Support capturing stdout/stderr in memory with nob_cmd_run / nob_cmd_run_opt

[webdevred]

Hi!

I’m using Nob to run commands and capture their output directly in memory (as a char* string). With the older functions (nob_cmd_run_async_redirect), this was straightforward using pipes.

char *run_cmd_and_get_output(Nob_Cmd *cmd) {
    int pipefd[2];
    if (pipe(pipefd) == -1) {
        perror("pipe");
        return NULL;
    }

    Nob_Cmd_Redirect cmd_red = {0};
    cmd_red.fdout = &pipefd[1];
    nob_cmd_run_async_redirect(*cmd, cmd_red);
    cmd->count = 0;

    close(pipefd[1]);

    char *buffer = NULL;
    size_t total_size = 0;
    char tmp_buffer[256];

    ssize_t bytes_read;
    while ((bytes_read = read(pipefd[0], tmp_buffer, sizeof(tmp_buffer))) > 0) {
        char *new_buffer = realloc(buffer, total_size + bytes_read + 1);
        if (!new_buffer) {
            free(buffer);
            close(pipefd[0]);
            return NULL;
        }
        buffer = new_buffer;
        memcpy(buffer + total_size, tmp_buffer, bytes_read);
        total_size += bytes_read;
    }

    if (buffer) {
        buffer[total_size] = '\0';
    }

    close(pipefd[0]);
    return buffer;
}

In the new API (nob_cmd_run / nob_cmd_run_opt):

• cmd->count is always reset (understood and not an issue).
• There is currently no simple official way to capture stdout/stderr in memory without requiring saving to a file and then reading it afterwards.

It would be very useful if Nob provided a first-class, easy way to run a command asynchronously and capture stdout/stderr directly in memory, without the need for file hacks. I could also use the new stdout option to nob_cmd_run_opt and then read that file. However I dont find it as clean, I think it is cleaner to not save to a file just to then read the same file.

This would make migrating from the old API much smoother for me.

Thank you!