[NSString -substringMatchingPattern:]

gistfile1.m

- (NSString *)substringMatchingPattern:(NSString *)pattern {
    NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:pattern options:0 error:nil];
    if (regex) {
        NSAssert1(regex.numberOfCaptureGroups == 1, @"Pattern must include exactly one capture group: %@", pattern);
        NSTextCheckingResult *match = [regex firstMatchInString:self options:0 range:NSMakeRange(0, self.length)];
        if (match && match.numberOfRanges == 2) {
            return [self substringWithRange:[match rangeAtIndex:1]];
        }
    }

    return nil;
}