Today I learned how to call a makefile from within another makefile.

Nested makefiles

I like to use make and makefiles on my projects and today I needed to call a makefile from within another makefile... I was pretty sure there was a “proper” way to do it, so I went ahead and looked it up.

A quick search revealed I should use $(MAKE) instead of typing make and that I could also use the option -C to change the directory from where I'm reading my makefile.

As a simple example, consider the following directory structure:

- root
  |- Makefile
  |- subfolder
     |- Makefile

Paste the following in root/Makefile:

root:
    @echo "Root directory makefile."

nest:
    @echo "About to call nested makefile."
    $(MAKE) -C subfolder $@

Running make root from within the folder root should print “Root directory makefile.”.

Now, paste the following in root/subfolder/Makefile:

nest:
    @echo "From nested Makefile"

up:
    @echo "About to call root makefile"
    $(MAKE) -C .. root

If you're in root, running make nest should print

About to call nested makefile.
/path/to/make -C subfolder nest
From nested Makefile

If you're in subfolder, running make up should print

About to call root makefile
path/to/make -C .. root
Root directory makefile.

Also note that in the top rule nest I used $@ to refer to a rule with the same name in subfolder/Makefile, whereas in the rule up I used the explicit target root.

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References

• GNU make manual, Recursive Use of make, https://www.gnu.org/software/make/manual/make.html#Recursion [last accessed 25-09-2024]
• GNU make manual, Options Summary, https://www.gnu.org/software/make/manual/make.html#Options-Summary [last accessed 25-09-2024]