PowerShell function to find all nested members of an Active Directory group.

function Get-ADNestedGroupMembers {
<#
.SYNOPSIS

Author: Piotr Lewandowski
Version: 1.01 (04.08.2015) - added displayname to the output, changed name to
samaccountname in case of user objects.

.DESCRIPTION

Get nested group membership from a given group or a number of groups.

Function enumerates members of a given AD group recursively along with nesting
level and parent group information. It also displays if each user account is
enabled.

When used with an -indent switch, it will display only names, but in a more
user-friendly way (sort of a tree view)

.EXAMPLE

Get-ADNestedGroupMembers "MyGroup" | Export-CSV .\NedstedMembers.csv -NoTypeInformation

.EXAMPLE

Get-ADGroup "MyGroup" | Get-ADNestedGroupMembers | ft -autosize

.EXAMPLE

Get-ADNestedGroupMembers "MyGroup" -indent

#>
param (
    [Parameter(ValuefromPipeline=$true,
    mandatory=$true)][String] $GroupName,
    [int] $nesting = -1,
    [int]$circular = $null,
    [switch]$indent
)

function indent
{
    Param($list)
    foreach($line in $list)
    {
        $space = $null
        for ($i=0;$i -lt $line.nesting;$i++)
        {
            $space += "    "
        }
        $line.name = "$space" + "$($line.name)"
    }
    return $List
}

$modules = get-module | select -expand name
    if ($modules -contains "ActiveDirectory")
    {
        $table = $null
        $nestedmembers = $null
        $adgroupname = $null
        $nesting++
        $ADGroupname = get-adgroup $groupname -properties memberof,members
        $memberof = $adgroupname | select -expand memberof
        write-verbose "Checking group: $($adgroupname.name)"
        if ($adgroupname)
        {
            if ($circular)
            {
                $nestedMembers = Get-ADGroupMember -Identity $GroupName -recursive
                $circular = $null
            }
            else
            {
                $nestedMembers = Get-ADGroupMember -Identity $GroupName | sort objectclass -Descending
                if (!($nestedmembers))
                {
                    $unknown = $ADGroupname | select -expand members
                    if ($unknown)
                    {
                        $nestedmembers=@()
                        foreach ($member in $unknown)
                        {
                        $nestedmembers += get-adobject $member
                        }
                    }
                }
            }

            foreach ($nestedmember in $nestedmembers)
            {
                $Props = @{Type=$nestedmember.objectclass;Name=$nestedmember.name;DisplayName="";ParentGroup=$ADgroupname.name;Enabled="";Nesting=$nesting;DN=$nestedmember.distinguishedname;Comment=""}

                if ($nestedmember.objectclass -eq "user")
                {
                    $nestedADMember = get-aduser $nestedmember -properties enabled,displayname
                    $table = new-object psobject -property $props
                    $table.enabled = $nestedadmember.enabled
                    $table.name = $nestedadmember.samaccountname
                    $table.displayname = $nestedadmember.displayname
                    if ($indent)
                    {
                        indent $table | select @{N="Name";E={"$($_.name)  ($($_.displayname))"}}
                    }
                    else
                    {
                        $table | select type,name,displayname,parentgroup,nesting,enabled,dn,comment
                    }
                }
                elseif ($nestedmember.objectclass -eq "group")
                {
                    $table = new-object psobject -Property $props

                    if ($memberof -contains $nestedmember.distinguishedname)
                    {
                        $table.comment ="Circular membership"
                        $circular = 1
                    }
                    if ($indent)
                    {
                        indent $table | select name,comment | %{
                        if ($_.comment -ne "")
                        {
                            [console]::foregroundcolor = "red"
                            write-output "$($_.name) (Circular Membership)"
                            [console]::ResetColor()
                        }
                        else
                        {
                            [console]::foregroundcolor = "yellow"
                            write-output "$($_.name)"
                            [console]::ResetColor()
                        }
                    }
                    }
                    else
                    {
                        $table | select type,name,displayname,parentgroup,nesting,enabled,dn,comment
                    }
                    if ($indent)
                    {
                        Get-ADNestedGroupMembers -GroupName $nestedmember.distinguishedName -nesting $nesting -circular $circular -indent
                    }
                    else
                    {
                        Get-ADNestedGroupMembers -GroupName $nestedmember.distinguishedName -nesting $nesting -circular $circular
                    }
               }
                else
                {
                    if ($nestedmember)
                    {
                        $table = new-object psobject -property $props

                        if ($indent)
                        {
                            indent $table | select name
                        }
                        else
                        {
                            $table | select type,name,displayname,parentgroup,nesting,enabled,dn,comment
                        }
                    }
                }
            }
        }
    }
    else
    {
        Write-Warning "Active Directory module is not loaded"
    }
}