh

This allows you to specify make abc and see xyzzy as output.

If you want to go beyond this, so that the behavior of a target changes based on what other targets are specified on the command line, we have two options: either have .PHONY targets that update a file used by your primary target, or do some processing of the MAKECMDGOALS variable:

Option 1:

xxx: xxx.temp
    @cat xxx.temp
    @rm xxx.temp

abc def:
    @echo $@ > xxx.temp

.PHONY: xxx abc def

This relies on the fact that the command line goals are processed in order (If you specify several goals, make processes each of them in turn, in the order you name them. -GNU Make Manual, section 9.2), so you must specify make abc xxx and not make xxx abc.

Option 2:

ifneq (,$(findstring abc,$(MAKECMDGOALS)))
    VAR=abc
else ifneq (,$(findstring def,$(MAKECMDGOALS)))
    VAR=def
endif

xxx:
    @echo $(VAR)

abc def:
    @echo -n > /dev/null

.PHONY: xxx abc def

The @echo -n > /dev/null suppresses the make: Nothing to be done for 'abc'. message. This seems much clumsier to me, and I would recommend Option 1 if you can tolerate the temp file.

Upvotes: 5

Related Questions