Variables

Setting variables

Use =, :=, or ::= and a value.
White space is ignored.

Simple

Example:

FOO =
CXX = g++
objects = main.o foo.o bar.o utils.o
SHELL = /bin/bash
JS_DIR = assets/js

Evaluate

Using != ....
If the result of the execution could produce a $, and you don’t intend what follows that to be interpreted as a make variable or function reference, then you must replace every $ with $$ as part of the execution.
```
  hash != printf '\043'
  file_list != find . -name '*.c'
```

Using := $(shell ...)

  hash := $(shell printf '\043')
  var := $(shell find . -name "*.c")

Default value

If you’d like a variable to be set to a value only if it’s not already set, then you can use the shorthand operator ?= instead of =. These two settings of the variable ‘FOO’ are identical:

FOO ?= bar

ifeq ($(origin FOO), undefined)
FOO = bar
endif

Export variables

This makes the variable available in subprocesses, after executing source command. But also make sure not to overwrite a value set already, such as with Netlify secrets.

export GITHUB_TOKEN := $(if $(GITHUB_TOKEN), $(GITHUB_TOKEN), '')

foo:
    # ...

Using the Bash export style.

foo:
	@export ENVIRONTMENT=prod
    # ...

Defaults files

Setup default values in another file.

Set defaults.

defaults.mk

  FIZZ=${FIZZ}
  BUZZ=${BUZZ}

  export

Import the defaults.

Makefile

  include defaults.mk

  foo:
      # ...