Monitor changes to an environment variable

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Hello everybody,

My English isn't good.

I have two apps A and B. App-A sets an environment variable, and App-B can potentially change this variable. I was wondering if it's possible for App-A to watch for changes to the environment variable. I was looking for something like the FileSystemWatcher except that I want to monitor environment variables rather than the file system. And I want to avoid having a worker thread in App-A that periodically polls the value to look for changes.

Posted 27-Jun-10 8:38am

mohammad meta

Updated 27-Jun-10 12:01pm

Nish Nishant

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you can use shell or process and execute DOS shell commands : set and echo more information here : http://en.wikipedia.org/wiki/Environment_variable or > WinAPI http://msdn.microsoft.com/en-us/library/ms683188(VS.85).aspx and add timer to check it! (maybe can help you)

Posted 27-Jun-10 9:47am

Adrabi Abderrahim

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Nish Nishant · Accepted Answer · 2010-06-27T12:18:00

As far as I know, there's no OS provided way to monitor changes to environment variables. Most apps read these variables at startup and don't bother with changes till the next time they are run. There is something you could try as a workaround though. In recent versions of Windows, environment variables are persisted in the registry. So instead of monitoring for changes directly, you could examine/monitor the following two registry keys:

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

And as to how you can monitor the registry, WMI provides a RegistryValueChangeEvent class that you can use to monitor changes to a specific key or value. But if I were you, I'd rethink my design and make it a basic expectation that the app will not be affected by environment variable changes once it's been started.

Tim Deveaux · Accepted Answer · 2010-06-27T14:03:00

You might have App-B broadcast a WM_SETTINGCHANGE message after a variable is changed - check the docs for WM_SETTINGCHANGE and notes here: http://support.microsoft.com/kb/104011[^].

It would be easier to code a handler for this message in App-A than to poll for changes, but might not handle the case when a user changes things with a set command from the command prompt.

Monitor changes to an environment variable

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