程式里的注释是很重要的。它们可以用自然语言告诉你某段程式码的功能是什么。在你想要临时移除一段程式码时，你还可以用注释的方式将这段程式码临时禁用。接下来的练习将让你学会注释：
# A comment, this is so you can read your program later.
# Anything after the # is ignored by Ruby.
puts "I could have code like this." # and the comment after is ignored
# You can also use a comment to "disable" or comment out a piece of code:
# print "This won't run."
puts "This will run."$ ruby ex2.rb
I could have code like this.
This will run.
$# 符号的作用。而且记住它的名称。（中文为井号，英文为 octothorpe 或者 pound character)。ex2.rb 档案，从后往前逐行检查。从最后一行开始，倒著逐个单词单词检查回去。