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

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: How do I run a Windows installer and get a succeed/fail value in PowerShell?

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