PowerShell Function

What is PowerShell Function?

A PowerShell function is a reusable block of code designed to perform a specific task. It allows you to encapsulate logic into a named procedure, which can be called multiple times throughout your script. Functions help improve readability, modularity, and maintainability of scripts—especially in automation-heavy environments like Microsoft 365 administration.

Functions can accept parameters, return values, and include conditional logic, loops, or even other function calls.

How PowerShell Function Operates?

The basic syntax for defining a function in PowerShell is:

function FunctionName {
param ([type]$parameter1, [type]$parameter2)
# Code block
}
                                        

• FunctionName is the custom name for the function.
• param defines input parameters the function can accept.
• The function can be called anywhere in your script by using its name and passing required arguments.

Functions are particularly useful for recurring tasks—like creating users, assigning licenses, or sending reports—because you can define the task once and reuse it as needed.

Usage Example

Here’s a PowerShell function that creates a new Microsoft 365 user when provided with a UserPrincipalName (UPN):

function Create-M365User {
param (
    [Parameter(Mandatory=$true)]
    [string]$UserPrincipalName
)
    # Extract username part before '@'
    $NamePart = $UserPrincipalName.Split('@')[0]
    # Convert to Title Case for DisplayName
    $DisplayName = -join ($NamePart -split '\.?' | ForEach-Object { $_.Substring(0,1).ToUpper() + $_.Substring(1).ToLower() })
    # MailNickname is same as NamePart (no domain)
    $MailNickname = $NamePart
    # Create the user
    New-MgUser -UserPrincipalName $UserPrincipalName `
    -DisplayName $DisplayName `
    -MailNickname $MailNickname `
    -AccountEnabled `
    -PasswordProfile @{
    ForceChangePasswordNextSignIn = $true
    Password = "TempP@ssw0rd!"
}
}

                                        

To create a user, simply call the function like this:

Create-M365User -UserPrincipalName "alex.ryan@yourtenant.com"

🔄 Tip: PowerShell functions are best defined and executed within scripts saved as .ps1 files for consistent behavior and reusability in automation tasks.

PowerShell functions bring structure and flexibility to your scripts, making them scalable, reusable, and easier to debug.

You can see the PowerShell function in action in this real-world script: Adding Microsoft 365 User to Multiple Groups that makes use of Add-UserToGroup function which takes in userId and a bunch of groupIds (as its function parameters) and adds the user to the provided groups.