当指定-Force标志时，如果文件夹已经存在，PowerShell将不会报错。

一行程序:

Get-ChildItem D:\TopDirec\SubDirec\Project* | `
  %{ Get-ChildItem $_.FullName -Filter Revision* } | `
  %{ New-Item -ItemType Directory -Force -Path (Join-Path $_.FullName "Reports") }

顺便说一下，要调度任务，请查看这个链接:调度后台任务。

试试-Force参数:

New-Item -ItemType Directory -Force -Path C:\Path\That\May\Or\May\Not\Exist

可以先使用Test-Path -PathType容器进行检查。

请参阅新项目MSDN帮助文章了解更多详细信息。

$path = "C:\temp\NewFolder"
If(!(test-path -PathType container $path))
{
      New-Item -ItemType Directory -Path $path
}

Test-Path -PathType容器检查路径是否存在，是否为目录。如果没有，它将创建一个新目录。如果路径存在但是一个文件，New-Item将引发一个错误(如果您有风险，可以使用-force参数覆盖该文件)。

当指定-Force标志时，如果文件夹已经存在，PowerShell将不会报错。

一行程序:

Get-ChildItem D:\TopDirec\SubDirec\Project* | `
  %{ Get-ChildItem $_.FullName -Filter Revision* } | `
  %{ New-Item -ItemType Directory -Force -Path (Join-Path $_.FullName "Reports") }

顺便说一下，要调度任务，请查看这个链接:调度后台任务。

从你的情况来看，听起来你需要每天创建一个“修订#”文件夹，里面有一个“报告”文件夹。如果是这样的话，你只需要知道下一个版本号是什么。编写一个函数来获取下一个修订号Get-NextRevisionNumber。或者你可以这样做:

foreach($Project in (Get-ChildItem "D:\TopDirec" -Directory)){
    # Select all the Revision folders from the project folder.
    $Revisions = Get-ChildItem "$($Project.Fullname)\Revision*" -Directory

    # The next revision number is just going to be one more than the highest number.
    # You need to cast the string in the first pipeline to an int so Sort-Object works.
    # If you sort it descending the first number will be the biggest so you select that one.
    # Once you have the highest revision number you just add one to it.
    $NextRevision = ($Revisions.Name | Foreach-Object {[int]$_.Replace('Revision','')} | Sort-Object -Descending | Select-Object -First 1)+1

    # Now in this we kill two birds with one stone.
    # It will create the "Reports" folder but it also creates "Revision#" folder too.
    New-Item -Path "$($Project.Fullname)\Revision$NextRevision\Reports" -Type Directory

    # Move on to the next project folder.
    # This untested example loop requires PowerShell version 3.0.
}

PowerShell 3.0安装。

$mWarningColor = 'Red'

<#
.SYNOPSIS
    Creates a new directory. 
.DESCRIPTION
    Creates a new directory. If the directory already exists, the directory will
    not be overwritten. Instead a warning message that the directory already
    exists will be output.
.OUTPUT
    If the directory already exists, the directory will not be overwritten.
    Instead a warning message that the directory already exists will be output.
.EXAMPLE    
    Sal-New-Directory -DirectoryPath '.\output'
#>
function Sal-New-Directory {
    param(
        [parameter(mandatory=$true)]
        [String]
        $DirectoryPath
    )
    $ErrorActionPreference = "Stop"
    try {
        if (!(Test-Path -Path $DirectoryPath -PathType Container)) {

            # Sal-New-Directory is not designed to take multiple 
            # directories. However, we use foreach to supress the native output
            # and substitute with a custom message.
            New-Item -Path $DirectoryPath -ItemType Container | `
              foreach {'Created ' + $_.FullName}
        } else {
            Write-Host "$DirectoryPath already exists and" `
                        "so will not be (re)created." `
                        -ForegroundColor $mWarningColor
        }
    } finally {
        $ErrorActionPreference = "Continue"
    }
}

“Sal”只是我自己的库的一个任意前缀。你可以移除它，或者用你自己的替换它。

另一个例子(放在这里，否则会破坏stackoverflow语法高亮显示):

Sal-New-Directory -DirectoryPath ($mCARootDir + "private\")