RFC Install-PowerShell

Draft-Accepted/RFC0065-Install-PowerShell.md

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+---
+RFC: RFC0065
+Author: Jason Helmick
+Status: Draft
+SupercededBy: N/A
+Version: 1.0
+Area: Core
+Comments Due: 6/30/2022
+Plan to implement: Yes
+---
+
+# Install-PowerShell7 Native Command
+
+This RFC proposes adding a `install-powershell7` native command to Windows to perform a simplified
+installation of the latest Long Term Service (LTS) release of PowerShell 7.
+
+## Motivation
+
+Many IT customers of PowerShell face a problem in which they don't control the landscape of software
+pre-installed on the Windows Servers they manage. Explicitly installing PowerShell is a blocker for
+some customers due to discoverability and some that have policies that don't allow for installing
+software onto Windows after initial provisioning.
+
+To compensate for these situations, customers will implement and use the "tools at hand" to perform
+management tasks. This leaves **Windows PowerShell 5.1**, not **PowerShell 7**, as the only
+automation solution available to many of them. While customers are missing out on useful new
+features that they may wish to have, they are certainly not receiving the performance and security
+improvements that come with each new release.
+
+This specification is an effort to help IT admins that wish to use new and updated releases of
+PowerShell 7. While this may not help customers that have post-deployment policy restrictions, it
+will help the majority of customers discover and update to the latest version of PowerShell for
+Windows.
+
+```
+As a user,
+I can discover and install PowerShell 7 from Windows PowerShell 5.1 or `cmd.exe` on my Windows machine,
+so that I can leverage new capabilities in PS7.
+```
+
+Additional scenarios are enabled when considering a native command versus a cmdlet. While Windows
+users would find benefit and familiarity to a cmdlet, a native command opens up scenarios where
+PowerShell is not pre-installed.
+
+Users can still use Windows Package Manager Client (winget) to install PowerShell 7, however, it is
+not available on all platforms.
+
+## Shipping in Windows
+
+There are several issues that prevent shipping PowerShell 7 in Windows:
+
+- Size
+- Support lifecycle differences
+
+### Size constraints
+
+ A complete installation of PowerShell 7 currently is around 200 MB (unpacked). This is due to
+ including everything (modules and .NET assemblies) to provide parity with what Windows PowerShell
+ 5.1 with .NET Framework provides. There is currently no plan by Windows or the .NET team to ship
+ newer .NET in Windows, so PS7 will need to continue to ship .NET with PS7.
+
+### Support lifecycle
+
+ Windows has a 5+5 year support lifecycle. .NET supports up to 3 years for Long Term Support (LTS)
+ versions. So even if size was not an issue, we cannot check in a version of PS7 with a .NET that is
+ not supported while Windows itself is supported.
+
+### Solution
+
+To solve these issues, the proposal is to ship a new command in Windows that would:
+
+- Be locally discoverable
+- Perform a simple download and install of the latest LTS release of PowerShell
+- Include parameter options to select Stable, Preview, or LTS releases
+
+## Goals/Non-Goals
+
+Goals:
+
+- By default, download and install the latest LTS release to the users CurrentUser Scope
+  - CurrentUser - default installation scope location
+  - AllUsers - Administrative users may explicit select this scope. AllUsers requires administrative
+    elevation and performs a silent install using the MSI defaults.
+- Allow advanced users to specify channel Stable/Preview/LTS
+- Tool will not partially install and leave any existing PowerShell in a non-functioning state.
+
+Non-goals:
+
+- Removal of PowerShell (Remove-PowerShell7)
+- Updating of PowerShell (Update-PowerShell7)
+- User selected versions prior to current (No version parameter)
+- Disconnected scenarios - Users that are air-gapped may download the appropriate release from GitHub.
+- Handling of additional MSI switch options - i.e. Enable PSRemoting
+- Cross platform support
+- Deployments at scale
+
+## Specification
+
+Command name: install-powershell7
+
+The default behavior is to install the zip package silently to CurrentUser scope, with the latest LTS
+release of PowerShell. If the user has administrative
+privilege, they can choose to install the msi package silently to the scope of AllUsers.
+
+- The stable and LTS package install location - $env:LOCALAPPDATA\Local\Programs\PowerShell
+  - If path exists, Provide an error "PowerShell 7 is already installed, use --clobber to overwrite
+    existing installation"
+- The preview package install location - $env:LOCALAPPDATA\Local\Programs\PowerShell-Preview
+  - If path exists, Provide an error "PowerShell 7 Preview is already installed, use --clobber to overwrite
+    existing installation"
+- Detect if Powershell is in use in the target folder and provide error "PowerShell is currently in
+  use. Please close all Powershell instances and run the command from Start->Run or cmd.exe."
+- The installer should update the `$ENV:PATH` and Users PATH in the registry.
+- The installer should enable Microsoft Updates for scope AllUsers.
+- The command should show a progress bar during the download and installation of PowerShell 7.
+- The command should produce an error if the download location (US based url) fails.
+
+The following parameters can be added by experienced PowerShell users to customize the installation.
+
+- Parameter: Scope - overrides the default of CurrentUser and allows the user to specify the
+  installation location AllUsers.
+- Parameter: Channel - options LTS/Stable/Preview - allows the user to select if they want the
+  current preview or LTS release (default).
+
+## Syntax
+
+The command `install-powershell7` is lower case and supports `-` or `--` parameters to be consistent
+with other command-line tools.
+
+```syntax
+install-powershell7  [--channel <option>] [--scope <option>] [--clobber]
+install-powershell7  [-c <option>] [-s <option>] [--clobber]
+```
+
+The `--channel <option>` must be one of the following:
+
+- `--channel preview`
+- `--channel stable`
+- `--channel lts`
+
+If you don't provide a channel option, the command defaults to `-channel lts`.
+
+The `--scope <option>` must be one of the following:
+
+- `--scope allusers`
+- `--scope currentuser`
+
+If you don't provide a scope option, the command defaults to `--scope currentuser`.
+
+Scope selection has an impact on receiving auto-updates from Microsoft Update:
+
+- `--scope allusers` is an MSI-based installation with Microsoft Update enabled.
+- `--scope currentuser` is a ZIP-based installation. Users will need to manually
+  update when a new version is released.
+
+The optional `--clobber` switch overwrites a previous installation.
+
+## Demo.txt
+
+- Install the latest LTS version by default.
+
+  ```powershell
+  install-powershell7 
+  ```
+
+- Install the Stable release using the current user scope.
+
+  ```powershell
+  install-powershell7 --channel stable --scope currentuser
+  ```
+
+- Alternative (short) to install the stable release using the current user scope.
+
+  ```powershell
+  install-powershell7 -c stable -s currentuser
+  ```