PowerShell Core for Linux Administrators Cookbook

By : Prashanth Jayaram, Ram Iyer

PowerShell Core for Linux Administrators Cookbook

By: Prashanth Jayaram, Ram Iyer

Overview of this book

PowerShell Core, the open source, cross-platform that is based on the open source, cross-platform .NET Core, is not a shell that came out by accident; it was intentionally created to be versatile and easy to learn at the same time. PowerShell Core enables automation on systems ranging from the Raspberry Pi to the cloud. PowerShell Core for Linux Administrators Cookbook uses simple, real-world examples that teach you how to use PowerShell to effectively administer your environment. As you make your way through the book, you will cover interesting recipes on how PowerShell Core can be used to quickly automate complex, repetitive, and time-consuming tasks. In the concluding chapters, you will learn how to develop scripts to automate tasks that involve systems and enterprise management. By the end of this book, you will have learned about the automation capabilities of PowerShell Core, including remote management using OpenSSH, cross-platform enterprise management, working with Docker containers, and managing SQL databases.

Preface

Who this book is for

What this book covers

To get the most out of this book

Sections

Get in touch

Free Chapter

Introducing PowerShell Core

Introduction

Installing PowerShell

Updating and using Help

Exploring about_ topics

Discovering cmdlets

Finding and installing PowerShell modules

Listing the various providers in PowerShell

Understanding objects

Parsing input from text to object

Comparing the outputs of Bash and PowerShell

Comparing Windows PowerShell and PowerShell Core

Working with aliases

Dissecting a .NET Core object

Listing out the execution policies and setting a suitable one

Preparing for Administration Using PowerShell

Introduction

Installing Visual Studio Code

Configuring automatic variables

Changing shell behavior using variables

Enabling automated execution of commands for each load

Customizing the Terminal prompt

Understanding standard redirection in PowerShell

Calling native Linux commands from PowerShell

Understanding cmdlets and parameters

Running cmdlets with minimal keystrokes

Finding parameter aliases

Calling a PowerShell script

Dot-sourcing a PowerShell script

Calling a PowerShell cmdlet from outside of PowerShell

Recording the cmdlets run on the PowerShell console

First Steps in Administration Using PowerShell

Introduction

Working with date properties

Working with date and time methods

Working with currently-running processes to measure resource consumption

Launching and stopping a process

Finding the owner of a process

Invoking an application based on the file type

Installing the CronTab PowerShell module

Scheduling jobs in PowerShell

Removing scheduled jobs in PowerShell

Passing Data through the Pipeline

Introduction

Selecting columns from the output

Limiting the number of output objects

Expanding the properties within properties

Filtering objects

Grouping the output

Sorting the output

Taking actions on the returned objects

Understanding pipeline-enabled parameters

Importing content into PowerShell

Using Variables and Objects

Introduction

Using environment variables

Storing the output of an instance of a .NET Core object

Adding custom properties to an object

Creating a custom object from a returned object

Understanding the extension of type data

Retaining object modifications across sessions

Removing custom type data

Understanding variables

Working with Strings

Introduction

Creating a literal string

Creating an expanding string

Understanding Here-Strings

Using basic string methods

Performing string matching operations

Replacing substrings within strings

Splitting and combining strings

Using the formatting operator

Flow Control Using Branches and Loops

Introduction

Using If–ElseIf–Else conditions to control script flow

Using Switch–Case conditions to control script flow

Learning to use delays

Writing a basic looping construct

Writing a more complex loop on a predefined array

Using the For loop construct

Using the While loop construct

Cleaning empty directories using the Do–While construct

Cleaning empty directories using the Do–Until construct

Performing Calculations

Introduction

Performing arithmetic operations

Performing calculations on the output

Working with administrative constants

Working with calculated properties

Working with binary numbers

Performing base conversions

Using Arrays and Hashtables

Introduction

Creating and working with a simple array

Accessing and manipulating array items

Sorting an array

Searching for an item in an array

Combining arrays

Item matching in an array

Removing elements from an array

Comparing arrays

Creating a simple hashtable

Performing simple tasks on a hashtable

Handling Files and Directories

Introduction

Reading content from a file

Sending output to a file

Adding and setting content to a file

Searching for content

Working with locations

Working with files and directories

Listing files and directories

Working with structured and unstructured files

Building Scripts and Functions

Introduction

Writing a simple script

Reading input from the host

Displaying an interactive menu

Showing progress of execution

Defining arguments for a script

Writing a simple function

Working with a script block

Measuring running duration

Important points to remember

Advanced Concepts of Functions

Introduction

Defining parameters

Working with parameter aliases

Working with parameter sets

Adding default values to the parameter

Adding validation to parameter input

Handling dependencies and prerequisites

Adding safety switches to functions

Adding help to functions

Adding support for pipeline input

Using the Main function

Writing a script module

Handling module cleanup

Debugging and Error Handling

Introduction

The Debug tab of Visual Studio Code

Writing debug output

Running a script in Debug mode

Tracing errors

Using breakpoints

Using conditional breakpoints

Using exit codes

Working with the Error variable

Controlling flow based on errors

Sending verbose output to a file

Enterprise Administration Using PowerShell

Introduction to OpenSSH

Installing OpenSSH on Windows

Configuring OpenSSH using sshd_config on Windows

Installing and configuring OpenSSH on Linux

Testing PowerShell remoting using OpenSSH

Testing PowerShell remoting with OpenSSH using keys between Linux machines

Testing PowerShell remoting with OpenSSH using keys between Linux and Windows machines

Running cmdlets on remote computers

Managing the administration of remote machines with PowerShell Jobs

Generating HTML reports

Sending email messages

PowerShell and Cloud Operations

Introduction to PowerShell for Cloud operations on Azure and AWS

Installation of the AzureRM.Netcore PowerShell module on Linux machines

Installation of the AWSPowerShell.NetCore module on Linux machines

Discovering AzureRM cmdlets discovery functions

Azure Cloud Shell in action

Provisioning a Ubuntu 18.04 LTS VM using AzureRM.Netcore cmdlets on the Azure Cloud

Provisioning Linux Docker containers using Docker Machine on Azure

Provisioning Linux VM using PowerShell script

Performing management tasks using ARM PowerShell cmdlets

PowerShell remoting to Azure VM using OpenSSH

Managing AWS credentials

Connecting an EC2 Linux instance using SSH from PowerShell

Using PowerShell for SQL Database Management

Introduction to PowerShell, SQL Server, and Python

Technical requirements

Installing .Net Core on Linux

Installing the SqlServer module

Overview of SQL Server SMO

Running cross-platform T-SQL queries

Running cross-platform T-SQL queries on multiple servers

Creating a repository for Get-Process in the SQL database

Data formatting examples with PowerShell

Overview of PowerShell, Bash, and Python integration

Using PowerShell with Docker

Introduction to Docker

Installation of Docker on Linux

Getting and listing the Docker management cmdlets

Overview of Docker Hub and its operations

Building an image from a Dockerfile using PowerShell

Pulling a Docker container image from the repository

Listing Docker containers and the images

Starting and stopping Docker containers

Removing containers and container images

Working with a container using miscellaneous Docker PowerShell cmdlets

Running a PowerShell script to set up Docker containers

Finding Docker tags using PowerShell cmdlets from the remote registry

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Updating and using Help

Help documentation is very important in PowerShell, regardless of whether a certain cmdlet is packaged by providers such as Microsoft, VMware, or Citrix, or community-created. Help is not a switch in PowerShell. PowerShell uses the Get-Help cmdlet (pronounced command-let) to fetch the Help information enclosed within cmdlets.

By default, PowerShell is installed with minimal Help information, which contains only the description and the parameters. In this recipe, we will update Help and learn to get Help by using cmdlets, specific parameters, or certain keywords.

Getting ready

To go through this recipe, you must have PowerShell 6 installed on your computer, and you must have administrator privileges available. To install PowerShell, refer the Installing PowerShell recipe in this chapter.

How to do it...

To update the Help files for the locally installed PowerShell modules, follow these steps:

Type exit to exit PowerShell. This is so that you can relaunch PowerShell with elevated privileges. This is required for some of the modules, based on the permissions used to install them.
Enter sudo pwsh (or sudo pwsh-preview) to launch PowerShell as a superuser.
At the PS> prompt, run Update-Help.

Wait for the update progress bar to appear. The bar will fill as the Help files download onto your computer:

Use exit to exit PowerShell as a superuser, and launch PowerShell as a regular user.

We can now proceed and fetch Help information for other cmdlets.

At the command prompt, enter the following command:

PS> Get-Help Write-Host

You will get an output similar to the following:

Next, gather different levels of Help information by using the following commands:

PS> Get-Help Write-Host -Full

PS> Get-Help Write-Host -Examples

PS> Get-Help Write-Host -Online

Pass a different cmdlet as a parameter to Get-Help. Note the two groups of parameters:

PS> Get-Help Get-Command

Compare the outputs of the different commands you ran.
Now, look for Help information for the specific parameter of Write-Host (the second command in the following code is for reference; this states what the first command means to PowerShell):

PS> get-help write-host -par foregroundcolor
PS> # Verbose version: Get-Help -Name Write-Host -Parameter ForegroundColor

Now let's look for a certain keyword within the Help information:

Convert the output of Get-Help Get-Command into text, one string at a time, rather than putting in the entirety of the Help information as a single string:

PS> get-help get-command | out-string -s
PS> # Verbose version: Get-Help Get-Command | Out-String -Stream

Pipe this to the Select-String cmdlet to perform a grep-like operation:

PS> get-help get-command | out-string -s | select-string 'wildcard'
PS> # Verbose version: Get-Help -Name Get-Command | Out-String -Stream | Select-String -Pattern 'wildcard'

This gives you an output of a line that contains wildcard:

How it works...

It is inconvenient to leave your Terminal to read Help online. We would prefer to have all of the Help available locally. PowerShell can potentially work on low-memory devices such as Raspberry, but saving all of the Help in the limited space we have is not advisable. This is one of the reasons PowerShell comes with minimal Help by default. The reason updating Help requires elevated privileges is that the Help information is stored within the shell. Therefore, non-administrators may not be able to update Help without administrator intervention.

As a general practice, cmdlets come pre-packaged with Help information, and Get-Help works like the man command in Linux. The output of Get-Help has the name of the cmdlet, the syntax to use with the cmdlet, the alias(es) available for the cmdlet and more online Help if required. -Full and -Examples are (mutually exclusive) switches that tell PowerShell about the level of Help you need.

The groups of parameters, as seen in the case of Get-Command, under SYNTAX, are called parameter sets. They tell us which parameters can be used together. Parameters not appearing in the same parameter set cannot be used together. For example, you cannot use -Noun and -Name with Get-Command at the same time; it wouldn't be logical to do so.

If the Help information seems elaborate, and you would like to learn about a specific parameter of a cmdlet, you can specify that parameter, and the Help will be filtered accordingly. Since the output of most PowerShell cmdlets is objects, it is easy to select the necessary object and discard the rest from the output. Also note that this is the recommended approach to fetch Help that's specific to a certain parameter.

PowerShell, in general, is case-insensitive. Therefore, Noun and noun, or Parameter and parameter, mean the same thing to it. The use of CamelCase is the general convention in PowerShell. With the almost ubiquitous tab completion, this is a cakewalk.

Next, let's talk about searching Help for specific keywords. PowerShell outputs objects. However, at the end, when the content comes to the host, the content can be processed by Linux commands such as grep. Therefore, to search Help for specific keywords, you could always pipe the output to grep. If you would like to go the PowerShell way (especially if you go by the write once, run everywhere philosophy), this requires minor modifications. First, we fetch the Help; the output is an object (so that it can be processed further if needed). We convert this into a string using Out-String, since search is nothing but string matching.

PowerShell cmdlets output single or multiple instances of objects (we will discuss objects in more detail in the Understanding objects recipe). Out-String waits for all of the Get-Help commands to be processed and converts the output into a single concatenated string. To break the string into chunks, we use the -Stream switch, which instructs Out-String to not concatenate the output. This way, each paragraph is processed separately. Next, we use the Select-String cmdlet, along with the search keyword to perform keyword matching. The output of this is the chunk (paragraph, in this case) with the keyword.

PowerShell Core for Linux Administrators Cookbook

By : Prashanth Jayaram, Ram Iyer

PowerShell Core for Linux Administrators Cookbook

By: Prashanth Jayaram, Ram Iyer

Overview of this book

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