如何在Erlang中执行系统命令并使用os:cmd/1获得结果? [英] How to execute system command in Erlang and get results using os:cmd/1?

问题描述

当我尝试执行以下返回错误或在Windows上不退出的命令时-我总是得到空列表，而不是以字符串形式返回错误，例如:

When I try to execute following command that returns error or doesn't exit on Windows - I always get empty list instead of error returned as string so for example:

我得到:

[] = os:cmd("blah").

代替

"command not found" = os:cmd("blah").

在linux中-一切正常，因此我得到了"/bin/sh:第1行:等等:找不到命令\ n"

In linux - everything works as expected so I get "/bin/sh: line 1: blah: command not found\n"

因此，当我需要知道执行的完成方式等时，我不能依赖该功能. 请提出一些通用的方法来执行命令并获得包括错误代码在内的结果.

Therefore I cannot rely on that function when I need to know how execution finished etc. Please suggest some general way how to execute command and get results including error code.

谢谢！

推荐答案

我完全不熟悉Windows，但是我敢肯定，您应该查看

I am not familiar with windows at all, but I'm sure, you should look this. This is implementation os:cmd/1 function.

os:cmd/1有问题.该功能不会告诉您命令执行是否成功，因此您仅需依赖某些命令外壳行为(取决于平台)即可.

There is problem with os:cmd/1. This function doesn't let you know, was command execution successful or not, so you only have to rely on certain command shell behaviour (which is platform dependent).

我建议您使用erlang:open_port/2功能.像这样的东西:

I'd recommend you to use erlang:open_port/2 function. Something like that:

my_exec(Command) ->
    Port = open_port({spawn, Command}, [stream, in, eof, hide, exit_status]),
    get_data(Port, []).

get_data(Port, Sofar) ->
    receive
    {Port, {data, Bytes}} ->
        get_data(Port, [Sofar|Bytes]);
    {Port, eof} ->
        Port ! {self(), close},
        receive
        {Port, closed} ->
            true
        end,
        receive
        {'EXIT',  Port,  _} ->
            ok
        after 1 ->              % force context switch
            ok
        end,
        ExitCode =
            receive
            {Port, {exit_status, Code}} ->
                Code
        end,
        {ExitCode, lists:flatten(Sofar)}
    end.

因此函数my_exec/1将返回进程退出代码以及进程标准输出.

So function my_exec/1 will return process exit code along with process stdout.

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