Obtener todos los websites de un web application mediante powershell

Add-PSSnapin Microsoft.SharePoint.PowerShell –erroraction SilentlyContinue
$webApplication = Get-SPWebApplication http://url_webApplication
$filePath = "C:\AllSites.txt"
$sites = $webApplication.Sites
foreach ($site in $sites)
{
    foreach ($web in $site.AllWebs)
    {      
        $web.Url | Out-File -FilePath $filePath -Append -Width 256        
    }   
}