PowerShell Performance: Write-Host

PowerShell Performance: Write-Host

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This month’s post will be a short one – and there’s not much code to this topic, it’s just an observation.  When I write scripts, I like the idea of adding some output to track what my script is doing, especially if there’s an issue with the script.  It’s so much easier to find bugs or performance issues if I can see the last task that completed successfully – I then know where to start looking for the issue in my code.  However, it is important to understand as more output is added, your script will slow down.  It may not seem like much but when you are calling write-host multiple times for thousands of objects, overall script performance will be impacted.

 

Let’s take an example script I wrote and assume the script will call a function in a foreach loop processing thousands of objects.  I’ll also add a write-host in my foreach loop each time I enter and exit a function.  That’s a lot of text but it could be meaningful if there is an issue.  Let’s run the following code:

function foo {
    Write-Host "Entering function 'foo'"
    # Some code
    Write-Host "Completed function 'foo'"
}

$startTime = Get-Date
write-host "script started at $starttime"
$Cycles = 10000

1..$Cycles | % {
    foo
}
Write-Host "Done"

$endTime = Get-Date
($endTime - $startTime).totalseconds

This takes about 10 seconds to execute on my computer, which is significant since the only thing running is the write-host command.  After commenting out the write-host commands, the script completes in about 1 second.  In my personal experience, I have seen scripts where over 30 minutes have been saved by removing write-host output.

My suggestion and what I do for most of my scripts: as an alternative to write-host, you can use write-verbose for output, and when you need to see what your script is doing you can call the script with the –verbose parameter.  Your script will execute faster under normal circumstances, and you will still be able to output diagnostic information when you need it - with no code changes.

Comments
  • I remember one of Powershell fathers (Don Jones ?) saying was Write-Host was a bane to avoid at all costs...

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