powershell 变量语法 $($a)? [英] powershell variable syntax $($a)?

问题描述

我有一个简单的问题，关于为什么某些事情会以这种方式工作，但我似乎无法轻易找出原因.我试图运行以下命令:

I have a simple question regarding why something works the way it does and I cant seem to readily find out why. I was trying to run the following command:

foreach($a in $list){set-mailboxcalendarpermissions -identity $($a):\calendar

虽然它工作得很好，但我不知道添加 $( ) 实际上做了什么.当我执行 ($a):\calendar 时，它会返回带括号的 (variable):\calendar ，但添加额外的 "$" 可以修复它.为什么?

while it works just fine, I don't know what adding the $( ) actually does. When I do ($a):\calendar it would return (variable):\calendar with the parenthesis, but adding the extra "$" fixes it. why?

感谢大家对这个措辞非常糟糕的问题的帮助.

Thank you all for your help with this terribly worded question.

推荐答案

$() 是一个 子表达式运算符.意思是先评估这个，然后单独做一个独立的陈述".

$() is a subexpression operator. It means "evaluate this first, and do it separately as an independent statement".

大多数情况下，它在您使用内联字符串时使用.说:

Most often, its used when you're using an inline string. Say:

$x = Get-ChildItem C:\;
$x | ForEach-Object {
    Write-Output "The file is $($_.FullName)";
}

比较:

$x = Get-ChildItem C:\;
$x | ForEach-Object {
    Write-Output "The file is $_.FullName";
}

您还可以执行诸如 $($x + $y).ToString() 或 $(Get-Date).AddDays(10) 之类的操作.

You can also do things like $($x + $y).ToString(), or $(Get-Date).AddDays(10).

在这里，如果没有子表达式，您将得到 $a:\calendar.好吧，问题在于变量后面的冒号是运算符.具体来说，范围运算符.为了防止 PowerShell 认为您正在尝试在 a 命名空间中查找变量，作者将该变量放在子表达式中.

Here, without the subexpression, you'd get $a:\calendar. Well, the problem there is that the colon after a variable is an operator. Specifically, the scope operator. To keep PowerShell from thinking you're trying to look for a variable in the a namespace, the author put the variable in a subexpression.

就我过去几年使用 PS 的情况而言，没有美元符号的括号本质上也是子表达式.当在字符串中时，它们不会被评估为子表达式，但否则它们通常会.没有明显区别是一种令人沮丧的怪癖.

As far as I've been able to tell using PS for the past few years, parentheses without the dollar sign are also essentially subexpressions. They won't be evaluated as a subexpression when within a string, but otherwise they usually will. It's kind of a frustrating quirk that there's no clear difference.

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