Collecting the output of an external command using OCaml

Question

What is the right way to call an external command and collect its output in OCaml?

In Python, I can do something like this:

os.popen('cmd').read()

How I can get all of an external program's output in OCaml? Or, better, OCaml with Lwt?

Thanks.

Answer 1

You want Unix.open_process_in, which is described on page 388 of the OCaml system manual, version 3.10.

Answer 2

For Lwt,

val pread : ?env:string array -> command -> string Lwt.t

seems to be a good contender. Documentation here: http://ocsigen.org/docu/1.3.0/Lwt_process.html

Answer 3

let process_output_to_list2 = fun command -> 
  let chan = Unix.open_process_in command in
  let res = ref ([] : string list) in
  let rec process_otl_aux () =  
    let e = input_line chan in
    res := e::!res;
    process_otl_aux() in
  try process_otl_aux ()
  with End_of_file ->
    let stat = Unix.close_process_in chan in (List.rev !res,stat)
let cmd_to_list command =
  let (l,_) = process_output_to_list2 command in l

Answer 4

There are lots of examples on PLEAC.