PowerShell: The Ultimate Beginners Guide to Learn PowerShell Step-by-Step by Reed Mark

Author:Reed, Mark [Reed, Mark]
Language: eng
Format: epub
Publisher: Publishing Factory
Published: 2020-08-19T16:00:00+00:00

Chapter Five:

Functions

Functions

A function constitutes a list of statements with a user-assigned name. The function can be executed by typing its name. The statements included within the list will execute as if they had been typed on the console.

A function may be simple, such as :

>function Get-PowerShellProcess { Get-Process PowerShell }

A function may also be more complex. It may have the complexity of an application or a cmdlet. Functions, similar to cmdlets, may contain parameters as well. These parameters may be positional, named, dynamic, or switch.

Either a pipeline or console can read a function. Functions can be constructed to return values, which can be shown. These values can also be made part of variable assignments passed to cmdlets or other functions. A function can have a particular return value specified through the keyword return. This keyword will not suppress or affect other output designated to be returned from the function. However, using return will trigger an exit from the function on that line.

A function can have separate statement lists categorised by the keywords Process, Begin, and End. These three types of statement lists have distinct methods for handling pipeline input. A filter is a particular class of functions designated with the keyword Filter. Functions can also be constructed to behave or operate similar to cmdlets without requiring C# programming.

Function Syntax

The syntax for specifying a function is as follows:

function [<scope:>]<name> [([type]$parameter1[,[type]$parameter2])]

{

param([type]$parameter1 [,[type]$parameter2])

dynamicparam {<statement list>}

begin {<statement list>}

process {<statement list>}

end {<statement list>}

}

A function has the following components:

● List of PowerShell statements demarcated with brace symbols {}

● Function keyword

● Scope which is optional

● User selected name

● Named parameters which are optional

Simple Functions

A simple function is simply a standard function deployed without the optional components (named parameters and a scope modifier).

A simple function syntax is as follows:

function <function-name> {statements}

To illustrate, this function starts PowerShell in Administrator mode:

function Start-PSAdmin {Start-Process PowerShell -Verb RunAs}

The function can be used by invoking it with its name:

>Start-PSAdmin

Statements can be added to a function by typing different statements on separate lines, or by demarcation with the semicolon symbol (;). At this stage, it would be informative to illustrate the concepts with a simple example.

Example: A function for finding .jpg files that were changed after a specific date

This function identifies all files with extension .jpg located in the path $env:UserProfile changed after the date specified by the $Start variable:

function Get-NewPix

{

$start = Get-Date -Month 1 -Day 1 -Year 2010

$allpix = Get-ChildItem -Path $env:UserProfile\*.jpg -Recurse

$allpix | Where-Object {$_.LastWriteTime -gt $Start}

}

Convenient functions can be organized into a toolbox and added into your profile.

Function Names

Functions may have any name assigned to them. The best practice recommendation, however, is for the names to conform to established standard PowerShell naming conventions for all commands. These conventions include a recommendation that the names comprise a pairing of a verb and a noun. In doing so, the noun characterizes the item the function acts on, and the verb describes the function’s action. The verb should be one of the approved PowerShell standard verbs for commands. Standard verbs help keep the names of all commands coherent, straightforward, and obvious to users.

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