powershell - 变量在不应该发生变化时发生变化

Question

我有一个非常简单的 PS 脚本设置为采用 3 个参数(远程 HTTP 文件、本地复制路径、所需文件的过滤器列表)，然后下载请求的文件。我正在使用 System.Net.WebClient和方法DownloadFile .我目前面临一个非常奇怪的错误:

Exception calling "DownloadFile" with "2" argument(s): "Could not find a part of the path 'C:\Users\lrichards\Desktop\US-LMI\PowerShell\BLS_Downloads\download.bls.gov\pub\time.series\la\la.area_type'." At C:\Users\lrichards\Desktop\US-LMI\PowerShell\BLS_Downloads\HTTP_based_downloader.ps1:45 char:13 + $wc.DownloadFile($sourceFile, $targetFile); + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + CategoryInfo : NotSpecified: (:) [], MethodInvocationException + FullyQualifiedErrorId : WebException

但是如果我 Write-Host在调用下载文件之前和之后，目标路径是有效的。当我调试该行时，它确实具有正确的路径。

正确的值应该是:

C:\Users\lrichards\Desktop\US-LMI\PowerShell\BLS_Downloads\la\la.area_type

但它正在某处更改为:

C:\Users\lrichards\Desktop\US-LMI\PowerShell\BLS_Downloads\download.bls.gov\pub\time.series\la\la.area_type

$sourceFile设定为:

download.bls.gov/pub/time.series/la/la.area_type

这是违规行:

$wc.DownloadFile($sourceFile, $targetFile);

完整代码:

param(
    # Required. Download source location (website).
     [Parameter(Mandatory=$True)]
     [string] $URL,
    # Required. Download target location (local drive).
     [Parameter(Mandatory=$True)]
     [string] $destinationFolder,
    # Required. File containing list of files to download. Must exist in same location as this script.
     [Parameter(Mandatory=$True)]
     [string] $fileList
)

process
{
    # Setup params
    if (!($destinationFolder.EndsWith("\"))) {
        $destinationFolder = $destinationFolder + "\";
    }

    if (!($URL.EndsWith("/"))) {
        $URL = $URL + "/";
    }

    # Get root domain for use in determining $soureFile
    [uri]$URL = $URL;
    $baseURL = $URL.Authority;

    # Get list of files requested from filter list file.
    $filesRequested =  gc $fileList;

    # Set up the web client for downloading the files.
    $wc = New-Object System.Net.WebClient;

    # Get list of files available at $URL
    $fileItems = Invoke-WebRequest -uri $URL | select -expand links | select -expand href;

    # Loop through list of available files and find matches in filter list.
    $fileItems | foreach {
        if ($filesRequested.Contains((split-path $_ -Leaf))) {        
            $sourceFile = $baseURL + $_;
            $targetFile = $destinationFolder + (split-path $_ -Leaf);
            Write-Host $sourceFile;
            Write-Host $targetFile;
            #Write-Host "Getting: "$sourceFile "Destination: "$targetFile;
            $wc.DownloadFile($sourceFile, $targetFile);
        }
    }
}

我是这样称呼它的:

.\HTTP_based_downloader.ps1 "http://download.bls.gov/pub/time.series/la/" "C:\Users\lrichards\Desktop\US-LMI\PowerShell\BLS_Downloads\la\" "la-file-list.txt"

la-file-list.txt的内容:

la.area la.area_type la.contacts

Answer 1

该错误是由无效的源路径引起的。$url.Authority value 不包含协议(protocol)名称，这使 value 成为字符串而不是 URI。

这使得 webclient 使用 DownloadFile(string,string)使用相对本地路径而不是 Downloadfile(uri,string) 作为源重载.上述脚本的解决方案类似于:

$baseurl = "$($URL.Scheme)://$($URL.Authority)"