142 lines
5.1 KiB
Markdown
142 lines
5.1 KiB
Markdown
# PowerShell Scripting Crash Course
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After having followed the [README.md](./README.md), `.ps1` scripts in the same folder as `$PROFILE.CurrentUserAllHosts` will be available in `$env:PATH` globally:
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```powershell
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# Open the $PROFILE folder
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explorer (Split-Path -Parent $PROFILE.CurrentUserAllHosts)
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codium (Split-Path -Parent $PROFILE.CurrentUserAllHosts)
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# Or start directly editing a script
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notepad "$(Split-Path -Parent $PROFILE.CurrentUserAllHosts)\my-script.ps1"
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codium "$(Split-Path -Parent $PROFILE.CurrentUserAllHosts)\my-script.ps1"
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```
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# variables
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[PowerShell is as case-insensitive as possible.](https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_case-sensitivity?view=powershell-7.3) This means `$MyInvocation` works just the same as `$mYinVoCAtiOn` among other things. Coming from a Unix background and preferring some consistency I like to pretend it is case-sensitive so in this repo I'll strive for that but it's worth keeping in mind. Especially since **the Microsoft docs use case a lot** in variable and cmdlet names.
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Variables use `$` to distinguish themselves and can be set with `=`
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```powershell
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$a_variable = "this one is a string"
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$interpolate_a_string = "like this: $a_variable"
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```
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## booleans
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There are a few constants to know: `$true`, `$false`, `$null`. Empty strings (`""`, `''`), `$null` and `0` evaluate as `$false`
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# if and while
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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:
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```powershell
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if ($val -eq "y") {
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Write-Host "value is a y"
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}
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else {
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Write-Host "value is not a y"
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}
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while ($num -lt 50) {
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$num = $num + 1
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}
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```
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# param
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At the beginning of scripts and functions `param` list can be specified like this
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```powershell
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param(
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[string]$name = "Anonymous",
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[int]$age,
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[switch]$silent
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)
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```
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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:
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```powershell
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# Name-And-Age.ps1
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if ($silent) { exit }
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Write-Host "Hello $name"
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if ($age) {
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Write-Host "according to the -age you provided you are: $age"
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}
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```
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And run like this:
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```powershell
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Name-And-Age.ps1 -name "Rose" -age "27"
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# or, arguments are also positional!
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Name-And-Age.ps1 "Rose" "27"
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```
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# Get-Help
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You can learn about the available `param` list for pretty much anything in PowerShell with the `Get-Help` cmdlet.
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```powershell
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Get-Help Get-Help
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Get-Help New-Item
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Get-Help Name-And-Age.ps1
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```
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# functions
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Functions use `param` too (instead of parenthesis like other languages). The last value is the `return` result, (which you can also use to `return` early... or just regularly if you want)
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```powershell
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function My-Add {
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param(
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[parameter(mandatory)][int]$x,
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[parameter(mandatory)][int]$y,
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)
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$x + $y
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}
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```
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# foreach
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Works on [arrays](https://learn.microsoft.com/en-us/powershell/scripting/lang-spec/chapter-09?view=powershell-7.3#92-array-creation), which can be concatenated with `+` and `+=` by the way.
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```powershell
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$letterArray = "a","b","c","d"
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foreach ($letter in $letterArray)
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{
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Write-Host $letter
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}
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```
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# items and paths
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In PowerShell files and folders are called items. Some useful cmdlets for working with them are:
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- [`New-Item`](https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.management/new-item?view=powershell-7.3#description) - create a file or folder
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- [`Remove-Item`](https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.management/remove-item?view=powershell-7.3#description) - delete a file or folder
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- [Move, Invoke, Rename etc...](https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.management/?view=powershell-7.3)
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Here's how to loop through files in a folder using [`Get-ChildItem`](https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.management/get-childitem?view=powershell-7.3#description):
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```powershell
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foreach ($image Get-ChildItem .\images\* -Include *.png) {
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Write-Host $image.BaseName
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}
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```
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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). Note that in PowerShell folders are `container`s and files are `leaf`s. Here are some examples:
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```powershell
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# Get parent folder
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Split-Path -Parent $path
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# Test if a file exists. For folder use `-PathType container`
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Test-Path -Path $path -PathType leaf
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```
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# See Also
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- [About scripts (learn.microsoft.com)](https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_scripts?view=powershell-7.3)
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