func main() {
  var user, pass string
  fmt.Println("username:")
  fmt.Scanln(&user) // ignore errors for brevity
  fmt.Println("password:")
  fmt.Scanln("&pass)

  cmd := exec.Command("mount", "-t", "cifs", "-o", "username="+user+",password="+pass, "//server/dir", "media/dir")
  cmd.Run()
}

cmd := exec.Command("mount", "-t", "cifs", "-o", "username=$USER,password=$PASS", "//server/dir", "media/dir")
cmd.Env = []string{"USER="+user, "PASS="+pass}
cmd.Run()