[Boost-build] exit code from SHELL

Subject: [Boost-build] exit code from SHELL
From: Ray Lambert (codemonkey_at_[hidden])
Date: 2010-07-23 20:56:04

Hi,

I'm having a minor problem with getting exit codes from SHELL and I'm 
hoping someone might know what's happening.

I'm invoking a Python script via the SHELL rule to perform some 
pre-build activities.  When I run the script manually I get a return 
code of either 0 or 1 (as intended):

     $ ./prebuild.py; echo $?
     1

When I run it using SHELL, if the script tries to return 0 SHELL also 
returns 0 but when the script tries to return 1 SHELL returns 256 instead:

     local result = [ SHELL "./prebuild.py" : exit-code ] ;
     echo $(result[2]) ;

     (outputs "256").

I wanted to test for " $(result[2]) == 1 " but that obviously fails if I 
get 256 back.  For now, my work around is " if $(result[2]) != 0 ".

I looked at the bjam source code and found that the exit code is just 
the result of pclose().  However, I can't find any return value of 256 
defined on my system (Fedora 12).

I looked at the pclose() man page and examined all related pages 
(pclose() apparently calls wait4() which apparently calls waitpid()) and 
I also scoured the system header files and I can't find any 256 value 
defined.

Note that when SHELL returns 256 the script does run successfully.

Anyone have any idea where this 256 is coming from or what it means?

Thanks,

~ray

-- 
In a world without walls and fences, who needs windows and gates?