Introduction to Scripting

Intro

When you are using PowerShell, you might find yourself repeating some commands again and again.
Therefore, it is better to store these commands or statements into a text file which ends with .ps1 extension.
The script involves calls to cmdlets, functions, variables and more.

Variables

You can use variables to store values and use them as inputs to to other commands.

Functions

Functions are a named set of statements which produce and output, which further can be used as input to other commands.

Flow Control

These are execution paths a program can take.
Statements like If, ElseIf and Else are helpful for this.

Loops

These are constructs which let you perform certain operations for a number of times.

Error Handling

There are terminating and there are non-terminating errors.

Expressions

These are representatives of values.

.NET And .NET Core Integration

PowerShell can integrate with .NET and .NET Core.

Run a Script

Scripts can be dangerous.
If you don't understand them, don't run them.

Relative Paths

The scripts require either an absolute path or relative path to be executed.
This ensures that you exactly know what you are running in case the script name overlaps with name of some other cmdlet.

Execution Policy

These are safety features which have different levels. 1. Local Computer 2. Current User 3. Current Session

Execution Policy

Get-ExecutionPolicy

This returns the execution policy
Possible values: 1. Restricted: The computer cannot run the scripts. 2. RemoteSigned: The computer can run the scripts. The scripts downloaded from internet, needs to be signed by a digital signature by a trusted publisher.

Variables

These are not just for scripts.
You can also define them on console.

$PI = 3.14

Working with Variables: Quotation Marks and Interpolation

You can use Write-Host or Write-Output to print stuff on the console.

Using double quotations, we can interpret values of the variables.
Code:

Write-Host "Value of PI is $PI"

Output:

Value of PI is 3.14

Using single quotations, there is no interpretation done.

Code:

Write-Host 'Value of PI is $PI'

Output:

Value of PI is $PI

We can also use $() for expressions.
Example:

Write-Host "Value of PI is $($PI + 1)"

Scope

These define where the variables and other things like functions etc are accessible.

Types of Scope

There are 3 types.

Global Scope

Things which are defined in this scope are accessible even after the session ends.
This exists as the PowerShell starts.

Script Scope

This is limited to the script file itself and everything defined inside it, is wiped away after the file is done running.
If you want to define variables at global scope then you prepend the global keyword during definition.

global $PI = 3.14

Local Scope

It is the current scope which can be global or any other scope.

Scope Rules

Scopes Can Nest

A scope can have a parent scope.
Conversely, a parent scope can have a child scope

Items Are Visible in the Current and Child Scopes

Items which are defined in a scope are available in that particular scope and any of its child scope.
This behavior can be changed by making the items private to the scope they were created in.

Items Can Be Changed only in the Created Scope

Items can only be changed in the scope they were created in.
This can be changed by specifying a different scope.

Profiles

These are scripts which run as soon as a new PowerShell session starts.

Profile Types

Description	Path
All users, All Hosts	$PSHOME\Profile.ps1
All users, current host	$PSHOME\Microsoft.PowerShell_profile.ps1
Current user, all hosts	$Home[My ]Documents\PowerShell\Profile.ps1
Current user, current host	$Home[My ]Documents\PowerShell\Microsoft.PowerShell_profile.ps1

The $PSHOME is the PowerShell installation directory
The $HOME is the Current User home directory

Create a Profile

You can do the following to print all profiles and the associated paths to them

$Profile | Select-Object *

Here the $Profile is the variable which holds path to the profiles.

To make your customizations: 1. Make a text file using the command

New-Item -Path $Profile.CurrentUserCurrentHost

Add your customizations to the text file.
Restart PowerShell