Windows PowerShell inherits PSModulePath from PowerShell Core

If you start Windows PowerShell from PowerShell Core, you get the $env:PSModulePath from PowerShell Core.

In my opinion, this should be a 6.0.0 blocker. Also, if any work needs to be done in Windows PowerShell to fix this, we should do it ASAP.

Steps to reproduce

From PowerShell Core:

Start-Process powershell

This will open a new instance of Windows PowerShell. From this instance:

$env:PSModulePath

Expected behavior

C:\Users\jaiello\Documents\WindowsPowerShell\Modules;C:\Program Files\WindowsPowerShell\Modules;C:\WINDOWS\system32\WindowsPowerShell\v1.0\Modules

Also, PSReadline should load.

Actual behavior

C:\Users\jaiello\Documents\PowerShell\Modules;C:\Program Files\PowerShell\Modules;c:\program files\powershell\6.0.0.12\Modules

Also, PSReadline doesn’t load because it can’t be found.

Environment data

For PowerShell Core:

Name                           Value
----                           -----
PSVersion                      6.0.0-alpha
WSManStackVersion              3.0
SerializationVersion           1.1.0.1
GitCommitId                    v6.0.0-alpha.12
CLRVersion
BuildVersion                   3.0.0.0
PSRemotingProtocolVersion      2.3
PSEdition                      Core
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0...}

For Windows PowerShell;

Name                           Value
----                           -----
PSVersion                      5.1.14931.1000
PSEdition                      Desktop
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0...}
BuildVersion                   10.0.14931.1000
CLRVersion                     4.0.30319.42000
WSManStackVersion              3.0
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1

[SteveL-MSFT]

Agree with @iSazonov this is by-design as child processes are expected to inherit environment from parent. The way to address this may be to have PSModulePath in https://github.com/PowerShell/PowerShell-RFC/blob/master/1-Draft/RFC0015-PowerShell-StartupConfig.md

[iSazonov]

It is expected because subprocess always inherits environment variables of parent process. If we change the default behavior it can confuse users. We would backup PSModulePath on startup and restore before create subprocess. Or create $env:PSModulePath_Backup and check it on PowerShell startup. The second is seems easier.