How to return one and only one value from a PowerShell function?

Question

I\'ve learned from this Stack Overflow question, that PowerShell return semantics are different, let\'s say, from C#\'s return semantics. Quote from the aforementioned quest

Answer 1

echo is an alias for Write-Output which sends the object to the next command.

Using Write-Host should help:

PS:> function Calculate
>> {
>>    # Every function that returns has to echo something
>>    Write-Host "test"
>>    return 11
>> }
>>
PS:> $A = Calculate
test
PS:> $A
11

Answer 2

PowerShell does pipes awkwardkly. To work around the return value problem and save the pipeline for real data, pass the function a value by reference, that is, an array. The array can be loaded with the value you wish to return. Here's a simple example:

# tp.ps1
#   test passed parameters
#   show that arrays are passed by reference, and can be used to provide
#   return values outside the pipeline
function doprint
{
    process { write-output "value now: $psitem" }
}

function recurse($thing,     $rtx)
{
    $thing++
    if($thing -lt 20) {
        if($thing -eq 15) { $rtx[0] = $thing }
        write-output $thing | doprint
        recurse $thing     $rtx
    }
}

j=0
$rtv=@(4)
recurse $j     $rtv
write-output $rtv[0]

Answer 3

Worth mentioning:

Any unmanaged command output inside your function will end up as a return value.

I use to get this trouble with a function managing XML content:

Function Add-Node(NodeName){
    $NewXmlNode = $Xml.createElement("Item")
    $Xml.Items.appendChild($NewXmlNode) | out-null
}

If you remove the Out-Null, the return of your function will be the Node basic properties... (You can also manage the exit code of the appendChild command ... it depends on the motivation) :)

Answer 4

@Michael Sorens's answer is useful, but it suggests a design strategy that seems rather onerous. I don't want to have to separate out data processing functions from functions that report progress or diagnostic messages. Reading his blogpost, I found a less hacky work-around to the OP's question. Here's the key sentence from the blog post:

A PowerShell function returns all uncaptured output.

So what if we capture our output?

function Calculate
{
   $junkOutput = echo "Calculate"
   return 11
}

$result = Calculate

Now $result just contains 11, as intended.