How to list Resource Groups across Azure Subscriptions using PowerShell?

Question

I'm writing a PowerShell script to list Resource Groups across Azure Subscriptions.

Get-AzureRmSubscription | 
select -ExpandProperty name |
 % { 
     Get-AzureRmResourceGroup | select -ExpandProperty resourcegroupname
 }

This code works. It returns results like this.

Resource group 1     
Resource group 2
Resource group 3 

How can I tweak the code to get the output like below?

Subscription 1,Resource group 1     
Subscription 1,Resource group 2
Subscription 2,Resource group 3 

Thank you so much.

Answer 1

Untested:

Get-AzureRmSubscription | 
 % { 
   $subscrName = $_.Name
   Select-AzureSubscription -Current -SubscriptionName $name
   (Get-AzureRmResourceGroup).resourcegroupname | % {     
     [pscustomobject] @{
       Subscription = $subscrName
       ResourceGroup = $_
     }
   }
 }

^{Note: The above changes the session's current subscription. In your real code you may want to restore the previously current one afterwards.}

The above outputs custom objects with .Subscription and .ResourceGroup properties; if you really only want to output strings, use:
"$name,$_"

Answer 2

Adding to @mklement's great answer, here is how you would do it with the latest Azure PowerShell Az module instead of AzureRM:

Get-AzSubscription | ForEach-Object {
    $subscriptionName = $_.Name
    Set-AzContext -SubscriptionId $_.SubscriptionId
    (Get-AzResourceGroup).ResourceGroupName | ForEach-Object {     
        [PSCustomObject] @{
            Subscription = $subscriptionName
            ResourceGroup = $_
        }
    }
}

To change to the active subscription, we can change the context with Set-AzContext, and pass the SubscriptionId From Get-AzSubscription. Should also be able to get away with passing the subscription name with Set-AzContext -Subscription $subscriptionName.

If you want to run AzureRM commands with the Az module, you can run Enable-AzureRmAlias, which allows you to use the AzureRM prefixes with Az modules.