Sourcing a bashfile before running a command

Question

Suppose I have the following file demo.env :

export VALUE="abcd"

How can I make this works from a Mafile rule?

bash -c "source demo.env; echo $${VALUE}"

Answer 1

Apparently one way to do so is:

bash -c "source demo.env; echo \${VALUE}"

And in a Makefile rule:

echo:
    bash -c "source demo.env; echo \$${VALUE}"