fsharp console app sample

fsConsoleapp.fs

module Program

(*

  fsharp console app sample with System.CommandLine

  require: dotnet add package system.commandline

  e.g.
  dotnet run --  --opdir ./hello --opfile ./hello/world.csv --opint 2021
  => hello world 2022

  see also
  Parse the Command Line with System.CommandLine
    us https://docs.microsoft.com/en-us/archive/msdn-magazine/2019/march/net-parse-the-command-line-with-system-commandline
    jp https://docs.microsoft.com/ja-jp/archive/msdn-magazine/2019/march/net-parse-the-command-line-with-system-commandline

*)

open System.IO
open System.CommandLine
open System.CommandLine.Invocation

[<EntryPoint>]
let main args =
  let rootCommand = RootCommand()
  rootCommand.Description <- "fsharp console app : happy new year!"

  // read as DirectoryInfo, show error hint if not exists folder
  let opFileDir = (new Option<DirectoryInfo>("--opdir")).ExistingOnly()
  rootCommand.AddOption opFileDir

  // read as FileInfo, show error hint if not exists file
  let opFileInfo = (new Option<FileInfo>("--opfile")).ExistingOnly()
  rootCommand.AddOption opFileInfo

  // read as Int
  let opInt = new Option<int>("--opint")
  rootCommand.AddOption opInt

  rootCommand.Handler <- CommandHandler.Create(

      fun (opint:int) (opdir:DirectoryInfo) (opfile:FileInfo) ->
        printfn "%s %s %i" (opdir.Name) (opfile.OpenText().ReadLine()) (opint + 1)

  )

  rootCommand.Invoke args