Borrowing a built-in PowerShell command to create a temporary folder

Sean Kearney

Q: Hey I have a question for you. It seems silly and I know I could probably put something together with Get-Random. But can you think of another way to create a temporary folder with a random name in PowerShell?

Ideally, I’d like it to be in a user’s own “Temporary Folder” is possible.

A: We sure can! If Doctor Scripto was sitting here right now, I’d see that little green haired person shout out “Never fear, Scripto is here!”

New-TemporaryFile Cmdlet

Within PowerShell there is a built in Cmdlet called New-TemporaryFile. Running this cmdlet simply creates a random 0 byte file in the $ENV:Temp folder in whichever platform you are working in.

However, we can borrow the filename created and use it to create a folder instead. It’s not really difficult, but maybe just not thought of very often.

When we execute the following cmdlet we get output similar to this as it generates a new 0 Byte random file in the User’s Temp folder stored in $ENV:Temp

PS> New-TemporaryFile

Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
-a----         3/31/2021   9:25 PM              0 tmpA927.tmp

Ok, that really wasn’t that impressive but what if we were to do this instead?

$File = New-TemporaryFile

Now we’ve created the file and stored it away in the $File object. With this we can remove the file of course using the Remove-Item cmdlet

Remove-Item -path $File -force

HA! I’ve already saved some time! The $File object is still there with the information I want to use.

So, I could access the name in the object property and use it to create a directory instead in the following manner.

New-Item -ItemType Directory -Path $File.Name

But the problem is that it would be in whatever default folder PowerShell was looking into at the time.

Hmmmmm…. How to solve that?

But there is a built in variable called $ENV:Temp which targets the exact Temporary folder that the New-TemporaryFile cmdlet uses as well!

I can then take that variable and the original name of the Temporary file and combine them together like this.

$ENV:Temp + '\' + $File.Name

or

I can even put them together in a single String like this.

"$($ENV:Temp)\$($File.Name)"

With this I could just create a new temporary directory under our temp folder in this manner.

New-Item -ItemType Directory -Path "$($ENV:Temp)\$($File.Name)"

Now to identify where the file ended up, I could same thing as last time by storing it as an object like $DirectoryName if I wanted. Then I could remove the “Random Directory name” later if I needed to.

$Folder=New-Item -ItemType Directory -Path "$($ENV:Temp)\$($File.Name)"

Then when I am done with that folder that was presumably used to hold some garbage data. I can just use Remove-Item again.

But because it’s a directory, I need to add -recurse -force to ensure all data and Subfolders are removed.

Remove-Item -Path $Folder -Recurse -Force

But here is the fun and neat bit. If you needed on a regular basis, we could make this into a quick function for your code, module or to impress friends with!

Function New-TemporaryFolder {
    # Create Temporary File and store object in $T
    $File = New-TemporaryFile

    # Remove the temporary file .... Muah ha ha ha haaaaa!
    Remove-Item $File -Force

    # Make a new folder based upon the old name
    New-Item -Itemtype Directory -Path "$($ENV:Temp)\$($File.Name)" 
}

Now at this point I had thought my journey was complete. It was until I posted the solution to the Facebook group for the PowerShell Community Blog to share.

A fellow member of the Community noted the approach, while neat, was not very efficient.

At that point I dug into the code on Github for the open source version of PowerShell 7.x to see how it was done there.

In reading the source code for New-TemporaryItem I was able to see the .NET object being used to generate the file. It turns out there is also a .NET method that can be used to create just that temporary name which all I wanted to use in the first place for the directory name.

When I ran this in the PowerShell Console it produced the following output of a New Temporary Folder

PS> [System.IO.Path]::GetTempFileName()
C:\Users\Administrator\AppData\Local\Temp\2\tmp3864.tmp

This was exactly what I wanted, that random temporary Name to be consumed for the New-Item Cmdlet. With this approach the function became a lot simpler and far more efficient!

Function New-TemporaryFolder {
    # Make a new folder based upon a TempFileName
    New-Item -ItemType Directory -Path([System.IO.Path]::GetTempFileName())
}

But alas my victory was short lived. This method still created the file, it didn’t just display the name. So the function ended up failing.

But since really I just wanted that format to be used for the temporary directory. Plus the format for the temporary filename was as simple as tmpxxxx.tmp where the xxxx was a random hexadecimal number, I came up with a better idea!

Just create a number between 0 and 65535 with Get-Random and use the [convert] accelerator to change it the 4 character Hexadecimal number instead.

The end result looked like this and gave me the desired result I wanted.

PS> "$($Env:temp)\tmp$([convert]::tostring((get-random 65535),16).padleft(4,'0')).tmp"
C:\Users\doctorscripto\AppData\Local\Temp\tmp5633.tmp

Now I ended up with a working function that could produce the desired output I wanted and in a more efficient manner.

Function New-TemporaryFolder {
    # Make a new folder based upon a TempFileName
    $T="$($Env:temp)\tmp$([convert]::tostring((get-random 65535),16).padleft(4,'0')).tmp"
    New-Item -ItemType Directory -Path $T
}

Why did all of this pop into my head? I was actually creating some PowerShell for customer and needed a consistent and random set of folders in a common and easily erasable location.

I was hoping that we had a New-TemporaryDirectory cmdlet, but found it was just as easy to write one by borrowing an existing cmdlet.

It was fun as well to discover how I could improve on the solution by reading the Source code for New-TemporaryItem on Github.

Thanks to a little nudging from the Community. So a big Thank you to Joel Bennett for the critique! 🙂

Sean Kearney – Customer Engineer/Microsoft – @PowerShellMan

“Remember with great PowerShell comes great responsibilty…”

Sean Kearney Customer Engineer - Microsoft, COGS Apps Infra Support

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