Register-EventObject does not update console while listening to process

Question

I am currently in the process of writing a process wrapper and i am trying to redirect the stdout, and stderr channels to the powershell console

the following code is the function I am using to invoke my process but the problem i seem to be having is that i don't get any output from the event handlers to update the console

the output and err output fine at the end but will not update as it happens

function Invoke-Executable($ExePath, $ExeArgs)
{
        #Setup ProcessInfo
        $pinfo = New-Object System.Diagnostics.ProcessStartInfo
        $pinfo.FileName = $ExePath
        $pinfo.RedirectStandardError = $true
        $pinfo.RedirectStandardOutput = $true
        $pinfo.UseShellExecute = $false
        $pinfo.Arguments = $ExeArgs

        #Setup Process
        $process = New-Object System.Diagnostics.Process
        $process.StartInfo = $pinfo


        #Setup Error Listener
        $errEvent = Register-ObjectEvent -InputObj $process `
        -Event "ErrorDataReceived" `
        -Action `
        {
            param
            (
                [System.Object] $sender,
                [System.Diagnostics.DataReceivedEventArgs] $e
            )
            Write-Error $e.Data
        }

        #Setup Out Listener 
        $outEvent = Register-ObjectEvent -InputObj $process `
        -Event "OutputDataReceived" `
        -Action `
        {
            param
            (
                [System.Object] $sender,
                [System.Diagnostics.DataReceivedEventArgs] $e
            )
            Write-Host $e.Data
        }

        # Start the process
        [Void] $process.Start()
        # Begin async read events
        # $process.BeginOutputReadLine()
        # $process.BeginErrorReadLine()

        while (!$process.HasExited)
        {
            Start-Sleep -Milliseconds 250
            Write-Host "ping"
        }
        $stdout = $process.StandardOutput.ReadToEnd()
        $stderr = $process.StandardError.ReadToEnd()
        # if ($stdout) {Write-Host "$stdout"}

        # if ($stderr) { Write-Error  "$stderr" }

} 

Answer 1

Uncomment these lines in your code and it should start working:

$process.BeginOutputReadLine()
$process.BeginErrorReadLine()

I modified Write-Error to Write-Host for reasons similar to what is discussed here: Write-Error does not print to console before script exits

Example used for output redir testing :

Invoke-Executable ping "127.0.0.1"

Example used for testing error redir :

Invoke-Executable powershell 'import-module nonexistant -ea continue;exit'

Full code :

function Invoke-Executable($ExePath, $ExeArgs)
{
        #Setup ProcessInfo
        $pinfo = New-Object System.Diagnostics.ProcessStartInfo
        $pinfo.FileName = $ExePath
        $pinfo.RedirectStandardError = $true
        $pinfo.RedirectStandardOutput = $true
        $pinfo.UseShellExecute = $false
        $pinfo.Arguments = $ExeArgs

        #Setup Process
        $process = New-Object System.Diagnostics.Process
        $process.StartInfo = $pinfo


        #Setup Error Listener
        $errEvent = Register-ObjectEvent -InputObj $process `
        -Event "ErrorDataReceived" `
        -Action `
        {
            param
            (
                [System.Object] $sender,
                [System.Diagnostics.DataReceivedEventArgs] $e
            )
             Write-host $e.Data
        }

        #Setup Out Listener 
        $outEvent = Register-ObjectEvent -InputObj $process `
        -Event "OutputDataReceived" `
        -Action `
        {
            param
            (
                [System.Object] $sender,
                [System.Diagnostics.DataReceivedEventArgs] $e
            )
            Write-Host $e.Data
        }

        # Start the process
        [Void] $process.Start()
        # Begin async read events
         $process.BeginOutputReadLine()
         $process.BeginErrorReadLine()

        while (!$process.HasExited)
        {
            Start-Sleep -Milliseconds 250
            Write-Host "ping"

        }

        # if ($stdout) {Write-Host "$stdout"}

        # if ($stderr) { Write-Error  "$stderr" }

}