Piping values to New-Item to create directories in PowerShell - powershell

Question

I've got a directory, C:\temp\test\, containing three DLL's I've called First.dll, Second.dll, Third.dll. I want to create sub-directories named after each of the DLL's.
This is what I've tried so far:
$dirName = "Tenth"
new-item $dirName -ItemType directory
That works. It created a sub-directory called "Tenth".
This also works:
(get-childitem -file).BaseName | select $_
It returns:
First
Second
Third
I've checked the type of the output from that command and it tells me "select $_" is of type System.String.
Now the bit that doesn't work:
(get-childitem -file).BaseName | new-item -Name $_ -ItemType directory
I get the following error repeated three times:
new-item : An item with the specified name C:\temp\test already exists.
At line:1 char:34
+ (get-childitem -file).BaseName | new-item -Name $_ -ItemType directory
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : ResourceExists: (C:\temp\test:String) [New-Item], IOException
+ FullyQualifiedErrorId : DirectoryExist,Microsoft.PowerShell.Commands.NewItemCommand
The current folder I'm executing the commands from is C:\temp\test\ .
I haven't been able to find any similar examples on the Internet to show me where I'm going wrong. Can anyone give me any pointers? Cheers.

Answer 1

Now the bit that doesn't work:
(get-childitem -file).BaseName | new-item -Name $_ -ItemType directory
This way, it works and doesn't need the ForEach-Object:
(dir -file).BaseName|ni -name{$_} -ItemType directory -WhatIf

Answer 2

$_ references each item as it comes along the pipeline so you will need to pipe to ForEach-Object for your line to work, like this:
(get-childitem -file).BaseName | ForEach-Object {new-item -Name $_ -ItemType directory}
This will create the item in the current powershell directory, you can also specify -Path if you want to create the folders somewhere else.
(get-childitem -file).BaseName | ForEach-Object {new-item -Name $_ -Path C:\MyFolder -ItemType directory}

Answer 3

New-Item accepts the parameter -Path to be piped and it can be an array of strings.
Then, you can create an object with a property Path that contains all the needed folders to be created
<#
# a simple array as example,
# but it could be the result of any enumerable,
# such as Get-ChildItem and stuff
#>
$FoldersToCreate = #('a', 'b', 'c')
# creates the folders a, b and c at the current working directory
[PSCustomObject]#{ Path = $FoldersToCreate } | New-Item -ItemType Directory
Or, alternatively :
$FoldersToCreate |
Select-Object #{ name = "Path"; expression = { "c:\testDir\$_" } } |
New-Item -ItemType Directory