PowerShell arguments or Parameters

Question

I have a script to rename computers on my network. I am trying to change it so that I can enter a current name and new name for the machine as an argument or parameter (which ever makes sense in this case.) Also I would like the script to check for the argument and if it does not exist import a CSV file.

This is what I came up with and it is not working. The param appear to be empty from the console output but the IF statement runs as if they are not.

param (
    $o = "oldname",
    $n = "newname"
)

if(!($o = $null)){
    if(!($n = $null)){
        Write-Host "Renaming computer from: $o to: $n"
        netdom renamecomputer $o /newName:$n /uD:domain\user /passwordD:* /force /reboot
    }
}else{
    Write-Host "Importing Computers from CSV file"
    $csvfile = "C:\Sysinternals\rename.csv"
    Import-Csv $csvfile | foreach { 
        $oldName = $_.OldName;
        $newName = $_.NewName;

        Write-Host "Renaming computer from: $oldName to: $newName"
        netdom renamecomputer $oldName /newName:$newName /uD:domain\username /passwordD:* /force /reboot
    }
}

This is very nearly an ideal case for the use of [CmdletBinding()] and [Parameter(Mandatory=$true)] or [Parameter(ValueFromPipeline=$true)]. See About_Functions_Advanced_Parameters for more information. (You can also get this information with Get-Help about_Functions_Advanced_Parameters in a Powershell console or the ISE.) — Jeff Zeitlin
– Jeff Zeitlin, Commented Jan 31, 2017 at 13:10
@JeffZeitlin His script is importing the new and the oldname from a csv in case the parameters are not specified. Why should he use the mandatory or valuefrompipeline attribute? — Martin Brandl
– Martin Brandl, Commented Jan 31, 2017 at 13:20
@MartinBrandl - Point taken. I'd actually end up rewriting this in one of two ways: (1) Two parameter sets - one for when I supply a computer name, and one when I want to import them from a file, or (2) ValueFromPipeline and then call it using Import-CSV $csvfile | This-Script. It ends up more flexible (I'm not locked to a particular CSV file name), and the code probably ends up easier to debug - to the extent that any debugging would be necessary in the first place. — Jeff Zeitlin
– Jeff Zeitlin, Commented Jan 31, 2017 at 13:35
@JeffZeitlin Agree, that would be a better function instead of magically doing it in the script. — Martin Brandl
– Martin Brandl, Commented Jan 31, 2017 at 13:43

Martin Brandl · Accepted Answer · 2017-01-31 13:21:30Z

3

You are assigning $o and $n to $null in your if statement - instead of comparing it. You can check whether $o is null like this:

if($o) 
{
}

But since you are comparing a string, you probably want to check whether the string is null or empty using the static [string]::IsNullOrEmptymethod. So your refactored code could look like this:

param (
    $o = "oldname",
    $n = "newname"
)

if ([string]::IsNullOrEmpty($o) -or [string]::IsNullOrEmpty($n))
{
    Write-Host "Importing Computers from CSV file"
    $csvfile = "C:\Sysinternals\rename.csv"
    Import-Csv $csvfile | foreach { 
        $oldName = $_.OldName;
        $newName = $_.NewName;

        Write-Host "Renaming computer from: $oldName to: $newName"
        netdom renamecomputer $oldName /newName:$newName /uD:domain\username /passwordD:* /force /reboot
    }
}
else
{
    Write-Host "Renaming computer from: $o to: $n"
    netdom renamecomputer $o /newName:$n /uD:domain\user /passwordD:* /force /reboot
}

edited Jan 31, 2017 at 13:21

answered Jan 31, 2017 at 13:06

Martin Brandl

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2 Comments

Joe Clark Over a year ago

if wanted to add the password as a parameter. would i just add a $password to the top of the param list?

Martin Brandl Over a year ago

sure you can do that.

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