The static blog generator, Octopress, does not generate per category RSS feeds by default. I thought I would need a plugin to do this but it is quite easy and a plugin is overkill. All that you need to do is create a feed file with the appropriate filtering to limit the category.
To create a per category feed, copy the default feed source/atom.xml
file to say source/emacs.xml. I updated the <title> value and
the for post loop to only use the emacs categories. Here is
my file:
<?xml version="1.0" encoding="utf-8"?>
<feed xmlns="http://www.w3.org/2005/Atom">
<title>{{ site.title | xml_escape }} - Emacs</title>
<link href="{{ site.url }}/atom.xml" rel="self"/>
<link href="{{ site.url }}/"/>
<updated>{{ site.time | date_to_xmlschema }}</updated>
<id>{{ site.url }}/</id>
<author>
<name>{{ site.author | xml_escape }}</name>
{% if site.email %}
<email>{{ site.email | xml_escape }}</email>
{% endif %}
</author>
<generator uri="http://octopress.org/">Octopress</generator>
{% for post in site.categories.emacs limit: 20 %}
<entry>
<title>{{ post.title | xml_escape }}</title>
<link href="{{ site.url }}{{ post.url }}"/>
<updated>{{ post.date | date_to_xmlschema }}</updated>
<id>{{ site.url }}{{ post.id }}</id>
<content type="html">{{ post.content | expand_urls: site.url | xml_escape }}</content>
</entry>
{% endfor %}
</feed>