Re: Variable export, recursion, and environment

[Sankaranarayanan K V]

On Mon, Oct 16, 2000 at 04:40:20PM -0400, Paul D. Smith wrote:
> %% Sankaranarayanan K V <address@hidden> writes:
> 
>   skv> Case 1:
> 
>   skv>   1. The environment does NOT have a variable VAR set.
>   skv>   2. The top level Makefile does NOT export VAR.
>   skv>   3. The top level Makefile sets VAR to x.
> 
>   skv>   Result: The sub-make invocation does NOT inherit a value for VAR.
> 
> Yes.
> 
>   skv> Case 2:
> 
>   skv>   Same as Case (1) except that the environment defines VAR=y.
> 
>   skv>   Result: The sub-make invocation inherits a value for VAR.
>   skv>   But the value is x (set by the parent Makefile) and not y.
> 
> Yes.
> 
>   skv> Somehow, this seems a bit strange to me.
>   skv> What is the rationale behind such a behaviour?
> 
> You should check the GNU make manual section "Variables from the
> Environment" to see how make handles this.
> 
>   skv> I would expect make to either pass the environment value 
>   skv> _or_ not to pass any value at all to the sub-make.
> 
> You're not thinking of this correctly.  Make uses variables the same way
> the shell does, basically.  Variables that are obtained from the parent
> process are considered "exported" and passed to any sub-processes, but
> any value changes that happen in the current process are also
> exported.

This behaviour is not the same for different shells:
 
  - bash behaves just as you have said --
    it passes on changes to the child even if the variable is not
    exported specifically in the parent.

  - sh (the Bourne shell) does NOT pass the changes to the child if the
    variable is not exported.

Now, isn't that strange? What does POSIX say?

BTW, I am on a Solaris 2.5.1. I am using bash 1.14.3(1).

> 
> You would find it darn strange if you changed the value of a variable in
> the shell, but any subshells got the _previous_ value and not the new
> one... well, make handles these the same way.


Regards
Sankar

-- 
Sankaranarayanan K. V.          | address@hidden
Motorola India Electronics Ltd  | http://www.mot.com/miel