How to Automate User Input for External Commands in Go?

Handling User Input for External Commands in Go

When executing external commands that require user input, it can be challenging to automate this process effectively. Consider the following scenario where an external command awaits inputs for username and password.

Filling Multiple Fields with User Input

The crux of this issue lies in providing inputs to multiple fields in the command's stdin. One approach is to employ a bytes buffer:

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

Here, a bytes buffer b is created and populated with the raw input values for username and password, separated by newline characters. The Stdin field of the login command is then linked to the buffer. This ensures that the external command reads input from the pre-populated buffer upon execution.

Working with the Input Buffer

The input buffer can handle multiple lines by storing the data sequentially. When the command reads input, it iterates through the buffer character by character, treating newline characters as field separators. This allows for the automated entry of multiple inputs into the command's stdin.

Conclusion

By utilizing a bytes buffer and setting it as the Stdin for the external command, you can efficiently input multiple values from within your program, eliminating the need for manual input or complex handling of input streams. This method provides a convenient way to automate input for external commands, simplifying your codebase and improving program flow.

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