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

.gsub /abc(?=[^abc]*$)/, 'ABC'

Matches a "abc" and then asserts ((?=) is positive lookahead) that no other characters up to the end of the string are "abc".