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Assuming a feed with a URL or title that matches the regular expression is
listed in your OPML file, only that feed is going to get updated.

There is no need to escape slashes in the regular expression: C<//rss/> works
just fine. Beware shell escaping, however. Most likely, you need to surround the
regular expression with single quotes if it contains spaces:

    jupiter update feed.opml '/Halberds & Helmets/'

Notice how we assume that named entities such as C<&amp;> have already been
parsed into the appropriate strings.

=head2 Generate the HTML

This is how you generate the C<index.html> file based on the feeds of your
C<feed.opml>. It assumes that you have already updated all the feeds (see
above).

    jupiter html feed.opml

See L</OPTIONS> for ways to change how the HTML is generated.

=head2 Generate the RSS feed

This happens at the same time as when you generate the HTML. It takes all the
entries that are being added to the HTML and puts the into a feed.

See L</OPTIONS> for ways to change how the HTML is generated.

=head2 Why separate the two steps?

The first reason is that tinkering with the templates involves running the
program again and again, and you don't want to contact all the sites whenever
you update your templates.

The other reason is that it allows you to create subsets. For example, you can
fetch the feeds for three different OPML files:

    jupiter update osr.opml indie.opml other.opml

And then you can create three different HTML files:

    jupiter html osr.html osr.opml
    jupiter html indie.html indie.opml
    jupiter html rpg.html osr.opml indie.opml other.opml

For an example of how it might look, check out the setup for the planets I run.
L<https://alexschroeder.ch/cgit/planet/about/>

=head2 What about the JSON file?

There's a JSON file that gets generated and updated as you run Planet Jupiter.
It's name depends on the OPML files used. It records metadata for every feed in
the OPML file that isn't stored in the feeds themselves.

C<message> is the HTTP status message, or a similar message such as "No entry
newer than 90 days." This is set when updating the feeds in your cache.

C<message> is the HTTP status code; this code could be the real status code from
the server (such as 404 for a "not found" status) or one generated by Jupiter
such that it matches the status message (such as 206 for a "partial content"
status when there aren't any recent entries in the feed). This is set when
updating the feeds in your cache.

C<title> is the site's title. When you update the feeds in your cache, it is
taken from the OPML file. That's how the feed can have a title even if the
download failed. When you generate the HTML, the feeds in the cache are parsed
and if a title is provided, it is stored in the JSON file and overrides the
title in the OPML file.

C<link> is the site's link for humans. When you generate the HTML, the feeds in
the cache are parsed and if a link is provided, it is stored in the JSON file.
If the OPML element contained a C<htmlURL> attribute, however, that takes
precedence. The reasoning is that when a podcast is hosted on a platform which
generates a link that you don't like and you know the link to the human-readable
blog elsewhere, use the C<htmlURL> attribute in the OPML file to override this.

C<last_modified> and C<etag> are two headers used for caching from the HTTP
response that cannot be changed by data in the feed.

If we run into problems downloading a feed, this setup allows us to still link
to the feeds that aren't working, using their correct names, and describing the
error we encountered.

=head2 Logging

Use the C<--log=LEVEL> to set the log level. Valid values for LEVEL are debug,
info, warn, error, and fatal.

=head1 LICENSE

GNU Affero General Public License

=head1 INSTALLATION

Using C<cpan>:

    cpan App::jupiter

Manual install:

    perl Makefile.PL
    make
    make install

=head2 Dependencies

To run Jupiter on Debian we need:

C<libmodern-perl-perl> for L<Modern::Perl>

C<libmojolicious-perl> for L<Mojo::Template>, L<Mojo::UserAgent>, L<Mojo::Log>,
L<Mojo::JSON>, and L<Mojo::Util>

C<libxml-libxml-perl> for L<XML::LibXML>

C<libfile-slurper-perl> for L<File::Slurper>

C<libdatetime-perl> for L<DateTime>