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From: Broeker AT axp02 DOT physik DOT rwth-aachen DOT de (Hans-Bernhard Broeker)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: [Q:] Recursive make ??
Date: 23 Apr 96 10:13:20 GMT
Organization: RWTH -Aachen / Rechnerbetrieb Informatik
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nicolas AT dsys DOT ceng DOT cea DOT fr (Eric NICOLAS) writes:


>So, if I understood well, there is absolutely no way of perform a 
>recursive make in a portable fashion ???

Doch. (Sorry, intranslatable to English)

Here's how: in the README, and at the top of your Makefile, put
this text:

"To build this program, you *will* need GNU make"

and then you can use a rule like this for recursive make-ing:

sub-all:
	$(MAKE) -C libsrc
	$(MAKE) -C utils
	$(MAKE) -C src

And that's it.  This method is about as portable as you can ever get
(works wherever someone managed to build GNU make, i.e.  pretty much
everywhere, and without any changes), but may be slightly uncomfortable
for non-GNU-infected users. 

BTW, Makefiles have *never* ever been really portable, at least not once
you want to use any kind of loop construction.  E.g., every true Unix
programmer would have written the above rule a little bit clearer, like
this (read some GNU or Linux Makefiles, and you'll see this *very*
often):

sub-all: libsrc utils src
	( for f in $^ ; do $(MAKE) -C $$f ; done )

For this to work portably, you'ld have to add a sufficiently correct
implementation of '/bin/sh' to the requirements for building your
program.  BAD THING if you try this in MS-DOG.

The same problem arises once you need advanced textutilities like
sed/awk or at least tr for your makefile.  You *can* have GNU Make do
some of their work, but at some point, you'll sure need The Real Thing
(tm:-), which might not be available on all desirable platforms.  There
could also be bugs in their implementation on some of the weirder OS's
out there, of which you won't ever know until someone gets hit by them
using your 'innocent' little makefile. 

Hans-Bernhard Broeker (Aachen, Germany)