Friday Fun: Creating Sample Files

documentNot too long ago I came across a PowerShell snippet, probably via Twitter, that showed how to use a few classes from the System.IO namespace to create dummy files. Sadly I forgot the record where I saw this first mentioned. What I liked about the code I saw was the ability to create a dummy file of any size. You’re probably wondering why you would ever want to do this. Way, way back in the day when storage was expensive I used to create a few 100MB of dummy files using an old command line utility which I think was called creatfil.exe. The reasoning was that if the server started running out of disk space unexpectedly, I could delete the dummy files and buy myself a little time and breathing room. Fortunately, I think we’ve advanced where that technique is no longer necessary.

But, where you might want some dummy or sample files, is to simulate a user folder with a variety of files. You could use this test directory to hone your PowerShell scripts. Any you may have your own reasons for needing a bunch of sample files. So I took the original code and ran with it, as I usually do. I came up with a function called New-SampleFile.

The function will create a randomly sized file in the specified folder. The default is the current location. As you look through the code you’ll see I’ve added a test to verify the path and to make sure it is a FileSystem path and not something like the registry. Also by default the function will use a randomly generated file name which will be something like rcstwqyg.34e. Personally, I’m going to specify a filename. The function will create the file of a random size between 5 bytes and the value of the MaximumSize parameter, which has a default of 100KB.

The function will not overwrite existing files unless you use –Force. Nor will you see any output unless you use –Passthru. Even those are common parameters, I had to write the PowerShell expressions to implement them. The same is true of –WhatIf. You’ll see in the cmdletbinding attribute that the function supports ShouldProcess. However, the .NET classes I’m calling have no concept of WhatIf. I had to handle that myself

Here’s the function in action:

This also makes it easy to create multiple files.

Or how about this? I want to create a variety of files with different names.

Now I have some test files I can work with

Normally I prefer to use cmdlets wherever possible. But since there is no cmdlet from Microsoft to create dummy files, I have no problem resorting to the .NET Framework. However, I think it is still worth the time to wrap the .NET commands in a user-friendly and easy to use advanced function as I’ve done today.

If you find a way to use this function, I hope you’ll let me know.

2 thoughts on “Friday Fun: Creating Sample Files

  1. I’m all about doing things with PowerShell but sometimes I think its easier to just keep it simple. That’s a lot of code to generate empty files when fsutil can do it so much easier.

    fsutil file createnew ([System.IO.Path]::GetRandomFileName()) (get-random -Minimum 5KB -Maximum 100KB)

    I use it frequently when I need files to test network speeds.

    ~NC

    • Yes it is a lot of code but with a purpose or “value-add” like support for Whatif. But sure, if you need to get something done quickly from the command prompt there’s nothing wrong with your approach.

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