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PowerShell is an object-oriented shell and scripting language designed for automation. It differs from Bash in that it works with objects rather than plain text. Here’s a deep dive into PowerShell syntax and concepts.

1. Shebang Equivalent

Unlike Bash, PowerShell scripts (.ps1 files) do not require a shebang. They are executed like this:

powershell -ExecutionPolicy Bypass -File script.ps1

However, to execute PowerShell scripts, you may need to change execution policies:

Set-ExecutionPolicy RemoteSigned -Scope CurrentUser

2. Variables & Expansion

2.1 Assigning Variables

$name = "Alice"
$age = 25
  • Variables always start with $
  • No need to declare types, but PowerShell supports strong typing:
[int]$number = 42
[string]$text = "Hello"

2.2 Referencing Variables

Write-Output "Hello, $name!"
Write-Output "Next year you will be $($age + 1)"
  • $(...) is used for inline expressions inside double-quoted strings.

2.3 Command Substitution (Backticks in Bash)

$date = Get-Date
Write-Output "Today is: $date"

3. Quoting & Escaping

PowerShell treats quotes differently:

Quote Type Effect
" " Expands variables
' ' Literal text, no expansion

Example:

$name = "Alice"
Write-Output "Hello, $name"  # Expands
Write-Output 'Hello, $name'  # Prints "Hello, $name"

Escaping:

  • Use backtick (```) for escaping:
Write-Output "This is a new`nline"
  • For special characters ($, ", @), use backticks:
Write-Output "`$name is a variable"

4. Arrays & Hash Tables

4.1 Indexed Arrays

$fruits = @("apple", "banana", "cherry")
Write-Output $fruits[0]   # apple
Write-Output $fruits[-1]  # Last element
Write-Output $fruits.Count

4.2 Hash Tables (Associative Arrays)

$capitals = @{
    "France" = "Paris"
    "Germany" = "Berlin"
}
Write-Output $capitals["France"]

5. Conditionals (if, switch)

5.1 Basic If-Else

if ($name -eq "Alice") {
    Write-Output "Hello, Alice!"
} else {
    Write-Output "Who are you?"
}
  • -eq, -ne, -gt, -lt are used for comparisons.

5.2 File Checks

if (Test-Path "C:\Windows") {
    Write-Output "Directory exists"
}

5.3 Switch Case

$color = "red"
switch ($color) {
    "red" { Write-Output "Stop!" }
    "yellow" { Write-Output "Slow down!" }
    "green" { Write-Output "Go!" }
}

6. Loops (for, foreach, while, do)

6.1 For Loop

for ($i = 1; $i -le 5; $i++) {
    Write-Output "Number $i"
}

6.2 Foreach Loop

$fruits = @("apple", "banana", "cherry")
foreach ($fruit in $fruits) {
    Write-Output "I like $fruit"
}

6.3 While Loop

$counter = 1
while ($counter -le 5) {
    Write-Output "Count: $counter"
    $counter++
}

6.4 Do-While Loop

$num = 1
do {
    Write-Output "Number: $num"
    $num++
} while ($num -le 5)

7. Functions

function Greet {
    param($name)
    Write-Output "Hello, $name!"
}
Greet "Alice"

Returning values:

function Add {
    param($a, $b)
    return $a + $b
}
$result = Add 3 5
Write-Output "Sum: $result"

8. Special Variables

Variable Description
$PSVersionTable.PSVersion PowerShell version
$env:Path System environment variable
$args Script arguments
$? Last command success status
$LASTEXITCODE Exit code of last external command

Example:

Write-Output "Last command succeeded: $?"

9. Redirection & Pipes

9.1 Redirect Output

Get-Process > processes.txt   # Save stdout
Get-Process >> processes.txt  # Append stdout
Get-Process 2> errors.txt     # Save stderr

9.2 Piping

Get-Process | Where-Object { $_.CPU -gt 10 }
  • | passes objects between commands.
  • { $_.Property } is used to reference object properties.

10. Process Management

Run commands in the background:

Start-Process -NoNewWindow -FilePath "notepad.exe"
  • Get-Process → Lists running processes
  • Stop-Process -Id 1234 → Terminates a process

11. Wildcards & Expansion

11.1 Wildcards

Pattern Meaning
* Matches anything
? Matches a single character
[a-c] Matches a, b, or c

Example:

Get-ChildItem C:\*.txt

Final Notes

  • Use Get-Help Command for documentation.
  • Debug scripts with Set-PSDebug -Trace 1.
  • PowerShell outputs objects, not plain text.