Functions

Functions in PowerShell are reusable blocks of code that can accept parameters, return results, and even process piped input. They are essential for organizing and modularizing scripts, making them easier to read, maintain, and reuse.

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1. What is a Function?

A function is a named block of code stored in the function:\ drive. Functions can:

• Accept parameters.

• Return results.

• Process piped input.

• Be called from scripts or the interactive shell.

Listing Functions

To see all available functions in your session:

Get-ChildItem Function:\

Viewing Function Code

To view the code of a specific function:

Get-Content Function:\mkdir

Or:

Get-Item Function:\mkdir | Select-Object -ExpandProperty ScriptBlock

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2. Creating a Function

Basic Function

A function is defined using the function keyword, followed by the function name and a script block ({}).

Example:

function Say-Hello {
    "Hello, World!"
}

Function with Parameters

Functions can accept parameters, which are variables passed into the function when it is called.

Example:

function Greet-User {
    param (
        [string]$Name
    )
    "Hello, $Name!"
}
Greet-User -Name "Alice"

Function with Multiple Parameters

You can define multiple parameters and even assign default values.

Example:

function Add-Numbers {
    param (
        [int]$Number1,
        [int]$Number2 = 10
    )
    $Number1 + $Number2
}
Add-Numbers -Number1 5

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3. Advanced Function Features

Switch Parameters

Switch parameters are boolean parameters that don’t require a value. They are either present ($true) or absent ($false).

Example:

function Test-Connection {
    param (
        [string]$ComputerName,
        [switch]$Ping
    )
    if ($Ping) {
        Test-Connection -ComputerName $ComputerName -Count 1
    } else {
        Test-NetConnection -ComputerName $ComputerName
    }
}
Test-Connection -ComputerName "server01" -Ping

Default Parameter Values

You can assign default values to parameters, which are used if no value is provided.

Example:

function Get-DiskUsage {
    param (
        [string]$Drive = "C:"
    )
    Get-Volume -DriveLetter $Drive
}
Get-DiskUsage

Parameter Types

You can enforce specific data types for parameters.

Example:

function Multiply-Numbers {
    param (
        [int]$Number1,
        [int]$Number2
    )
    $Number1 * $Number2
}
Multiply-Numbers -Number1 5 -Number2 3

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4. Processing Piped Input

Functions can process objects piped into them using the $input variable or the Process block.

Using $input

The $input variable contains all piped objects.

Example:

function Process-Input {
    foreach ($item in $input) {
        "Processing: $item"
    }
}
1, 2, 3 | Process-Input

Using the Process Block

The Process block processes each piped object individually.

Example:

function Process-Input {
    process {
        "Processing: $_"
    }
}
1, 2, 3 | Process-Input

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5. Returning Results

Functions return the output of their last executed command. You can use the return keyword to explicitly return a value and exit the function.

Example:

function Add-Numbers {
    param (
        [int]$Number1,
        [int]$Number2
    )
    return $Number1 + $Number2
}
$result = Add-Numbers -Number1 5 -Number2 3

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6. Error Handling

You can control how errors are handled using the -ErrorAction parameter.

Example:

function Test-Connection {
    param (
        [string]$ComputerName
    )
    Test-Connection -ComputerName $ComputerName -ErrorAction SilentlyContinue
}
Test-Connection -ComputerName "nonexistent"