Function providing missing -Recurse parameter for Get-DistributionGroup.

Get-DistributionGroupRecursive.ps1

function Get-DistributionGroupRecursive {
  <#
      .SYNOPSIS
      Function providing missing -Recurse parameter for Get-DistributionGroup.

      .DESCRIPTION
      Takes an identity string and returns the matching distribution group and any nested groups beneath it.
      Only distribution groups are returned, not mailboxes, etc.

      .EXAMPLE
      Get-DistributionGroupRecursive "My Distribution Group"

      .EXAMPLE
      Get-DistributionGroupRecursive "mydistributiongroup@example.org"
  #>
  Param (
    [Parameter(Mandatory=$true, Position=0)][string[]]$Identity,
    [Parameter(Mandatory=$false, DontShow)][string[]]$LastResults,
    [Parameter(Mandatory=$false, DontShow)][switch]$ChildSearch = $false
  )

  $Condition = { $_.RecipientType -eq "MailUniversalDistributionGroup" -and $LastResults -notcontains $_ }
  $Identity | ForEach-Object {
    if ($ChildSearch) {
      $Results = Get-DistributionGroupMember -Identity $_ -ResultSize Unlimited | Where-Object $Condition | Get-DistributionGroup
    } else {
      $Results = Get-DistributionGroup -Identity $_ -ResultSize Unlimited | Where-Object $Condition
    }
    if (($Results | Measure-Object).Count -gt 0) {
      $Results
      Get-DistributionGroupRecursive -Identity $Results.Name -LastResults ($LastResults + $Results.Name) -ChildSearch
    }
  }
}