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18.6 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. The default is t, meaning display in the echo area.

Variable: print-quoted

If this is non-nil, that means to print quoted forms using abbreviated reader syntax, e.g., (quote foo) prints as 'foo, and (function foo) as #'foo.

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.

    

  


  

    
User
    Option: eval-expression-print-length


    
User
    Option: eval-expression-print-level


    

      
These are the values for print-length and
      print-level used by
      eval-expression, and thus, indirectly, by many
      interactive evaluation commands (see 
      Evaluating Emacs-Lisp Expressions in The GNU Emacs
      Manual).

    

  


  
These variables are used for detecting and reporting circular
  and shared structure:


  

    
Variable:
    print-circle


    

      
If non-nil, this variable enables detection
      of circular and shared structure in printing. See Circular
      Objects.

    

  


  

    
Variable:
    print-gensym


    

      
If non-nil, this variable enables detection
      of uninterned symbols (see Creating
      Symbols) in printing. When this is enabled, uninterned
      symbols print with the prefix ‘#:’,
      which tells the Lisp reader to produce an uninterned
      symbol.

    

  


  

    
Variable:
    print-continuous-numbering


    

      
If non-nil, that means number continuously
      across print calls. This affects the numbers printed for
      ‘#n=’ labels and
      ‘#m#’ references.
      Don’t set this variable with setq; you
      should only bind it temporarily to t with
      let. When you do that, you should also bind
      print-number-table to nil.

    

  


  

    
Variable:
    print-number-table


    

      
This variable holds a vector used internally by printing
      to implement the print-circle feature. You
      should not use it except to bind it to nil when
      you bind print-continuous-numbering.

    

  


  

    
Variable:
    float-output-format


    

      
This variable specifies how to print floating-point
      numbers. The default is nil, meaning use the
      shortest output that represents the number without losing
      information.


      
To control output format more precisely, you can put a
      string in this variable. The string should hold a
      ‘%’-specification to be used in the
      C function sprintf. For further restrictions on
      what you can use, see the variable’s documentation
      string.

    

  

  


  

    
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