如何在 PowerShell 命令中使用 cmd 变量?

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英文:

How can i use a cmd variable in a powershell command?

问题

我已经创建了一个简单的 .bat 文件。在这个批处理文件中,我有一个名为 urlExample 的变量,它等于 "example.com"。

在同一个批处理文件中,我想在一个 PowerShell 命令中使用这个变量 urlExample

具体来说,考虑以下代码:

@echo off
set urlExample="example.com";

powershell -ExecutionPolicy Bypass -Command "& {$WebClient = New-Object System.Net.WebClient;$WebClient.DownloadFile($urlExample,"C:\.....somePath")}

如何在 WebClient 命令中使用 urlExample

附注:我不想简单地将 URL 放在 DownloadFile 的第一个参数中。我想使用批处理变量传递它。

英文:

I have created a simple .bat file. In this batch file i have a variable named urlExample which is equal to "example.com".
In the same batch file i want to use this variable urlExample in a powershell command.

Specifically, consider the following code:

@echo off
set urlExample = "example.com"


powershell -ExecutionPolicy Bypass -Command "& {$WebClient = New-Object System.Net.WebClient;$WebClient.DownloadFile($urlExample,"C:\.....somePath")

How could i achieve using the urlExample inside the WebClient command?

P.s. I don't want to simply put the url in the DownloadFile's first argument. I want to pass it with a batch variable.

Thanks in advance

答案1

得分: 3

  • cmd.exe 中,所有 变量也都是 环境 变量,比如你的情况下的 %urlExample%,以及 子进程,比如调用 powershell.exe,Windows PowerShell CLI,会 继承 环境变量。

    • 与此相反,PowerShell 还具有仅限于该会话的 shell(-only) 变量 (例如,$urlExample),而 环境 变量必须通过 env 命名空间访问 (例如,$env:urlExample - 参见概念性的 about_Environment_Variables 帮助主题)。
  • 尽管你可以在 cmd.exe 那一侧使用字符串插值来“嵌入”cmd.exe定义的环境变量的 ,通过将 %urlExample% 嵌入 -Command 参数,但更健壮的方法是让 PowerShell 访问环境变量,通过引用 $env:urlExample

因此:

@echo off

:: 注意:名字和值周围没有空格,使用双引号
set "urlExample=example.com"

:: 注意对 $env:urlExample 的引用
:: 嵌入的双引号字符被转义为 \"
powershell -ExecutionPolicy Bypass -Command "$WebClient = New-Object System.Net.WebClient; $WebClient.DownloadFile($env:urlExample, \"C:\.....somePath\")"

注意:

  • -ExecutionPolicy Bypass 在这种情况下不是绝对必要的,因为这里没有涉及执行脚本 文件 (.ps1) (无论是直接使用 -File 还是间接使用 -Command 参数)。

  • 然而,考虑到在使用 -Command 时(powershell.exe的默认参数),有效的 执行策略 也适用于不太明显的情况,比如(可能是隐式的)加载一个脚本模块(*.psm1)和/或包含格式/类型定义数据(*.ps1xml)的模块 - 使用 -ExecutionPolicy Bypass 是一种良好的习惯,以确保可预测的执行,假设你信任你要调用的代码

  • 正如Compo指出的,确保可预测的执行环境的另一个好习惯是使用 -NoProfile,它绕过了加载 PowerShell 的配置文件。除了防止配置文件对执行环境进行可能不必要/不想要的修改之外,绕过配置文件的加载还可以加快命令的执行速度。

英文:

<!-- language-all: sh -->

  • In cmd.exe, all variables are also environment variables, such as %urlExample% in your case, and child processes - such as a call to powershell.exe, the Windows PowerShell CLI, inherit environment variables.

    • By contrast, PowerShell also has shell(-only) variables (e.g., $urlExample, limited to that session only), whereas environment variables must be accessed via the env namespace (e.g. $env:urlExample - see the conceptual about_Environment_Variables help topic).
  • While you can use string interpolation on the cmd.exe side to "bake in" the values of cmd.exe-defined environment variables, by embedding %urlExample% in the -Command argument, it is more robust to let PowerShell access the environment variable, by referencing $env:urlExample.

Therefore:

@echo off

:: Note: No spaces around &quot;=&quot;, double-quote the name *and* the value.
set &quot;urlExample=example.com&quot;

:: Note the reference to $env:urlExample
:: Embedded &quot; chars. are escaped as \&quot;
powershell -ExecutionPolicy Bypass -Command &quot;$WebClient = New-Object System.Net.WebClient; $WebClient.DownloadFile($env:urlExample, \&quot;C:\.....somePath\&quot;)&quot;

Note:

  • -ExecutionPolicy Bypass isn't strictly needed in this case, given that no execution of a script file is (.ps1) is involved here (whether directly with -File or indirectly, as part of a -Command argument).

  • However, given that the effective execution policy also applies in less obvious scenarios when you use -Command (the default parameter of powershell.exe)<sup>[1]</sup> - such as (possibly implicitly) loading a module that is either a script module (*.psm1) and / or contains formatting / type-definition data (*.ps1xml) - using -ExecutionPolicy Bypass is a good habit to form to ensure predictable execution, assuming that you trust the code you're invoking.

  • As Compo points out, another good habit to form to ensure a predictable execution environment is to use -NoProfile, which bypasses loading of PowerShell's profile files. In addition to preventing potentially unnecessary / unwanted modifications of the execution environment by the profiles, bypassing profile loading also speeds up the command.


<sup>[1] Note that pwsh, the PowerShell (Core) CLI, now defaults to -File.</sup>

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  • 本文由 发表于 2023年2月19日 03:43:25
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