Windows Powershell functions for system path

PSSystemPath.ps1

function Get-SystemPath {
    $keyName = 'SYSTEM\CurrentControlSet\Control\Session Manager\Environment'
    $key = [Microsoft.Win32.Registry]::LocalMachine.OpenSubKey($keyName, 'ReadOnly')
    try {
        return $key.GetValue('Path', '', 'DoNotExpandEnvironmentNames') -split [IO.Path]::PathSeparator
    } finally {
        if ($null -ne $key) {
            $key.Dispose()
        }
    }
}

function Add-SystemPath([Parameter(Mandatory=$true)][string[]]$Folder) {
    $keyName = 'SYSTEM\CurrentControlSet\Control\Session Manager\Environment'
    $key = [Microsoft.Win32.Registry]::LocalMachine.OpenSubKey($keyName, $true)
    try {
        # Get current PATH
        $currentPathFolders = $key.GetValue('Path', '', 'DoNotExpandEnvironmentNames') -split [IO.Path]::PathSeparator

        # Add new folders to the current PATH
        $newPathFolders = $currentPathFolders + @($Folder)

        # Normalize folders to remove trailing slashes and duplicates
        $result = [Collections.Generic.HashSet[string]]::new([StringComparer]::InvariantCultureIgnoreCase)
        $newPathFolders |
            ForEach-Object {
                $normalized = $_.TrimEnd([IO.Path]::DirectorySeparatorChar).Trim()
                if ($normalized -ne '') {
                    $result.Add($normalized)
                }
            } > $null

        # Build new PATH and save it
        $newPath = $result -join [IO.Path]::PathSeparator
        $key.SetValue('Path', $newPath, 'ExpandString')

        return $result
    } finally {
        if ($null -ne $key) {
            $key.Dispose()
        }
    }
}

function Remove-SystemPath([Parameter(Mandatory=$true)][string[]]$Folder) {
    $keyName = 'SYSTEM\CurrentControlSet\Control\Session Manager\Environment'
    $key = [Microsoft.Win32.Registry]::LocalMachine.OpenSubKey($keyName, $true)
    try {
        # Get current PATH
        $currentPathFolders = $key.GetValue('Path', '', 'DoNotExpandEnvironmentNames') -split [IO.Path]::PathSeparator
        
        # Normalize folders to remove
        $foldersToRemove = $Folder | ForEach-Object { $_.TrimEnd([IO.Path]::DirectorySeparatorChar) }
        
        # Filter out the folders to remove (case-insensitive)
        $result = [Collections.Generic.HashSet[string]]::new([StringComparer]::InvariantCultureIgnoreCase)
        $currentPathFolders | 
            Where-Object { 
                $normalizedFolder = $_.TrimEnd([IO.Path]::DirectorySeparatorChar)
                $foldersToRemove -notcontains $normalizedFolder 
            } | 
            ForEach-Object { $result.Add($_) } > $null
        
        # Build new PATH and save it
        $newPath = $result -join [IO.Path]::PathSeparator
        $key.SetValue('Path', $newPath, 'ExpandString')
        
        return $result
    } finally {
        if ($null -ne $key) {
            $key.Dispose()
        }
    }
}

Why go through all this just to update the system PATH?

1. Must go through the registry directly
Using $env:PATH or [Environment]::SetEnvironmentVariable() reads/writes the already-expanded value — %SystemRoot%\System32 becomes System32. Save that back and you've permanently destroyed the portable, machine-agnostic references. So the script opens the registry key manually.

2. DoNotExpandEnvironmentNames when reading
This flag is how you get the raw, unexpanded string (%SystemRoot%\System32) instead of the resolved path. Without it, round-tripping PATH corrupts it.

3. ExpandString (REG_EXPAND_SZ) when writing
PATH must be stored as REG_EXPAND_SZ in the registry, not as a plain REG_SZ string. If you write it as the wrong type, Windows stops expanding %...% references for all processes.

4. Case-insensitive deduplication
Windows paths are case-insensitive, so C:\Foo and c:\foo are the same entry. A plain array comparison would miss this, hence the HashSet<string> with InvariantCultureIgnoreCase. Trailing-slash normalization (TrimEnd) handles C:\Foo\ vs C:\Foo.