Obtaining ExitCode using Start-Process and WaitForExit instead of -Wait

I'm trying to run a program from PowerShell, wait for the exit, then get access to the ExitCode, but I am not having much luck. I don't want to use -Wait with Start-Process, as I need some processing to carry on in the background.

Here's a simplified test script:

cd "C:\Windows"

# ExitCode is available when using -Wait...
Write-Host "Starting Notepad with -Wait - return code will be available"
$process = (Start-Process -FilePath "notepad.exe" -PassThru -Wait)
Write-Host "Process finished with return code: " $process.ExitCode

# ExitCode is not available when waiting separately
Write-Host "Starting Notepad without -Wait - return code will NOT be available"
$process = (Start-Process -FilePath "notepad.exe" -PassThru)
$process.WaitForExit()
Write-Host "Process exit code should be here: " $process.ExitCode

Running this script will cause Notepad to be started. After this is closed manually, the exit code will be printed, and it will start again, without using -wait. No ExitCode is provided when this is quit:

Starting Notepad with -Wait - return code will be available
Process finished with return code:  0
Starting Notepad without -Wait - return code will NOT be available
Process exit code should be here:

I need to be able to perform additional processing between starting the program and waiting for it to quit, so I can't make use of -Wait. How can I do this and still have access to the .ExitCode property from this process?

There are two things to remember here. One is to add the -PassThru argument and two is to add the -Wait argument. You need to add the wait argument because of this defect.

-PassThru [<SwitchParameter>]
    Returns a process object for each process that the cmdlet started. By default,
    this cmdlet does not generate any output.

Once you do this a process object is passed back and you can look at the ExitCode property of that object. Here is an example:

$process = start-process ping.exe -windowstyle Hidden -ArgumentList "-n 1 -w 127.0.0.1" -PassThru -Wait
$process.ExitCode

# This will print 1

If you run it without -PassThru or -Wait, it will print out nothing.

The same answer is here: https://stackoverflow.com/questions/4749186/how-do-i-run-a-windows-installer-and-get-a-succeed-fail-value-in-powershell/7109778#7109778

It's also worth noting that there's a workaround mentioned in the "defect report" link above, which is as following:

# Start the process with the -PassThru command to be able to access it later
$process = Start-Process 'ping.exe' -WindowStyle Hidden -ArgumentList '-n 1 -w 127.0.0.1' -PassThru

# This will print out False/True depending on if the process has ended yet or not
# Needs to be called for the command below to work correctly
$process.HasExited

# This will print out the actual exit code of the process
$process.GetType().GetField('exitCode', 'NonPublic, Instance').GetValue($process)

While trying out the final suggestion above, I discovered an even simpler solution. All I had to do was cache the process handle. As soon as I did that, $process.ExitCode worked correctly. If I didn't cache the process handle, $process.ExitCode was null.

example:

$proc = Start-Process $msbuild -PassThru
$handle = $proc.Handle # cache proc.Handle
$proc.WaitForExit();

if ($proc.ExitCode -ne 0) {
    Write-Warning "$_ exited with status code $($proc.ExitCode)"
}

Two things you could do I think...

1. Create the System.Diagnostics.Process object manually and bypass Start-Process
2. Run the executable in a background job (only for non-interactive processes!)

Here's how you could do either:

$pinfo = New-Object System.Diagnostics.ProcessStartInfo
$pinfo.FileName = "notepad.exe"
$pinfo.RedirectStandardError = $true
$pinfo.RedirectStandardOutput = $true
$pinfo.UseShellExecute = $false
$pinfo.Arguments = ""
$p = New-Object System.Diagnostics.Process
$p.StartInfo = $pinfo
$p.Start() | Out-Null
#Do Other Stuff Here....
$p.WaitForExit()
$p.ExitCode

OR

Start-Job -Name DoSomething -ScriptBlock {
    & ping.exe somehost
    Write-Output $LASTEXITCODE
}
#Do other stuff here
Get-Job -Name DoSomething | Wait-Job | Receive-Job

The '-Wait' option seemed to block for me even though my process had finished.

I tried Adrian's solution and it works. But I used Wait-Process instead of relying on a side effect of retrieving the process handle.

So:

$proc = Start-Process $msbuild -PassThru
Wait-Process -InputObject $proc

if ($proc.ExitCode -ne 0) {
    Write-Warning "$_ exited with status code $($proc.ExitCode)"
}

Or try adding this...

$code = @"
[DllImport("kernel32.dll")]
public static extern int GetExitCodeProcess(IntPtr hProcess, out Int32 exitcode);
"@
$type = Add-Type -MemberDefinition $code -Name "Win32" -Namespace Win32 -PassThru
[Int32]$exitCode = 0
$type::GetExitCodeProcess($process.Handle, [ref]$exitCode)

By using this code, you can still let PowerShell take care of managing redirected output/error streams, which you cannot do using System.Diagnostics.Process.Start() directly.

Here's a variation on this theme. I want to uninstall Cisco Amp, wait, and get the exit code. But the uninstall program starts a second program called "un_a" and exits. With this code, I can wait for un_a to finish and get the exit code of it, which is 3010 for "needs reboot". This is actually inside a .bat file.

If you've ever wanted to uninstall folding@home, it works in a similar way.

rem uninstall cisco amp, probably needs a reboot after

rem runs Un_A.exe and exits

rem start /wait isn't useful
"c:\program files\Cisco\AMP\6.2.19\uninstall.exe" /S

powershell while (! ($proc = get-process Un_A -ea 0)) { sleep 1 }; $handle = $proc.handle; 'waiting'; wait-process Un_A; exit $proc.exitcode