How to use environment variables defined inside a makefile? - makefile

Question

I currently have a Makefile that looks something like this:
some_process:
VAR1=1
VAR2=2
python3 ./main.py --arg1 /home/user1/something/ \
--arg2 $VAR1 \
--arg3 $VAR2
When I run this code I get the error:
main.py: error: argument --arg2: expected one argument
I've tried using brackets around VAR1 and VAR2, but I noticed that if I do that then the Makefile doesn't recognize(?) the arguments. I also tried escaping the $ sign (i.e. $$VAR1) but this also does not work.
What is the proper way to use a Makefile for environment variables? Thanks.
EDIT
Just in case it's unclear from the original question, I'm using the Makefile to replicate what I'd usually do in the command line:
user#thing:$ export VAR1=1
user#thing:$ export VAR2=2
user#thing:$ python3 ./main.py --arg1 /home/user1/something --arg2 $VAR1 --arg3 $VAR2

Answer 1

There are two basic problems with the code shown...
some_process:
VAR1=1
VAR2=2
python3 ./main.py --arg1 /home/user1/something/ \
--arg2 $VAR1 \
--arg3 $VAR2
Firstly, make runs each line from the commands section of a rule in its own shell. So VAR1=1 is run in a shell and then, effectively, lost. Secondly, tokens such as $VAR1 will be expanded by make rather than the shell. In this case -- because there's no parentheses -- $VAR1 will be interpreted by make as $(V)AR1. That is, the value of the variable V followed by the text AR1. You can use $$ to force make to ignore the expansion.
Taking all of the above into account you could try (untested)...
some_process:
VAR1=1; \
VAR2=2; \
python3 ./main.py --arg1 /home/user1/something/ \
--arg2 $$VAR1 \
--arg3 $$VAR2

Answer 2

Firstly, as #G.M. pointed out, make runs each command in a rule in separate sub-shells; so variable assignments in separate lines won't work. Also beware of the variable reference format. $(VAR1) or ${VAR1} if it needs to be expanded by make, $$VAR1 if it needs to be expanded in a sub-shell.
Having said that, you can define VAR1 and VAR2 as make variables and export them to make them available for your some_process rule.
VAR1 := 1
VAR2 := 2
export VAR1 VAR2
some_process:
python3 ./main.py --arg1 /home/user1/something/ \
--arg2 $$VAR1 \
--arg3 $$VAR2
This way, you can override the variable values when you invoke the rule if needed.
$ make some_process VAR2=22
By the way, as you're explicitly giving the variables as command line arguments to your python script, they don't need to be exported; so the following should work just fine.
VAR1 := 1
VAR2 := 2
some_process:
python3 ./main.py --arg1 /home/user1/something/ \
--arg2 $(VAR1) \
--arg3 $(VAR2)