read-char &optional input-stream eof-error-p eof-value recursive-p → char

input-stream — an input stream designator. The default is standard input.

eof-error-p — a generalized boolean. The default is true.

eof-value — an object. The default is nil.

recursive-p — a generalized boolean. The default is false.

char — a character or the eof-value.

read-char returns the next character from input-stream.

When input-stream is an echo stream, the character is echoed on input-stream the first time the character is seen. Characters that are not echoed by read-char are those that were put there by unread-char and hence are assumed to have been echoed already by a previous call to read-char.

If recursive-p is true, this call is expected to be embedded in a higher-level call to read or a similar function used by the Lisp reader.

If an end of file₂ occurs and eof-error-p is false, eof-value is returned.

 (with-input-from-string (is "0123") 
    (do ((c (read-char is) (read-char is nil 'the-end))) 
        ((not (characterp c))) 
     (format t "~S " c))) 
⊳ #\0 #\1 #\2 #\3 
→ NIL

*standard-input*, *terminal-io*.

If an end of file₂ occurs before a character can be read, and eof-error-p is true, an error of type end-of-file is signaled.

read-byte, read-sequence, write-char, read

The corresponding output function is write-char.