Start-Process does not populate the process object's exit code with NoNewWindow switch

[unlikelier]

Prerequisites

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• Refer to Differences between Windows PowerShell 5.1 and PowerShell.

Steps to reproduce

I noticed that the Start-Process cmdlet sometimes does not populate the ExitCode property in the output, I believe it should.
This happed at least when -PassThru, -Wait, and -NoNewWindow switches are provided. -NoNewWindow seems to be the reason, since the exit code is available without it.

Steps to reproduce

You can see this behavior with this simple test script

Set-Content -Value "exit 1" -Path script.ps1
$p = start-process "pwsh" script.ps1 -PassThru -NoNewWindow -Wait
$p.ExitCode  # Should output: 1
$p = start-process "pwsh" script.ps1 -PassThru -Wait
$p.ExitCode # Outputs: 1

Expected behavior

PS C:\> set-content -Value "exit 1" -Path script.ps1
PS C:\> $p = start-process "pwsh" script.ps1 -PassThru -NoNewWindow -Wait
PS C:\> $p.ExitCode
1
PS C:\> $p = start-process "pwsh" script.ps1 -PassThru -Wait
PS C:\> $p.ExitCode
1

Actual behavior

PS C:\> set-content -Value "exit 1" -Path script.ps1
PS C:\> $p = start-process "pwsh" script.ps1 -PassThru -NoNewWindow -Wait
PS C:\> $p.ExitCode
PS C:\> $p = start-process "pwsh" script.ps1 -PassThru -Wait
PS C:\> $p.ExitCode
1

Error details

No response

Environment data

PS C:\> $PSVersionTable

Name                           Value
----                           -----
PSVersion                      7.4.0-preview.5
PSEdition                      Core
GitCommitId                    7.4.0-preview.5
OS                             Microsoft Windows 10.0.20348
Platform                       Win32NT
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

Visuals

No response

[mklement0]

Although the symptoms have changed a bit, the root cause is likely the same as in:

• Process objects created with Start-Process -NoNewWindow and/or -RedirectStandard* never report their exit code on Windows. #5421 (comment)

That is, it seems that an exception occurs behind the scenes due to the process handle not being available (for reasons unknown to me), which PowerShell quietly swallows, causing $null to be returned from .ExitCode (and .Handle).

This now seems to always happen with -NoNewWindow, whereas it previously didn't happen if -Wait was specified too.

That is, both ($p = start-process "pwsh" script.ps1 -PassThru -NoNewWindow -Wait).Handle and $p = start-process "pwsh" script.ps1 -PassThru -NoNewWindow; $p.WaitForExit(); $p.Handle now output nothing, and therefore also return $null via .ExitCode.

In Windows PowerShell (and seemingly also earlier versions of PS Core), the -Wait variant (only) does work.

The problem does NOT occur when System.Diagnostics.Process is used directly, so this can serve as a workaround

# NOTE: You may also have to set the working dir. to PowerShell's.
$p = [System.Diagnostics.Process]::Start('pwsh', (Convert-Path 'script.ps1'))
$p.WaitForExit()
"Exit code: [$($p.ExitCode)]" # OK

Update: @derkveenhof found a simpler workaround: cache the process handle:

$p = Start-Process -NoNewWindow -PassThru pwsh '-c whoami'
$dummy = $p.Handle # Cache the handle
$p.WaitForExit()
"Exit code: [$($p.ExitCode)]" # OK

However, it should be noted that these workarounds aren't fully equivalent, though it will probably often not make a difference: -Wait waits for the child process as well as any of ITS child processes, which .WaiForExit() and Wait-Process do not. See:

• Start-Process -Wait behaves inconsistently vs Wait-Process when the new process launches children then exits before the children #15555

[shoddyguard]

We've just hit this too (as we have PowerShell Core set to auto-update).
Unfortunately we use Start-Process in a lot of places so it's going to be quite painful to implement the above workaround 😞

[prayaas-a]

+1

[alexvergilis]

+1

[chrispy81]

+1

[jlpetz]

what the heck, this is pretty bad. How did this slip past testing? I have a number of scripts using '-wait' which are now all bonkers, because the ExitCode and various other properties on System.Diagnostics.Process objects (returned by start-process) are now missing since 7.4 PowerShell update. Can this please be fixed this ASAP

[jlpetz]

Weird, is this as known issue too?

In one of my scripts I tried swapping from in Start-Process

$runresult = Start-Process "$initExe" -ArgumentList "$initExeArgs" -wait -NoNewWindow -PassThru
if ($runresult.exitcode -ne 0)

to a simple call operator ('&'), thinking this would do the trick

& "$initExe" $initExeArgs
$runresult = $LASTEXITCODE
if ($runresult -ne 0)

And while it works in a Terminal prompt, where the EXE sends prompt output to the terminal and then waits for input (as below)

Enter password for your user: 

If I run that same '&' call embedded in a .ps1 script. It seems to have the Input/Output redirection issues, as the same EXE in the same terminal doesn't output the prompt text. Instead it just hangs waiting for input. It still works, but it's confusing as to why the prompt goes missing in that context?

[jlpetz]

Ok, got it working similar to what @mklement0 posted in #20400 (comment)

The one difference is that to get the same behaviour in terms of screen output when running manually in a terminal AND when running it as part of a larger .ps1, I had to merge the WaitForExit() line (with a semicolon ';' on a single line). If I didn't do this, then the Output (input prompt) from the EXE was showing up on a PS prompt line (with the current directory prefix) when it was run manually in a terminal (but not when run in a large .ps1).

I have no idea why that would be the case. But by merging these onto a single line for some reason the EXE prompt goes to a new line (consistent with running the same command in a larger .ps1)

So in the end I went from

$runresult = Start-Process "$init" -ArgumentList "$initOptions" -wait -NoNewWindow -PassThru
if ($runresult.exitcode -ne 0)

to (leaving extra lines, as the initoptions as an array might help others)

$init = "c:\a path with spaces\init.exe"
$initoptions = @()
$initoptions += '-s'
$initoptions += '--abc'
$runresult = [System.Diagnostics.Process]::Start('pwsh', "-command & '$init' $initoptions") ; $runresult.WaitForExit()
if ($runresult.ExitCode -ne 0)
{
    Write-Host "ERROR: Exit code was non zero value - $($runresult.ExitCode)"
}

[softwarebear]

Just to add ... this doesn't happen on MacOS ...

Name                           Value
----                           -----
PSVersion                      7.4.0
PSEdition                      Core
GitCommitId                    7.4.0
OS                             Darwin 23.1.0 Darwin Kernel Version 23.1.0: Mon Oct  9 21:27:24 PDT 2023; root:xnu-10002.41.9~6/RELEASE_ARM64_T6000
Platform                       Unix
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

[mklement0]

Good to know, @softwarebear.
Similarly, Linux seems to be unaffected (simple test command, for all platforms:
(Start-Process -Wait -NoNewWindow -PassThru whoami).ExitCode
Should print both the username and exit code 0)

[mklement0]

@jlpetz, @derkveenhof found a simpler workaround - see my updated comment above.

[softwarebear]

Just to add ... this doesn't happen on MacOS ...

Name                           Value
----                           -----
PSVersion                      7.4.0
PSEdition                      Core
GitCommitId                    7.4.0
OS                             Darwin 23.1.0 Darwin Kernel Version 23.1.0: Mon Oct  9 21:27:24 PDT 2023; root:xnu-10002.41.9~6/RELEASE_ARM64_T6000
Platform                       Unix
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

Just to be consistent ...

PS /Users/softwarebear/dev> (Start-Process -Wait -NoNewWindow -PassThru whoami).ExitCode
softwarebear                    
0
PS /Users/softwarebear/dev> (Start-Process -Wait -PassThru whoami).ExitCode                
softwarebear                    
0
PS /Users/softwarebear/dev>