Collecting the output of an external command using OCaml
What开发者_Python百科 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.
You want Unix.open_process_in, which is described on page 388 of the OCaml system manual, version 3.10.
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
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
There are lots of examples on PLEAC.
You can use the third party library Rashell which uses Lwt to define some high-level primitives to read output from processes. These primitives, defined in the module Rashell_Command, are:
exec_utility
to read the output of a process as a string;exec_test
to only read the exit status of a process;exec_query
to read the output of a process line by line as astring Lwt_stream.t
exec_filter
to use an external program as astring Lwt_stream.t -> string Lwt_stream.t
transformation.
The command
function is used to create command contexts on which the previous primitives can be applied, it has the signature:
val command : ?workdir:string -> ?env:string array -> string * (string array) -> t
(** [command (program, argv)] prepare a command description with the
given [program] and argument vector [argv]. *)
So for instance
Rashell_Command.(exec_utility ~chomp:true (command("", [| "uname" |])))
is a string Lwt.t
which returns the “chomped” string (new line removed) of the “uname” command. As a second example
Rashell_Command.(exec_query (command("", [| "find"; "/home/user"; "-type"; "f"; "-name"; "*.orig" |])))
is a string Lwt_stream.t
whose elements are the paths of the file found by the command
find /home/user -type f -name '*.orig'
The Rashell library defines also interfaces to some commonly used commands, and a nice interface to the find
command is defined in Rashell_Posix
– which by the way guarantees POSIX portability.
精彩评论