Install and update Lexware Warenwirtschaft premium via GPO startup scripts

lxsetup.ps1

# Install & update Lexware Warenwirtschaft Premium in server/client-setup at startup via GPO startup scripts.
# This should update the Lexware client whenever you update the server, without needing to login to every single
# computer in the domain with Administrator credentials.

# registry persistence path and Lexware setup path
$REG = "HKLM:\Software\myCorp"
$LEX = "\\LEXWARE\lexware_premium_setup"
$APP = "warenwirtschaft premium"

# get current version from payload xml
$payload = [xml]@(cat "$LEX\payload\client_package.xml")
$version = $payload.lxsetuppackages.package.Attributes["requiredversion"].'#text'

# check if version exists
if ($version -eq "") {
	echo "version could not be parsed from $LEX\payload\client_package.xml"
	exit 1
}

# create registry path for persistence if it does not exist
if (!(Test-Path $REG)) {
	echo "create registry path $REG ..."
	New-Item -Path $REG >$null
}

# action to be run
function lxsetup {
	# I would prefer to '-Wait' here but the setup launches the Lexware Info Service and Start-Process
  # won't return until that process is also stopped, since it is a child process.
	Start-Process "$LEX\$APP\LxSetup.exe" -ArgumentList "-automation"
}

# check if registry key exists and is current version
if ((Get-ItemProperty $REG $APP 2>$null) -And ((Get-ItemProperty $REG $APP) -eq $version)) {
	echo "already on current version: $version"
	exit 0
} else {
	# otherwise run setup and save version
	lxsetup
	Set-ItemProperty $REG $APP $version
}