PowerShell New-Item Positional Parameter Oddities

Question

Given the Microsoft documentation for PowerShell, I can see no reason why the following code should fail with the given error. Then again, PowerShell can fail when a script just gets too long. All the paths are double-quote strings.

##### ALGORITHM Take in keystore path, make a backup in an adjacent directory
$ksPath = $java_store_path.Substring(0, $java_store_path.LastIndexOf('\') + 1)
$backupPath = $ksPath + "backups"
New-Item $backupPath PowerShell -type directory -force

New-Item : A positional parameter cannot be found that accepts argument 'PowerShell'.

https://technet.microsoft.com/en-us/library/ee176914.aspx

New-Item c:\scripts\Windows PowerShell -type directory

If that's valid, mine should be too. I'm running on Server 2012 R2.

Answer 1

The example on that page is just plain wrong. It seems they meant to refer to the path C:\\Scripts\\WindowsPowerShell or they forgot to quote the directory with spaces in it.

So it should have been one of these:

New-Item c:\scripts\WindowsPowerShell -type directory
New-Item 'c:\scripts\Windows PowerShell' -type directory
New-Item "c:\scripts\Windows PowerShell" -type directory

Ask yourself, what would PowerShell alone have been referring to? What parameter would it have corresponded to?

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Edit: as the commenters have pointed out, the example was supposed to show the nameSet parameters, where a separate -Path and -Name are specified, and purportedly PowerShell was supposed to be a value to the -Name parameter. That does look correct. The reason the example didn't work (and yours as well), is because the -Name parameter cannot be specified positionally, which you can see in the MSDN article I linked to below, and in the built-in help:

 Type: String Parameter Sets: nameSet Aliases: Required: True Position: Named Default value: None Accept pipeline input: True (ByPropertyName) Accept wildcard characters: False 

In that case, their example should have been something like these:

New-Item c:\scripts\Windows -Name PowerShell -type directory
New-Item -Path c:\scripts\Windows -Name PowerShell -type directory

So reiterating, named parameters would have worked here, and would have avoided confusion.

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Generally, you shouldn't be using positional parameters in scripts, unless they're extremely clear (and even then, I'd recommend avoiding).

Using named parameters would have made this easier to figure out. And tab-completion helps with filling in the parameter names and in completing paths (usually with proper quoting too).

I think you should change yours to:

New-Item -Path $backupPath -Type Directory -Force

And looking over that technet article, it's really not so good. The MSDN article on New-Item is better, and this is the information you should see when running Get-Help New-Item as well.

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Side question:

Then again, PowerShell can fail when a script just gets too long.

What?