Functions

Functions work similarly to script blocks, but are named:

function Get-Fullname($firstname, $lastName)
{
    Write-Host ($firstName + " " + $lastName)
}

Get-Fullname "Conner" "Taylor"

Can pass an argument by reference, but it will be turned into an object, thus requiring the .Value syntax:

function Set-FVar([ref] $myparam)
{
    $myparam.Value = 33
}

Clear-Host
$fvar = 42
"Before Set-FVar: $fvar"
Set-FVar ([ref] $fvar)    # Must add ref to call
"After Set-FVar: $fvar"

Can enable pipelining with process just like with script blocks:

function Get-TextFiles ()
{
    begin { $retval = "Here are the text files: `r`n" }
    process
    {
        if ($_.Name -like "*.txt")
        {
            $retval = $retval + "`t" + $_.Name + "`r`n"
        }
    }
    end { return $retval }
}

Clear-Host
Set-Location "C:\Temp"
Get-ChildItem | Get-TextFiles

Can use filter to remove unwanted objects:

filter Show-TextFiles
{
    $filename = $_.Name
    if ($filename -like "*.txt")
    {
        return $_
    }
}

Set-Location "C:\Temp"
Clear-Host
Get-ChildItem | Show-TextFiles

Example handling switches and writing to different types of output:

function Get-ChildName()
{
    param([switch]$verbose, [switch]$debug)

    if ($verbose.IsPresent)
    {
        $VerbosePreference = "Continue"    # $VerbosePreference is a special powershell var
    }
    else
    {
        $VerbosePreference = "SilentlyContinue"    # Default value
    }

    if ($debug.IsPresent)
    {
        $DebugPreference = "Continue"
    }
    else
    {
        $DebugPreference = "SilentlyContinue"
    }

    Write-Verbose "Current working location is $(Get-Location)"
    Write-Output (Get-ChildItem | Select-Object "Name")
    Write-Debug "Files found."
}

Set-Location "C:\Temp"
Get-ChildName -verbose -debug | Where-Object {$_.Name -like "*.txt"}

Can add custom help to a function, will be displayed in Get-Help:

function Get-ChildName()
{
<#
    .SYNOPSIS
    Returns a list of only the names for the child items in the current location.

    .DESCRIPTION
    This function is similar to Get-ChildItem, except that it only returns the name property.

    .INPUTS
    None.

    .OUTPUTS
    System.String. Sends a collection of strings out the pipeline.

    .EXAMPLE
    Example 1 - Simple use
    Get-ChildName

    Example 2 - Passing to another object in the pipeline
    Get-ChildName | Where-Object {$_.Name -like ".txt"}

    .LINK
    Get-ChildItem
#>
    param([switch]$verbose, [switch]$debug)

    if ($verbose.IsPresent)
    {
        $VerbosePreference = "Continue"    # $VerbosePreference is a special powershell var
    }
    else
    {
        $VerbosePreference = "SilentlyContinue"    # Default value
    }

    if ($debug.IsPresent)
    {
        $DebugPreference = "Continue"
    }
    else
    {
        $DebugPreference = "SilentlyContinue"
    }

    Write-Verbose "Current working location is $(Get-Location)"
    Write-Output (Get-ChildItem | Select-Object "Name")
    Write-Debug "Files found."
}

Use trap to catch and handle errors:

function Divide-Numbers($num, $denom)
{
    Write-Host "Begin division."
    $result = $num / $denom
    Write-Host "Result: $result"
    Write-Host "End division."

    trap [System.DivideByZeroException]
    {
        Write-Host "You aren't powerful enough to divide by zero!"
        continue
    }

    trap
    {
        Write-Host "Error:"
        Write-Host $_.ErrorID
        Write-Host $_.Exception.Message
        continue    # Continues with the next line of code after the error
    }
}

Clear-Host
Divide-Numbers 33 11
Divide-Numbers 33 0