Stop altering the PATH env variable by honoring the `PSHome` path in `CommandDiscovery` by daxian-dbw · Pull Request #27757 · PowerShell/PowerShell

Dongbo Wang (daxian-dbw) · 2026-08-03T21:56:26Z

Context

Altering the PATH env variable causes a problem to cmake-based build system when running in the MSIX PowerShell installation because they cache the location of PowerShell sometimes.

At startup, PowerShell adds $PSHOME to the beginning of PATH, and for MSIX installation, $PSHOME contains version numbers that change when PowerShell is updated.

When cmake is started from MSIX PowerShell, the path it caches will be that $PSHOME, which will become invalid after an update of the MSIX PowerShell.

PR Summary

The main change of this PR is to move the logic for ensuring the current PowerShell's executable directory ($PSHOME) is prioritized in command lookup from prepend it to PATH at startup to the CommandDiscovery process itself. This results in a more accurate and less intrusive handling of PATH. The PR also improves test coverage for these scenarios.

Refactoring of PATH handling:

The logic for prepending PSHOME to the PATH environment variable is removed from ConsoleHost.cs, so PowerShell no longer alters PATH during startup.
The logic to ensure PSHOME is always the first lookup directory is now implemented in CommandDiscovery.cs within the GetLookupDirectoryPaths method, regardless of the state of the PATH variable. This includes handling cases where PATH is unset and expanding ~ to the user home directory.
Skip the duplicate path of _psHome when constructing _cachedLookupPaths.

Code cleanup and caching improvements:

Removed the _cachedPath field and streamlined the caching logic for lookup paths in CommandDiscovery.cs.

Test updates:

Updated and added tests in ConsoleHost.Tests.ps1 to verify that running pwsh always starts the current version and that PATH remains unaltered during startup, including when PATH is unset.

PR Checklist

…andDiscovery

azure-pipelines · 2026-08-03T21:56:36Z

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Copilot

Pull request overview

This PR stops PowerShell from modifying the PATH environment variable at startup and instead ensures the current PowerShell installation directory ($PSHOME) is prioritized during command lookup inside CommandDiscovery, addressing issues with tools (e.g., CMake) caching an MSIX-versioned pwsh path. It also updates/extends tests to validate pwsh resolution and behavior when PATH is unset.

Changes:

Removed startup-time PATH mutation from ConsoleHost.
Updated CommandDiscovery.GetLookupDirectoryPaths() to always prioritize the current pwsh location (including global tool path correction) without editing PATH.
Updated Pester tests to validate pwsh version resolution and that startup does not populate PATH when it is unset.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
`src/Microsoft.PowerShell.ConsoleHost/host/msh/ConsoleHost.cs`	Removes logic that prepended `$PSHOME` to `PATH` during startup.
`src/System.Management.Automation/engine/CommandDiscovery.cs`	Prioritizes `$PSHOME` in lookup paths and streamlines path caching/tilde expansion.
`test/powershell/Host/ConsoleHost.Tests.ps1`	Adjusts/adds tests for `pwsh` resolution and verifies `PATH` remains unaltered when unset.

Justin Chung (jshigetomi) · 2026-08-04T18:38:13Z

Would this effect embedded pwsh runspaces and their command discovery look up order? For embedded pwsh, I believe the location of SMA.dll would be the pshome that gets prepended to the path by command discovery.

Any name collision in that SMA.dll location would be unintended. I can't imagine this happening often.

Dongbo Wang (daxian-dbw) · 2026-08-04T22:38:29Z

That's a good point Justin Chung (@jshigetomi). Let me think about the impact to the applications that host PowerShell using the NuGet packages.

Dongbo Wang (daxian-dbw) · 2026-08-05T17:45:40Z

Justin Chung (@jshigetomi) I've updated the changes to take into account the "PowerShell hosted by application via NuGet packages" scenario. In that case, we will use the PATH as is. Can you please review again?

Justin Chung (jshigetomi)

LGTM

Dongbo Wang (daxian-dbw) · 2026-08-07T18:36:01Z

Converted this PR to draft.
There are 2 concerns about this change:

It will cause behavior change to console apps started from pwsh. For example, when you use fzf with a preview command that launches pwsh, it may be using a different pwsh after this change.
Do it in command discovery adds a bit of magic to gcm pwsh. If something went wrong, it'd be hard for a user to reason the root cause.

I submitted another draft PR at #27782 as a different approach for solving the cmake issue stemmed from MSIX installation. Ilya (@iSazonov), please take a look and share your thoughts.

Dongbo Wang (daxian-dbw) · 2026-08-10T22:10:34Z

Stop altering the PATH env variable by honoring the PSHome path in CommandDiscovery by daxian-dbw · Pull Request #27757 · PowerShell/PowerShell
- Pros:
  - Less work during startup.
  - No PATH change so less intrusive.
- Cons:
  - Behavior change for console app started from pwsh. For example, when you use ‘fzf’ with a preview command that launches ‘pwsh’, it may use a different pwsh after this change.
  - "gcm pwsh" acts with a bit of magic after the change.
  - A nested ‘pwsh’ will inherit the PSModulePath of the top-level ‘pwsh’ and inserts its PSHOME module path before the top-level pwsh’s PSHOME module path in majority cases, but it’s still possible for a user to mess with the PSModulePath with the intent to break the nested ‘pwsh’
Handle MSIX installation specially when prepend to PATH by daxian-dbw · Pull Request #27782 · PowerShell/PowerShell
- Pros:
  - No behavior change to console app started from pwsh.
  - No magic to “gcm pwsh”
  - Less possible for a nested pwsh to go wrong with the PSModulePath
- Cons:
  - More work during startup
  - More future issues caused by altering PATH? Not sure about it.

The team discussed the pros/cons of those 2 approaches and decided to go with #27782, because it's less risky.
So, closing this PR.

Dongbo Wang (daxian-dbw) added 2 commits August 3, 2026 14:18

Stop altering the PATH env variable but honor the PSHome path in Comm…

c981321

…andDiscovery

Minor change

57ab3f0

Dongbo Wang (daxian-dbw) requested a review from a team as a code owner August 3, 2026 21:56

Copilot AI review requested due to automatic review settings August 3, 2026 21:56

Copilot started reviewing on behalf of Dongbo Wang (daxian-dbw) August 3, 2026 21:56 View session

Copilot AI reviewed Aug 3, 2026

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Comment thread test/powershell/Host/ConsoleHost.Tests.ps1 Outdated

Comment thread test/powershell/Host/ConsoleHost.Tests.ps1

Comment thread test/powershell/Host/ConsoleHost.Tests.ps1 Outdated

Comment thread src/System.Management.Automation/engine/CommandDiscovery.cs Outdated

Dongbo Wang (daxian-dbw) added 2 commits August 3, 2026 15:22

Skip duplicate path of $PSHOME

9da7c31

Address Copilot feedback

201b9ac

Dongbo Wang (daxian-dbw) added the CL-Engine Indicates that a PR should be marked as an engine change in the Change Log label Aug 3, 2026

Fix a Start-Process test

c91cf83

Ilya (iSazonov) reviewed Aug 4, 2026

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Comment thread src/System.Management.Automation/engine/CommandDiscovery.cs

Dongbo Wang (daxian-dbw) added 3 commits August 4, 2026 17:42

Detect hosted PowerShell

dedfa78

Small update

0fc9ec5

Rename _psHome to _psExeHome to differentiate it from $PSHOME

09c0e34

Justin Chung (jshigetomi) approved these changes Aug 5, 2026

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Ilya (iSazonov) reviewed Aug 6, 2026

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Comment thread src/System.Management.Automation/engine/CommandDiscovery.cs Outdated

Ilya (iSazonov) approved these changes Aug 7, 2026

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Dongbo Wang (daxian-dbw) marked this pull request as draft August 7, 2026 18:31

Dongbo Wang (daxian-dbw) added 2 commits August 10, 2026 14:55

Revert code changes

1cf844b

Revert test changes

75a101a

Dongbo Wang (daxian-dbw) force-pushed the env-path branch from d872919 to 75a101a Compare August 10, 2026 22:02

Dongbo Wang (daxian-dbw) closed this Aug 10, 2026

Dongbo Wang (daxian-dbw) deleted the env-path branch August 10, 2026 22:51

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Stop altering the PATH env variable by honoring the `PSHome` path in `CommandDiscovery` - #27757

Stop altering the PATH env variable by honoring the `PSHome` path in `CommandDiscovery`#27757
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