Returns the next byte (character) of incoming serial data without removing it from the internal serial buffer. That is, successivecalls to peek() will return the same character, as will the next call to read(). peek() inherits from the Stream utilityclass.
Serial.peek()
Arduino Mega only:
Serial1.peek()
Serial2.peek()
Serial3.peek()
None
the first byte of incoming serial data available (or -1 if no data is available) - int
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