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RFC0065-Install-PowerShell.md

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RFC Author Status SupercededBy Version Area Comments Due Plan to implement
RFC0065
Jason Helmick
Draft
N/A
1.0
Core
6/30/2022
true

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.

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.

    install-powershell7

  • Install the Stable release using the current user scope.

    install-powershell7 --channel stable --scope currentuser

  • Alternative (short) to install the stable release using the current user scope.

    install-powershell7 -c stable -s currentuser