Compare two list and find names that are in list one and not list two using powershell
I assume $FolderList and $AdUserName are arrays of strings? You don't really need Compare-Object to compare arrays. It's as simple as this:
$FolderList | ?{$AdUserName -notcontains $_}
Compare-Object is for comparing the specified properties of collections of objects with common properties. You could do this with Compare-Object if you really want, like this:
Compare-Object $FolderList $AdUserName | ?{$_.SideIndicator -eq '<='} | Select-Object -ExpandProperty InputObjectBut as you can see, it's overkill for this task.
To output the result to another variable, simply assign it:
$AnotherVariable = $FolderList | ?{$AdUserName -notcontains $_}