Read a byte from the file without advancing to the next one. That is, successive calls to peek() will return the same value, as will the next call to read().
This function is part of the Stream class, and is called by any class that inherits from it (Wire, Serial, etc). See the Stream class main page for more information.
stream : an instance of a class that inherits from Stream.
The next byte (or character), or -1 if none is available.