open Unix;;
let process_output_to_list2 = fun command ->
  let chan = 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 = close_process_in chan in (List.rev !res,stat)
let cmd_to_list command =
  let (l,_) = process_output_to_list2 command in l;;

let lines = cmd_to_list "tput cols" in
prerr_endline (List.hd (lines));;