2019-04-02 13:06
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My application works with all kind of shell commands, provided from the console (curl, date, ping, whatever). Now I'd like to cover the case with interactive shell commands (like mongo shell), using os/exec.

  • e.g. as a first step, connect to mongodb: mongo --quiet --host=localhost blog

  • then perform arbitrary number of commands, getting the result on every step db.getCollection('posts').find({status:'INACTIVE'})

  • and then exit

I tried the following, but it allows me to perform only one command per mongo connection:

func main() {

    cmd := exec.Command("sh", "-c", "mongo --quiet --host=localhost blog")

    cmd.Stdout = os.Stdout
    cmd.Stderr = os.Stderr

    stdin, _ := cmd.StdinPipe()

    go func() {
        defer stdin.Close()
        io.WriteString(stdin, "db.getCollection('posts').find({status:'INACTIVE'}).itcount()")
        // fails, if I'll do one more here


Is there a way to run multiple commands, getting stdout result per executed command?

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我的应用程序可使用从控制台( curl date ping ,等等)。 现在,我想使用 os / exec 通过交互式shell命令(如mongo shell)来介绍这种情况。

  • 例如 第一步,连接到mongodb: mongo --quiet --host = localhost Blog

  • 然后执行任意 命令数,获取每一步的结果 db.getCollection('posts')。find({status:'INACTIVE'})

  • 然后再 退出

    我尝试了以下操作,但它允许我 每个mongo连接仅执行一个命令:

      func main(){
     cmd:= exec.Command(“ sh”,“ -c”,“ mongo  --quiet --host = localhost Blog“)
     cmd.Stdout = os.Stdout 
     cmd.Stderr = os.Stderr 
     stdin,_:= cmd.StdinPipe()
     go  func(){
     io.WriteString(stdin,“ db.getCollection('posts')。find({status:'INACTIVE'})。itcount()”)
     // 失败,如果我在这里再做一次


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1条回答 默认 最新

  • duanfu3634 2019-04-02 13:44

    As Flimzy noted, you should absolutely be using a mongo driver to work with mongo, not trying to interact with it via shell exec.

    However, to answer the root question, of course you can execute multiple commands - there's no reason you can't. Every time you write to the process' stdin, it's like you're at a terminal typing into it. There's no secret limitation on that, other than processes which specifically detect if they're connected to a TTY.

    Your code has several issues, though - you should definitely review the os/exec package documentation. You're calling cmd.Run, which:

    starts the specified command and waits for it to complete.

    And then calling cmd.Wait, which... also waits for the command to complete. You're writing to the stdin pipe in a goroutine, even though this is a very serialized process: you want to write to the pipe to execute a command, get the result, write another command, get another result... concurrency only muddles matters and should not be used here. And you're not sending newlines to tell Mongo you're done writing a command (just like you'd do in the shell - Mongo won't just start executing as soon as you enter the closing paren, you have to hit enter).

    What you would want to do to interact with a process via stdin/stdout (again, noting that this is absolutely not the way to interact with a database, but could be valid for other external commands):

    cmd := exec.Command("sh", "-c", "mongo --quiet --host=localhost blog")
    cmd.Stdout = os.Stdout
    cmd.Stderr = os.Stderr
    stdin, _ := cmd.StdinPipe()
    // Start command but don't wait for it to exit (yet) so we can interact with it
    // Newlines, like hitting enter in a terminal, tell Mongo you're done writing a command
    io.WriteString(stdin, "db.getCollection('posts').find({status:'INACTIVE'}).itcount()
    io.WriteString(stdin, "db.getCollection('posts').find({status:'ACTIVE'}).itcount()
    // Quit tells it you're done interacting with it, otherwise it won't exit
    io.WriteString(stdin, "quit()
    // Lastly, wait for the process to exit
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