PowerShell Scripting Crash Course

After having followed the README.md, .ps1 scripts in the same folder as $PROFILE.CurrentUserAllHosts will be available in $env:PATH globally:

# Open the $PROFILE folder
explorer (Split-Path -Parent $PROFILE.CurrentUserAllHosts)
codium (Split-Path -Parent $PROFILE.CurrentUserAllHosts)
# Or start directly editing a script
notepad "$(Split-Path -Parent $PROFILE.CurrentUserAllHosts)\my-script.ps1"
codium "$(Split-Path -Parent $PROFILE.CurrentUserAllHosts)\my-script.ps1"

variables

PowerShell is as case-insensitive as possible. This means $MyInvocation works just the same as $mYinVoCAtiOn among other things. Coming from a Unix background and preferring some consistency I like to pretend it is case-sensitive so in this repo I'll strive for that but it's worth keeping in mind. Especially since the Microsoft docs use case a lot in variable and cmdlet names.

Variables use $ to distinguish themselves and can be set with =

$a_variable = "this one is a string"
$interpolate_a_string = "like this: $a_variable"

booleans

There are a few constants to know: $true, $false, $null. Empty strings ("", ''), $null and 0 evaluate as $false

if and while

There are a handful of comparison operators which can be used with if or while like this:

if ($val -eq "y") {
  Write-Host "value is a y"
}
else {
  Write-Host "value is not a y"
}

while ($num -lt 50) {
  $num = $num + 1
}

param

At the beginning of scripts and functions param list can be specified like this

param(
  [string]$name = "Anonymous",
  [int]$age,
  [switch]$silent
)

There are a lot of different powers behind the square bracket syntax, including custom validation, but these are the basics. Use [parameter(mandatory)] to require one otherwise they are optional. The above param block could be used in a script like this:

# Name-And-Age.ps1
if ($silent) { exit }
Write-Host "Hello $name"
if ($age) {
  Write-Host "according to the -age you provided you are: $age"
}

And run like this:

Name-And-Age.ps1 -name "Rose" -age "27"
# or, arguments are also positional!
Name-And-Age.ps1 "Rose" "27"

Get-Help

You can learn about the available param list for pretty much anything in PowerShell with the Get-Help cmdlet.

Get-Help Get-Help
Get-Help New-Item
Get-Help Name-And-Age.ps1

functions

Functions use param too (instead of parenthesis like other languages). The last value is the return result, (which you can also use to return early... or just regularly if you want)

function My-Add {
  param(
    [parameter(mandatory)][int]$x,
    [parameter(mandatory)][int]$y,
  )

  $x + $y
}

foreach

Works on arrays, which can be concatenated with + and += by the way.

$letterArray = "a","b","c","d"
foreach ($letter in $letterArray)
{
  Write-Host $letter
}

items and paths

In PowerShell files and folders are called items. Some useful cmdlets for working with them are:

New-Item - create a file or folder
Remove-Item - delete a file or folder
Move, Invoke, Rename etc...

Here's how to loop through files in a folder using Get-ChildItem:

foreach ($image Get-ChildItem .\images\* -Include *.png) {
    Write-Host $image.BaseName
}

There are also a handful of useful functions for dealing with path strings by the names of [Verb]-Path. Note that in PowerShell folders are containers and files are leafs. Here are some examples:

# Get parent folder
Split-Path -Parent $path
# Test if a file exists. For folder use `-PathType container`
Test-Path -Path $path -PathType leaf

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