Writing CLI Applications with Elixir

• How do you parse command line arguments?

• The main function has the command line arguments as a list of Strings as it's input. The most straightforward way to parse them is to use the OptionParser module that is part of the standard elixir libraries.

      
    def main(args) do
        args |> parse_args |> process |> cleanup
    end
  
    def parse_args(args) do
      # Default options
      options = %{ :greeting => "Hello" ,
                   :audience => "World" }
  
      cmd_opts = OptionParser.parse(args, 
                                    switches: [help: :boolean , greeting: :string, audience: :string],
                                    aliases: [h: :help, g: :greeting, a: :audience])
  
      case cmd_opts do
        { [ help: true], _, _}   -> :help
        { [], args, [] }         -> { options, args }
        { opts, args, [] }       -> { Enum.into(opts,options), args }
        _                        -> :help
      end
  
    end
    
    

• Keeping the parsed options and args in a { Map, List } tuple that is used as the first arg of your processing functions works out well.