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How the PowerShell Pipeline Really Works

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This is the first in a seven part series on how to use the PowerShell pipeline. I’ve been teaching PowerShell since 2009.  The biggest hurdle that I have found for IT Professionals is understanding how the pipeline works.  So this past week after class, I wrote up a 24 page document to augment my class delivery.  Hope you enjoy it.

The PowerShell pipeline is a key feature of our favorite scripting language.  It has the potential to greatly reduce your coding efforts.  Here are two examples that produce the same answer.  The difference is that the first example uses the PowerShell pipeline, and the second does not:

Ex 1 : Using the PowerShell Pipeline
Get-Process |
    Where-Object CPU -gt 10 |
    Measure-Object -Property CPU -sum |
    Select-Object -ExpandProperty Sum

Ex 2 : Not using the PowerShell Pipeline
$Procs = Get-Process
$Sum = $Null
ForEach ($Proc in $Procs)
{
    If ($Proc.CPU -gt 10)
    {
        $Sum += $Proc.cpu
    }
}
Write-Output $Sum

Here are the same two examples executed using the cmdlet Measure-Object.  Notice the difference in the amount of time that it takes to complete these two tasks.

Ex 3 : Processing time comparison between Ex 1 and Ex 2.
Measure-Command -Expression {
    Get-Process |
        Where-Object CPU -gt 10 |
        Measure-Object -Property CPU -sum |
        Select-Object -ExpandProperty Sum
} | Select-Object -ExpandProperty TotalMilliseconds


Measure-Command -Expression {
    $Procs = Get-Process
    $Sum = $Null
    ForEach ($Proc in $Procs)
    {
        If ($Proc.CPU -gt 10)
        {
            $Sum += $Proc.cpu
        }
    }
    Write-Output $Sum
} | Select-Object -ExpandProperty TotalMilliseconds

3.9183
5.4664

In many cases, the pipeline will run faster than using traditional structural programming.

Even with these advantages, the PowerShell pipeline is a technology that is very hard to grasp for most IT professionals.  Not only are we treading into the world of the developer, but just the concept of the pipeline is a mystery to many. 
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