gsub, gsub!

String#subは置換した文字列を返す。gsubはすべてを置換した文字列を返す。gsub!はselfを書き換える。
以下は与えられた文字列中の数字を\dに置き換えるスクリプト。

s = "This coin is 100yen."
puts s.sub(/\d/, '\d')    #=> This coin is \d00yen.
puts s                    #=> This coin is 100yen.
puts s.gsub(/\d/, '\d')   #=> This coin is \d\d\dyen.
puts s                    #=> This coin is 100yen.
puts s.gsub!(/\d/, '\d')  #=> This coin is \d\d\dyen.
puts s                    #=> This coin is \d\d\dyen.