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How to set environmental variables before running another command?
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Subject Author Date
How to set environmental variables before running another command? Meal 06-03-2008
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Posted by Meal on June 3, 2008, 2:27 pm
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 Hi Perl expert,
I=92m writing a simple script for a building system on windows vista.
This script will run a .cmd file which sets a lot of environmental
variables. After this, the script need to run a build command.
The build command depends on these environmental variables.
If I run the .cmd file with system or exec and then run the build
command, the build command will not run within the correct
environment. The system or exec simply start a new process and set the
environmental variables there.
My current solution is as below.
exec(".\myenv.cmd&build -cC -amd64");
It works since there's an "&", but I doubt in the future I need to
add more complex commands. Absolutely I cannot concatenate each of
them with an '&'.
What's the correct solution for this issue?
Thanks.
Meal.

Posted by smallpond on June 3, 2008, 4:38 pm
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 Meal wrote:
> Hi Perl expert,
> I’m writing a simple script for a building system on windows vista.
> This script will run a .cmd file which sets a lot of environmental
> variables. After this, the script need to run a build command.
> The build command depends on these environmental variables.
> If I run the .cmd file with system or exec and then run the build
> command, the build command will not run within the correct
> environment. The system or exec simply start a new process and set the
> environmental variables there.
> My current solution is as below.
> exec(".\myenv.cmd&build -cC -amd64");
> It works since there's an "&", but I doubt in the future I need to
> add more complex commands. Absolutely I cannot concatenate each of
> them with an '&'.
> What's the correct solution for this issue?
> Thanks.
> Meal.


Why not set the environment variables within perl?

$ENV = 'C:\BDIR';

perldoc perlvar

The hash %ENV contains your current environment. Setting a value in "ENV"
changes the environment for any child processes you subsequently fork() off.

** Posted from http://www.teranews.com **

Posted by Jürgen Exner on June 3, 2008, 4:52 pm
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> I’m writing a simple script for a building system on windows vista.
>This script will run a .cmd file which sets a lot of environmental
>variables. After this, the script need to run a build command.
> The build command depends on these environmental variables.

This has nothing to do with Perl but everything with how environment
settings are inherited between processes. And for obvious reasons
children are not allowed to change environment variables of their
parent (you Perl script) or even worse their siblings (the build
command).

Just set the env vars in the parent process (i.e. your Perl script) and
the child processes (build script) will inherit them.

jue

Posted by Meal on June 3, 2008, 4:56 pm
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> > =A0I=92m writing a simple script for a building system on windows vista.=

> >This script will run a .cmd file which sets a lot of environmental
> >variables. After this, the script need to run a build command.
> > =A0The build command depends on these environmental variables.
>
> This has nothing to do with Perl but everything with how environment
> settings are inherited between processes. And for obvious reasons
> children are not allowed to change =A0environment variables of their
> parent (you Perl script) or even worse their siblings (the build
> command).
>
> Just set the env vars in the parent process (i.e. your Perl script) and
> the child processes (build script) will inherit them.
>
> jue

Thanks to both of you.
It seems there's no other way.
The .cmd file to set the variables is rather large, I definitely don't
want to set that much variables manually.

Posted by Jürgen Exner on June 3, 2008, 5:02 pm
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>> Just set the env vars in the parent process (i.e. your Perl script) and
>> the child processes (build script) will inherit them.
>>
>> jue
>
>Thanks to both of you.
>It seems there's no other way.
>The .cmd file to set the variables is rather large, I definitely don't
>want to set that much variables manually.

Nobody is talking about setting them manually. Just set them in your
Perl script.

jue

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