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GNU Emacs Lisp Reference Manual

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19.6 Variables Affecting Output

Variable: standard-output
The value of this variable is the default output stream--the stream that print functions use when the stream argument is nil.

Variable: print-escape-newlines
If this variable is non-nil, then newline characters in strings are printed as `\n' and formfeeds are printed as `\f'. Normally these characters are printed as actual newlines and formfeeds.

This variable affects the print functions prin1 and print that print with quoting. It does not affect princ. Here is an example using prin1:

 
(prin1 "a\nb")
     -| "a
     -| b"
     => "a
b"

(let ((print-escape-newlines t))
  (prin1 "a\nb"))
     -| "a\nb"
     => "a
b"

In the second expression, the local binding of print-escape-newlines is in effect during the call to prin1, but not during the printing of the result.

Variable: print-escape-nonascii
If this variable is non-nil, then unibyte non-ASCII characters in strings are unconditionally printed as backslash sequences by the print functions prin1 and print that print with quoting.

Those functions also use backslash sequences for unibyte non-ASCII characters, regardless of the value of this variable, when the output stream is a multibyte buffer or a marker pointing into one.

Variable: print-escape-multibyte
If this variable is non-nil, then multibyte non-ASCII characters in strings are unconditionally printed as backslash sequences by the print functions prin1 and print that print with quoting.

Those functions also use backslash sequences for multibyte non-ASCII characters, regardless of the value of this variable, when the output stream is a unibyte buffer or a marker pointing into one.

Variable: print-length
The value of this variable is the maximum number of elements to print in any list, vector or bool-vector. If an object being printed has more than this many elements, it is abbreviated with an ellipsis.

If the value is nil (the default), then there is no limit.

 
(setq print-length 2)
     => 2
(print '(1 2 3 4 5))
     -| (1 2 ...)
     => (1 2 ...)

Variable: print-level
The value of this variable is the maximum depth of nesting of parentheses and brackets when printed. Any list or vector at a depth exceeding this limit is abbreviated with an ellipsis. A value of nil (which is the default) means no limit.

These variables are used for detecting and reporting circular and shared structure--but they are only defined in Emacs 21.

Variable: print-circle
If non-nil, this variable enables detection of circular and shared structure in printing.

Variable: print-gensym
If non-nil, this variable enables detection of uninterned symbols (see section 8.3 Creating and Interning Symbols) in printing. When this is enabled, uninterned symbols print with the prefix `#:', which tells the Lisp reader to produce an uninterned symbol.

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