pwd vs $PWD, bash, cygwin vs Linux

[John Williams <jwilliams at itee dot uq dot edu dot au>]

Hello,

I am resurrecting a topic that has been discussed before, but there 
doesn't seem to be a clear resolution (at least not clear to me!).  It 
relates to the behaviour of the PWD variable in the case of multiply 
nested Makefiles.  it was touched upon e.g. here:

http://www.mail-archive.com/cygwin@sources.redhat.com/msg16375.html

I'm doing a side by side comparison between Cygwin 1.5.16-1 and Linux 
RedHat 8.0, both using bash shell 2.05b.0(1)-release, and make version 
3.79.1

Here's my test setup (sorry for dodgy ASCII art)

Maketest
 |
 + topdir
     |
     + Makefile
     |
     + subdir
          |
          + Makefile

topdir/Makefile looks like this:

#####
#topdir/Makefile
TOPDIR := $(shell echo $$PWD)

all:
        @echo In topdir, TOPDIR=$(TOPDIR)
        @echo In topdir, PWD=$$PWD
        make -C subdir all

.EXPORT_ALL_VARIABLES:
######

and topdir/subdir/Makefile looks like this:

#####
#topdir/subdir/Makefile
all:
        @echo in subdir, TOPDIR=$(TOPDIR)
        @echo in subdir, PWD=$$PWD
#####

Now, from the top-top level (Maketest), I run 'make -C topdir'.  Under 
my Cygwin setup, I get this:

[jwilliams@JWILLIAMS Maketest]$ make -C topdir
make: Entering directory `/cygdrive/z/Maketest/topdir'
In topdir, TOPDIR=/cygdrive/z/Maketest
In topdir, PWD=/cygdrive/z/Maketest
make -C subdir all
make[1]: Entering directory `/cygdrive/z/Maketest/topdir/subdir'
in subdir, TOPDIR=/cygdrive/z/Maketest
in subdir, PWD=/cygdrive/z/Maketest
make[1]: Leaving directory `/cygdrive/z/Maketest/topdir/subdir'
make: Leaving directory `/cygdrive/z/Maketest/topdir'
[jwilliams@JWILLIAMS Maketest]$

while under the identical setup on Linux, I get this:

[jwilliam@g512-9029 Maketest]$ make -C topdir
make: Entering directory `/mnt/home2/jwilliam/Maketest/topdir'
In topdir, TOPDIR=/mnt/home2/jwilliam/Maketest/topdir
In topdir, PWD=/mnt/home2/jwilliam/Maketest/topdir
make -C subdir all
make[1]: Entering directory `/mnt/home2/jwilliam/Maketest/topdir/subdir'
in subdir, TOPDIR=/mnt/home2/jwilliam/Maketest/topdir
in subdir, PWD=/mnt/home2/jwilliam/Maketest/topdir/subdir
make[1]: Leaving directory `/mnt/home2/jwilliam/Maketest/topdir/subdir'
make: Leaving directory `/mnt/home2/jwilliam/Maketest/topdir'
[jwilliam@g512-9029 Maketest]$

Essentially under Cygwin the PWD variable seems to be "frozen" at its 
value upon first launching Make from the commandline, while under Linux 
it is being updated for each child process spawned by `make -C XXX`

I know that Cygwin != Linux, however is it a reasonable expectation that 
under the same shells, the same behaviour should apply?

The real context for all of this is building the net-tools package, 
which uses these sort of constructs to manage its recursive Makefile 
structure.  I'm sure there are plenty of other GNU-esque packages out 
there doing similarly.

Any insights or workarounds would be greatly appreciated.

Thanks,

John

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