We’re going to load an environment from a dotenv file and using the source command in the Makefile. Then the values in the dotenv file can be used as shell variables directly (like with echo or as arguments for a command) or accessed within a command on the enviroment variables.

Source

Given dotenv file:

  • .env 
      MY_VAR=abc

test:
	source .env && echo "$$MY_VAR"

Notes:

  • Variables are not persisted across lines in a target. So make sure to join the lines with &&.
  • The variable is known to shell, but not to Make. You cannot access as Make variable like echo $(MY_VAR) here.

Export

If you want to use the variable in a subshell (such as to access an environment variable), then you need add use of export on the Make variable. You don’t need to set a value.

export MY_VAR

test:
	source .env && echo $$MY_VAR
	source .env && bash -c 'echo $$MY_VAR'  # Bash subshell.
	source .env && ./my_script              # Command that accesses MY_VAR.

Defaults

You can set a default like this with ?= or even plain = syntax. This default gets used if MY_VAR is not in .env at all. If it is included there as an empty value like MY_VAR='' then it will appear here as an empty variable.

export MY_VAR = my fallback