Setting environment variables

[Sami Viitanen]

Hello,

Is there any other way to set variables than os.putenv().

Putenv doesn't actually put any values to actual system variables..

I'm trying to set CVSEDITOR variable automatically from script
so that user wouldn't have to set that him/herself. CVS can't use variable
set with putenv().


Thanks in advance.

[Erik Max Francis]

Re: Setting environment variables

Sami Viitanen wrote:
[color=blue]
> Is there any other way to set variables than os.putenv().
>
> Putenv doesn't actually put any values to actual system variables..
>
> I'm trying to set CVSEDITOR variable automatically from script
> so that user wouldn't have to set that him/herself. CVS can't use
> variable
> set with putenv().[/color]

Yep, and this is a feature, at least in Unix operating systems.
Subshells cannot directly affect the operating environment of parent
shells, and shouldn't try. (One can do such things indirectly, but they
require the cooperation of the parent shell, such as sourcing the output
of a program, which is not an uncommon approach to the problem.) I
don't know if there's any way for Windows applications to affect parent
environments, but I doubt it.

--
Erik Max Francis && max@alcyone.com && http://www.alcyone.com/max/
__ San Jose, CA, USA && 37 20 N 121 53 W && &tSftDotIotE
/ \ Perfect situations must go wrong
\__/ Florence, _Chess_

[Peter Hansen]

Re: Setting environment variables

Erik Max Francis wrote:[color=blue]
>
> Sami Viitanen wrote:
>[color=green]
> > Is there any other way to set variables than os.putenv().
> >
> > Putenv doesn't actually put any values to actual system variables..
> >
> > I'm trying to set CVSEDITOR variable automatically from script
> > so that user wouldn't have to set that him/herself. CVS can't use
> > variable
> > set with putenv().[/color]
>
> Yep, and this is a feature, at least in Unix operating systems.
> Subshells cannot directly affect the operating environment of parent
> shells, and shouldn't try. (One can do such things indirectly, but they
> require the cooperation of the parent shell, such as sourcing the output
> of a program, which is not an uncommon approach to the problem.) I
> don't know if there's any way for Windows applications to affect parent
> environments, but I doubt it.[/color]

Short of bizarre hacks that are generally unacceptable, no there's no
way to do it even under Windows.

Under both operating systems, the best approach is to contrive a way
for another script to be executed *after* the application runs. That
other script either accesses data that is generated by the application,
or is actually itself generated by the application as needed, and because
it's a script (e.g. .BAT or .CMD for Windows, .sh etc. for Unix) it
is able to change the shell. (And I know you already knew this, EMF,
I was of course responding for others. :-)

-Peter

[David C. Fox]

Re: Setting environment variables

Erik Max Francis wrote:[color=blue]
> Sami Viitanen wrote:
>
>[color=green]
>>Is there any other way to set variables than os.putenv().
>>
>>Putenv doesn't actually put any values to actual system variables..
>>
>>I'm trying to set CVSEDITOR variable automatically from script
>>so that user wouldn't have to set that him/herself. CVS can't use
>>variable
>>set with putenv().[/color]
>
>
> Yep, and this is a feature, at least in Unix operating systems.
> Subshells cannot directly affect the operating environment of parent
> shells, and shouldn't try. (One can do such things indirectly, but they
> require the cooperation of the parent shell, such as sourcing the output
> of a program, which is not an uncommon approach to the problem.) I
> don't know if there's any way for Windows applications to affect parent
> environments, but I doubt it.
>[/color]

In [t]csh:

alias cvsscript "setenv CVSEDITOR `python myscript.py`"
cvsscript

or miscellaneous variants in other shells. Of course, you can't use
cvsscript from within another subshell, or it will only set the variable
in that subshell.

David

[Donald 'Paddy' McCarthy]

Re: Setting environment variables

Sami Viitanen wrote:[color=blue]
> Hello,
>
> Is there any other way to set variables than os.putenv().
>
> Putenv doesn't actually put any values to actual system variables..
>
> I'm trying to set CVSEDITOR variable automatically from script
> so that user wouldn't have to set that him/herself. CVS can't use variable
> set with putenv().[/color]

You could do the equivalent of:
Paddy@maximilli an ~ : echo $SHELL
/bin/bash
Paddy@maximilli an ~ : unset foo
Paddy@maximilli an ~ : eval `python -c 'print "foo=Hello;expo rt foo"'`
Paddy@maximilli an ~ : echo $foo
Hello
Paddy@maximilli an ~ :

I use the following for setting up quite complex environments at work:

http://modules.sourceforge.net/

Pad.