readStringUntil() reads characters from a stream into a String. The function terminates if the terminator character is detected or it times out (see setTimeout()).

This function is part of the Stream class, and can be called by any class that inherits from it (Wire, Serial, etc). See the Stream class main page for more information.

stream.readStringUntil(terminator)

stream: an instance of a class that inherits from Stream.
terminator: the character to search for. Allowed data types: char.

The entire String read from a stream, up to the terminator character. If the terminator character can’t be found, or if there is no data before the terminator character, it will return NULL.

The terminator character is discarded from the stream. If the terminator character can’t be found, all read characters will be discarded.