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An example to illustrate my question:
Top level makefile
rootdir = $(realpath .)
export includedir = $(rootdir)/include
default:
@$(MAKE) --directory=$(rootdir)/src/libs/libfoo
Makefile for src/libfoo
currentdir = $(realpath .)
includedir = $(function or magic to make a relative path
from $(currentdir) to $(includedir),
which in this example would be ../../../include)
Another example:
current dir = /home/username/projects/app/trunk/src/libs/libfoo/
destination = /home/username/projects/app/build/libfoo/
relative = ../../../../build/libfoo
How can this be done, while trying to be as portable as possible?
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The absolutePath function works by beginning at the starting folder and moving up one level for each "../" in the relative path. Then it concatenates the changed starting folder with the relative path to produce the equivalent absolute path.
You can use shell function: current_dir = $(shell pwd) . Or shell in combination with notdir , if you need not absolute path: current_dir = $(notdir $(shell pwd)) .
A path is either relative or absolute. An absolute path always contains the root element and the complete directory list required to locate the file. For example, /home/sally/statusReport is an absolute path.
Relative path Relative paths make use of two special symbols, a dot (.) and a double-dot (..), which translate into the current directory and the parent directory. Double dots are used for moving up in the hierarchy. A single dot represents the current directory itself.
Doing what you want does not look easy. It may be possible using a lot of combined $(if in the makefile but not portable (gmake only) and cumbersome.
IMHO, you are trying to solve a problem that you create yourself. Why don't you send the correct value of includedir as a relative path from the Top-level Makefile? It can be done very easily as follows:
rootdir = $(realpath .)
default:
@$(MAKE) --directory=$(rootdir)/src/libs/libfoo includedir=../../../include
Then you can use $(includedir) in the sub-makefiles. It is already defined as relative.
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