How to Provide Multiple Input Fields to External Commands in Go?

Go - Writing to Stdin for External Commands with Multiple Input Fields

When executing external commands from a Go program, it can be necessary to provide input to the command's standard input (stdin). However, when the external command requires multiple fields of input, it can be challenging to determine how to supply them in the most efficient and reliable manner.

In the example provided, the login command is executed and expects the user to manually enter two fields: a username and a password. To provide these inputs programmatically, it is possible to use a byte buffer.

The bytes.Buffer type in Go can be used to hold and manipulate a sequence of bytes in memory. By writing the username and password into the buffer and then setting the login.Stdin field to the buffer, it is possible to supply the inputs to the command without user interaction.

A code snippet that illustrates this approach:

<code class="go">import (
    "bytes"
    "fmt"
    "os"
    "os/exec"
)

func main() {
    cmd := "login"

    // Prepare the byte buffer with username and password
    var b bytes.Buffer
    username := "exampleUsername"
    password := "examplePassword"
    b.Write([]byte(fmt.Sprintf("%s\n%s\n", username, password)))

    // Execute the command with stdin set to the buffer
    login := exec.Command(cmd)
    login.Stdin = &b
    login.Stdout = os.Stdout
    login.Stderr = os.Stderr

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

By using this technique, the Go program can automatically provide the necessary inputs to the external command, streamlining the execution process and eliminating the need for manual user input.

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