我不能在ForEach-Object中使用begin/process/end块？

Question

我有以下代码:

function f()
{
    begin{$count=0}
    process{$count+=10}
    end{$count}
}
1..10|f # OK
1..10|%{
    begin{$count=0}
    process{$count+=10}
    end{$count}
} # Error

第一个"f"调用成功,而%{}块显示错误:

100
% : The script block cannot be invoked because it contains more than one clause. The Invoke() method can only be used on script blocks that contain a single clause.
At D:\Untitled1.ps1:13 char:7
+ 1..10|%{
+       ~~
    + CategoryInfo          : InvalidOperation: (:) [ForEach-Object], PSInvalidOperationException
    + FullyQualifiedErrorId : InvalidOperation,Microsoft.PowerShell.Commands.ForEachObjectCommand

但为什么？ForEach-Object不支持begin/ process/ end块？

Answer 1

ForEach-Object 将各个块作为单独的命名参数.

在你的情况下,那将是:

1..10 |ForEach-Object -Begin {$count=0} -Process {$count+=10} -End {$count}

这在帮助文件中有详细记录 - 来自Get-Help ForEach-Object -Parameter *:

-Begin <ScriptBlock>
    Specifies a script block that runs before processing any input objects.

    Required?                    false
    Position?                    named
    Default value                None
    Accept pipeline input?       false
    Accept wildcard characters?  false


-End <ScriptBlock>
    Specifies a script block that runs after processing all input objects.

    Required?                    false
    Position?                    named
    Default value                None
    Accept pipeline input?       false
    Accept wildcard characters?  false

<# ... #>

-Process <ScriptBlock[]>
    Specifies the operation that is performed on each input object. Enter a script
    block that describes the operation.

    Required?                    true
    Position?                    1
    Default value                None
    Accept pipeline input?       false
    Accept wildcard characters?  false