CheckDuplicateDisplayName.ps1

$users = Get-ADUser -Filter * -Properties displayNamePrintable, DisplayName, mail
$displayNamePrintables = $users.displayNamePrintable
$duplicateUsers = $displayNamePrintables | Where-Object {if(($displayNamePrintables -eq $_).count -ge 2){$_}} | Sort-Object | Get-Unique


Write-Output "表示名 `t DisplayNamePrintable `t メールアドレス"
foreach($user in $users)
{
    $duplicateUsers | ForEach-Object {
        if($user.displayNamePrintable -eq $_)
        {
            Write-Output ($user.displayName + "`t" + $user.displayNamePrintable + "`t" + $user.mail)
        }
    }
}