readLineSync method

String readLineSync ({Encoding encoding: systemEncoding, bool retainNewlines: false })

Synchronously read a line from stdin. This call will block until a full line is available.

The argument encoding can be used to changed how the input should be decoded. Default is systemEncoding.

If retainNewlines is false, the returned String will not contain the final newline. If true, the returned String will contain the line terminator. Default is false.

If end-of-file is reached after any bytes have been read from stdin, that data is returned. Returns null if no bytes preceded the end of input.

Implementation 

String readLineSync(
    {Encoding encoding: systemEncoding, bool retainNewlines: false}) {
  const CR = 13;
  const LF = 10;
  final List<int> line = <int>[];
  // On Windows, if lineMode is disabled, only CR is received.
  bool crIsNewline = Platform.isWindows &&
      (stdioType(stdin) == StdioType.terminal) &&
      !lineMode;
  if (retainNewlines) {
    int byte;
    do {
      byte = readByteSync();
      if (byte < 0) {
        break;
      }
      line.add(byte);
    } while (byte != LF && !(byte == CR && crIsNewline));
    if (line.isEmpty) {
      return null;
    }
  } else if (crIsNewline) {
    // CR and LF are both line terminators, neither is retained.
    while (true) {
      int byte = readByteSync();
      if (byte < 0) {
        if (line.isEmpty) return null;
        break;
      }
      if (byte == LF || byte == CR) break;
      line.add(byte);
    }
  } else {
    // Case having to handle CR LF as a single unretained line terminator.
    outer:
    while (true) {
      int byte = readByteSync();
      if (byte == LF) break;
      if (byte == CR) {
        do {
          byte = readByteSync();
          if (byte == LF) break outer;

          line.add(CR);
        } while (byte == CR);
        // Fall through and handle non-CR character.
      }
      if (byte < 0) {
        if (line.isEmpty) return null;
        break;
      }
      line.add(byte);
    }
  }
  return encoding.decode(line);
}