如何检查输入字符串?

Here is my code:

这是我的代码:

loop do
  print "Input word: "
  word = gets.chomp
  if word.nil? or word.empty?
    puts "Nothing to input."
  else
    if word.index(":") != -1
      puts "Illegal character ':'"
    else
      break
    end
  end
end
loop do
  print "I