Simplified Common Lisp reference
Symbol class: Input and output
Symbol type: function
read-charinput-stream(optional)eof-error-p(optional)eof-value(optional)recursive-p(optional) => char
Argument description:
input-stream an input stream, default is standard input
eof-error-p a boolean, true (default) is EOF should be signaled
eof-value an object that is returned as EOF value
recursive-p flag to note recursive processing

READ-CHAR function reads a character from input stream.

(let ((s (make-string-input-stream (format nil "line 1~%line 2~%line 3)")))) (read-char s))
=> #\l
Function indexFull documentation for read-char (HyperSpec)