Dynamically create PowerShell scriptblock from scriptblock

Question

I want to write a powershell function that returns a scriptblock by creating one dynamically based on a scriptblock passed in as an input parameter. I don't seem to be having much luck.

It's easy to write a method to invoke the scriptblock twice.

$x = { write-host "Hello" }
function DoIt([scriptblock] $s) { $s.Invoke(); }
function DoItTwice([scriptblock] $s) { $s.Invoke(); $s.Invoke(); }

DoIt($x)
DoItTwice($x)

It's harder to write a method that returns a scriptblock that has the effect of invoking the (input) scriptblock twice. The following doesn't work

function TwiceAsScriptBlock([scriptblock] $s)
{
    function twice
    {
        $s.Invoke();
        $s.Invoke();
    }
    return { twice }
}

Musaab Al-Okaidi · Accepted Answer · 2013-02-14 16:22:30Z

10

This will do the trick for you:

function TwiceAsScriptBlock([scriptblock] $s)
{

    $ScriptBlock = [System.Management.Automation.ScriptBlock]::Create("$s ; $s")
    Return $ScriptBlock 
}

Powershell Return Scriptblock

edited Feb 14, 2013 at 16:22

answered Feb 14, 2013 at 16:12

Musaab Al-Okaidi

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4 Comments

Rob Over a year ago

I tried variants along these lines. If I call Invoke() on the scriptblock returned, I get the following error: TwiceAsScriptBlock : Cannot process argument transformation on parameter 's'.

Musaab Al-Okaidi Over a year ago

It worked for me, I'll put a screenshot. What version of powersehll are you running?

Musaab Al-Okaidi Over a year ago

check the updated answer, As you can see when I Invoke the new scriptblock it output the message twice.

Rob Over a year ago

Ok - think I've been staring at this too long. I was trying TwiceAsNewScriptBlock($x).Invoke() - which is why I thought it didn't work. Thanks!

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