Optimize-Path.ps1

<#
.SYNOPSIS
Sorts, prunes, and normalizes both user and system Path entries.

#>

#Requires -Version 3
[CmdletBinding(ConfirmImpact='High',SupportsShouldProcess=$true)][OutputType([void])] Param(
<#
Look for commands with the same name within multiple Path entries, and move the entry
with the newest version ahead of the others.
#>
[switch]$ResolveConflicts
)

function Initialize-PathCollection
{
	# initialize collections
	$Script:app,$Script:user = @{},@()
	# get command extensions
	$Script:pathext = $env:PATHEXT -split ';'
	# get list of directory environment variables
	$Script:evmatch = Get-ChildItem env: |
		Where-Object {Test-Path $_.Value -PathType Container} |
		Where-Object {'windir','TMP','ProgramW6432','CommonProgramW6432','SystemDrive','HomeDrive','HomePath' -inotcontains $_.Name} |
		ForEach-Object {$_.Value = '^' + ($_.Value.Trim('\') -replace '(\W)','\$1') + '(?=\\|$)'; $_} |
		Sort-Object @{e={$_.Value.Length};asc=$false},@{e={$_.Name.Length};asc=$true}
}

function Backup-Path([Parameter(Position=0,Mandatory=$true)][EnvironmentVariableTarget]$Target)
{
	mkdir $env:LOCALAPPDATA\OptimizePath |Out-Null
	"$(Get-Date -Format u)`t$($Target)`t$([Environment]::GetEnvironmentVariable('Path',$Target))" |
		Add-Content -Path $env:LOCALAPPDATA\OptimizePath\Backup.tsv
}

filter Get-PathDetail([Parameter(Position=0,Mandatory=$true)][EnvironmentVariableTarget]$Target,
						[Parameter(Position=1,ValueFromPipeline=$true)][string]$Entry)
{
	if([string]::IsNullOrWhiteSpace($Entry)) {return}
	$fullpath = [Environment]::ExpandEnvironmentVariables($Entry)
	Write-Verbose "$Target Path: $Entry$(if($Entry -ne $fullpath){' ('+$fullpath+')'})"
	if(!(Test-Path $fullpath -PathType Container)) {Write-Warning "$Target Path: Entry $Entry not found!"; return}
	if($Target -ne 'User' -and $entry.StartsWith("$env:USERPROFILE\")) {Write-Warning "$Target Path: Entry $entry under user profile!"; $user+= $entry; continue}
	[IO.FileInfo[]]$cmd = Get-ChildItem $fullpath -File |Where-Object {$pathext -icontains $_.Extension}
	if(!$cmd) {Write-Warning "$Target Path: Entry $Entry contains no executables."; return}
	elseif($cmd.Count -eq 1) {Write-Warning "$Target Path: Entry $Entry contains only one command! ($($cmd[0].Name))"}
	else {Write-Verbose "$Target Path: Entry $Entry contains $($cmd.Count) commands."}
	foreach($c in $cmd)
	{
		if($app[$c.Name]) {$app[$c.Name]+=$Entry}
		else {[string[]]$app[$c.Name] = $Entry}
	}
	$ev = $evmatch |Where-Object {$Entry -match $_.Value} |Select-Object -First 1
	if($ev) {Write-Verbose "$Target Path: $entry matches $($ev.Name) /$($ev.Value)/"}
	$evpath =
		if($Entry -like '%*') {$Entry}
		elseif(!$ev) {$fullpath}
		else {$Entry -ireplace $ev.Value,"%$($ev.Name)%"}
	return [pscustomobject]@{
		Name       = $Entry
		Path       = $fullpath
		EnvVarPath = $evpath
		Commands   = $cmd
		Precede    = [string[]]@()
	}
}

function Get-PathDetail([Parameter(Position=0,Mandatory=$true)][EnvironmentVariableTarget]$Target)
{
	$path = [Environment]::GetEnvironmentVariable('Path',$Target) -split ';'
	switch($Target)
	{
		Machine {$path |Get-PathDetail $Target}
		User    {($Script:user + $path) |Get-PathDetail $Target}
	}
}

function Resolve-PathConflict([Parameter(Position=0,Mandatory=$true)][EnvironmentVariableTarget]$Target,
							   [Parameter(Position=1,Mandatory=$true)][Collections.Generic.List[psobject]]$PathDetails)
{
	# examine conflicts
	if(!(Get-Command -Verb Test -Noun NewerFile)) {Set-Alias Test-NewerFile "$PSScriptRoot\Test-NewerFile.ps1"}
	foreach($c in $app.Keys |Where-Object {$app.$_.Count -gt 1})
	{
		$newest,$rest = $app[$c]
		[string[]]$precede = @()
		foreach($r in $rest)
		{
			if(Test-NewerFile (Join-Path $newest $c) (Join-Path $r $c)) {$precede += $newest; $newest = $r}
		}
		if($precede)
		{
			Write-Verbose "Executable conflict ${c}: $newest needs to be moved ahead of $($precede -join ', ')."
			$npos,$rpos = 0,0
			foreach($i in 0..($precede.Length))
			{
				if($PathDetails[$i].Name -eq $newest) {$npos = $i}
				elseif($rpos -ne 0 -and $precede -contains $PathDetails[$i].Name) {$rpos = $i}
			}
			if($npos -gt $rpos)
			{
				$n = $PathDetails[$npos]
				$PathDetails.RemoveAt($npos)
				$PathDetails.Insert($rpos,$n)
			}
		}
	}
	return $PathDetails
}

function Update-Path
{
	[CmdletBinding(SupportsShouldProcess=$true)] Param(
	[Parameter(Position=0,Mandatory=$true)][EnvironmentVariableTarget]$Target
	)
	[Collections.Generic.List[psobject]]$path = Get-PathDetail $Target
	if($ResolveConflicts) {$path = Resolve-PathConflict $path}
	if($PSCmdlet.ShouldProcess("$Target Path",'Update'))
	{
		$newpath = ($path |Select-Object -Unique -ExpandProperty EnvVarPath) -join ';'
		Write-Verbose "New $Target Path: $newpath"
		Backup-Path $Target
		[Environment]::SetEnvironmentVariable('Path',$newpath,$Target)
	}
}

Initialize-PathCollection
Update-Path Machine
Update-Path User