PowerShell/CrashCourse.md

# PowerShell Scripting Crash Course

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

```powershell
# 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.](https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_case-sensitivity?view=powershell-7.3) This means `$MyInvocation` works just the same as `$mYinoCAtiOn` 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 `=`

```powershell
$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](https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_comparison_operators?view=powershell-7.3) which can be used with `if` or `while` like this:

```powershell
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

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

There are [a lot of different powers](https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_functions_advanced_parameters?view=powershell-7.3) behind the square bracket syntax, [including custom validation](https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_functions_advanced_parameters?view=powershell-7.3#validatescript-validation-attribute), 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:

```powershell
if ($silent) { exit }
Write-Host "Hello $name"
if ($age) {
  Write-Host "according to the -age you provided you are: $age"
}
```

And run like this:

```powershell
name_and_age.ps1 -name "Rose" -age "27"
# or, arguments are also positional!
name_and_age.ps1 "Rose" "27"
```

# 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)

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

  $x + $y
}
```

# foreach

Works on [arrays](https://learn.microsoft.com/en-us/powershell/scripting/lang-spec/chapter-09?view=powershell-7.3#92-array-creation), which can be concatenated with `+` and `+=` by the way.

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

And also works for results from `Get-ChildItem` like when looping through files in a folder.

```powershell
foreach ($file in Get-ChildItem)
{
  if ($file.length -gt 100KB)
  {
    Write-Host $file
  }
}
```

# items and paths

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

- [`New-Item`](https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.management/new-item?view=powershell-7.3#description) - create a file or folder
- [`Remove-Item`](https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.management/remove-item?view=powershell-7.3#description) - delete a file or folder
- [Move, Invoke, Rename etc...](https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.management/?view=powershell-7.3)

Here's how to loop through files in a folder using [`Get-ChildItem`](https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.management/get-childitem?view=powershell-7.3#description):

```powershell
foreach ($image Get-ChildItem $path -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](https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.management/?view=powershell-7.3). Here are some examples:

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

# See Also

- [About scripts (learn.microsoft.com)](https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_scripts?view=powershell-7.3)