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, a string input stream from with-input-from-string, or a TCP or TLS socket handle -- on a socket the character is assembled from the wire's UTF-8 bytes, so read-char and read-byte can be mixed on one connection. At end of input it signals an end-of-file condition unless eof-error-p is nil, in which case it returns eof-value (default nil). Because the condition is the registered end-of-file class, the usual CL lexer shape -- a read loop wrapped in (handler-case ... (end-of-file (e) ...)) -- terminates as written. 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.