import ( "github.com/mitchellh/packer/packer" ) func main() { cmd := &packer.RemoteCmd{ Command: "ls /nonexistent", } if err := cmd.Start(); err != nil { // handle error } cmd.Wait() if cmd.Stderr != "" { fmt.Println("Error:", cmd.Stderr) } }In this example, we create a new RemoteCmd to execute the "ls /nonexistent" command. We start the command, wait for it to finish, and then check if there was any error output on stderr. If there was, we print the error message. This package/library provides a convenient way to execute remote commands and capture output on both stdout and stderr.