Ocaml module Sys

utop # Sys.executable_name;;
- : string = "/Users/hwu/.opam/4.01.0/bin/utop"

utop # Sys.argv;;
- : string array = [|"/Users/hwu/.opam/4.01.0/bin/utop"|]

utop # Sys.getenv "PWD";;
- : string option = Some "/Users/hwu"

utop # Sys.getcwd ();;
- : string = "/Users/hwu/test"

utop # Sys.getcwd () |> Sys.readdir ;;
- : string array = [|"a.txt"; "b.txt"; "c.txt"|]


Use Sys to get information about the system  

utop # Sys.os_type;;
- : string = "Unix"

utop # Sys.word_size;;
- : int = 64

utop # Sys.ocaml_version;;
- : string = "4.01.0+rc1"

utop #  module M = Sys;;

module M :
  sig  
    val argv : string array
    val executable_name : string
    val file_exists : ?follow_symlinks:bool -> string -> [ `No | `Unknown | `Yes ]
    val file_exists_exn : ?follow_symlinks:bool -> string -> bool
    val is_directory : ?follow_symlinks:bool -> string -> [ `No | `Unknown | `Yes ]
    val is_file : ?follow_symlinks:bool -> string -> [ `No | `Unknown | `Yes ]
    val is_directory_exn : ?follow_symlinks:bool -> string -> bool
    val is_file_exn : ?follow_symlinks:bool -> string -> bool
    val remove : string -> unit
    val rename : string -> string -> unit
    val getenv : string -> string option
    val getenv_exn : string -> string
    val command : string -> int
    val command_exn : string -> unit
    val chdir : string -> unit
    val getcwd : unit -> string
    val readdir : string -> string array
    val fold_dir : init:'acc -> f:('acc -> string -> 'acc) -> string -> 'acc
    val ls_dir : string -> string list
    val interactive : bool ref
    val os_type : string
    val word_size : int
    exception Break
    val catch_break : bool -> unit
    val ocaml_version : string
    val execution_mode : unit -> [ `Bytecode | `Native ]
    external c_int_size : unit -> int = "c_int_size" "noalloc"
  end