Tree Processor Extension Example

Purpose

Detect literal blocks that contain shell commands, strip the prompt character and style the command using CSS in such a way that the prompt character cannot be selected (as seen on help.github.com).

sample-with-shell-session.adoc

 $ echo "Hello, World!"
 > Hello, World!

 $ gem install asciidoctor

ShellSessionTreeProcessor

class ShellSessionTreeProcessor < Asciidoctor::Extensions::TreeProcessor
  def process document
    return unless document.blocks?
    process_blocks document
    nil
  end

  def process_blocks node
    node.blocks.each_with_index do |block, i|
      if block.context == :literal &&
          (((first_line = block.lines.first).start_with? '$ ') ||
            (first_line.start_with? '> '))
        node.blocks[i] = convert_to_terminal_listing block
      else
        process_blocks block if block.blocks?
      end
    end
  end

  def convert_to_terminal_listing block
    attrs = block.attributes
    attrs['role'] = 'terminal'
    prompt_attr = (attrs.has_key? 'prompt') ?
        %( data-prompt="#{block.sub_specialchars attrs['prompt']}") : nil
    lines = block.lines.map do |line|
      line = block.sub_specialchars line.chomp
      if line.start_with? '$ '
        %(<span class="command"#{prompt_attr}>#{line[2..-1]}</span>)
      elsif line.start_with? '&gt; '
        %(<span class="output">#{line[5..-1]}</span>)
      else
        line
      end
    end
    create_listing_block block.document, lines * EOL, attrs, subs: nil
  end
end

Usage

Asciidoctor::Extensions.register do
  tree_processor ShellSessionTreeProcessor
end

Asciidoctor.convert_file 'sample-with-shell-session.adoc', :safe => :safe