site/jekyll/_includes/blog_post.html

<h1><a href="{{ page.url }}">{{ page.title }}</a></h1>
<p class="meta">{{ page.date | date_to_string }} by {{ page.author }}</p>

<div id="post">
{% if content != '' %}
  {{ page.excerpt }}
{% else %}
  {{ page.content }}
{% endif %}
</div>