Redirecting output of an external application started with glib

Question

I'm trying to use vala to start an external application using GLib with spawn_command_line_sync(). According to the documentation (http://valadoc.org/#!api=glib-2.0/GLib.Process.spawn_sync) you can pass a string to store the output of the external application.

While this works fine when starting a script which prints a couple of lines, I need to call a program which will print the content of a binary file. (for example "cat /usr/bin/apt-get")

Is there any way how I can receive the output of the external program not in a string, but in a DataStream or something like that ?

I'm planning to write the ouput of the external program to a file, so just calling "cat /usr/bin/apt-get > outputfile" would be an alternative (not as nice), but it doesn't seem to work.

Anyway I would prefer it to get some kind of Output Stream. I would appreciate any help.

Code im using:

using GLib;

static void main(string[] args) {
    string execute = "cat /usr/bin/apt-get";
    string output = "out";

    try {
        GLib.Process.spawn_command_line_sync(execute, out output);
    } catch (SpawnError e) {
        stderr.printf("spawn error!");
        stderr.printf(e.message);
    }

    stdout.printf("Output: %s\n", output);
}

apmasell · Accepted Answer · 2013-02-10 18:19:06Z

2

GLib.Process.spawn_async_with_pipes will let you do just that. It spawns the processes and returns a file descriptor for each of stdout, stderr, and stdin. There's a sample of code in the ValaDoc on how to set up IOChannels to monitor the output.

answered Feb 10, 2013 at 18:19

apmasell

7,16323 silver badges28 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Ansgar · Accepted Answer · 2013-02-10 22:58:55Z

1

Thanks for that, I must have overread spawn_async_with_pipes() returning ints and not strings.

Is there anything wrong with doing it this way ? (besides the buffer size of 1)

using GLib;

static void main(string[] args) {

    string[] argv = {"cat", "/usr/bin/apt-get"};
    string[] envv = Environ.get();
    int child_pid;
    int child_stdin_fd;
    int child_stdout_fd;
    int child_stderr_fd;

    try {
        Process.spawn_async_with_pipes(
            ".",
            argv,
            envv,
            SpawnFlags.SEARCH_PATH,
            null,
            out child_pid,
            out child_stdin_fd,
            out child_stdout_fd,
            out child_stderr_fd);

    } catch (SpawnError e) {
        stderr.printf("spawn error!");
        stderr.printf(e.message);
        return;
    }

    FileStream filestream1 = FileStream.fdopen(child_stdout_fd, "r");
    FileStream filestream2 = FileStream.open("./stdout", "w");

    uint8 buf[1];
    size_t t;
    while ((t = filestream1.read(buf, 1)) != 0) {
        filestream2.write(buf, 1);
    }
}

answered Feb 10, 2013 at 22:58

Ansgar

3713 silver badges15 bronze badges

2 Comments

apmasell Over a year ago

Nothing wrong, but you should call waitpid or add a ChildWatch to your main loop so you can collect your child's exist status. If not, it becomes a zombie until you exit and it is re-parented by init and reaped.

nemequ Over a year ago

You might want to consider using GLib.OutputStream.splice (in gio-2.0) instead.

Collectives™ on Stack Overflow

Redirecting output of an external application started with glib

2 Answers 2

Comments

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related