如何在 PowerShell 中退出 ForEach-Object [英] How to exit from ForEach-Object in PowerShell

问题描述

我有以下代码:

$project.PropertyGroup | Foreach-Object {
    if($_.GetAttribute('Condition').Trim() -eq $propertyGroupConditionName.Trim()) {
        $a = $project.RemoveChild($_);
        Write-Host $_.GetAttribute('Condition')"has been removed.";
    }
};

问题 1:如何退出 ForEach-Object?我尝试使用break"和继续"，但它不起作用.

Question #1: How do I exit from ForEach-Object? I tried using "break" and "continue", but it doesn't work.

问题 #2:我发现我可以在 foreach 循环中更改列表...我们不能像在 C# 中那样做...为什么 PowerShell 允许我们这样做?

Question #2: I found that I can alter the list within a foreach loop... We can't do it like that in C#... Why does PowerShell allow us to do that?

推荐答案

首先，Foreach-Object 不是一个实际的循环并调用 break 将取消整个脚本而不是跳到它后面的语句.

First of all, Foreach-Object is not an actual loop and calling break in it will cancel the whole script rather than skipping to the statement after it.

相反，break 和 continue 将在实际的 foreach 循环中按预期工作.

Conversely, break and continue will work as you expect in an actual foreach loop.

项目#1.在 foreach 循环中放置一个 break 确实会退出循环，但不会停止管道.听起来你想要这样的东西:

Item #1. Putting a break within the foreach loop does exit the loop, but it does not stop the pipeline. It sounds like you want something like this:

$todo=$project.PropertyGroup 
foreach ($thing in $todo){
    if ($thing -eq 'some_condition'){
        break
    }
}

第 2 项.PowerShell 允许您在该数组的 foreach 循环内修改该数组，但这些更改在您退出循环之前不会生效.尝试运行以下代码作为示例.

Item #2. PowerShell lets you modify an array within a foreach loop over that array, but those changes do not take effect until you exit the loop. Try running the code below for an example.

$a=1,2,3
foreach ($value in $a){
  Write-Host $value
}
Write-Host $a

我无法评论为什么 PowerShell 的作者允许这样做，但大多数其他脚本语言 (Perl、Python 和 shell)允许类似的结构.

I can't comment on why the authors of PowerShell allowed this, but most other scripting languages (Perl, Python and shell) allow similar constructs.

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