title: arduino Serial.readStringUntil('\r') - multiple lines input
body: <p>I'm quite new to Arduino programming and to coding itself.<br>
  I'm trying to read some strings from serial (to send them later by ESP8266) and my simple sketch works with no problems with a lot of them.</p>
  
  <pre><code>while(Serial.available()){
  String termdata = Serial.readStringUntil('\r');
  </code></pre>
  
  <p>There's a case when my <code>termdata</code> string (actually a GSM AT command) is split onto two lines.</p>
  
  <p>e.g.</p>
  
  <pre><code>AT+CMGW=+39XXXXXXXXXX,
  1234567890abcdef
  </code></pre>
  
  <p>and that <code>\r</code> terminator (I guess) gives me just the first line of my stream, while I actually should need to get the second one (<code>1234567890abcdef</code>).</p>
  
  <p>Since I need to read other strings too that are using <code>\r</code> terminator, how could I get data from that second line without loosing other strings?</p>