Syntax Highlighting with Pygments for Org-mode Src Blocks

Org-mode uses special backend to export the document in the certain format. Backend describes rules for processing and converting all elements. The solution of my issue — create my own backend based on existing one and customize function that is responsible for code blocks processing.

So, we need a function that will execute the following shell command and then pass an output back to the backend.

pygmentize -l <syntax> -f html <input_file>

It will be much easier to write code blocks to the temporary files and pass them to the script then try to escape all possible character combinations for using stdin.

Based on the source code of the HTML exporting backend we can write our own function for processing code that will accept three parameters: code, contents and info. We will work with code parameter that represents org-element.

According to Org-mode API for "Src Block" object we need to get values of :language and :value properties that are responsible for syntax and code accordingly.

(require 'org)
(require 'ox)
(require 'ox-html)

;; Path for pygments or command name
(defvar pygments-path "pygmentize")

(defun pygments-org-html-code (code contents info)
  ;; Generating tmp file path.
  ;; Current date and time hash will ideally pass our needs.
  (setq temp-source-file (format "/tmp/pygmentize-%s.txt"(md5 (current-time-string))))
  ;; Writing block contents to the file.
  (with-temp-file temp-source-file (insert (org-element-property :value code)))
  ;; Exectuing the shell-command an reading an output
  (shell-command-to-string (format "%s -l \"%s\" -f html %s"
				   pygments-path
				   (or (org-element-property :language code)
				       "")
				   temp-source-file)))

Now let's define a new backend pelican-html based on html and replace functions for processing src-block and example-block:

(org-export-define-derived-backend 'pelican-html 'html
  :translate-alist '((src-block .  pygments-org-html-code)
		     (example-block . pygments-org-html-code)))

Note: despite that API describes :language property for example-block— in fact does not support it (looks like a bug in the docs), so syntax setting will work only for src-block.

In my case, this backend is using for exporting blog posts through org-reader for Pelican not directly from Emacs buffer. The source code of my blog and the working example can be found here.

For more detailed information about export through Emacs configuring backend, please see the documentation.

1. Emacs StackExchange: How to use my custom layout for generating HTML files from org files instead of using the default layout?
2. Pygments: Command Line Interface
3. Org Element API