Scripting PowerShell Functions

Introduction to Scripting PowerShell Function

As you may expect from a top-notch scripting language, PowerShell supports functions.  There are several advantages of investing in the time needed to create functions.  One advantage of a function is that once you get it working, it's easy to call the commands later in the same script, moreover, once perfected, the code works consistently.  Another advantage of functions is that they help organize a long script into manageable chunks.

PowerShell Function Topics

• Our Practical Task - Enumerate svchost
• A function called plist
• Here is the code for the plist function
• How to create a function
• Summary of PowerShell Functions

Our Practical Task - Enumerate svchost

The task that I have set for our function is to enumerate which services are in each of the generic svchosts processes that you see in Task Manager.  Incidentally, the reason for multiple svchosts is that certain processes 'fight' and thus must be kept separate.  The solution is for the operating system to create multiple svchosts; for example, RemoteRegistry cannot co-exist with TermService.

Preliminary Commands

To get the idea of what we want to achieve, try these two commands individually:

And then

Our mission is to create a function which combines both of the above commands and thus achieves a single list of all the svchosts with their corresponding services.

This is the output of our goal, we want our function called plist to produce this output:

An Example of a PowerShell Function called plist

When you declare a function it requires as a minimum: Functionname {Block of Work}  The actual work is done by the PowerShell statements between the required {braces}.  Functions may include optional parameters, these are enclosed in (parenthesis) and are introduced after the function's name and before it gets to work with the {}.

Here is the code for the plist function

Learning Points from the Function Example

Note 1:  Plist will be a string function and not an integer and is declared thus:
function plist([string]$name="*")

Note 2:  $Name="*" returns all the names of the objects that get processed.

Note 3:  Let us consider the instructions inside the {Braces}, starting with the variable $Svc.  What this does is get the wmi win32_service.  Here is the command:
$Svc = get-wmiobject win32_service | sort ProcessId | group-Object ProcessId

Note 4:  The loop is covered by this While construction, the key is lt (less than):
while($i -lt $ps.count -and $j -lt $svc.count)

Note 5:  The process name is controlled by:
$ps = @(get-Process $name | sort Id)

Note 6:  This is the clever line that appends all the services to each individual svchost
$ps[$i]| add-Member NoteProperty service $Svc[$j].group;

Footnote - Simpler code

It is possible to replace the plist function (above) with more efficient code, nevertheless, remember that the purpose of this page is to introduce PowerShell functions.

Here is the alternative code if you just wish to check the instances of svchost

Summary of PowerShell Functions

The purpose of this page is to understand how a function is constructed.  Take it one line at a time.  My goal was to break down a complex task into a series of single commands.  The vehicle for our example task was drilling down into the SVCHOST processes that you see in the task manager.

See more PowerShell syntax

• PowerShell Home  • Syntax  • -f format  • Pipeline  • Quotes  • Format-table  • Group  • Select-String

Please write in if you see errors of any kind.  Please report any factual mistakes, grammatical errors or broken links, I will be happy to not only to correct the fault, but also to give you credit.

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