Setting environment variables for use outside program

**guesst** · 09-03-2008

I have a program that is trying to set the environment variable in a XP environment so that it can be used outside of the program. Unfortunately it seems that one the program terminates any environment variables that it creates are immediately forgotten. For example:

setenvtest.c

Code:

#include <stdio.h>
#include <stdlib.h>

int main() {
    putenv ("TEST=Works");
    system ("echo %TEST%");
    return 0;
}

Run it and it works fine within in itself, but run the exe as part of a batch file like:

test.bat

Code:

@echo off
setenvtest
echo %TEST%
pause

And it treats %TEST% like it is unassigned outside of the program.

So how do I fix that?

**Salem** · 09-03-2008

There's no easy way for a program to change the environment of it's parent process.
It's almost certainly impossible to do it without the any involvement of the parent process.

Typically, the child writes the information to a file, which the parent can then run as a batch file.

**~~master5001~~** · 09-03-2008

Well I am looking at different code using SetEnvironmentVariable() and I see nothing useful for contributing to the parent process. I will keep kicking this around, its actually kind of a nifty idea. But like many nifty ideas, sometimes you need to just do whatever works (i.e. do as Salem suggested). I am going to play with the code a bit since you have piqued my curiosity a little.

**Greenhorn__** · 09-03-2008

Moin,

the only way I know is to set the values in the Windows Registry under

Code:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment

Set the value name to Works, the type to REG_EXPAND_SZ and the value itself to %TEST%.

This should do what you want, but you need Admin-Rights to write to the Registry.
And don't forget to delete the value if you're done !

EDIT:

You can do it by calling

Code:

 system ("reg add HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment /v "Works" /t REG_EXPAND_SZ /d "%TEST%" /f

or with the RegSetValueEx Function

Greetz

**~~master5001~~** · 09-03-2008

True, but he is wanting to (and jump in and correct me if I am mistaken) alter the environment variables of a parent process that already exists.

**Greenhorn__** · 09-03-2008

Originally Posted by guesst

I have a program that is trying to set the environment variable in a XP environment so that it can be used outside of the program.
...
Run it and it works fine within in itself, but run the exe as part of a batch file

I understood this like he want's to set a global env to the system with the parent process.
If he do what I pointed to, other applications/scripts can also use the env.

Give it a try, maybe it is what you're asked for ...

Greetz

**~~master5001~~** · 09-03-2008

A suitable solution pending you are not aiming for environment variables for an already running program to be altered. Try out Greenhorn__'s solution, see if it can get the job done for ya.

**cpjust** · 09-03-2008

If you were using Bash on Linux you could do:

Code:

source ./your_Prog

and then any environment variables your_prog sets would still exist in your current shell environment.

But since you're on Windows, I don't have an answer at the moment.

**BobS0327** · 09-03-2008

Originally Posted by Greenhorn__

Moin,

the only way I know is to set the values in the Windows Registry under

Code:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment

Set the value name to Works, the type to REG_EXPAND_SZ and the value itself to %TEST%.

This should do what you want, but you need Admin-Rights to write to the Registry.
And don't forget to delete the value if you're done !

EDIT:

You can do it by calling

Code:

 system ("reg add HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment /v "Works" /t REG_EXPAND_SZ /d "%TEST%" /f

or with the RegSetValueEx Function

Greetz

Just an addedum. Windows will still not be aware of your changes unless you log off or reboot. Thus, you should also broadcast a WM_SETTINGCHANGE to all of the windows in the system.

**Salem** · 09-03-2008

Think about the security problems of having some child program change the parent's PATH variable for instance.

**guesst** · 09-04-2008

Thanks guys. In the end I just decided to go with the batch file solution. It seems the most friendly, and since this was just supposed to be a simple thing I don't want to complicate matters... for now. But it's good to have options if I decide to revisit it any time later.

If you're curious, this is what I was using it for.

**~~master5001~~** · 09-04-2008

I actually have never encountered an instance where I needed to do that in an intrusive way. The way Salem mentioned earlier seems to be the least invasive method since the parent is granting the child's priv's to do make such changes, instead of the child just acquiring them.

Are you trying to hack another program or something by ghosting one of its child processes?

**guesst** · 09-09-2008

Originally Posted by master5001

I actually have never encountered an instance where I needed to do that in an intrusive way. The way Salem mentioned earlier seems to be the least invasive method since the parent is granting the child's priv's to do make such changes, instead of the child just acquiring them.

Are you trying to hack another program or something by ghosting one of its child processes?

No, I believe I laid all my cards on the table when I gave the link as to what I was doing.

I'm going to go back and try Salem's method. I'll tell you all how it goes.

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