PowerShell error: computer name invalid in custom function

Question

I am trying use Read-Host -Prompt to fill out multiple server names and user account names, and then pass those into the invoke-command to complete the task - which is to make someone local admin. I am unable to figure out why PowerShell throws me this error: "One or more computer names are not valid. If you are trying to pass a URI, use the -ConnectionUri parameter, or pass URI objects instead of strings.".

In addition, I am also getting the error:

"Add-LocalGroupMember : Object reference not set to an instance of an object."

Code example below:

if ($OptPrompt -eq 1) { 

    $prompt1 = Read-Host -Prompt 'Test Accounts'

    $prompt1.Split(",")

    $prompt1_1 = Read-Host -Prompt 'Test Servers'

    $prompt1_1.Split(",")

    Invoke-Command -ComputerName $prompt1_1 -ScriptBlock {Add-LocalGroupMember -Group 'Administrators' -Member $Using:prompt1} 

}

More info:

Servers are online

Servers have "-" in them, for example, "Server-22-test"

Servers are responding to ping (hostname and IP address)

Using Invoke-Command on its own works, but not inside the function

There is no firewall or security blocking the account(s) in question

Thank you for your help.

$prompt1_1.Split(",") does not update $prompt1_1. It only outputs the split method result. You need $prompt1_1 = $prompt1_1.Split(",") first. The same applies for $prompt1 = $prompt1.Split(",") — AdminOfThings
– AdminOfThings, Commented Apr 14, 2020 at 20:40
You can make your variables as descriptive as you want, and the guidance, generally, is that you should! I'd rename those variables to $testAccounts and $testServers. Also, @AdminOfThings was right on the money, you need to recommit the variable, like so. $testAccounts = $testAccounts.Split(",") — FoxDeploy
– FoxDeploy, Commented Apr 14, 2020 at 20:48
This has fixed my issue. Also, figured out later that becasue of the .Split(",") I had to enter my server names as is - without quotes - to get the script to work. Something new I learned today. Thank you. — John Doe
– John Doe, Commented Apr 14, 2020 at 22:36

AdminOfThings · Accepted Answer · 2020-04-14 21:02:05Z

It appears that you are expecting $prompt1 and $prompt1_1 to contain comma-delimited names. By using Read-Host to populate the variables, they will be type String. You will need to rely on users to enter the comma separators manually with your code. With that said, executing the .Split() method on a String object does not update the String object. You must either update the variable assignment or pass the method outputs as expressions into Invoke-Command.

# Method 1: Reassigning Variable Before Invoke-Command
if ($OptPrompt -eq 1) { 
    $prompt1 = Read-Host -Prompt 'Test Accounts'
    $prompt1 = $prompt1.Split(",")
    $prompt1_1 = Read-Host -Prompt 'Test Servers'
    $prompt1_1 = $prompt1_1.Split(",")
    Invoke-Command -ComputerName $prompt1_1 -ScriptBlock {Add-LocalGroupMember -Group 'Administrators' -Member $Using:prompt1} 
}


# Method 2: Passing Expressions into Invoke-Command
if ($OptPrompt -eq 1) { 
    $prompt1 = Read-Host -Prompt 'Test Accounts'
    $prompt1_1 = Read-Host -Prompt 'Test Servers'
    Invoke-Command -ComputerName $prompt1_1.Split(",") -ScriptBlock {Add-LocalGroupMember -Group 'Administrators' -Member ($using:prompt1).Split(",") } 
}

The advantage of using expressions is your original variables remain unchanged.

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