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

Perl is portable! Here's a solution using the abs2rel function from the core Perl module File::Spec (resp. File::Spec::Functions):

current_dir= /home/username/projects/app/trunk/src/libs/libfoo/ 
destination= /home/username/projects/app/build/libfoo/ 
relative=    $(shell perl -MFile::Spec::Functions=abs2rel -E 'say abs2rel(shift, shift)' $(destination) $(current_dir))

makefile_target:
    @echo "Use now $(relative)"