Untitled

#Grab all devices
Function FetchAllDevices {
    try{
		$listOfDevices = Get-MgDevice -All $true
	}catch{
		Write-Error "Could not fetch devices"
	}
    return $listOfDevices
}

#Add device to target-group
Function AddNewMemberToTargetGroup {
    param(
         [Parameter(Mandatory=$true, Position=0)][Object[]]$device,
		 [Parameter(Mandatory=$true, Position=1)][String]$targetDeviceGroup
    )
	try{
		New-MgGroupMember -GroupId $targetDeviceGroup -DirectoryObjectId $device.Id
		Write-Output "New Member $($device.id) added to DeviceTargetGroup $($targetDeviceGroup)"
	}catch{
		Write-Error "Could not add new member $($device.id) to DeviceTargetGroup $($targetDeviceGroup)"
		Write-Error "Maybe the device is already member of the group"
	}
}

#Main Script
Function Main {
	param(
		 [Parameter(Mandatory=$true, Position=1)][AllowNull()][Object[]]$devicesOfTargetGroup
    )
	try{
		#Grab all devices
		$listOfDevices = FetchAllDevices()
			
		if($listOfDevices){
			foreach ($device in $listOfDevices){
				AddNewMemberToTargetGroup $device <OBJECT_ID of DeviceGroup>
			}
		}		
	}catch{
		Write-Error $_
		Write-Error "Unexpected error!"
	}
}

# IT ALL STARTS HERE
try{
	#Fetch all group-members
	$devicesOfTargetGroup = Get-MgGroupMember -GroupId <OBJECT_ID of DeviceGroup>
	
	Main $devicesOfTargetGroup
}catch{
	Write-Error $_
	Write-Error "Unexpected error!"
	exit
}