exporting header files before compiling submakes

[Alexander Farber]

Hi,

this probably a frequent situation: I have a couple of header files,
which should be exported before I go through the sub-makefiles.
I wonder how to perform the creation of the export directories best.

Here is my testcase with 2 header files to be exported:

    bolinux72:exp-test {570} mkdir src
    bolinux72:exp-test {571} touch src/pnmsg.h src/pnmsg.inl
    bolinux72:exp-test {569} cat Makefile 
    SUBMAKES =
    EXPFILES = include/pnmsg.h \
               include/internal/pnmsg.inl
    EXPDIRS  = $(dir $(EXPFILES))

    all: export

    clean: rm_files rm_dirs

    all clean: $(SUBMAKES)
            for sub in $(SUBMAKES); do \
                    $(MAKE) -f $$sub $@; \
            done

    export: $(EXPDIRS) $(EXPFILES)

    $(EXPDIRS):
            mkdir -p $@

    rm_files:
            rm -f $(EXPFILES)

    rm_dirs:
            -rmdir $(EXPDIRS)

    .PHONY: all export clean export rm_files rm_dirs

    include/pnmsg.h: src/pnmsg.h
            cp -f "$<" "$@"

    include/internal/pnmsg.inl: src/pnmsg.inl
            cp -f "$<" "$@"

It seems to run ok:

    bolinux72:exp-test {572} gmake 
    mkdir -p include
    mkdir -p include/internal
    cp -f "src/pnmsg.h" "include/pnmsg.h"
    cp -f "src/pnmsg.inl" "include/internal/pnmsg.inl"
    for sub in ; do \
            gmake -f $sub all; \
    done

And even if I create a file in an export dir, 
the copying doesn't start again:

    bolinux72:exp-test {573} ls -ld include/
    drwxr-xr-x    3 afarber  nmpbo        4096 Aug 27 12:35 include/
    bolinux72:exp-test {574} touch include/xxx
    bolinux72:exp-test {575} ls -ld include/
    drwxr-xr-x    3 afarber  nmpbo        4096 Aug 27 12:38 include/
    bolinux72:exp-test {576} gmake 
    for sub in ; do \
            gmake -f $sub all; \
    done

I wonder it it's ok this way or if I should list the $(EXPDIRS)
as an "order-only" prerequisite (but for what reason?).

And also, if I would list the $(EXPDIRS) as "order-only", how
do I still make sure that $(EXPDIRS) are made before $(EXPFILES)? 

    export: $(EXPFILES) | $(EXPDIRS)

- has a wrong order, doesn't it? 

And one more question is if there is a way to solve cleaning
up the created dirs. Sort them by their length and call "rmdir"?

Thanks for any hints and suggestions
Alex