Sets a System level environment variable to machine, currentuser, or process scope.

Set-EnvironmentVariable.ps1

function Set-EnvironmentVariable {
  <#
  .SYNOPSIS
  Sets a system environment variable
  
  .DESCRIPTION
  Sets an environment variable in either machine, currentuser, or process scope
  
  .PARAMETER Scope
  The scope to set variable too
  
  .PARAMETER Name
  The name of the env variable
  
  .PARAMETER Value
  The value of the environment variable
  
  .EXAMPLE
  Set-EnvironmentVariable -Scope Machine -Name Test -Value 'ThisIsCool'
  
  .NOTES
  Name and Value must be below 32767 characters. Anything higher will cause an error when setting the variable.
  #>
  [cmdletBinding()]
  Param(
    [Parameter(Mandatory)]
    [ValidateSet('Machine', 'User', 'Process')]
    [String]
    $Scope,

    [Parameter(Mandatory)]
    [ValidateScript( {
        if ($_.Length -gt 32767) {
          throw "Parameter value too long. Must be below 32767 characters"
        }
        else { $true }
      })]
    [String]
    $Name,

    [Parameter(Mandatory, ValueFromPipeline)]
    [ValidateScript( {
        if ($_.Length -gt 32767) {
          throw "Parameter value too long. Must be below 32767 characters"
        }
        else { $true }
      })]
    [String]
    $Value
  )

  process {
    try {
      [Environment]::SetEnvironmentVariable($Name, $Value, $Scope)
      Write-Output 'Environment variable successfully created. You will need to re-open PowerShell to pick it up.'
    }
    catch { $_.Exception.message }
  }
}