Fixes #11038 - Clarify which env vars need to be set outside of PowerShell

[sdwheeler]

PR Summary

Clarify which env vars need to be set outside of PowerShell

• Fixes AB#247899
• Fixes about_Telemetry POWERSHELL_TELEMETRY_OPTOUT  #11038
• Fixes Clarify that most of the environment variables that PowerShell respects must be set BEFORE starting PowerShell #11039

PR Checklist

• Descriptive Title: This PR's title is a synopsis of the changes it proposes.
• Summary: This PR's summary describes the scope and intent of the change.
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• Style: This PR adheres to the style guide.

[learn-build-service-prod]

Learn Build status updates of commit 90011ab:

✅ Validation status: passed

File	Status	Preview URL	Details
reference/5.1/Microsoft.PowerShell.Core/About/about_Environment_Variables.md	✅Succeeded	View (powershell-5.1)
reference/7.2/Microsoft.PowerShell.Core/About/about_Environment_Variables.md	✅Succeeded	View (powershell-7.2)
reference/7.2/Microsoft.PowerShell.Core/About/about_Telemetry.md	✅Succeeded	View (powershell-7.2)
reference/7.3/Microsoft.PowerShell.Core/About/about_Environment_Variables.md	✅Succeeded	View (powershell-7.3)
reference/7.3/Microsoft.PowerShell.Core/About/about_Telemetry.md	✅Succeeded	View (powershell-7.3)
reference/7.4/Microsoft.PowerShell.Core/About/about_Environment_Variables.md	✅Succeeded	View (powershell-7.4)
reference/7.4/Microsoft.PowerShell.Core/About/about_Telemetry.md	✅Succeeded	View (powershell-7.4)
reference/7.5/Microsoft.PowerShell.Core/About/about_Environment_Variables.md	✅Succeeded	View (powershell-7.5)
reference/7.5/Microsoft.PowerShell.Core/About/about_Telemetry.md	✅Succeeded	View (powershell-7.5)

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[mklement0]

Thanks for the quick turnaround; I think "changes the execution policy current process." should be "changes the execution policy for the current process."

[mklement0]

Note that /etc/zshrc is the appropriate file to use only if zsh is the user's default shell.

If PowerShell is the default shell, /etc/profile must be used, because PowerShell, when invoked with -l (as happens implicitly on macOS for the default shell), reinvokes itself via zsh -l with the latter in POSIX compatibility mode, where /etc/profile rather than /etc/zshrc is sourced.

[sdwheeler]

@mklement0, can you point to documentation for zsh that states that. The documentation I found indicated that /etc/zshrc would be invoked by zsh -l.

[mklement0]

@sdwheeler, when PowerShell re-invokes itself via /bin/zsh -l, it sets argv[0] to /bin/sh, which means that Zsh runs in POSIX compatibility mode, and therefore sources /etc/profile and ~/.profile instead. See https://github.com/PowerShell/PowerShell/blob/b968e101b910c9013988685b6b7b33a1451cc1ce/src/powershell/Program.cs#L274-L303

Here's the relevant Zsh docs link: https://zsh-manual.netlify.app/invocation#42-compatibility

This is somewhat unfortunate, as it means that extra effort is needed for users who want to centralize environment-variable definitions while supporting switching the default shell between zsh and PowerShell. I've updated #10696 (comment) to hopefully now paint the complete picture.

[mklement0]

As also noted in the linked issue, the /etc/profile / /etc/profile.d approaches on non-GUI Linux distros - e.g. in Docker images - require explicit invocation via pwsh -l to take effect.