chapter_2_powershell.md

Chapter II: Powershell

Powershell is a universal automation, scripting and development tool and is developped to automate tasks without programming knowledge

Some interesting commands:

• Get-Alias: shows list of aliases (zal een onderliggende commando representeren), de volledige list krijg je enkel op Windows
• Get-Command: shows list of commands
  • Different flavours:
    • most are cmdlets, often written in C#
    • Functions are commands written in Powershell
• Get-Help: Same as man in Linux
• Update-Help: update its help information

These commands also have parameters. These values will change the behaviour of the command. Powershell does not have sudo, so it can be annoying sometimes to use.

Basic Concepts

Variables

$var

The strict mode will prevent you from using the var without defining it first (Set-StrictMode -Version Latest)

Automatic Variables

has premade variables. You can change these, but maybe dont :)

$null -> represents nothing, but you initialise it. This is used a lot to give a var a value as response of output of a certain function

$LASTEXITCODE -> returns code of last external executable program, 0 = success, anything else does is not a success.

Data Types

basically same as things we know: strings, int32 (standard), int64, bools, float (32 bits), double (64 bits)...

'' -> no variable expansion "" -> variable expansion _ -> powershell will treat this as a commando

Objects

In powershell, everything is an object

• $color, is a string object

Every object has properties -> object -Property

The Get-Member method will show you all the functions for an object

Utilizing methods (not important)

Array Data Structure

$color_picker = @('blue', 'yellow')

Using + will make a new array Using += will append item to array

ArrayLists are dynamic (vectors) and are better for when you have arrays with heavy objects. Cast your array to an arraylist :)

In an arrayList, + and += do not exist, use Add(), Remove()

HashTable Datastructure

$users = @{ Niels = ... }

manipulation -> Add(), ContainsKey(), Remove()

Creating Custom Objects

Utilize new-object cmdlet

This object can then be used like anyother object

Using a Pipeline

The output of one command will be piped to another command.

for example: Get-Service | Start-Service

Piping arrays between commands

Shows an example

Parameter Binding

Passing parameters to a command, PS inits a process knwon as parameter binding, in which it matches each object into the command to the various parameters specified by the command's creator.

To see if a pipeline is possible you must use Full parameter on the Get-Help command.

Writing Scripts

By default you cannot run a script. You then need to customize the Execution Policies, just put it on Unrestricted -> Allows to run any script.

you also have:

• Restricted: does not allow running scripts
• AllSigned: scripts need to be signed
• RemoteSigned: run scripts you made or script downloaded that where signed by others

Script Signing

A script signature is an encrypted string at the end of your script

Scripting in Powershell

extension is .ps1.

Expressions

• eq

• ne

• gt

• ge

• lt

• le

• contains

• not

• Quiet -> gives the essential information of a method

IF-statement

if () {} else if

Switch Statement

Hier ga je alle condities controleren (niet als je een break gebruikt), bij else if else if else if niet.

Loops

• foreach, for, do/while, ...

.... We already know this stuff..

for each is under the hood the best way

for ($i = 0 ; $i lt 10 ; $i ++)

Error Handling

two types of errors:

• Terminating error: any error that stopt execution of the code

• Non-terminating error: error that is not servere enough to halt the rest of the code

Decision is made by the developer!

Handling non-terminating errors

some information...

Handling terminating errors

try catch block

catch does not catch non-terminating errors

each error is stored in a PS automatic variable $Error

Writing Functions

Code can be broken down into functions

• Similar to cmdlets such as Start-Service and Write-Host

function {code_block}

use the Noun-Verb name

Adding parameters

Mandatory Parameter Attribute

This can force you to use the parameter

default parameters and parameter validation also exist

ValidateSet can be used to validate the parameters, @{'1', '2'} -> Only Version 1 and 2 are applicable

Accepting Pipeline Input

• ByValue (entire object)
• ByPropertyName (single object property)

You need to however add a process block, because otherwise it will only do it on the last iteration

Modules

Importing

...

• .psm1 file extensionm can be a PS module

• Module manifest '.psd1' file

There is a Powershell Gallery to view all modules

Running Scripts Remotely

This can be done using PSSessions

Working with scriptblocks

essentially lamda functions

when we define a var to a codeblock, we need to add & before the var to execute the codeblock

Invoke-Command:

two way to use it:

• first is when running ad hoc commands
• second is using interactive sessions

You can also use Invoke-Command to execute entire scripts

best way is to use $using before any local variable name

Creating new session

...

Invoking Commands in a Session

Opening Interactive Session

use Enter-PSSession

Powershell is really good to parse CSV files

Using Import-CSV to process data

Essentially, this import tool is really strong

You can also create CSV files

Same with JSON, ConvertFrom-JSON, takes raw JSON and converts it to a PS object.

You can also just create JSON

Querying and parsing a Rest API (Important for labs)

This is also truly possible, wow! 😎

Manipulating Active Directory

This is just a keyvalue store (manage printers, servers, ...)

ActiveDirectory module is required!

Search Adaaccount and returning single objects

• Search-ADAccount command:

Sometimes, when you know which AD object your looking for, you don't need a filter

Finding User accounts that have not changed password

Creating and changing AD objects: Users and computers (Lab II)

...

Each user can be part of a group

Assigning random passwords

whatever

Labs

Labs are mandatory

V, VI, VII are dangerous, because the clusters could get destroyed, make sure to be proactive