Powershell’s Write-Host sometimes is better than Write-Output

Despite what’s being said about the danger of Write-Host, I have found a scenario where it actually is the desired cmdlet to use over Write-Output.

Consider the code snippet below:

function Get-Array
{
    "I am not supposed to be in the array."

    $a = @("I am the only item in the array.")
    return $a
}

$array = Get-Array

cls

"`$array.count: [$($array.count)]"
$array

When I first encountered this piece of code (the simplified version shown above), I was quite frustrated with the output:

$array.count: [2]
I am not supposed to be in the array.
I am the only item in the array.

Why the hell was my print statement showing up in the array? Well, after hours of debugging and googling now I know it has everything to do with the behaviour of Write-Output:

The Write-Output cmdlet sends the specified object down the pipeline to the next command. If the command is the last command in the pipeline, the object is displayed in the console.
Write-Output sends objects down the primary pipeline, also known as the “output stream” or the “success pipeline.” To send error objects down the error pipeline, use Write-Error.
This cmdlet is typically used in scripts to display strings and other objects on the console. However, because the default behavior is to display the objects at the end of a pipeline, it is generally not necessary to use the cmdlet. For instance, Get-Process | Write-Output is equivalent to Get-Process.

The Get-Array function was explicitly returning an array object, but the assignment later on was also passing on whatever was in the primary pipeline. Gotcha!

A simple solution to this gotcha is by replacing the implicit Write-Output to Write-Host:

function Get-Array
{
    Write-Host "I am not supposed to be in the array."

    $a = @("I am the only item in the array.")
    return $a
}

$array = Get-Array

cls

"`$array.count: [$($array.count)]"
$array

As expected, you’d get the output below:

$array.count: [1]
I am the only item in the array.

This works because Write-Host behaves quite differently to Write-Output:

Write-Host sends the objects to the host. It does not return any objects. However, the host might display the objects that Write-Host sends to it.

Understanding the differences between the seemingly simple commands can save loads of wasted time in debugging, especially in a scripting world.