PowerShell - Beware What Your Function Returns

 Your PowerShell script could return something totally different from what you would have thought. Considering below function/script:

function demo-returnValues {

    "1"

    "2"

    return [string]"3"

}

$dn = demo-returnValues

write-host "return Type: $($dn.gettype().fullname)"

write-host "element count $($dn.count)"

write-host " Values:"

$dn|foreach {write-host "[[$_]]"}

It doesn't return a string of value "3"! Rather it returns an array of 3 elements. See its output:

return Type: System.Object[]

element count 3

Values:

[[1]]

[[2]]

[[3]]

This is because anything within a function that emits value that are not caught will be added to a pipeline. What you intend to return is also added to this pipeline. Finally it is this pipeline that gets returned.

 To fix this, you can do one of below 3

1. Assigned to variable
2. Suppressed by [void]
3. piped to out-null

Revised function below. This returns only a string of "4"

function demo-returnValues {

    [void]"1"

    $uselessVar = "2"

    "3" | out-null

    return [string]"4"

}