This section describes the Lisp functions and variables that pertain to reading.
In the functions below,
stream stands for an input stream (see the previous section). If
nil or omitted, it defaults to the value of
end-of-file error is signaled if reading encounters an unterminated list, vector, or string.
function read \&optional stream
This function reads one textual Lisp expression from
stream, returning it as a Lisp object. This is the basic Lisp input function.
function read-from-string string \&optional start end
This function reads the first textual Lisp expression from the text in
string. It returns a cons cell whose CAR is that expression, and whose CDR is an integer giving the position of the next remaining character in the string (i.e., the first one not read).
start is supplied, then reading begins at index
start in the string (where the first character is at index 0). If you specify
end, then reading is forced to stop just before that index, as if the rest of the string were not there.
(read-from-string "(setq x 55) (setq y 5)")
⇒ ((setq x 55) . 11)
(read-from-string "\"A short string\"")
⇒ ("A short string" . 16)
;; Read starting at the first character.
(read-from-string "(list 112)" 0)
⇒ ((list 112) . 10)
;; Read starting at the second character.
(read-from-string "(list 112)" 1)
⇒ (list . 5)
;; Read starting at the seventh character,
;; and stopping at the ninth.
(read-from-string "(list 112)" 6 8)
⇒ (11 . 8)
This variable holds the default input stream—the stream that
read uses when the
stream argument is
nil. The default is
t, meaning use the minibuffer.
nil, this variable enables the reading of circular and shared structures. See Circular Objects. Its default value is
When reading or writing from the standard input/output streams of the Emacs process in batch mode, it is sometimes required to make sure any arbitrary binary data will be read/written verbatim, and/or that no translation of newlines to or from CR-LF pairs is performed. This issue does not exist on POSIX hosts, only on MS-Windows and MS-DOS. The following function allows you to control the I/O mode of any standard stream of the Emacs process.
function set-binary-mode stream mode
stream into binary or text I/O mode. If
mode is non-
nil, switch to binary mode, otherwise switch to text mode. The value of
stream can be one of
stderr. This function flushes any pending output data of
stream as a side effect, and returns the previous value of I/O mode for
stream. On POSIX hosts, it always returns a non-
nil value and does nothing except flushing pending output.