Reset environment variables

env-reset.ps1

# initial stash of process vars that will overwrite Machine / User vars
if (! $processVars)
{
  # capture all variables by name, using whats currently available in-proc for values (already expanded)
  $processVars = [Environment]::GetEnvironmentVariables('Process').Keys |
    % -Begin { $h = @{} } -Process { $h.$_ = (Get-Item Env:\$_).Value } -End { $h }

  # Write-Host "Initially captured process vars:`n`n$($processVars | Out-String)"

  # eliminate Machine / User vars so that we have only process vars
  'Machine', 'User' |
    % { [Environment]::GetEnvironmentVariables($_).GetEnumerator() } |
    ? { $processVars.ContainsKey($_.Name) -and ($processVars[$_.Name] -eq $_.Value) } |
    % { $processVars.Remove($_.Name) }

  # Write-Host "Stored process vars:`n`n$($processVars | Out-String)"
}


# query Machine vars from registry, ensuring expansion EXCEPT for PATH
$vars = [Environment]::GetEnvironmentVariables('Machine').GetEnumerator() |
  % -Begin { $h = @{} } -Process { $v = if ($_.Name -eq 'Path') { $_.Value } else { [Environment]::GetEnvironmentVariable($_.Name, 'Machine') }; $h."$($_.Name)" = $v } -End { $h }

# Write-Host "Read MACHINE vars:`n`n$($vars | Out-String)"

# query User vars from registry, ensuring expansion EXCEPT for PATH
[Environment]::GetEnvironmentVariables('User').GetEnumerator() |
  % {
    if ($_.Name -eq 'Path') { $vars[$_.Name] += ';' + $_.Value }
    else
    {
      $value = [Environment]::GetEnvironmentVariable($_.Name, 'User')
      $vars[$_.Name] = $value
      # Write-Host "Re-read $($_.Name) from User as $value / stored as $($vars[$_.Name])"
    }
  }

# Write-Host "Vars updated with USER vars:`n`n$($vars | Out-String)"

$processVars.GetEnumerator() | % { $vars[$_.Name] = $_.Value }

# Write-Host "Vars updated with Process vars:`n`n$($vars | Out-String)"

Remove-Item Env:\*

$vars.GetEnumerator() |
  % { Set-Item -Path "Env:\$($_.Name)" -Value $_.Value }

One interesting thing to note is that the restored environment has unexpanded environment variables (which is OK / expected for PATH), but might be a problem in ComSpec and windir - so there might need to be special handling there. Calling GetEnvironmentVariable will expand, while GetEnvironmentVariables does not expand.

I have modified the code so that everything is captured / reinstated verbatim, including observing existing behavior around which variables are expanded, etc.

https://gist.github.com/Iristyle/9a870f96f1896710c01f#file-env-reset-ps1-L11

Note, this is going to destroy $env:PSMODULEPATH. We would need to skip this one.

Oh sweet, capturing the Process variables 👍

After line 40 $processVars has 26 items, wheres (ls env:).Count has 38. The variables missing cripple the shell to the point where the process crashes. Still figuring out what is missing here

$vars has the full process list, but still the process crashes after line 44

The fix, strangely enough, was to sort the $processVars by Name before attempting to pass it to the next block. This originates from passing the results of the inner PS session $processVars to the outer PS session, then back into the inner PS session later on.