NSRegularExpression

NSRegularExpression *regEx;
regEx = [NSRegularExpression regularExpressionWithPattern:@"..d"
                                                                             Option:0
                                                                             error:&err];

NSString *str = @"good food today";
NSRange r = NSMakeRange(0,[str length]);
NSArray *array = [regEx matchesInString:str options:0 range:r];

결과
   ..d   ..d  ..d
good food today

NSString *res = [regEx stringByReplacingMatchesInstring:str options:0 range:r withTemplate:@"#"];

결과
--> g# f# #ay