Set Makefile variable inside target

Question

I have a target inside a makefile:

all: $(TARGETS)

I want a variant that differs from all only by the fact that it sets an environment variable. Something like:

all-abc: $(TARGETS)
    ABC=123

but that doesn't work because the dependencies are processed before the variable is set. I've thought about having another dependency before the real ones that just sets the environment variable but I don't think the environment persists across targets. That is to say that

abc:
    ABC=123
all-abc: abc $(TARGETS)

doesn't work. What I ultimately want to be able to do is

$ make all-abc

instead of

$ ABC=123 make

Is it possible to set an environment variable like this ?

(GNU Make 3.82)

prefer not to have to worry about the values to set the variables to (i.e. in the example I don't want to have to remember 123) — starfry
– starfry, Commented Mar 5, 2013 at 18:09

RSFalcon7 · Accepted Answer · 2013-03-05 17:49:30Z

48

try this:

all:
    @#usual rule, if you call `make all-abc`, this will print "123"
    @echo $(ABC)

all-abc: ABC=123
all-abc: all
    @#what you put here it's going to be executed after the rule `all`

answered Mar 5, 2013 at 17:49

RSFalcon7

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4 Comments

starfry Over a year ago

yes that's good. I didn't think of adding two targets with the same name. Good one!

MadScientist Over a year ago

starfry: I don't think you're understanding what this does exactly. You should read the section of the GNU make manual on target-specific variables.

James Moore Over a year ago

To add to what @MadScientist said: there are not two targets with the same name here. "all-abc: ABC=123" defines a target-specific variable; it is not a target. gnu.org/software/make/manual/html_node/Target_002dspecific.html

Terite Over a year ago

I use xargs within a target command, and I needed to do all-abc: export ABC=123 to make the variable accessible from the command executed by xargs

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