Measure the run-time of a PowerShell command with Measure-Command

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Adam Bertram

Adam Bertram is a 20-year IT veteran, Microsoft MVP, blogger, and trainer.

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The Measure-Commandcmdlet couldn't be simpler. It only has two parameters: Expressionand InputObject. In fact, InputObjectjust represents one or more expressions anyway. It's simple in nature but provides useful metrics to give you a glimpse into the performance of your code.

Let's use Measure-Commandin a real-world performance-tuning example. Some people know that not all arrays in PowerShell are created equal. Did you know that every time you add an element to an existing array using +=, you're actually destroying it and creating it again, and it's reallyslow? Let me prove it.

Say I have an array defined as $arr($arr = @()). I then add a whole bunch of elements to it. To keep it simple, I'll use some integers created with a range. I'll then add each of these numbers to the array using +=.

$arr = @()
0..25000 | ForEach-Object { $arr += $_ }

This takes awhile but how long is awhile? Let's find out with Measure-Command. We can wrap the code inside a scriptblock representing an expression and use that as the Expressionparameter for Measure-Command.

Measure-Command -Expression { 0..25000 | ForEach-Object { $arr += $_ }}

Using Measure Command's Expression parameter

Notice that Measure-Commandreturns time broken down into various categories. We don't need to perform math to convert the time to seconds, minutes, or hours. It's all part of the object Measure-Commandreturns.

If we need to reference total seconds, we'd just reference the TotalSecondsproperty. Need that in minutes? Just find the property. We could assign the output of Measure-Commandto a variable and reference all the properties we need.

$slow_performance = Measure-Command -Expression { 0..25000 | ForEach-Object { $arr += $_ }}

Let's now use the quicker way of adding elements to an array by using an ArrayListand see how fast that is.

$arr = [System.Collections.ArrayList]@()
$fast_performance = Measure-Command -Expression { 0..25000 | ForEach-Object { $arr += $_ }}

Fast array performance

It's a lot faster! We have real numbers using Measure-Command. We can even calculate how much faster it is using the numbers we retrieved from Measure-Command. You can see below that by using an ArrayListover an array, we were able to perform the same task 135 times faster! These numbers wouldn't be possible without Measure-Command'sgranular time metrics.

PS> [math]::Round($slow_performance.TotalSeconds / $fast_performance.TotalSeconds,0)
135

Measure-Commandis one of those PowerShell cmdlets that is simple yet extremely useful. This cmdlet can provide real numbers to any piece of code (expression). This gives you the data you can then compare with other methods to tune your scripts to be as fast as possible.