PowerShell Write-Output inside "if" does not output anything

Question

I am learning PowerShell recently, and found a behavior that I cannot understand. Let me explain in code below:

function func1()
{
    Write-Output "output from func1()"
    func2
    return $true
}

function func2()
{
    Write-Output "output from func2()"
    func3
}

function func3()
{
    Write-Output "output from func3()"
}

Write-Output "*** 1. run alone ****"
func1

Write-Output "*** 2. run inside if ****"
if (func1) {
    #do nothing
}

It is strange when func1 is called directly, it can output message as expected, but if put inside "if" statement, it will not. See output as below:

*** 1. run alone ****
output from func1()
output from func2()
output from func3()
True
*** 2. run inside if ****

You can see it's empty. Why is that, and how can I enable the output like the first example? Thanks!

Dan Atkinson · Accepted Answer · 2019-04-04 09:22:56Z

14

PowerShell functions are not like their traditional language counterparts: they can output multiple things. When you're using Write-Output, you are sending things down the pipeline, so func1() will return both a String and a Boolean. If you try this:

$return_values = func1;
$return_values | Get-Member

You will see that you get both System.String and System.Boolean objects in $return_values. Indeed the 'return' statement is more like an 'exit' or 'break' in traditional languages: it marks an exit point, but the function will actually return with whatever was already outputted (+ the optional return argument).

The quick fix to the issue is to change Write-Output to Write-Host, though they do slightly different things.

edited Apr 4, 2019 at 9:22

Dan Atkinson

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answered Jul 2, 2014 at 8:38

PeterK

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Comments

Community · Accepted Answer · 2017-05-23 12:30:50Z

7

You can achieve desired results by replacing Write-Output with Write-Host. This is suitable only if your main concern is to produce output in the console as Write-Host does not go to stdout stream.

You can read more about difference between the 2 cmdlets in this SO thread :Which should I use: "Write-Host", "Write-Output", or "[console]::WriteLine"?

edited May 23, 2017 at 12:30

CommunityBot

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answered Jul 2, 2014 at 8:37

Raf

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Comments

Stepan Solovyev · Accepted Answer · 2024-02-27 10:26:08Z

0

using this inline c# code can solve the problem

Add-Type -Language CSharp @"
using System; 
namespace Test 
{
public static class Write 
{ 
    public static void StdOut() 
    {
        Console.WriteLine("hello world");
    }
}
}
"@;

function func1()
{
# Write-Output "output from func1()"
[Test.Write]::StdOut()
return $true
}

Write-Output "*** 1. run alone ****"
func1

Write-Output "*** 2. run inside if ****"
if (func1) {

}

# checking for func1 members - there are Boolean only value returned
$return_values = func1;
$return_values | Get-Member

answered Feb 27, 2024 at 10:26

Stepan Solovyev

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