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Powershell

Table of Contents

    Introduction to PowerShell

    What is PowerShell?

    PowerShell is a powerful tool from Microsoft designed for task automation and configuration management. It combines a command-line interface and a scripting language built on the .NET framework.

    Why Use PowerShell Scripting?

    There are a few key reasons why you might want to use PowerShell:

    • Automation : PowerShell allows you to automate repetitive tasks, saving you time and reducing the risk of human error. You can write scripts to perform complex tasks with just a few commands.
    • System Administration : PowerShell provides a powerful set of commands (called "cmdlets") that allow you to manage various aspects of your Windows system, such as managing services, configuring network settings, and more.
    • Cross-Platform : While PowerShell was originally developed for Windows, it is now also available on other platforms like macOS and Linux, allowing you to use the same tool across different operating systems.

    Setting Up Your Environment

    Install Powershell

    • Windows : PowerShell is pre-installed on most modern Windows systems. If you need to update it, you can download the latest version from the Microsoft PowerShell GitHub repository.
    • macOS and Linux : You can install PowerShell on these platforms by following the instructions on the PowerShell documentation site. Powershell_Linux , Powershell_macOS

    Run Powershell

    • Windows :
      • Start Menu : Type powershell in the Windows Start Menu search bar, then click on Windows PowerShell or PowerShell from the results.
      • Run Dialog : Press Win + R to open the Run dialog, type powershell, and hit Enter.
      • File Explorer : Navigate to any folder, then type powershell in the address bar, and press Enter. This opens PowerShell in that specific directory.
      • Task Manager : Open the Task Manager, go to File > Run new task, type powershell, and press Enter.
    • macOS and Linux : Open the Terminal application and type pwsh to start the PowerShell session.

    PowerShell Basics

    Running Commands

    You can run different types of command in Powershell, like : Cmdlets (ex: Get-Process), Functions, Scripts (ex: .ps1), Executables (ex: notepad.exe), Aliases (ex: ls), Operators (ex: 7*7) etc.

    Writing Your First Script

    • Create a script file (script.ps1) and add the following:
      Code powershell
      Write-Host "Hello World, FROM PowerShell!!"
    • Run the script using .\script.ps1

    Comments

    • Single-line comments start with #:
      Code powershell
      # This is a comment
Write-Host "This line will execute"
    • Multi-line comments are enclosed in <# and #>:
      Code powershell
      <#
This is a
multi-line comment
#>

    Cmdlets

    PowerShell cmdlets are built-in commands that follow the naming convention Verb-Noun.

    Variables and Data Types

    Defining Variables

    Variables in PowerShell are prefixed with $ :

    Code powershell
    $name = "John"
Write-Host "Hello, $name"

    Common Data Types

    PowerShell is a dynamically typed language and automatically infers data types:

    Code powershell
    $num = 42        # Integer
$text = "Hello"  # String
$flag = $true    # Boolean

    Variable Scopes

    Variables can have different scopes (Global, Local, Private, Script):

    Code powershell
    $global:globalVar = "I am Global"  # Accessible anywhere in the current powershell session
$script:scriptVar = "I am Script Scoped"  # Accessible only within this script

function TestScope {
    $local:localVar = "I am Local"  # Accessible only within this function
    $private:privateVar = "I am Private"  # Not inherited by child scopes

    Write-Host "Inside Function:"       # Inside Function:
    Write-Host "Global: $globalVar"     # Global: I am Global
    Write-Host "Script: $scriptVar"     # Script: I am Script Scoped
    Write-Host "Local: $localVar"       # Local: I am Local
    Write-Host "Private: $privateVar"   # Private: I am Private
}

TestScope

Write-Host "Outside Function:"
Write-Host "Global: $globalVar"  # Global: I am Global
Write-Host "Script: $scriptVar"  # Script: I am Script Scoped
Write-Host "Local: $localVar"  # Not accessible (undefined)
Write-Host "Private: $privateVar"  # Not accessible (undefined)

    Conditional Statements

    if-else Statements

    Used to execute different code blocks based on a condition.

    Code powershell
    # Syntax of if-else 
if (condition) {
    # code to execute if condition is true
} else {
    # code to execute if condition is false
}

    switch Statements

    Used to execute different code blocks based on multiple conditions.

    Code powershell
    # Syntax of switch statement
switch (variable) {
    condition1 { 
        # code to execute if variable matches condition1
    }
    condition2 {
        # code to execute if variable matches condition2  
    }
    default {
        # code to execute if variable doesn't match any condition
    }
}

    Loops

    for Loop

    Executes a block of code a specific number of times.

    Code powershell
    for ($i = 0; $i -lt 5; $i++) {
    # code to execute in the loop
}

    foreach Loop

    Iterates over a collection of items and executes a block of code for each item.

    Code powershell
    $myArray = 1, 2, 3, 4, 5
foreach ($item in $myArray) {
    # code to execute for each item in the array
}

    while Loop

    Executes a block of code as long as a condition is true.

    Code powershell
    $counter = 0
while ($counter -lt 5) {
    # code to execute in the loop
    $counter++
}

    Functions

    Declaring Functions

    A function is defined using the function keyword. Example:

    Code powershell
    function Greet {
    Write-Output "Hello, Welcome to PowerShell!"
}

    A function can be run directly into Powershell. To call above function run Greet in powershell.

    Function with parameter/s

    Using param($PARAMETER1,$PARAMETER2) to take parameters. Example:

    Code powershell
    function Add-Numbers {
    param([int]$a, [int]$b)
    return $a + $b
}

$result = Add-Numbers -a 5 -b 10
Write-Output "Sum: $result"

    Input and Output

    Reading User Input

    PowerShell provides the Read-Host cmdlet to prompt the user for input.

    Code powershell
    $name = Read-Host "What is your name?"

    Writing to Files

    You can use the Out-File cmdlet to write output to a file.

    Code powershell
    $data | Out-File -FilePath "output.txt"

    Redirecting Output

    You can use the > operator to redirect output to a file.

    Code powershell
    Get-Process > processes.txt   # Redirects standard output to a file
Get-Content "nonexistent.txt" 2> error.log  # Redirects error to a file
Get-Process *> alloutput.log   # Redirects all output (success & errors) to a file

    Error Handling

    Try-Catch-Finally

    Used to handle exceptions and errors in your scripts

    Code powershell
    try {
    # code that might throw an exception
}
catch {
    # code to handle the exception
}
finally {
    # code to execute regardless of whether an exception was thrown
}

    $Error Variable

    PowerShell maintains an array of recent errors in the $Error variable.

    Code powershell
    try {
    # code that might throw an exception
}
catch {
    Write-Host "An error occurred: $($_.Exception.Message)"
    $Error[0] # access the most recent error
}

    Advanced Topics

    Arrays and Hash Tables

    Array : An array stores multiple values in a single variable.

    Code powershell
    $numbers = @(1, 2, 3, 4, 5)
$numbers[0]  # Access first element
$numbers += 6  # Add new element

    Hash table : A hash table stores key-value pairs.

    Code powershell
    $person = @{ Name = "Alice"; Age = 25; Role = "Admin" }
$person["Name"]  # Access value
$person["Age"] = 26  # Modify value

    Pipelines

    Pipelines (|) pass output from one command as input to another.

    Code powershell
    Get-Process | Sort-Object -Property CPU -Descending | Select-Object -First 5

    This gets running processes, sorts by CPU usage, and selects the top 5.