Re: Correct way to set environment

[Peter Stephenson <p.w.stephenson@ntlworld.com>]

On Sat, 15 Dec 2012 14:29:24 +0100
Florian Lindner <mailinglists@xgm.de> wrote:
> I'm a bit puzzled about the way to set global environment variables.
> 
> I've ushed .zshenv for that purpose since it is sourced on every shell
> invocation.
> 
> florian@horus ~ % cat .zshenv
> PATH=$HOME/flof/src:$HOME/software/bin:$PATH
> PATH=/home/florian/software/src/boar:$PATH
> 
> PYTHONPATH=$HOME/flof/src:$PYTHONPATH
> 
> 
> No other relevant z-files are present. This works as far as it sets
> the PYTHONPATH variable but if I launch python it is not taken into
> account. When I use export PYTHONPATH, the pythonpath gets longer and
> longer if I invoke a zsh session within a zsh session.
> 
> What is the best way to set some environment variables, no matter how
> (login, interactive, ...) the shell is invoced?

There are various things here:

(i) you need to ensure variables get exported, as Stefan pointed out, so
use the "export" keyword.  You don't need to do this every time you set the
variable, only once within each shell;

(ii) you need to put them in a file that gets sourced for all shells
(except when you give the "-f" option when starting the shell): .zshenv
is fine, as long as you understand the effect, though for some reason
this occasionally inspires holy wars (I think on the basis that
sometimes people don't understand the effect);

(iii) you don't want the paths to keep getting extended with repeated
values: for this, zsh has the -U (unique) keyword.  It only works on
colon-separated arrays if the shell knows that's what they are.  To do
that, you can associate the array with ("tie" it to) a real array ---
you can still set the colon-separated array, however, so if you want you
can ignore the real array completely.  This is already done for you for
PATH and path, because they're special, but you need to do it explicitly
for PYTHONPATH and pythonpath.  (PATH is probably already exported but
it doesn't have the -U flag by default; I've used the "export" keyword
anyway to express the intention.)

So put the following in .zshenv:


export -U PATH=$HOME/flof/src:$HOME/software/bin:$PATH
PATH=/home/florian/software/src/boar:$PATH
 
export -TU PYTHONPATH=$HOME/flof/src:$PYTHONPATH pythonpath


-- 
Peter Stephenson <p.w.stephenson@ntlworld.com>
Web page now at http://homepage.ntlworld.com/p.w.stephenson/