Getting output from process spawned from powershell

Updated 02-10-2011: Fixed a small bug that could make SmartProcess consume 100%
There is several ways you can spawn a new process from within PowerShell. Start-Process for instance. If you create a new object of type System.Diagnostics.Process or call Start-Process and get such an object back, you can now get access to the Standard Input/Standard Output … there is a “catch” thou. These only get updated every time the process sends a complete line including a newline.

So lets say you spawn nslookup and want to catch every time i t expects input, it wont work.

function StartProcess([String]$FileName){
    $process = New-Object "System.Diagnostics.Process" 
    $startinfo = New-Object "System.Diagnostics.ProcessStartInfo" 
    $startinfo.FileName = $FileName
    #$startinfo.Arguments = $arguments 
    #$startinfo.WorkingDirectory = $pwd.Path 
    $startinfo.UseShellExecute = $false
    $startinfo.RedirectStandardInput = $true
    $startinfo.RedirectStandardOutput = $true
    $startinfo.RedirectStandardError = $false
    #$startinfo.WindowStyle = [System.Diagnostics.ProcessWindowStyle]::Hidden 
    $startinfo.WindowStyle = [System.Diagnostics.ProcessWindowStyle]::Normal

    $process.StartInfo = $startinfo 
    $temp = $process.start()
    return $process
}

function GetPrompt([System.Diagnostics.Process]$process, [Int]$waitSec){
    $str = ''
    $i = 1
    while( (!([String]$str).contains("> ")) -and (!$process.HasExited) -and ($i -le $waitSec) -and ($process.StandardOutput.Peek() -eq -1) ){
        # Write-Host ("Peek: " + $process.StandardOutput.Peek())
        while($process.StandardOutput.Peek() -ge 0){
            $iChar = $process.StandardOutput.Read()
            $str = ($str + [Convert]::ToChar($iChar))
        }
        if(!([String]$str).contains("> ")){ Write-Host "."; Start-Sleep -s 1; }
        $i = $i + 1
    }
    return $str
}

if($true){
    #[void] [System.Reflection.Assembly]::LoadWithPartialName("'System.Windows.Forms")
    #[System.Windows.Forms.SendKeys]::SendWait("skadefro.dk")

    if(!$process.HasExited){ Write-Host "Killing process"; $process.kill(); $process.StandardOutput.ReadToEnd() }
    $process = StartProcess 'nslookup'
    GetPrompt $process 2
    $process.StandardInput.WriteLine('set q=MX')
    GetPrompt $process 2
    $process.StandardInput.WriteLine('skadefro.dk')
    $process.StandardInput.Flush()
    #$process.StandardOutput.ReadToEnd()
    GetPrompt $process 2

}
if(!$process.HasExited){ $process.kill() }

So you could write some code and hook up to the ErrorDataReceived and OutputDataReceived events. but those have the same problem, so you need to dig a bit deeper. You need to take each stream object and hook up to BaseStream.BeginRead

So that is what I have done. Inside my SuperOffice Add in I have added a new command called New-SmartProcess

And now the above code will look cleaner and actually work

function WaitForPrompt([wingu.SmartProcess]$process, [Int]$waitSec){
    $str = ''
    $i = 1
    while( (!($process.StandardOutput.contains("> ")) -and (!$process.HasExited) -and ($i -le $waitSec))){
        if(!([String]$str).contains("> ")){ Write-Host "."; Start-Sleep -s 1; }
        $i = $i + 1
    }
    return $str
}

if($process){ if(!$process.HasExited){ Write-Host "Killing process"; $process.kill(); $process.StandardOutput.ReadToEnd() } }
$process = New-SmartProcess 'nslookup'
WaitForPrompt $process 2
$process.StandardOutput
$process.StandardOutput = ''
$process.WriteLine('set q=MX')
WaitForPrompt $process 2
$process.StandardOutput
$process.StandardOutput = ''
$process.WriteLine('skadefro.dk')
WaitForPrompt $process 2
$process.StandardOutput
$process.StandardOutput = ''
if(!$process.HasExited){ $process.kill() }

You can find my SuperOffice PowerShell snapin inclucing Source code here