using negative conditions within regular expressions

Question

Is it possible to use negative matches within gsub expressions? I want to replace strings starting by hello except those starting by hello Pe

Answer 1

Sounds like you want a negative lookahead:

>> "hello foo".gsub(/hello (?!peter)/, 'lala ') #=> "lala foo"
>> "hello peter".gsub(/hello (?!peter)/, 'lala ') #=> "hello peter"