Use PowerShell to Start a Process at Random Times


Summary: Microsoft Scripting Guy, Ed Wilson, talks about using Windows PowerShell to start a process at random intervals.

Hey, Scripting Guy! Question Hey, Scripting Guy! I have a rather unusual request. I am testing a new monitoring application, and I need a script that will start processes at random intervals so I can check the effectiveness of the solution. Is this something you can help me with?

—BB

Hey, Scripting Guy! Answer Hello BB,

Microsoft Scripting Guy, Ed Wilson, is here. This morning I am sitting on the porch, sipping a nice cup of green tea with orange flavorings in it. The tea is called Orange Cream, and it tastes exactly like the old Dreamsicles I used to eat when I was a kid. It is a different way to start the morning. I am cooling off after spending an hour in the gym. I have my Surface Pro 3 that the Scripting Wife got for me for my birthday (it was an early birthday present…I have had it for awhile now), and I am catching up with email sent to scripter@microsoft.com and Facebook. I don’t know about you, but lately, it seems like I am always multitasking. I find it hard to sit and do just one thing at a time anymore. I’m not sure if this is a good thing or a bad thing.

Picking out tools

BB, there are many ways to write a Windows PowerShell script that will generate new processes at random intervals. But when I hear this requirement, I think that I will need the following:

  • Get-Random  To generate random numbers. I also know that I will need to specify minimum and maximum values. I will accept the default seed.
  • Start-Process   To start the processes and give me a bit of control over the way they start. For testing purposes, I probably want to use a minimized window style so that it does not block other things (such as the Windows PowerShell ISE for example), and so I will still be able to see that the processes have in fact started. Obviously, I will need a way to specify the program name (and path if needed). I can do this with a variable.
  • Start-Sleep  To control the amount of time between the startup of the process. I will use the –seconds parameter and use the number I get back from Get-Random to control the sleeping. This also means that I will need to use numbers large enough to be minutes instead of seconds (for example, 300 for five minutes).
  • While statement  To put the script in an infinite loop. I am only testing the script at this point, so this will work well because I am sitting here monitoring it. Later I may want to increase my minimum and maximum random values, and run the script over a twelve hour period of time. For this, I will use the For statement and control exactly how many times I want the script to execute.

Writing the script

Because I did a good job analysis, and I know pretty much all of the commands I am going to use in the script, writing the script does not take me very long at all. In fact, here is the script I wrote:

   Note  Using While ($true) puts the script into an infinite loop. To stop the loop, press the red square (stop button) in the Windows PowerShell ISE.

# StartProcessesAtRandomTimes.ps1

$prog = "notepad.exe"

while ($true)

{

 $rnd = Get-Random -Minimum 1 -Maximum 5

 Start-Sleep -Seconds $rnd

 start-process -FilePath $prog -WindowStyle Minimized}

Testing the script

To test the script, I load it in the Windows PowerShell ISE, press the green triangle, and then wait for a while. Nothing appears, and nothing appears to happen. But, at least on my laptop, I see the screen flash every once in a while, and on my task bar, I see several Notepads stacked up. So I press the red square, and stop the script. Still nothing appears to have happened—at least not from looking at the Windows PowerShell ISE. Here is the screenshot:

Image of command output

In the interactive pane, I use Get-Process to find all the Notepad processes. As shown here, there were quite a few generated:

Image of command output

That is cool. Now I want to see if my randomizer is working—that is, at what time were the Notepad processes generated. That is easy enough. I use the StartTime property. It is probably best to also sort them. So I use the following script:

PS C:\> Get-Process notepad | Select StartTime | sort  -Descending

The problem is that it does not sort properly. It looks like it is sorted, but I try the ascending and the descending sorts, and I see the order does not change. Dude.

I then realize that I need to expand the DateTime object (that is contained in the StartTime property) so I can specify WHAT I want to sort on. Obviously, I am interested in the TimeOfDay. So I revise my command to the following:

Get-Process notepad | select -expand StartTime | sort timeofday    

Now I try it, and I see that it is working. In fact, I am getting random offsets between the process starts. This is shown here:

Image of command output

BB, that is all there is to using Windows PowerShell to create processes at random intervals. Process Week will continue tomorrow when I will talk about launching random processes at random times.

I invite you to follow me on Twitter and Facebook. If you have any questions, send email to me at scripter@microsoft.com, or post your questions on the Official Scripting Guys Forum. See you tomorrow. Until then, peace.

Ed Wilson, Microsoft Scripting Guy 

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