Visualizing PowerShell pipeline

A picture1 is worth a thousand words.

Occasionally, I see people having issues while trying to understand how PowerShell pipeline is executed. Most of them have no problems when Begin/Process/End blocks are in the single function. And if in doubt, I can always point them to the Don Jones’ The Advanced Function Lifecycle article. But when multiple cmdlets are chained into the one single pipeline, things become a little less clear.

Consider this example.

function Use-Begin {
    Begin {
        Write-Host 'Begin'
    }
}

function Use-End {
    End {
        Write-Host 'End'
    }
}

Let’s try to pipe one function into another:

PS C:\Users\beatcracker> Use-Begin | Use-End

Begin
End

So far, so good, nothing unexpected. The Begin block of the Use-Begin function executes first, and the End block of the Use-End function executes last.

But what happens if we swap the functions in our pipeline?

Continue reading

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