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11.6 Literal Examples

You can include literal examples that should not be subjected to markup. Such examples are typeset in monospace, so this is well suited for source code and similar examples.

#+BEGIN_EXAMPLE
  Some example from a text file.
#+END_EXAMPLE

Note that such blocks may be indented in order to align nicely with indented text and in particular with plain list structure (see Plain Lists). For simplicity when using small examples, you can also start the example lines with a colon followed by a space. There may also be additional whitespace before the colon:

Here is an example
   : Some example from a text file.

If the example is source code from a programming language, or any other text that can be marked up by Font Lock in Emacs, you can ask for the example to look like the fontified Emacs buffer111. This is done with the code block, where you also need to specify the name of the major mode that should be used to fontify the example112, see Structure Templates for shortcuts to easily insert code blocks.

#+BEGIN_SRC emacs-lisp
  (defun org-xor (a b)
    "Exclusive or."
    (if a (not b) b))
 #+END_SRC

Both in ‘example’ and in ‘src’ snippets, you can add a ‘-n’ switch to the end of the ‘#+BEGIN’ line, to get the lines of the example numbered. The ‘-n’ takes an optional numeric argument specifying the starting line number of the block. If you use a ‘+n’ switch, the numbering from the previous numbered snippet is continued in the current one. The ‘+n’ switch can also take a numeric argument. This adds the value of the argument to the last line of the previous block to determine the starting line number.

#+BEGIN_SRC emacs-lisp -n 20
  ;; This exports with line number 20.
  (message "This is line 21")
#+END_SRC

#+BEGIN_SRC emacs-lisp +n 10
  ;; This is listed as line 31.
  (message "This is line 32")
#+END_SRC

In literal examples, Org interprets strings like ‘(ref:name)’ as labels, and use them as targets for special hyperlinks like ‘[[(name)]]’—i.e., the reference name enclosed in single parenthesis. In HTML, hovering the mouse over such a link remote-highlights the corresponding code line, which is kind of cool.

You can also add a ‘-r’ switch which removes the labels from the source code113. With the ‘-n’ switch, links to these references are labeled by the line numbers from the code listing. Otherwise links use the labels with no parentheses. Here is an example:

#+BEGIN_SRC emacs-lisp -n -r
  (save-excursion                 (ref:sc)
     (goto-char (point-min))      (ref:jump)
#+END_SRC
In line [[(sc)]] we remember the current position. [[(jump)][Line (jump)]]
jumps to point-min.

Finally, you can use ‘-i’ to preserve the indentation of a specific code block (see Editing Source Code).

If the syntax for the label format conflicts with the language syntax, use a ‘-l’ switch to change the format, for example

#+BEGIN_SRC pascal -n -r -l "((%s))"

See also the variable org-coderef-label-format.

HTML export also allows examples to be published as text areas (see Text areas in HTML export).

Because the ‘#+BEGIN’ … ‘#+END’ patterns need to be added so often, a shortcut is provided (see Structure Templates).

C-c ' (org-edit-special)

Edit the source code example at point in its native mode. This works by switching to a temporary buffer with the source code. You need to exit by pressing C-c ' again114. The edited version then replaces the old version in the Org buffer. Fixed-width regions—where each line starts with a colon followed by a space—are edited using artist-mode115 to allow creating ASCII drawings easily. Using this command in an empty line creates a new fixed-width region.

Calling org-store-link (see Handling Links) while editing a source code example in a temporary buffer created with C-c ' prompts for a label. Make sure that it is unique in the current buffer, and insert it with the proper formatting like ‘(ref:label)’ at the end of the current line. Then the label is stored as a link ‘(label)’, for retrieval with C-c C-l.


Footnotes

(111)

This works automatically for the HTML backend (it requires version 1.34 of the ‘htmlize.el’ package, which you need to install). Fontified code chunks in LaTeX can be achieved using either the listings package or the minted package. Refer to org-export-latex-listings for details.

(112)

Source code in code blocks may also be evaluated either interactively or on export. See Working with Source Code for more information on evaluating code blocks.

(113)

Adding ‘-k’ to ‘-n -rkeeps the labels in the source code while using line numbers for the links, which might be useful to explain those in an Org mode example code.

(114)

Upon exit, lines starting with ‘*’, ‘,*’, ‘#+’ and ‘,#+’ get a comma prepended, to keep them from being interpreted by Org as outline nodes or special syntax. These commas are stripped when editing with C-c ', and also before export.

(115)

You may select a different-mode with the variable org-edit-fixed-width-region-mode.


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