param(
    $backupPath = $("You must enter a location to place the backup files")
)

$ver = $host | select version
if ($ver.Version.Major -gt 1)  {$Host.Runspace.ThreadOptions = "ReuseThread"}
Add-PsSnapin Microsoft.SharePoint.PowerShell

$fileDate = get-date -f yyyyMMdd
get-spwebapplication | get-spsite | %{$filePath = $backupPath + $_.URL.Replace("http://", "").Replace("/", "-") + "_" + $fileDate + ".bak" ; backup-spsite -identity $_.URL -path $filePath}

$files = get-childitem -path $backupPath | where{$_.Extension -eq ".bak"}
foreach($file in $files)
{
    if($file.CreationTime -lt (get-date).addDays(-3))
    {
        remove-item $file.FullName -force
    }
}