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makefile path regex shell

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

发布于 2010-07-27 07:25:36

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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Didier Trosset 2010-07-27 17:29:15

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.

Norman Gray 2010-07-27 13:09:43

This meta-answer is the best one -- avoid the problem! Note also that --directory isn't portable: cd $(rootdir)/src/libs/libfoo; $(MAKE) ... would be more reliable.

Norman Gray 2010-07-29 17:51:06

I don't think I'd go as far as wrong, but not all make commands support it (and it's not in posix, for example), so if this makefile is for distribution, then it might create problems. In any case, I tend to think that cd foo; $(MAKE)... expresses the intention more clearly.

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