Running a function error

Question

I am getting the following error when I run the function below:

Invoke-Command : Cannot validate argument on parameter 'ComputerName'. The argument is null or empty. Supply an argument that is not null or empty and then try the command again. At C:\Users\usernameone\Desktop\script.ps1:16 char:29 + Invoke-Command -ComputerName <<<< $_ -ScriptBlock $s -Credential $cred + CategoryInfo : InvalidData: (:) [Invoke-Command], ParameterBindingValidationException + FullyQualifiedErrorId : ParameterArgumentValidationError,Microsoft.PowerShell.Commands.InvokeCommandCommand

$username = "username"
$password = "password"
$secstr = New-Object -TypeName System.Security.SecureString
$password.ToCharArray() | ForEach-Object {$secstr.AppendChar($_)}
$cred = new-object -typename System.Management.Automation.PSCredential -argumentlist $username,    $secstr
$_="192.168.10.4"

function test{
    $s = $ExecutionContext.InvokeCommand.NewScriptBlock("mkdir C:\'Documents and    Settings'\username\Desktop\Testfolder")
    Invoke-Command -ComputerName $_ -ScriptBlock $s -Credential $cred 
}

Do you have any ideas as to what I've done wrong?

$_ is not defined in your function. Use a function parameter. — algorhythm
– algorhythm, Commented Oct 20, 2014 at 16:30
I just want to run the function without entering parameters.. So i just want to type the function name test! and would like to execute the command and make a new directory on the remote computer. — Jendizer
– Jendizer, Commented Oct 20, 2014 at 16:59

x0n · Accepted Answer · 2014-10-20 16:28:56Z

1

The special variable $_ is only populated when the function or scriptblock containing it is involved in an active pipeline. It should work if you invoke test like this:

PS> "computername" | test

Follow?

As an aside, why are you creating a scriptblock in that awkward fashion? Use literal syntax:

$s = { mkdir 'c:\...\blah' }

If you want to create scriptblocks programmatically from text, there's an easier way:

$s = [scriptblock]::create('...')

Don't forget to use single quotes if you don't want references to variables to be resolved before the scriptblock is parsed.

answered Oct 20, 2014 at 16:28

x0n

52.6k8 gold badges97 silver badges116 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Jendizer Over a year ago

it does not work! I am still getting the same error :S..I just typed "computername" | test within the console in powershell ISE and i received the same error.. Sorry i am new to powershell

Paul Over a year ago

thats because your function does not use pipeline input, you should eiter work with parameters, hardcode your values or read up on the basics first

Community · Accepted Answer · 2017-05-23 12:11:42Z

Rename your variable $_ and it will work...

Explanation:

$_ is "reserved" for the current value in an iteration e.g. foreach or a pipeline. See here: What does $_ mean in PowerShell?

If you call your function as @x0n said, then it could make sense. If you want your function to create a folder everytime on the same machine, then don't use a variable. But if you want your function to create the folder on different machines your function should know on which computer you want the folder. That is normally done with a function parameter.

[...]
$ipaddress = "192.168.10.4";

function test([string]$ip, [System.Management.Automation.PSCredential]$credentials) {
    $s = $ExecutionContext.InvokeCommand.NewScriptBlock("mkdir C:\'Documents and    Settings'\username\Desktop\Testfolder");
    Invoke-Command -ComputerName $ip -ScriptBlock $s -Credential $credentials;
}

// then call it like this
test $ipaddress $cred;

Here is a list of all those reserved things: http://www.neolisk.com/techblog/powershell-specialcharactersandtokens

Collectives™ on Stack Overflow

Running a function error

2 Answers 2

2 Comments

Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Linked

Related