CODEWITHSUNDEEP
go
Alessandro Resta
Alessandro Resta

Reputation: 1172

Go - write to stdin on external command

I have the following code which executes an external command and output to the console two fields waiting for the user input. One for the username and other for the password, and then I have added them manually.

Could anyone give me a hint about how to write to stdin in order to enter these inputs from inside the program?

The tricky part for me is that there are two different fields waiting for input, and I'm having trouble to figure out how to fill one after the other.

login := exec.Command(cmd, "login")

login.Stdout = os.Stdout
login.Stdin = os.Stdin
login.Stderr = os.Stderr

err := login.Run()
if err != nil {
    fmt.Fprintln(os.Stderr, err)
}

SOLUTION:

login := exec.Command(cmd, "login") 

var b bytes.Buffer
b.Write([]byte(username + "\n" + pwd + "\n"))

login.Stdout = os.Stdout
login.Stdin = &b
login.Stderr = os.Stderr

Upvotes: 7

Views: 12688

Answers (1)

Elwinar
Elwinar

Reputation: 9509

I imagine you could use a bytes.Buffer for that. Something like that:

login := exec.Command(cmd, "login")

buffer := bytes.Buffer{}
buffer.Write([]byte("username\npassword\n"))
login.Stdin = &buffer

login.Stdout = os.Stdout
login.Stderr = os.Stderr

err := login.Run()
if err != nil {
    fmt.Fprintln(os.Stderr, err)
}

The trick is that the stdin is merely a char buffer, and when reading the credentials, it will simply read chars until encountering a \n character (or maybe \n\r). So you can write them in a buffer in advance, and feed the buffer directly to the command.

Upvotes: 9

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