Developers are using Octopress to deliver information to other developers. It is important that we consider those other developers when creating our content and how that content is displayed. Defining a custom liquid tag helps you represent your content in a way that is easy to understand. The following gist contains all the content you need to …

sample_entry.markdown

To get started with Rails we need to install the gem. From the terminal type:

{% terminal %}
$ gem install rails
Fetching: i18n-0.6.1.gem (100%)
Fetching: multi_json-1.3.6.gem (100%)
Fetching: activesupport-3.2.8.gem (100%)
...
{% endterminal %}

terminal.css

/*-----------------------------------------------------------------------------------*/
/* Window
/*-----------------------------------------------------------------------------------*/

.window {
  margin: 0px auto 30px auto;
  background: -webkit-linear-gradient(rgba(233, 233, 233, 1.0), rgba(178, 178, 178, 1.0) 21px, #EDEDED, #EDEDED 23px);
  background: -moz-linear-gradient(rgba(233, 233, 233, 1.0), rgba(178, 178, 178, 1.0) 21px, #EDEDED, #EDEDED 23px);
  border-radius: 5px;
  box-shadow:inset 0 1px 0 rgba(255,255,255,.6), 0 22px 50px 4px rgba(0,0,0,0.56), 0 0 0 1px rgba(0, 0, 0, 0.3);
  text-align: left;
  z-index:0;
  visibility:hidden;
  opacity:0;
  visibility:visible;
  opacity:1;
}

.container {
  border-radius: 5px;
}

h1.titleInside {
  margin: 0px;
  position:relative;
  z-index:2;
  color:#3c3c3c;
  font-size:13px;
  line-height:21px;
  text-decoration:none;
  text-shadow: 0 1px 1px #e7e7e7;
  text-align:center;
  text-transform:capitalize;
}

nav.control-window {
  float: left;
  padding: 2px 0px 0px 10px;
  left:5px;
  top:3px;
  z-index:10;
  height:19px;
}

nav.control-window a {
  display: inline-block;
  margin: 2px 0px 3px 1px;
  width: 12px;
  height: 12px;
  border-radius: 100%;
  box-shadow: 0px 1px 0px rgba(255,255,255,.5);
  text-indent: -9999px;
  position: relative;
}
nav.control-window a:before {
  content: '';
  display: block;
  position: absolute;
  border-radius: 100%;
  box-shadow:inset 0 1px 4px rgba(0, 0, 0, .8);
  top: 0px;
  left: 0px;
  bottom: 0px;
  right: 0px;
}
nav.control-window a:after {
  content: '';
  display: block;
  position: absolute;
  top: 2px;
  left: 1px;
  bottom: 1px;
  right: 1px;
  border-radius: 100%;
  background: -webkit-linear-gradient(white, rgba(255, 255, 255, .9) 2%, white, rgba(255, 255, 255, .4) 16%, rgba(255, 255, 255, 0) 43%, rgba(255, 255, 255, .74), rgba(255, 255, 255, .7) 122%, rgba(255, 255, 255, .7));
  background: -moz-linear-gradient(white, rgba(255, 255, 255, .9) 2%, white, rgba(255, 255, 255, .4) 16%, rgba(255, 255, 255, 0) 43%, rgba(255, 255, 255, .74), rgba(255, 255, 255, .7) 122%, rgba(255, 255, 255, .7));
  box-shadow: inset 0px -3px -5px 3px rgba(255, 255, 255, 0.2), inset 0px 2px -5px 3px rgba(255, 255, 255, 0.2);
}
nav.control-window a.close {
  background: #FD4E4E;
}
nav.control-window a.minimize {
  background: #F3BB55;
}
nav.control-window a.maximize {
  background: #96D16F;
}
nav.control-window a.deactivate {
  background: #b5b5b5;
}

/*-----------------------------------------------------------------------------------*/
/* Terminal Console Layout
/*-----------------------------------------------------------------------------------*/

.terminal {
  background: #333;
  color: #DDD;
  white-space: pre-line;
  border-bottom-left-radius: 5px;
  border-bottom-right-radius: 5px;
  width: 100%;
}

.terminal table {
  margin-left: 10px;
  margin-right: 10px;
}

div.terminal td {
  vertical-align: top;
}

div.terminal pre {
  background: none;
  border: none;
  padding-left: 0px;
  box-shadow: none;
  -webkit-box-shadow: none;
}

div.terminal pre span {
  display: block;
}

div.terminal {
  overflow-x: auto;
  overflow-y: hidden;
}

div.terminal pre.line-numbers span {
  display: inline;
}

div.terminal span.command { color: #FFF; }
div.terminal span.output { color: #BBB; }

terminal_tag.rb

module Jekyll

  class TerminalTag < Liquid::Block
    include TemplateWrapper

    def initialize(tag_name, markup, tokens)
      super
    end

    def render(context)
      output = super(context)

      %{<div class="window">
          <nav class="control-window">
            <a href="#finder" class="close" data-rel="close">close</a>
            <a href="#" class="minimize">minimize</a>
            <a href="#" class="deactivate">deactivate</a>
          </nav>
          <h1 class="titleInside">Terminal</h1>
          <div class="container"><div class="terminal">#{promptize(output)}</div></div>
        </div>}
    end

    def promptize(content)
      content = content.strip
      gutters = content.lines.map { |line| gutter(line) }
      lines_of_code = content.lines.map { |line| line_of_code(line) }

      table = "<table><tr>"
      table += "<td class='gutter'><pre class='line-numbers'>#{gutters.join("\n")}</pre></td>"
      table += "<td class='code'><pre><code>#{lines_of_code.join("")}</code></pre></td>"
      table += "</tr></table>"
    end

    def gutter(line)
      gutter_value = line.start_with?(command_character) ? command_character : "&nbsp;"
      "<span class='line-number'>#{gutter_value}</span>"
    end

    def line_of_code(line)
      if line.start_with?(command_character)
        line_class = "command"
        line = line.sub(command_character,'').strip
      else
        line_class = "output"
      end
      "<span class='line #{line_class}'>#{line}</span>"
    end

    def command_character
      "$"
    end

  end

end

Liquid::Template.register_tag('terminal', Jekyll::TerminalTag)

My fork has the necessary code that @jasonhodges mentioned, as well as updated styling for osx 10.11
https://gist.github.com/neight-allen/656ba7206dcc7d85044ff1777008399e