Prof. Powershell

A Defining Moment

The beauty of PowerShell is simplifying the oft-repeated task. Here's an example where you can create functions on the fly for common troubleshooting.

• By Jeffery Hicks
• 08/23/2010

In Windows PowerShell, a function is a self-contained collection of PowerShell expressions. Almost always a function serves as a way to modularize a task so you don't have to manually re-create the commands every time. Let's say you need to run this command more than once a day because you're troubleshooting a problem:

get-eventlog -LogName System -ComputerName Server01 -EntryType Error -newest 10 | select Timewritten,Source,Message,machinename

That's a lot to type and you'll most likely flub it more than once. Instead, just create a function on the fly:

PS C:\> Function Get-Errors {get-eventlog -LogName System -ComputerName Server01 -EntryType Error -newest 10 | select Timewritten,Source,Message,machinename }

Now you can simply type Get-Errors to run this command:

PS C:\> get-errors | out-file report.txt

But PowerShell comes with a number of its own functions which you can see by getting a directory listing of the Function: PSDrive:

PS C:\> dir function:

You may be wondering how some of these work. Well, when you ran the listing, what you are seeing is a FunctionInfo object which has a property called Definition. If the definition is simple and short, you'll see it. But for the rest, you'll need to grab the complete property:

PS C:\> dir function:mkdir | Select-Object -ExpandProperty Definition

If you run this you'll see the definition of the mkdir function that ships with Windows PowerShell. A related alternative is to use Get-Command:

PS C:\> get-command mkdir | Select-Object -ExpandProperty Definition

Or you can even simplify this further:

PS C:\> (get-command mkdir).Definition

Hey, why don't we create a function on the fly to return function definitions?

PS C:\> function Get-Definition {param ([string]$name) (get-command $name).definition}

This function accepts a name as a parameter. Try this and you should get the function code:

PS C:\> Get-Definition disable-psremoting

Or let's gaze at our inner navel:

PS C:\> get-definition get-definition

If you'd like to learn more, including how to save functions you've created on the fly, be sure to go here.

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