How to set child process' environment variable in Makefile

Question

I would like to change this Makefile:

SHELL := /bin/bash
PATH  := node_modules/.bin:$(PATH)

boot:
    @supervisor         \
      --harmony         \
      --watch etc,lib       \
      --extensions js,json      \
      --no-restart-on error     \
        lib

test:
    NODE_ENV=test mocha         \
      --harmony             \
      --reporter spec       \
        test

clean:
    @rm -rf node_modules

.PHONY: test clean

to:

SHELL := /bin/bash
PATH  := node_modules/.bin:$(PATH)

boot:
    @supervisor         \
      --harmony         \
      --watch etc,lib       \
      --extensions js,json      \
      --no-restart-on error     \
        lib

test: NODE_ENV=test
test:
    mocha                   \
      --harmony             \
      --reporter spec       \
        test

clean:
    @rm -rf node_modules

.PHONY: test clean

Unfortunately the second one does not work (the node process still runs with the default NODE_ENV.

What did I miss?

Solution 1

Make variables are not exported into the environment of processes make invokes... by default. However you can use make's export to force them to do so. Change:

test: NODE_ENV = test

to this:

test: export NODE_ENV = test

(assuming you have a sufficiently modern version of GNU make >= 3.77 ).

Solution 2

As MadScientist pointed out, you can export individual variables with:

export MY_VAR = foo  # Available for all targets

Or export variables for a specific target (target-specific variables):

my-target: export MY_VAR_1 = foo
my-target: export MY_VAR_2 = bar
my-target: export MY_VAR_3 = baz

my-target: dependency_1 dependency_2
  echo do something

---

You can also specify the .EXPORT_ALL_VARIABLES target to—you guessed it!—EXPORT ALL THE THINGS!!!:

.EXPORT_ALL_VARIABLES:

MY_VAR_1 = foo
MY_VAR_2 = bar
MY_VAR_3 = baz

test:
  @echo $$MY_VAR_1 $$MY_VAR_2 $$MY_VAR_3

see .EXPORT_ALL_VARIABLES

Solution 3

I only needed the environment variables locally to invoke my test command, here's an example setting multiple environment vars in a bash shell, and escaping the dollar sign in make.

SHELL := /bin/bash

.PHONY: test tests
test tests:
    PATH=./node_modules/.bin/:$$PATH \
    JSCOVERAGE=1 \
    nodeunit tests/

Solution 4

I would re-write the original target test, taking care the needed variable is defined IN THE SAME SUB-PROCESS as the application to launch:

test:
    ( NODE_ENV=test mocha --harmony --reporter spec test )

View more solutions

Comments

[truthadjustr]

Your Unfortunately comment stems from a misunderstanding between an environment variable versus a Makefile variable. The best way to prove that an environment variable has been set, is to query this environment variable inside another program that make wil call. Only doing echo $(BLAH) is merely evaluating Makefile's key/value mechanism inside the Makefile. In python, you can print(os.getenv("MURDOC")) to truly query the environment variable.

[Gauthier]

I have GNU make 3.81, and all: <\n\t>export PROJ_ROOT=$(CURDIR)<\n\t>echo $(PROJ_ROOT)<\n> outputs the correct expansion for the first row, but only echo for the second one. PROJ_ROOT is not set after running make. Spaces around = give "bad variable name" for export. Having the first row as prerequisite as in your example gives "commands commence before first target"

[MadScientist]

@Gauthier yes of course. That's not what I wrote. You added a <\n\t> after the all:, which is not in my example. My example is intended to be used as written: it's defining a target-specific variable, NOT adding a command to the recipe. Also you cannot use a recipe and a target-specific variable on a target at the same time: you have to write the target twice. See the second example in the question, and ask a new question if this doesn't help explain it: there's not enough space or formatting in comments.

[mickmackusa]

Please edit your answer to include some explanation. Code-only answers do very little to educate future SO readers. Your answer is in the moderation queue for being low-quality.

[Keith Hanlan]

ThorSummoner, this solution is not as flexible as the approach above. For example, one might wish to have one single rule for invoking a command and then several other rules which modify that behaviour by setting environment variables. Consider: test: cmd perf: export PERF="yes" perf: test If 'cmd' is complicated (and it usually is), then this approach is a lot easier to maintain. Your approach to setting the environment variable in the cmd rule makes this more difficult.

[AnthonyC]

Oddly enough I did test it earlier that showed it worked.. (not sure why now..) I can go back and delete the comment I guess..

[holms]

What about multiple variables?

[MadScientist]

Each variable has to be set on its own separate line in the makefile.

[holms]

That's fine but your added it to the head of target. Just listing them in context of target won't work? Because it doesn't work for me

[MadScientist]

Sorry but I don't understand what you mean. Probably you should file a new question rather than asking in the comments here.

[jjmerelo]

How modern is modern?

[MadScientist]

Target-specific variables were added in GNU make 3.77. They are exportable as of GNU make 3.81. See git.savannah.gnu.org/cgit/make.git/tree/NEWS

[Sergei]

@AnthonyC It works because there are two MY_VARs: one is makefile variable accessed as ${MY_VAR} and another one is bash exported variable, accessed as $$MY_VAR

[Eric Chen]

Useful. But cannot find a way to export only a set of variables.

[smac89]

Note if the variable already exists in your makefile and you just want to export it to another command, you can use the syntax export var ?= without assigning a new value

[Ken]

.EXPORT_ALL_VARIABLES is right answer