Setting Windows PowerShell environment variables

These scripts are idempotent (can be run more than once).
They update both the Windows path and the current / future Powershell sessions:

# Permanently add path
``` powershell
$targetDir="c:\bin"
$oldPath = [System.Environment]::GetEnvironmentVariable("Path","Machine")
$oldPathArray=($oldPath) -split ';'
if(-Not($oldPathArray -Contains "$targetDir")) {
write-host "Adding $targetDir to Machine Path"
$newPath = "$oldPath;$targetDir" -replace ';+', ';'
[System.Environment]::SetEnvironmentVariable("Path",$newPath,"Machine")
$env:Path = [System.Environment]::GetEnvironmentVariable("Path","User"),[System.Environment]::GetEnvironmentVariable("Path","Machine") -join ";"
}
write-host "Windows paths:"
($env:Path).Replace(';',"`n")
```

# Permanently remove path
``` powershell
$targetDir="c:\bin"
$oldPath = [System.Environment]::GetEnvironmentVariable("Path","Machine")
$oldPathArray=($oldPath) -split ';'
if($oldPathArray -Contains "$targetDir") {
write-host "Removing $targetDir from Machine path"
$newPathArray = $oldPathArray | Where-Object { $_ –ne "$targetDir" }
$newPath = $newPathArray -join ";"
[System.Environment]::SetEnvironmentVariable("Path",$newPath,"Machine")
$env:Path = [System.Environment]::GetEnvironmentVariable("Path","User"),[System.Environment]::GetEnvironmentVariable("Path","Machine") -join ";"
}
write-host "Windows paths:"
($env:Path).Replace(';',"`n")
```