Makefile won't assign variable values in `ifeq` statement within function definition

Question

I'm trying to assign a value to a variable in make when a condition is met, inside a function:

Without $() around the ifeq statements:

VARIABLE=true

define test_ifeq
    FOO := foo
    ifeq (${VARIABLE}, true)
        FOO := true
    else
        FOO := false
    endif

    echo "value: ${FOO}"
endef

all:
    $(call test_ifeq)

Result:

FOO := foo
make: FOO: No such file or directory
make: *** [Makefile:15: all] Error 127

With $() around the ifeq and variable assignment statements:

VARIABLE=true

define test_ifeq
    $(FOO := foo)
    $(ifeq (${VARIABLE}, true)
        FOO := true
    else
        FOO := false
    endif)

    echo "value: ${FOO}"
endef

all:
    $(call test_ifeq)

Result:

echo "value: "
value:

Why does this not work?

You appear to be mixing Make and shell syntax. Do you want *Make* to do all of this, or do you want to pass it to *the shell, inside a recipe?* — Beta, Mar 27 '20 at 17:39
I don’t really care. I’m just trying to make it work and there doesn’t seem to be a way to compare strings with pure make, or the shitty documentation doesn’t have a decent example of branching and assigning different values to variables. — Neil, Mar 27 '20 at 17:40

score 1 · Answer 1 · answered Mar 27 '20 at 17:45

1

The ifeq and the likes are evaluated at the moment when make reads the makefile, that means there is no actual ifeq present in the assigned value of your test_ifeq variable.

To achieve what you need you have to use $(if ...) and $(filter ...) built in functions along with $(eval ...).

It should look something like this:

VARIABLE=true

define test_ifeq
    $(eval FOO := $(if $(filter $(VARIABLE),true), true, false))

    echo "value: $(FOO)"
endef

all:
    $(call test_ifeq)

NOTE: I haven't tested it, wrote it straight out of head...

answered Mar 27 '20 at 17:45

igagis

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Thanks! This worked for me. Has me re-thinking the use of makefiles for my build process over the long haul and to move to something more like magefiles. Makefile is like working with an evil trickster once you go beyond a hello world complexity. – Kuberchaun Jul 27 '20 at 16:25
I have my own non-recursive build system written in `GNU make`, check its complexity :) https://github.com/igagis/prorab/blob/master/src/prorab.mk There is a nice tutorial in case you would like to use it https://github.com/igagis/prorab/blob/master/wiki/TutorialBuildApplication.md – igagis Jul 28 '20 at 15:05

Beta · Answer 2 · 2020-03-27T17:53:39.857

To do it with Make:

VARIABLE=true

define test_ifeq
  FOO := foo
  ifeq (${VARIABLE}, true)
    FOO := true
  else
    FOO := false
  endif

$$(info "value: $${FOO}")

endef

$(eval $(call test_ifeq))

To do it on the command line (assuming bash):

VARIABLE=true; FOO=foo; if [ $VARIABLE = true ]; then FOO=true; else FOO=false; fi; echo $FOO

To do it within a rule in a makefile:

all:
    VARIABLE=true; \                                                                                  
  FOO=foo; \
  if [ $$VARIABLE = true ]; then \
  FOO=true; else \
  FOO=false; \
  fi; \
  echo $$FOO

To do it within a rule, using a function:

VARIABLE=true

define test_ifeq2
  FOO=foo; \
  if [ $(VARIABLE) = true ]; then \
  FOO=true; else \
  FOO=false; \
  fi; \
  echo $$FOO
endef

all:
    $(call test_ifeq2)

Makefile won't assign variable values in `ifeq` statement within function definition

2 Answers2