Powershell – What’s the difference between “Write-Host”, “Write-Output”, or “[console]::WriteLine”

powershell

There are a number of different ways to output messages. What is the effective difference between outputting something via Write-Host, Write-Output, or [console]::WriteLine?

I also notice that if I use:

write-host "count=" + $count

The + gets included in the output. Why's that? Shouldn't the expression be evaluated to produce a single concatenated string before it gets written out?

Best Answer

Write-Output should be used when you want to send data on in the pipe line, but not necessarily want to display it on screen. The pipeline will eventually write it to out-default if nothing else uses it first.

Write-Host should be used when you want to do the opposite.

[console]::WriteLine is essentially what Write-Host is doing behind the scenes.

Run this demonstration code and examine the result. 

function Test-Output {
    Write-Output "Hello World"
}

function Test-Output2 {
    Write-Host "Hello World" -foreground Green
}

function Receive-Output {
    process { Write-Host $_ -foreground Yellow }
}

#Output piped to another function, not displayed in first.
Test-Output | Receive-Output

#Output not piped to 2nd function, only displayed in first.
Test-Output2 | Receive-Output 

#Pipeline sends to Out-Default at the end.
Test-Output

You'll need to enclose the concatenation operation in parentheses, so that PowerShell processes the concatenation before tokenizing the parameter list for Write-Host, or use string interpolation

write-host ("count=" + $count)
# or
write-host "count=$count"

BTW - Watch this video of Jeffrey Snover explaining how the pipeline works. Back when I started learning PowerShell I found this to be the most useful explanation of how the pipeline works.

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