R devel - Sep 1999 - getenv() can't differentiate "defined but empty" and "undefined"

getenv(<varname>)  currently returns  ""
if the <varname> is undefined.

However, if <varname> is defined but empty,
getenv(<varname>) still only returns "".

I think this is quite unfortunate  
but consistent with the prototype.

---
I'd propose to change the current behavior.
Something which should be pretty back compatible would 
for the first case (undefined environment variable)
to return "" with an attribute "defined" set to FALSE
i.e.  return(structure("", defined = FALSE))

Does anyone see a problem with this approach ?

Martin Maechler <maechler@stat.math.ethz.ch>
http://stat.ethz.ch/~maechler/
Seminar fuer Statistik, ETH-Zentrum  LEO D10	Leonhardstr. 27
ETH (Federal Inst. Technology)	8092 Zurich	SWITZERLAND
phone: x-41-1-632-3408		fax: ...-1228			<><
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On Wed, 29 Sep 1999, Martin Maechler wrote:
> getenv(<varname>)  currently returns  ""
> if the <varname> is undefined.
> 
> However, if <varname> is defined but empty,
> getenv(<varname>) still only returns "".
> 
> I think this is quite unfortunate  
> but consistent with the prototype.
> 
> ---
> I'd propose to change the current behavior.
> Something which should be pretty back compatible would 
> for the first case (undefined environment variable)
> to return "" with an attribute "defined" set to FALSE
> i.e.  return(structure("", defined = FALSE))
> 
> Does anyone see a problem with this approach ?
I think it should really be NULL if undefined: attributes which may or may
not be there are a nuisance.  The only problem I can see is in
system.gnw.r, whihc doe use nchar on getenv.

Small point: when do you want to change this? It is platform-specific code.

-- 
Brian D. Ripley,                  ripley@stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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