function find(str, keys) {
  while (keys != "") {
    p = pos(keys, "\n");
    if (p > 0) {
      key = left(keys, p - 1);
      keys = mid(keys, p + 1);
    } else {
      key = keys;
      keys = "";
    }

    if (key != "" && pos(str, key) > 0) {
      return true;
    }
  }
  return false;
}

keys = InputBoxMultiLine("検索する文字列を改行区切りで入力してください。");
if (keys == "") {
  return;
}

for (y = Bottom; y >= 2; y--) {
  if (find([2,y], keys)) {
    [1,y] = "■";
  }
}