PowerShell实现文件下载(类wget)

对Linux熟悉的读者可能会对Linux通过wget下载文件有印象，这个工具功能很强大，在.NET环境下提到下载文件大多数人熟悉的是通过System.Net.WebClient进行下载，这个程序集能实现下载的功能，但是有缺陷，如果碰上类似于.../scripts/?dl=417这类的下载链接将无法正确识别文件名，下载的文件通常会被命名为dl=417这样古怪的名字，其实对应的文件名是在访问这个链接返回结果的HTTP头中包含的。事实上微软也提供了避免这些缺陷的程序集System.Net.HttpWebRequest 和 HttpWebResponse，本文将会使用这两个程序集来实现PowerShell版wget的功能。

代码不怎么复杂，基本上就是创建HttpWebRequest对象，设定UserAgent和CookieContainer以免在遇到设置防盗链的服务器出现无法下载的情况。然后通过HttpWebRequest对象的GetResponse()方法从http头中获取目标文件的大小以及文件名，以便能在下载到文件时提示当前下载进度，在下载完文件后，列出当前目录下对应的文件。代码不复杂，有任何疑问的读者可以留言给我，进行交流，下面上代码：

=====文件名：Get-WebFile.ps1===== function Get-WebFile { <# Author:fuhj(powershell#live.cn ,http://fuhaijun.com) Downloads a file or page from the web .Example Get-WebFile http://mirrors.cnnic.cn/apache/couchdb/binary/win/1.4.0/setup-couchdb-1.4.0_R16B01.exe Downloads the latest version of this file to the current directory #> [CmdletBinding(DefaultParameterSetName="NoCredentials")] param( # The URL of the file/page to download [Parameter(Mandatory=$true,Position=0)] [System.Uri][Alias("Url")]$Uri # = (Read-Host "The URL to download") , # A Path to save the downloaded content. [string]$FileName , # Leave the file unblocked instead of blocked [Switch]$Unblocked , # Rather than saving the downloaded content to a file, output it. # This is for text documents like web pages and rss feeds, and allows you to avoid temporarily caching the text in a file. [switch]$Passthru , # Supresses the Write-Progress during download [switch]$Quiet , # The name of a variable to store the session (cookies) in [String]$SessionVariableName , # Text to include at the front of the UserAgent string [string]$UserAgent = "PowerShellWget/$(1.0)" ) Write-Verbose "Downloading &#39;$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]'&#40;?i)filename=(.*)$').Match( $res.Headers["Content-Disposition"] ).Groups[1].Value $fileName = $fileName.trim("&#92;/""'") $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] $fileName = $fileName.trim("\/") if(!$fileName) { $fileName = Read-Host "Please provide a file name" } $fileName = $fileName.trim("\/") if(!([IO.FileInfo]$fileName).Extension) { $fileName = $fileName + "." + $res.ContentType.Split(";")[0].Split("/")[1] } } $fileName = Join-Path (Convert-Path (Get-Location -PSProvider "FileSystem")) $fileName } if($Passthru) { $encoding = [System.Text.Encoding]::GetEncoding( $res.CharacterSet ) [string]$output = "" } [int]$goal = $res.ContentLength $reader = $res.GetResponseStream() if($fileName) { try { $writer = new-object System.IO.FileStream $fileName, "Create" } catch { Write-Error $_.Exception -Category WriteError return } } [byte[]]$buffer = new-object byte[] 4096 [int]$total = [int]$count = 0 do { $count = $reader.Read($buffer, 0, $buffer.Length); if($fileName) { $writer.Write($buffer, 0, $count); } if($Passthru){ $output += $encoding.GetString($buffer,0,$count) } elseif(!$quiet) { $total += $count if($goal -gt 0) { Write-Progress "Downloading $Uri" "Saving $total of $goal" -id 0 -percentComplete (($total/$goal)*100) } else { Write-Progress "Downloading $Uri" "Saving $total bytes..." -id 0 } } } while ($count -gt 0) $reader.Close() if($fileName) { $writer.Flush() $writer.Close() } if($Passthru){ $output } } if(Test-Path variable:res) { $res.Close(); } if($fileName) { ls $fileName } }

调用方法，如下：

Get-WebFile http://mirrors.cnnic.cn/apache/couchdb/binary/win/1.4.0/setup-couchdb-1.4.0_R16B01.exe

这里下载couchdb的最新windows安装包。

执行效果如下图所示：

能够看到在下载文件的过程中会显示当前已下载数和总的文件大小，并且有进度条显示当前下载的进度，跟wget看起来是有些神似了。下载完毕后会显示已经下载文件的情况。

作者: 付海军
出处：http://fuhj02.blog.51cto.com
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