PowerShell, stream Process output and errors while running external process

Is there any way in PowerShell I can stream the content of the Output and the Error while the process is running? In pure .NET we can subscribe to events of the Process class, can I do the same in PowerShell?

Sure you can! What you need is an Object Events:

An object event is a .Net object that not only has the usual Properties and Methods in the object, but also has another member called Event, which you can register a subscription on using Register-ObjectEvent

Here is slightly modified example from the the PowerShell forums. It will output data from the ping command asynchronously (at least from the script point of view):

# Setup stdin\stdout redirection
$StartInfo = New-Object System.Diagnostics.ProcessStartInfo -Property @{
                FileName = 'ping.exe'
                Arguments = '-t 127.0.0.1'
                UseShellExecute = $false
                RedirectStandardOutput = $true
                RedirectStandardError = $true
            }

# Create new process
$Process = New-Object System.Diagnostics.Process

# Assign previously created StartInfo properties
$Process.StartInfo = $StartInfo

# Register Object Events for stdin\stdout reading
$OutEvent = Register-ObjectEvent -Action {
    Write-Host $Event.SourceEventArgs.Data
} -InputObject $Process -EventName OutputDataReceived

$ErrEvent = Register-ObjectEvent -Action {
    Write-Host $Event.SourceEventArgs.Data
} -InputObject $Process -EventName ErrorDataReceived

# Start process
[void]$Process.Start()

# Begin reading stdin\stdout
$Process.BeginOutputReadLine()
$Process.BeginErrorReadLine()

# Do something else while events are firing
do
{
    Write-Host 'Still alive!' -ForegroundColor Green
    Start-Sleep -Seconds 1
}
while (!$Process.HasExited)

# Unregister events
$OutEvent.Name, $ErrEvent.Name |
    ForEach-Object {Unregister-Event -SourceIdentifier $_}