Is there an Erlang os:cmd equivalent that takes a list of strings instead of a single command?

Question

Is there a Erlang call where I can do Retval = subprocess:call(["cmd", "arg1", "arg2", "arg3"])?

If I'm building a complex command to execute, with os:cmd/1 it is easy to make escaping mistakes. Compare to Python's subprocess.call() method where I pass in a list of strings and know that it is passed verbatim to the subprocess, nothing mangled.

Thanks.

Answer 1

Can't you just do os:cmd(string:join(["cmd", "arg1", "arg2"], " ")) ?

Answer 2

Nowadays you can do open_port({spawn_executable, Command}, [{args, [A1, ..., An]}]), but there is no convenient wrapper for this in the os module yet. You could take the code for os:cmd/1 and tweak it to use spawn_executable. Check the docs for erlang:open_port/2 for more details.

Answer 3

This is what I have come up with.

-module(mycmd).
-export([cmd/2]).

cmd(Cmd, Args) ->
    Tag = make_ref(), 
    {Pid, Ref} = erlang:spawn_monitor(fun() ->
            Rv = cmd_sync(Cmd, Args),
            exit({Tag, Rv})
        end),
    receive
        {'DOWN', Ref, process, Pid, {Tag, Data}} -> Data;
        {'DOWN', Ref, process, Pid, Reason} -> exit(Reason)
    end.

cmd_sync(Cmd, Args) ->
    P = open_port({spawn_executable, os:find_executable(Cmd)}, [
            binary, use_stdio, stream, eof, {args, Args}]),
    cmd_receive(P, []).

cmd_receive(Port, Acc) ->
    receive
        {Port, {data, Data}} -> cmd_receive(Port, [Data|Acc]);
        {Port, eof}          -> {ok, lists:reverse(Acc)}
    end.