PowerShell小技巧之实现文件下载(类wget)

      [string]$UserAgent = "PowerShellWget/$(1.0)"
   )

   Write-Verbose "Downloading '$Uri'"
   $EAP,$ErrorActionPreference = $ErrorActionPreference, "Stop"
   $request = [System.Net.HttpWebRequest]::Create($Uri);
   $ErrorActionPreference = $EAP
   $request.UserAgent = $(
         "{0} (PowerShell {1}; .NET CLR {2}; {3}; http://fuhaijun.com)" -f $UserAgent,
         $(if($Host.Version){$Host.Version}else{"1.0"}),
         [Environment]::Version,
         [Environment]::OSVersion.ToString().Replace("Microsoft Windows ", "Win")
      )

   $Cookies = New-Object System.Net.CookieContainer
   if($SessionVariableName) {
      $Cookies = Get-Variable $SessionVariableName -Scope 1
   }
   $request.CookieContainer = $Cookies
   if($SessionVariableName) {
      Set-Variable $SessionVariableName -Scope 1 -Value $Cookies
   }

   try {
      $res = $request.GetResponse();
   } catch [System.Net.WebException] {
      Write-Error $_.Exception -Category ResourceUnavailable
      return
   } catch {
      Write-Error $_.Exception -Category NotImplemented
      return
   }

   if((Test-Path variable:res) -and $res.StatusCode -eq 200) {
      if($fileName -and !(Split-Path $fileName)) {
         $fileName = Join-Path (Convert-Path (Get-Location -PSProvider "FileSystem")) $fileName
      }
      elseif((!$Passthru -and !$fileName) -or ($fileName -and (Test-Path -PathType "Container" $fileName)))
      {
         [string]$fileName = ([regex]'(?i)filename=(.*)$').Match( $res.Headers["Content-Disposition"] ).Groups[1].Value
         $fileName = $fileName.trim("\/""'")

         $ofs = ""
         $fileName = [Regex]::Replace($fileName, "[$([Regex]::Escape(""$([System.IO.Path]::GetInvalidPathChars())$([IO.Path]::AltDirectorySeparatorChar)$([IO.Path]::DirectorySeparatorChar)""))]", "_")
         $ofs = " "

         if(!$fileName) {
            $fileName = $res.ResponseUri.Segments[-1]