In a makefile, how to get the relative path from one absolute path to another?

Question

An example to illustrate my question:

Top level makefile

rootdir = $(realpath .)
export includedir = $(rootdir)/include
default:
    @$(MAKE) --directory         


        

Answer 1

The shell has this feature using realpath(1) and the --relative-to flag so you could just invoke the shell.

Here is an example:

RELATIVE_FILE1_FILE2:=$(shell realpath --relative-to $(FILE1) $(FILE2))

You can even process a whole list of files with one invocation of realpath(1) since it knows how to process many file names.

Here is an example:

RELATIVES:=$(shell realpath --relative-to $(RELATIVE) $(FILES))