Cubicle 1.1.2 documentation and source : Pretty.vt

let vt_width =
  if js_mode () then 80
  else
    try
      let scol = syscall "tput cols" in
      let w = int_of_string (remove_trailing_whitespaces_end scol) in
      set_margin w;
      w
    with Not_found | Failure _ -> 80