//char* lines[8] = { nullptr };
char txt[168] = { '\0' };

void setup() {
  Serial.begin(115200);
  strcpy(txt, "line one\nline two\nline three\nline four\nline five\nline six\nline seven\nline eight\n");
  int index = 0;
  int offset = 2;
  char *sep;
  const char *str = txt;
  char **ptr = &str;
  char* lines[8];

  do {
    sep = strchr(*ptr, '\n');
    if (sep) {
      *sep = '\0';

      if (index >= offset && index < offset+8) {
        lines[index] = *ptr;
        Serial.print(index-offset); Serial.print(" "); Serial.println(lines[index]);
      }

      sep++;
      *ptr = sep;
    }
    index++;
  } while (*ptr);

  for (int i=0; i<8; i++) {
    Serial.print(i); Serial.print(" "); Serial.println(lines[i]);
  }

  ptr = &str;
  Serial.println(*ptr);
  /*
  for (int i=0; i<strlen(txt); i++) {
  Serial.print(*ptr++);
    if (*ptr[i] == '\n') {
      *ptr = '\0'; ptr++;
    }
  }  
  Serial.println();
  */
}

void loop() {
  delay(10);
}