How to replace the last occurrence of a substring in ruby?

Question

I want to replace the last occurrence of a substring in Ruby. What\'s the easiest way? For example, in abc123abc123, I want to replace the last abc

Answer 1

I've used this handy helper method quite a bit:

def gsub_last(str, source, target)
  return str unless str.include?(source)
  top, middle, bottom = str.rpartition(source)
  "#{top}#{target}#{bottom}"
end

If you want to make it more Rails-y, extend it on the String class itself:

class String
  def gsub_last(source, target)
    return self unless self.include?(source)
    top, middle, bottom = self.rpartition(source)
    "#{top}#{target}#{bottom}"
  end
end

Then you can just call it directly on any String instance, eg "fooBAR123BAR".gsub_last("BAR", "FOO") == "fooBAR123FOO"