anchor.diff:      startServer port -1 agent.Post <| fun listen ->
           Async.Start listen
           let workingDir = Directory.GetCurrentDirectory()
  -        let p = startProcess workingDir exec args (Some (port.ToString()))
  +        let p =
  +            ProcessOptions(envVars=Map["FABLE_SERVER_PORT", string port])
  +            |> startProcess workingDir exec args
           Console.CancelKeyPress.Add (fun _ ->
               Server.stop port |> Async.RunSynchronously
               printfn "Killing process..."
  
positive.code:   --version           Print version
    add                 Add one or several Fable npm packages
    start               Start Fable server
    --port              Port number (default 61225) or "free" to choose a free port. 
    --timeout           Stop the server if timeout (ms) is reached
    npm-run             Start a server, run an npm script and shut it down
      <script>            Name of the npm script, e.g.: `dotnet fable npm-run start`
      --port              Port number (default 61225) or "free" to choose a free port. 
      --args              Args for the npm script, e.g.: `dotnet fable npm-run build --args "-p --output-filename bundle.js"`
    webpack             Start a server and invoke webpack (must be installed in current or a parent dir)
      --port              Port number (default 61225) or "free" to choose a free port. 
      --args              Args for Webpack, e.g.: `dotnet fable webpack --args -p`
    shell-run           Start a server, run an abritrary command and shut it down
      <cmd>            Name of the command to run, e.g.: `dotnet fable shell-run make`
      --port              Port number (default 61225) or "free" to choose a free port. 
      --args              Args for the command, e.g.: `dotnet fable shell-run make --args "build"`
    webpack-dev-server  Same as `webpack` command but invokes webpack-dev-server
  """
  
negative.code: open System.Runtime.InteropServices
  open System.Net
  open Microsoft.FSharp.Compiler.SourceCodeServices
  open Newtonsoft.Json
  open Parser
  open State
  
  type ProcessOptions(?envVars, ?redirectOutput) =
      member val EnvVars = defaultArg envVars Map.empty<string,string>
      member val RedirectOuput = defaultArg redirectOutput false
  
  let startProcess workingDir fileName args (opts: ProcessOptions) =
      let fileName, args =
          let isWindows =
              #if NETFX
  