Make an Arduino stream which writes reads and writes from two streams. The first stream will get read and write preference.

This libarary is very much in beta. It hasn't been fully tested nor are all Serial class methods implemented yet.

As usual, download zip, unzip and rename to remove the dash character and place in your Arduino Libraries folder, on MacOSX ~/Documents/Arduino/libraries/

First stream argument will get priority.

MergedStreams mergedStreams(Serial, Serial);

Then use it just like a stream.

mergedStreams.write('a');
Serial.println((char)mergedStreams.read());