This section describes the Lisp functions for printing Lisp objects—converting objects into their printed representation.
Some of the Emacs printing functions add quoting characters to the output when necessary so that it can be read properly. The quoting characters used are ‘"’ and ‘\’; they distinguish strings from symbols, and prevent punctuation characters in strings and symbols from being taken as delimiters when reading. See Printed Representation and Read Syntax, for full details. You specify quoting or no quoting by the choice of printing function.
If the text is to be read back into Lisp, then you should print with quoting characters to avoid ambiguity. Likewise, if the purpose is to describe a Lisp object clearly for a Lisp programmer. However, if the purpose of the output is to look nice for humans, then it is usually better to print without quoting.
Lisp objects can refer to themselves. Printing a self-referential object in the normal way would require an infinite amount of text, and the attempt could cause infinite recursion. Emacs detects such recursion and prints ‘#level’ instead of recursively printing an object already being printed. For example, here ‘#0’ indicates a recursive reference to the object at level 0 of the current print operation:
(setq foo (list nil)) ⇒ (nil) (setcar foo foo) ⇒ (#0)
In the functions below, stream stands for an output stream.
(See the previous section for a description of output streams. Also
See external-debugging-output, a useful stream value for debugging.)
If stream is
nil or omitted, it defaults to the value of
(progn (print 'The\ cat\ in) (print "the hat") (print " came back")) -| -| The\ cat\ in -| -| "the hat" -| -| " came back" ⇒ " came back"
This function outputs the printed representation of object to
stream. It does not print newlines to separate output as
(progn (prin1 'The\ cat\ in) (prin1 "the hat") (prin1 " came back")) -| The\ cat\ in"the hat"" came back" ⇒ " came back"
This function outputs the printed representation of object to stream. It returns object.
This function is intended to produce output that is readable by people,
read, so it doesn’t insert quoting characters and doesn’t
put double-quotes around the contents of strings. It does not add any
spacing between calls.
(progn (princ 'The\ cat) (princ " in the \"hat\"")) -| The cat in the "hat" ⇒ " in the \"hat\""
This function outputs a newline to stream. The name stands for
“terminate print”. If ensure is non-
nil no newline is printed
if stream is already at the beginning of a line. Note in this
case stream can not be a function and an error is signaled if
it is. This function returns
t if a newline is printed.
This function outputs character to stream. It returns character.
This function returns a string containing the text that
would have printed for the same argument.
(prin1-to-string 'foo) ⇒ "foo"
(prin1-to-string (mark-marker)) ⇒ "#<marker at 2773 in strings.texi>"
If noescape is non-
nil, that inhibits use of quoting
characters in the output. (This argument is supported in Emacs versions
19 and later.)
(prin1-to-string "foo") ⇒ "\"foo\""
(prin1-to-string "foo" t) ⇒ "foo"
format, in Formatting Strings, for other ways to obtain
the printed representation of a Lisp object as a string.
This macro executes the body forms with
up to feed output into a string. Then it returns that string.
For example, if the current buffer name is ‘foo’,
(with-output-to-string (princ "The buffer is ") (princ (buffer-name)))
"The buffer is foo".
This function outputs object to stream, just like
prin1, but does it in a prettier way. That is, it’ll
indent and fill the object to make it more readable for humans.
If you need to use binary I/O in batch mode, e.g., use the functions described in this section to write out arbitrary binary data or avoid conversion of newlines on non-POSIX hosts, see set-binary-mode.