read-char

(read-char &optional stream eof-error-p eof-value)

Reads one character from stream (default: standard input) and returns it. The stream may be a file stream opened by open/with-open-file or a string input stream from with-input-from-string. At end of input it signals an error unless eof-error-p is nil, in which case it returns eof-value (default nil). On the interpreter and the JVM backend a character is a UTF-16 code unit, matching the rest of the string representation; on the WASM backend strings are byte-indexed (like char/schar), so a character read is a byte read.