Relaunching PowerShell script as admin user - powershell

Question

I have a quite a few computer systems which we need to deploy software. I've been using a simple method for detecting if a user is a local admin, then detecting if they have admin rights. If needed, the script relaunches with elevated privileges. If the user is not a local admin, the script relaunches using a different credentials (local admin). The script works great on systems which have a later version of PowerShell such as Windows 8 and Windows 10.
The problem is when the user is not an admin and the script is running on Windows 7. The script uses $PSScriptPath to relaunch the script. I don't think this works in earlier versions of PowerShell. So I tried setting $PSScriptRoot myself if the Major PowerShell version is < 3. The problem is then the script gets stuck in a loop of some sort where it just constantly opens and closes windows and then I have to kill it... If I don't define $PSScriptRoot I get the error
Cannot bind argument to parameter 'Path' because it is null
I assume this is because $PSScriptRoot isn't defined in PowerShell 2.0.
Here's an example of what I'm trying to do:
#Check if PowerShell version is greater than 2. If not, set $PSSriptRoot.
if ($PSVersionTable.PSVersion.Major -lt 3) {
$PSScriptRoot = Split-Path -Parent $MyInvocation.MyCommand.Definition
}
#Check if the user is a local admin. If they are, set $LocalAdmin to $True.
$LocalAdmin = $false
if ((net localgroup administrators) -match ([System.Environment]::UserDomainName + "\\" + [System.Environment]::Username)) {
$LocalAdmin = $true
}
if ($LocalAdmin) {
#Check if the local admin needs to run the script as administrator
if (-not ([Security.Principal.WindowsPrincipal][Security.Principal.WindowsIdentity]::GetCurrent()).IsInRole([Security.Principal.WindowsBuiltInRole] "Administrator")) {
$arguments = "& '" + $MyInvocation.MyCommand.Definition + "'"
Start-Process powershell -Verb runas -ArgumentList $arguments
break
}
} else {
#Not a local admin. Relaunch script as admin user.
Start-Process -Credential $credential (Join-Path $PSHome powershell.exe) -ArgumentList (#("-File",
(Join-Path $PSScriptRoot $MyInvocation.MyCommand)) + $args)
exit
}

Answer 1

Don't re-define automatic variables. Nothing good will come of it.
Besides, why do you want to anyway? The only thing you use $PSScriptRoot for is to reconstruct the script path you already have. Just assign that path to a variable and use that in your script.
$script = $MyInvocation.MyCommand.Definition
$ps = Join-Path $PSHome 'powershell.exe'
$isLocalAdmin = [bool]((net localgroup administrators) -match "$env:USERDOMAIN\\$env:USERNAME")
if ($isLocalAdmin) {
if (-not ([Security.Principal.WindowsPrincipal][Security.Principal.WindowsIdentity]::GetCurrent()).IsInRole([Security.Principal.WindowsBuiltInRole]'Administrator')) {
Start-Process $ps -Verb runas -ArgumentList "& '$script'"
exit
}
} else {
Start-Process $ps -ArgumentList (#('-File', $script) + $args) -Credential $credential
exit
}