对于PowerShell cmdlet，是否可以始终将脚本块传递给字符串参数?

问题描述

我正在查看Rename-Item的文档，并且有一个这样的示例.

I'm looking at the document of Rename-Item and there is an example like this.

PS C:\>Get-ChildItem *.txt | Rename-Item -NewName { $_.name -Replace '\.txt','.log' }

此命令将当前目录中的所有.txt文件重命名为 .log.

This command renames all of the .txt files in the current directory to .log.

该命令使用Get-ChildItem cmdlet来获取其中的所有文件 具有.txt文件扩展名的当前文件夹.然后呢 使用管道运算符(|)将这些文件发送到Rename-Item.

The command uses the Get-ChildItem cmdlet to get all of the files in the current folder that have a .txt file name extension. Then, it uses the pipeline operator (|) to send those files to Rename-Item .

NewName的值是一个脚本块，该脚本块在该值之前运行 提交给NewName参数.

The value of NewName is a script block that runs before the value is submitted to the NewName parameter.

注意最后一句话:

NewName的值是一个脚本块，该脚本块在将值提交给NewName参数之前运行.

The value of NewName is a script block that runs before the value is submitted to the NewName parameter.

实际上NewName是字符串:

[-NewName] <String>

那么这是否意味着当所需的参数类型为字符串时，我总是可以使用脚本块吗?

So does that means I can always use a script block when the required parameter type is a string?

推荐答案

延迟绑定脚本块参数是 隐式 >功能:

Delay-bind script-block arguments are an implicit feature that:

• 仅与旨在接受管道输入的参数一起使用 ，

• only works with parameters that are designed to take pipeline input,

• 任何类型的除了以下，在这种情况下会发生常规参数绑定，这意味着您不能直接修改调用者的变量，例如在输入对象之间增加计数器.
  解决方法是，使用在调用方作用域中声明的[ref]类型变量，并在脚本块内访问其.Value属性-请参见这个答案为例.

  Note: Unlike script blocks passed to ForEach-Object or Where-Object, for example, delay-bind script blocks run in a child variable scope, which means that you cannot directly modify the caller's variables, such as incrementing a counter across input objects.
  As a workaround, use a [ref]-typed variable declared in the caller's scope and access its .Value property inside the script block - see this answer for an example.

  [1]错误条件:

  • 如果您错误地尝试将脚本块传递给不是管道绑定或[scriptblock]-或[object]类型(未键入)的参数， 常规参数绑定:

  • If you mistakenly attempt to pass a script block to a parameter that is either not pipeline-binding or is [scriptblock]- or [object]-typed (untyped), regular parameter-binding occurs:

  • 在流水线输入处理开始之前(如果有的话)在一次中传递脚本块.
    也就是说，脚本块作为(可能是转换的)值传递，并且没有评估发生.
    • 对于类型为[object]或[scriptblock]的参数/可以转换为脚本块的委托类型(例如System.Func)，脚本块将按原样绑定 .
    • 对于(非管道绑定)[string]类型的参数，脚本块的文字内容作为字符串值传递.
    • 对于所有其他类型，参数绑定(以及整个命令)将简单地失败，因为无法从脚本块进行转换.
    • The script block is passed once, before pipeline-input processing begins, if any.
      That is, the script block is passed as a (possibly converted) value, and no evaluation happens.
      • For parameters of type [object] or [scriptblock] / a delegate type such as System.Func that is convertible to a script block, the script block will bind as-is.
      • In the case of a (non-pipeline-binding) [string]-typed parameter, the script block's literal contents is passed as the string value.
      • For all other types, parameter binding - and therefore the command as a whole - will simply fail, since conversion from a script block is not possible.

      如果您忽略提供管道输入，而将延迟绑定脚本块传递给支持的管道绑定参数，则会得到以下错误:

      If you neglect to provide pipeline input while passing a delay-bind script block to a pipeline-binding parameter that does support them, you'll get the following error:

      • Cannot evaluate parameter '<name>' because its argument is specified as a script block and there is no input. A script block cannot be evaluated without input.

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