Changing environment variables of the calling process

Question

This one seems trivial but the answer has eluded me for a few days now.

I have a Windows batch file, that calls a C# program to do an extra verification that cannot be done in a batch file. After the verification is complete I need to return a status and a string back to the calling shell.

Now the return value is trivial and my C# console app simply sets a return value (exit code if you will). And I thought the string will also be a piece of cake. I attempted to define a new shell variable using the:

Environment.SetEnvironmentVariable("ERR", "Some text");

This call should (and does) define a shell variable within the current process - that is the very C# process that created the variable. The value is lost as soon as the C# app terminates and the shell that created the C# app knows nothing about the variable. So... A call with no particular use... At all... Unless perhaps if I created a child process from the C3 app, perhaps it would inherit my variables.

The EnvironmentVariableTarget.Machine and EnvironmentVariableTarget.User targets for the SetEnvironmentVariable call don't solve the problem either, as only a newly created process will get these new values from the registry.

So the only working solution I can think of is:

• write to stdout
• write to a file
• encode extra meaning into the return value

The first two are a bit ugly and the last one has its limitations and problems.

Any other ideas (how to set a shell variable in the parent process)? Maybe such shell variable modifications are a security concern (think PATH)...

Thank-you for your time.

Answer 1

I had the same problem as Ryan and the only thing that came to my mind as a work-around was to write a batch in error out to set the variable and to call it from the batch.

ConsoleApplication1.exe:

'put some sensible code here
'put result in variable myResult
Dim myResult As String = Guid.NewGuid().ToString("D").ToUpperInvariant()
Console.WriteLine("Normal output from the consonle app")
Console.Error.WriteLine("@ECHO OFF")
Console.Error.WriteLine("SET zzzResult={0}", myResult)

Test.cmd (the calling batch):

@ECHO OFF
:Jump to folder of batch file
PUSHD %~d0%~p0

:Define a temp file
SET zzzTempFile=%TEMP%\TMP%Random%.CMD

:Call .NET console app
ConsoleApplication1.exe 2>%zzzTempFile%

:Call the generated batch file
CALL %zzzTempFile%

:Clean up temp file
DEL %zzzTempFile%

:Clean up variable
SET zzzTempFile=

:Do something with the result
ECHO Yeah, we finally got it!
ECHO:
ECHO The value is "%zzzResult%".
ECHO:

:Clean up result variable
SET zzzResult=

:Go back to original folder
POPD

That should do the trick. And yes, I do know this is an old post and Ryan is solving other issues by now, but there might be still somebody else out there having the same problem...