User:Riviera/Podcast rss: Difference between revisions

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__TOC__
__TOC__
<span id="podcasts-are-rss-feeds"></span>
<span id="podcasts-are-rss-feeds"></span>
= Podcasts are RSS feeds =
= Podcasts are RSS feeds =
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=== Lines 1 - 6 ===
=== Lines 1 - 6 ===


<div class="captioned-content">
<div class="caption">
this is a test
</div>
<syntaxhighlight lang="fish">#!/usr/bin/fish
<syntaxhighlight lang="fish">#!/usr/bin/fish
function skeleton -d "Generate an RSS channel for a podcast" -a channel
function skeleton -d "Generate an RSS channel for a podcast" -a channel
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</syntaxhighlight>
</syntaxhighlight>


</div>
I have adjusted the code such that different flags create different ways of interacting with the command. I have added three flags, <code>-h</code>, <code>-g</code> and <code>-a</code>, in full <code>--help</code>, <code>--generate</code> and <code>--add</code>. These are stored in the <code>options</code> variable. The <code>add</code> flag can be passed to <code>skeleton</code> multiple times. Furthermore, <code>skeleton</code> now takes a channel as an argument. This is more flexible than taking a directory as an argument. I have made use of <code>if</code> statements to make the function do things under certain conditions. The first if statement relates to the <code>help</code> flag. If that flag is passed to <code>skeleton</code>, then text detailing how to use the command is displayed. The second if statement prevents the user from adding items to rss feeds and generating rss feeds simultaneously. <code>--add</code> and <code>--generate</code> become mutually exclusive options. The remaining if statements control what the programme does when the <code>generate</code> and <code>add</code> flags are passed to <code>skeleton</code>. Some lines have been omitted because it makes sense to place them elsewhere following these changes.
I have adjusted the code such that different flags create different ways of interacting with the command. I have added three flags, <code>-h</code>, <code>-g</code> and <code>-a</code>, in full <code>--help</code>, <code>--generate</code> and <code>--add</code>. These are stored in the <code>options</code> variable. The <code>add</code> flag can be passed to <code>skeleton</code> multiple times. Furthermore, <code>skeleton</code> now takes a channel as an argument. This is more flexible than taking a directory as an argument. I have made use of <code>if</code> statements to make the function do things under certain conditions. The first if statement relates to the <code>help</code> flag. If that flag is passed to <code>skeleton</code>, then text detailing how to use the command is displayed. The second if statement prevents the user from adding items to rss feeds and generating rss feeds simultaneously. <code>--add</code> and <code>--generate</code> become mutually exclusive options. The remaining if statements control what the programme does when the <code>generate</code> and <code>add</code> flags are passed to <code>skeleton</code>. Some lines have been omitted because it makes sense to place them elsewhere following these changes.


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</div>
</div>
<span id="the-add-flag"></span>
== The add flag ==
<span id="draft-two-of-script"></span>
<span id="draft-two-of-script"></span>
== Draft two of script ==
== Draft two of script ==
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end
end
</syntaxhighlight>
</syntaxhighlight>
<span id="draft-three-of-script"></span>
== Draft three of script ==
<syntaxhighlight lang="fish">#!/usr/bin/fish
function skelegen -d "Generate an RSS channel for a podcast"
    set -l options (fish_opt -s h -l help);
    set options $options (fish_opt --short=g --long=generate --required-val);
    set options $options (fish_opt --short=a --long=add --required-val --multiple-vals);
    set options $options (fish_opt --short=c --long=channel --required-val);
    argparse $options -- $argv;
    or return
    if set -ql _flag_help
        echo "skelegen [ -g DIR | -a FILE | -h ] -c XML_FILE
        -h --help                Display this text
        -g --genenerate DIR      Generate an RSS feed for DIR
        -a --add FILE            Add an item to a channel
        -c --channel XML_FILE    Specify an output channel
Skelegen is a command line application for generating and writing RSS feeds for podcasts. Skelegen is capable of generating an RSS feed for a directory of audio recordings. It is also possible to add audio recordings to a channel.
EXAMPLE USAGE
skelegen --generate ~/Music/podcast --channel ~/public_html/podcasts/mypodcast.xml
skelegen --add ~/Music/podcast/episode.mp3 --chamnel ~/public_html/podcasts/myotherpodcast.xml"
    end
    if set -ql _flag_generate and set -ql _flag_add;
        echo 'ERROR: skelegen cannot add and generate simultaneously';
        return 1;
    end
    if not set -ql _flag_channel;
        echo "ERROR: channel must be specified.";
        return 1;
    end
    if set -ql _flag_channel;
        set -l channelprefix (echo $_flag_channel | sed -E 's/\\/([^\\/]*.xml)/\\/\n\1/' | grep -Ev "[^/]*.xml");
        mkdir -p $channelprefix;
    end
    if set -ql _flag_generate
        set -l showid (uuidgen);
        set -l channelprefix (echo $_flag_channel | sed -E 's/\\/([^\\/]*.xml)/\\/\n\1/' | grep -Ev "[^/]*.xml");
        set -l publicprefix (echo $channelprefix | sed -E 's/\\/home\\/riviera\\/public_html\\/([^\\/]+\\/)/https:\\/\\/hub.xpub.nl\\/chopchop\\/~river\\/\1/');
        set -l channelfile (echo $_flag_channel | sed -E 's/\\/([^\\/]*.xml)/\\/\n\1/' | grep -Eo "[^/]*.xml");
        mkdir -p {$channelprefix}{$showid};
        set -l channel {$channelprefix}{$showid}/{$channelfile};
        # # write the channel data
        echo '<rss version="2.0" xmlns:atom="http://www.w3.org/2005/Atom">' > $channel;
        echo '<channel>' >> $channel;
        echo '<ttl>60</ttl>' >> $channel;
        echo '<generator>skeleton</generator>' >> $channel;
        read -l channelname -P "Channel Title: ";
        echo '<title>'$channelname'</title>' >> $channel;
        echo '<link>https://hub.xpub.nl/chopchop/worm/</link>' >> $channel;
        echo '<atom:link href="'$publicprefix$showid'" ref="self" type="application/rss+xml"/>' >> $channel;
        echo '<language>en</language>' >> $channel;
        read -l channeldesc -P "Channel Description: ";
        echo '<description><![CDATA['$channeldesc']]></description>' >> $channel;
        echo '<image><url>'{$publicprefix}{$showid}'/image.jpg</url>' >> $channel;
        echo '<link>https://hub.xpub.nl/chopchop/worm/</link>' >> $channel;
        echo '<title>'$channelname'</title>' >> $channel;
        echo '</image>' >> $channel;
        for file in (ls $_flag_generate);
            set -l guid (sha256sum {$_flag_generate}/{$file} | grep -Eo "[[:alnum:]]{64}");
            mkdir -p {$channelprefix}{$showid}/e/{$guid};
            ln -s {$_flag_generate}/{$file} {$channelprefix}{$showid}/e/{$guid}/{$file};
            set i (math $i + 1);
            set -l itemfile (printf '%s%s/e/%s/item-%i' $channelprefix $showid $guid $i);
            echo "<item>" > $itemfile;
            read -l title -P "Item $i Title: ";
            read -l desc -P "Item $i Description: ";
            echo "<title>"$title"</title>" >> $itemfile;
            echo "<pubDate>"(date)"</pubDate>" >> $itemfile;
            echo '<enclosure url="'$publicprefix$showid'/e/'$guid'/'$file'" length="'(soxi -D {$_flag_generate}/{$file})'" type="'(file -b --mime-type {$_flag_generate}/{$file})'"/>' >> $itemfile;
            sed -i 's/\\/\\/[^.]*\(\\/[^\\/]*.mp3\)/\1/' $itemfile;
            echo '<guid isPermaLink="false">'$guid'</guid>' >> $itemfile;
            set -l link "https://hub.xpub.nl/chopchop/~river/podcasts/$showid/e/$guid/$file";
            echo '<link>'$link'</link>' >> $itemfile;
            echo '<description><![CDATA['$desc']]></description>' >> $itemfile;
            echo '</item>' >> $itemfile;
        end
        # concatenate items in reverse order and append to the channel file
        for item in (ls -t {$channelprefix}*/e/*/item-*);
            cat $item >> $channel;
        end
        # close the rss and channel tags
        echo '</channel>' >> $channel;
        echo '</rss>' >> $channel;
        mkdir -p ~/.skeleton;
        touch ~/.skeleton/channellist;
        echo $channel >> ~/.skeleton/channellist;
    end
    if set -ql _flag_add
        ...
    end
end
</syntaxhighlight>
<span id="the-add-flag"></span>
== The add flag ==

Latest revision as of 08:23, 9 October 2023

Podcasts are RSS feeds

$ wget http://feeds.libsyn.com/330110/rss

On Monday 2nd, we briefly discussed podcasts as the antithesis of radio. That radio is live whereas podcasts are prerecorded and that modes of engaging with podcasts and radio differ. Podcasts are built upon Really Simple Syndication (RSS). In other words, in terms of code, there's little difference between the XML for an blog feed and the XML for a podcast feed. The following command combines a regular expression with the grep command to retrieve a list of all the XML tags in RSS feed for the Call Me Mother podcast. 

$ grep -E "<[[:alpha:]]+" rss

This command prints results such as 

<pubDate>Fri, 02 Apr 2021 15:25:34 GMT</pubDate>

<title>Stephen Whittle</title>

and 

<link>https://www.novel.audio</link>

These tags also appear in RSS feeds for written blogs. However, the command also prints results such as 

<itunes:explicit>yes</itunes:explicit>

and 

<acast:showId>62b087ec4f1d1f0014025b79</acast:showId>

To make two files which record the different itunes and acast tags: 

$ grep -E "<itunes:[[:alpha:]]+>" rss > itunes.txt
$ grep -E "<acast:[[:alpha:]]+>" rss > acast.txt

Or, to create one file with both sets of tags: 

$ grep -E "<itunes:[[:alpha:]]+>|<acast:[[:alpha:]]+>" rss > both.txt

Editing

What I want to retrieve is a list of the tags only. At the moment, I'm not interested in what's in between the tags. Ideally I'd like to use built in commands to generate a text which contains an outline of tags along the lines of the following listing. 

1 <tag>
2 <subtag>
3 </subtag>
4 </tag>

First Attempt

Can this be achieved by making two files, open.txt and close.txt? The first file should contain all the opening tags and the latter all the closing tags. 

$ grep -Eon "<[[:alpha:]]+>" rss > open.txt
$ grep -Eon "</[[:alpha:]]+>" rss > close.txt

It should then be possible to cat both files and sort the result by line number producing the desired outcome. 

$ cat open.txt close.txt | sort -n > sorted.txt && cat sorted.txt | less

Second Attempt

Whilst reading through the output of the first attempt (sorted.txt), I discovered that

  1. the </guid> tags had no correlating opening tag
  2. That the closing tags were sorted before the opening tags

Problem 1: Some information was missing

I had already deliberately omitted acast and itunes tags. In doing so I worked on the assumption that there were no other relevant, colon-separated tags in the rss file. Fortunately, retrieving the additional data was a quick fix: 

$ grep -Eon "<[[:alpha:]]+>|<[[:alpha:]]+ [^z-A]*>" rss > open.txt

Figuring out a way to sort the file such that the closing tags followed the opening tags was another matter. The general outline was there, but if I could sort out the details this could become a template for a podcast RSS generator. And that could potentially be useful in relation to Worm's sonic archive.

Problem 2: Adding whitespace with sed

The following command prepends a new line to each instance of '</' in the rss file. 

sed 's/<\\//\n<\\//' rss >rss-out;

Now it's time to write the open.txt and close.txt files. 

$ grep -Eon "<[[:alpha:]]+>|<[[:alpha:]]+ [^z-A]*>" rss-out > open.txt
$ grep -Eon "</[[:alpha:]]+>>" rss-out > close.txt

Placing a newline before each closing tag increases the line number on which each closing tag appears. Now it's time to concatenate open.txt and close.txt and view the output. 

$ cat open.txt close.txt | sort -n > sorted.txt && cat sorted.txt | less

Third Attempt

On closer inspection of the output of sorted.txt I noticed a further lack of information. Various closing anchor tags had no corresponding opening tag. I therefore had to write a regular expression capable of matching the additional data in these tags. This might make the output of sorted.txt a little less readable, Although there may be a way to tidy up this information. For completeness, it would also make sense to include the acast and itunes tags. 

$ grep -Eon "<[[:alpha:]]+>|<[[:alpha:]]+ [^z-A]*>|<[[:alpha:]]+ [[:alpha:]]+([=\":/'.;_ ]|[[:alnum:]])*>|<itunes:[[:alpha:]]+>|<acast:[[:alpha:]]+>" rss-out > open.txt
$ grep -Eon "</[[:alpha:]]+>|</itunes:[[:alpha:]]+>|</acast:[[:alpha:]]+>" rss-out > close.txt

Then, as above 

$ cat open.txt close.txt | sort -n > sorted.txt && cat sorted.txt | less

Fourth Attempt

I refined the regular expression. It now matches every opening and closing tag. Also, it's necessary to pass the global option to the sed substitution command. The second sed command prepends whitespace to every opening tag. This improves the structure of the output 

sed 's/<\\//\n<\\//g' rss >rss-out
sed "s/<\([[:alpha:]][^>]*>\)/\n<\1/g" rss-out > rss-out-out
grep -Eon "<[[:alpha:]]([^>]*>)" rss-out-out > open.txt
grep -Eon "</([^>]*>)" rss-out-out > close.txt
cat open.txt close.txt | sort -n > sorted.txt
grep -Eo "<([^>]*>)" sorted.txt | less > skeleton.xml
chromium sorted.xml

The webpage complains about unmatched horizontal rule tags. I deleted all of these using the query replace function in Emacs. The webpage subsequently complained about <br> and <br /> tags, so I deleted all of these too. The result is what I wanted. It views well in the browser; I am able to collapse tags for an abbreviated overview of the document.

Fleshing out the skeleton

item tags are the primary constituent parts of the channel tag in skeleton.xml. However, the channel tag also contains several other tags. I have decided to design the podcast generator around this feature. This raises questions about the possible options the command might take. How does the user provide input? There are three aspects to the overall design.

  1. creating a system for generating items
  2. Creating a system for generating channel information
  3. Creating a system for adding items to a document containing channel information.

Wishlist

  • Create a system for updating channel information in the form of skeleton --add foo.mp3 bar.xml

A closer look at items

Each Item tag is made up of 15 tags. Many of these belong to the itunes schema. 

<itunes:title>

<itunes:duration>

<itunes:explicit>

<itunes:episodeType>

<itunes:season>

<itunes:episode>

<itunes:image href="https://assets.pippa.io/shows/62b087ec4f1d1f0014025b79/show-cover.jpg"/>

<itunes:summary>

Others belong to the acast schema. 

<acast:episodeId>

<acast:showId>

<acast:episodeUrl>

<acast:settings>

And then there's the rest. 

<title>

<pubDate>

<enclosure url="https://sphinx.acast.com/p/open/s/62b087ec4f1d1f0014025b79/e/62f2226a61f23900137394a3/media.mp3" length="56168488" type="audio/mpeg"/>

<guid isPermaLink="false">

<description>

<link>

I intend only to make a basic podcast generator, so I'm not going to focus on the itunes and acast schemas.

Draft one of script

General Outline

The following shell script defines the function skeleton. It takes a directory as an argument, asks the user for some information and writes an xml file. 

#!/usr/bin/fish
function skeleton -d "Generate an RSS channel for a podcast" -a directory
    set -l showid (uuidgen);
    set -l options (fish_opt -s h -l help);
    argparse --name='skeleton' 'h/help' -- $argv;
    mkdir -p /tmp/skeleton/{$showid}/e/;
    set -l channelfile /tmp/skeleton/{$showid}/rss.xml;
    # write the channel data
    echo '<rss version="2.0" xmlns:atom="http://www.w3.org/2005/Atom">' > $channelfile;
    echo '<channel>' >> $channelfile;
    echo '<ttl>60</ttl>' >> $channelfile;
    echo '<generator>skeleton</generator>' >> $channelfile;
    read -l channelname -P "Channel Title: ";
    echo '<title>'$channelname'</title>' >> $channelfile;
    echo '<link>https://hub.xpub.nl/chopchop/worm/</link>' >> $channelfile;
    echo '<atom:link href="hub.xpub.nl/chopchop/worm/'$showid'" ref="self" type="application/rss+xml"/>' >> $channelfile;
    echo '<language>en</language>' >> $channelfile;
    read -l channeldesc -P "Channel Description: ";
    echo '<description><![CDATA['$channeldesc']]></description>' >> $channelfile;
    echo '<image><url>https://hub.xpub.nl/chopchop/worm/'$showid'/image.jpg</url>' >> $channelfile;
    echo '<link>https://hub.xpub.nl/chopchop/worm/</link>' >> $channelfile;
    echo '<title>'$channelname'</title>' >> $channelfile;
    echo '</image>' >> $channelfile;
    # write the item data
    for file in (ls $argv);
        set -l guid (sha256sum {$argv}/{$file} | grep -Eo "[[:alnum:]]{64}");
        mkdir -p /tmp/skeleton/{$showid}/e/{$guid};
        ln -s {$argv}/{$file} /tmp/skeleton/{$showid}/e/{$guid}/{$file};
        set i (math $i + 1);
        set -l itemfile (printf '/tmp/skeleton/%s/e/%s/item-%i' $showid $guid $i);
        echo "<item>" > $itemfile;
        read -l title -P "Item $i Title: ";
        read -l desc -P "Item $i Description: ";
        echo "<title>"$title"</title>" >> $itemfile;
        echo "<pubDate>"(date)"</pubDate>" >> $itemfile;
        echo '<enclosure url="https://hub.xpub.nl/chopchop/worm/'$showid'/e/'$guid'/'$file'" length="'(soxi -D {$argv}/{$file})'" type="'(file -b --mime-type {$argv}/{$file})'"/>' >> $itemfile;
        sed -i 's/\\/\\/[^.]*\(\\/[^\\/]*.mp3\)/\1/' $itemfile;
        echo '<guid isPermaLink="false">'$guid'</guid>' >> $itemfile;
        set -l link (grep -Eo "https://[^.].mp3" $itemfile);
        echo '<link>'$link'</link>' >> $itemfile;
        echo '<description><![CDATA['$desc']]></description>' >> $itemfile;
        echo '</item>' >> $itemfile;
    end
    # concatenate items in reverse order and append to the channel file
    for item in (ls -t /tmp/skeleton/*/e/*/item-*);
        cat $item >> $channelfile;
    end
    # close the rss and channel tags
    echo '</channel>' >> $channelfile;
    echo '</rss>' >> $channelfile;
end

Analysis of draft one

Lines 1 - 6

#!/usr/bin/fish
function skeleton -d "Generate an RSS channel for a podcast" -a directory
    set -l showid (uuidgen);
    set -l options (fish_opt -s h -l help);
    argparse --name='skeleton' 'h/help' -- $argv;
    mkdir -p /tmp/skeleton/{$showid}/e/;

The function skeleton is given a description and takes a directory as an argument. Next two local variables are set showid and options. The former has the value of evaluating the command uuidgen. The latter allows for the user to pass -h or --help to skeleton which will display help information. I need to figure out how to enable more options than 'help' alone. argparse is a command which defines how the skeleton command takes both options and arguments. The script next calls the command mkdir to create a temporary file structure. The showid variable expands to the value which was set in line 3.

Lines 7 - 15

set -l channelfile /tmp/skeleton/{$showid}/rss.xml;
# write the channel data
echo '<rss version="2.0" xmlns:atom="http://www.w3.org/2005/Atom">' > $channelfile;
echo '<channel>' >> $channelfile;
echo '<ttl>60</ttl>' >> $channelfile;
echo '<generator>skeleton</generator>' >> $channelfile;

Previously, the programme took a directory as an argument. Now it takes a channel as an argument. Taking a directory as an argument resembles the generate option. Consequently, much of the code from before can be placed within a newly written if statement. This extends to, with some adjustments, some of the lines which were omitted above. 

read -l channelname -P "Channel Title: ";
echo '<title>'$channelname'</title>' >> $channelfile;
echo '<link>https://hub.xpub.nl/chopchop/worm/</link>' >> $channelfile;

Next, the user is prompted to provide a title for the channel. The input is stored in the variable channelname. echo is used to encase the value of channelname within within xml title tags. This line of code is appended to the channelfile. No adjustments need to be made to these three lines.

Line 16

This line of code implicitly suggests a location for the overall output of the skeleton command. 

echo '<atom:link href="hub.xpub.nl/chopchop/worm/'$showid'" ref="self" type="application/rss+xml"/>' >> $channelfile;

This line of code suggests it will eventually be necessary to create the directory /media/worm/radio/$showid on chopchop. Doing so would intervene in the current structure of radio worm's archive and I am hesitant about doing so for two reasons:

  1. Space
  2. Risk Management

Space

What is the output of the skeleton command when it takes a directory as an argument? 

/tmp/skeleton/
/tmp/skeleton/$showid/
/tmp/skeleton/$showid/rss.xml
/tmp/skeleton/$showid/e/
/tmp/skeleton/$showid/e/$guid/
/tmp/skeleton/$showid/e/$guid/item-n
/tmp/skeleton/$showid/e/$guid/symbolic-link-to.mp3

The implication of line 16 is that eventually these temporary files are moved to /media/worm/radio/ which corresponds to the public url https://hub.xpub.nl/chopchop/worm/. Adding files and directories to this location will take up space on the harddrive; perhaps more space than there is available.

Risk Management

The shell is powerful and there's no undo function. Consequently, caution and care must be exercised when executing shell commands on files. Whereas chopchop has a backup of Radio Worm's sonic archive it would be time consuming and undesirable to have to recopy data from the original hard drive in the event of data loss. Whilst this is unlikely as long as the rm command is not used, things can still go wrong. For this reason, it might be better to situate the final, non-temporary location of the files at a distance from Worm's archive itself. Perhaps in the home folder of a user called 'podcasts', or on a separate hard drive.

Line 17

echo '<language>en</language>' >> $channelfile;

I have set the channel language to English. This could be changed or made into a user defined variable. However, I will not make these changes here.

lines 18 - 23

The following lines do not need adjusting. 

read -l channeldesc -P "Channel Description: ";
echo '<description><![CDATA['$channeldesc']]></description>' >> $channelfile;
echo '<image><url>https://hub.xpub.nl/chopchop/worm/'$showid'/image.jpg</url>' >> $channelfile;
echo '<link>https://hub.xpub.nl/chopchop/worm/</link>' >> $channelfile;
echo '<title>'$channelname'</title>' >> $channelfile;
echo '</image>' >> $channelfile;

Lines 24 - 43

# write the item data
for file in (ls $argv);

The for loop acts upon the result of calling ls on the value of argv. Currently, the value of argv is supposed to be a directory full of .mp3 files. The for loop uses the name of each file to write item data in an xml format for each mp3 file in a given directory. 

set -l guid (sha256sum {$argv}/{$file} | grep -Eo "[[:alnum:]]{64}");

Each mp3 file is assigned a guid which is equivalent to the sha256sum of the mp3 file. This was Thijs' suggestion. Piping the result of calling sha256sum on the full path of the mp3 file through a grep command is required to retrieve the sha256sum alone. This was discussed above. Notably, $argv is used here to prefix the full path to the value of the mp3 file. I intend to change the value of argv to a channel and consequently the way in which the value of guid is set will have to change. 

mkdir -p /tmp/skeleton/{$showid}/e/{$guid};

In any case, the value of guid is utilised to make a temporary directory, which is okay. 

ln -s {$argv}/{$file} /tmp/skeleton/{$showid}/e/{$guid}/{$file};

A symbolic link is created. The idea is that the url specified by the enclosure tag is a symbolic link to the publicly available sound files. 

set i (math $i + 1);

An incremental counter is set. 

set -l itemfile (printf '/tmp/skeleton/%s/e/%s/item-%i' $showid $guid $i);
echo "<item>" > $itemfile;
read -l title -P "Item $i Title: ";
read -l desc -P "Item $i Description: ";
echo "<title>"$title"</title>" >> $itemfile;
echo "<pubDate>"(date)"</pubDate>" >> $itemfile;

Those lines can stay the same. 

echo '<enclosure url="https://hub.xpub.nl/chopchop/worm/'$showid'/e/'$guid'/'$file'" length="'(soxi -D {$argv}/{$file})'" type="'(file -b --mime-type {$argv}/{$file})'"/>' >> $itemfile;

That line will have to change. $argv will be changed to $_flag_generator and the url will need to correspond to the final location of the output files. 

sed -i 's/\\/\\/[^.]*\(\\/[^\\/]*.mp3\)/\1/' $itemfile;
echo '<guid isPermaLink="false">'$guid'</guid>' >> $itemfile;
set -l link (grep -Eo "https://[^.].mp3" $itemfile);
echo '<link>'$link'</link>' >> $itemfile;
echo '<description><![CDATA['$desc']]></description>' >> $itemfile;
echo '</item>' >> $itemfile;
end

A change is needed here. The second regular expression currently matches nothing due to an absent asterisk.

Lines 44 - 47

# concatenate items in reverse order and append to the channel file
for item in (ls -t /tmp/skeleton/*/e/*/item-*);
    cat $item >> $channelfile;
end

This for loop is limited by the fact that it reads every item in /tmp/skeleton/*/e/*/. This could become problematic if left unattended. If the files remain in their temporary location too much data will be gathered next time the command is called. However, it's not an issue if the output files are moved to their permanent location after this part of the code has been executed.

Lines 48 - 50

# close the rss and channel tags
echo '</channel>' >> $channelfile;
echo '</rss>' >> $channelfile;

The final few lines of the script closes open tags and terminates the command.

Improvements to draft one

Lines 1 - 6

this is a test 

#!/usr/bin/fish
function skeleton -d "Generate an RSS channel for a podcast" -a channel
    set -l options (fish_opt -s h -l help);
    set options $options (fish_opt --short=g --long=generate --required-val); 
    set options $options (fish_opt --short=a --long=add --required-val --multiple-vals);
    argparse $options -- $argv;
    or return
    if set -ql _flag_help
        echo "skeleton [ -g DIR | -a FILE | -h ] CHANNEL
        -h --help                Display this text
        -g --genenerate DIR      Generate an RSS feed for DIR
        -a --add FILE            Add an item to a channel

        Skeleton is a command line tool for generating and writing RSS feeds for podcasts."
        return 0
    end
    if set -ql _flag_generate and set -ql _flag_add;
        echo 'ERROR: skeleton cannot add and generate simultaneously'
        return 1
    end

    if set -ql _flag_generate
        # echo $_flag_generate
    end
    if set -ql _flag_add
        # echo $_flag_add
    end
end

I have adjusted the code such that different flags create different ways of interacting with the command. I have added three flags, -h, -g and -a, in full --help, --generate and --add. These are stored in the options variable. The add flag can be passed to skeleton multiple times. Furthermore, skeleton now takes a channel as an argument. This is more flexible than taking a directory as an argument. I have made use of if statements to make the function do things under certain conditions. The first if statement relates to the help flag. If that flag is passed to skeleton, then text detailing how to use the command is displayed. The second if statement prevents the user from adding items to rss feeds and generating rss feeds simultaneously. --add and --generate become mutually exclusive options. The remaining if statements control what the programme does when the generate and add flags are passed to skeleton. Some lines have been omitted because it makes sense to place them elsewhere following these changes.

Lines 7 - 15

set -l showid (uuidgen);
mkdir -p /tmp/skeleton/{$showid};

Due to the resemblance described above the remainder of the script (lines 7 - 50) will be placed inside the third if statement. The code goes on to create a temporary directory using the value of the showid variable. 

touch /tmp/skeleton/index
echo $_flag_generate $showid >> /tmp/skeleton/index

Somehow, when using the add flag, skeleton will need to retrieve the value of showid for a given channel. This will ensure coherent and consistent output. I'm going to write a file which pairs the showid with the value of flag_generate. The code for the add flag will consult this file when it sets the value of showid. 

set -l channelfile /tmp/skeleton/{$showid}/rss.xml;
# write the channel data
echo '<rss version="2.0" xmlns:atom="http://www.w3.org/2005/Atom">' > $channelfile;
echo '<channel>' >> $channelfile;
echo '<ttl>60</ttl>' >> $channelfile;
echo '<generator>skeleton</generator>' >> $channelfile;

A channelfile is then set. Redirecting the output of echo to the value of channelfile creates the file and stores the output there.

Line 16

echo '<atom:link href="hub.xpub.nl/chopchop/river/public_html/podcasts/'$showid'" ref="self" type="application/rss+xml"/>' >> $channelfile;

It's evident that line 16 is bound up with the final location of the generated files. I'll eventually place the rss.xml file in ~/public_html/podcasts/$showid/. Therefore line 16 can be changed to the above.

Lines 24 - 43

for file in (ls $_flag_generate);
    set -l guid (sha256sum {$_flag_generate}/{$file} | grep -Eo "[[:alnum:]]{64}");
    mkdir -p /tmp/skeleton/{$showid}/e/{$guid};
    ln -s {$argv}/{$file} /tmp/skeleton/{$showid}/e/{$guid}/{$file};
    set i (math $i + 1);
    set -l itemfile (printf '/tmp/skeleton/%s/e/%s/item-%i' $showid $guid $i);
    echo "<item>" > $itemfile;
    read -l title -P "Item $i Title: ";
    read -l desc -P "Item $i Description: ";
    echo "<title>"$title"</title>" >> $itemfile;
    echo "<pubDate>"(date)"</pubDate>" >> $itemfile;
    echo '<enclosure url="https://hub.xpub.nl/chopchop/river/public_html/podcasts/'$showid'/e/'$guid'/'$file'" length="'(soxi -D {$_flag_generate}/{$file})'" type="'(file -b --mime-type {$_flag_generate}/{$file})'"/>' >> $itemfile;
    sed -i 's/\\/\\/[^.]*\(\\/[^\\/]*.mp3\)/\1/' $itemfile;
    echo '<guid isPermaLink="false">'$guid'</guid>' >> $itemfile;
    set -l link "https://hub.xpub.nl/chopchop/river/public_html/podcasts/$showid/e/$guid/$file";
    echo '<link>'$link'</link>' >> $itemfile;
    echo '<description><![CDATA['$desc']]></description>' >> $itemfile;
    echo '</item>' >> $itemfile;

(Re)Moving temporary files

To avoid errors and save the temporary files, it's important to move them to a different location. 

mkdir -p ~/public_html/podcasts/
mv /tmp/skeleton/* ~/public_html/podcasts/
touch ~/public_html/podcasts/index;
cat /tmp/skeleton/index >> ~/public_html/podcasts/index;
rm -r /tmp/skeleton/;

Repositioning lines 7 - 50

Having made these changes, lines 7 - 50 should be placed within the third if statement in the rewriting of lines 1 - 6. 

if set -ql _flag_generate
    ...
end

Draft two of script

#!/usr/bin/fish
function skelegen -d "Generate an RSS channel for a podcast"
    set -l options (fish_opt -s h -l help);
    set options $options (fish_opt --short=g --long=generate --required-val); 
    set options $options (fish_opt --short=a --long=add --required-val --multiple-vals);
    argparse $options -- $argv;
    or return
    if set -ql _flag_help
        echo "skelegen [ -g DIR | -a FILE | -h ] CHANNEL
        -h --help                Display this text
        -g --genenerate DIR      Generate an RSS feed for DIR
        -a --add FILE            Add an item to a channel

        Skelegen is a command line tool for generating and writing RSS feeds for podcasts."
        return 0
    end
    if set -ql _flag_generate and set -ql _flag_add;
        echo 'ERROR: skelegen cannot add and generate simultaneously'
        return 1
    end

    if set -ql _flag_generate
          set -l showid (uuidgen);
          mkdir -p /tmp/skeleton/{$showid};
          touch /tmp/skeleton/index;
          echo $_flag_generate $showid >> /tmp/skeleton/index;
          set -l channelfile /tmp/skeleton/{$showid}/rss.xml;
          # write the channel data
          echo '<rss version="2.0" xmlns:atom="http://www.w3.org/2005/Atom">' > $channelfile;
          echo '<channel>' >> $channelfile;
          echo '<ttl>60</ttl>' >> $channelfile;
          echo '<generator>skeleton</generator>' >> $channelfile;

          read -l channelname -P "Channel Title: ";
          echo '<title>'$channelname'</title>' >> $channelfile;
          echo '<link>https://hub.xpub.nl/chopchop/worm/</link>' >> $channelfile;
          echo '<atom:link href="hub.xpub.nl/chopchop/river/public_html/podcasts/'$showid'" ref="self" type="application/rss+xml"/>' >> $channelfile;
          echo '<language>en</language>' >> $channelfile;

          read -l channeldesc -P "Channel Description: ";
          echo '<description><![CDATA['$channeldesc']]></description>' >> $channelfile;
          echo '<image><url>https://hub.xpub.nl/chopchop/worm/'$showid'/image.jpg</url>' >> $channelfile;
          echo '<link>https://hub.xpub.nl/chopchop/worm/</link>' >> $channelfile;
          echo '<title>'$channelname'</title>' >> $channelfile;
          echo '</image>' >> $channelfile;
          for file in (ls $_flag_generate);
              set -l guid (sha256sum {$_flag_generate}/{$file} | grep -Eo "[[:alnum:]]{64}");
              mkdir -p /tmp/skeleton/{$showid}/e/{$guid};
              ln -s {$_flag_generate}/{$file} /tmp/skeleton/{$showid}/e/{$guid}/{$file};
              set i (math $i + 1);
              set -l itemfile (printf '/tmp/skeleton/%s/e/%s/item-%i' $showid $guid $i);
              echo "<item>" > $itemfile;
              read -l title -P "Item $i Title: ";
              read -l desc -P "Item $i Description: ";
              echo "<title>"$title"</title>" >> $itemfile;
              echo "<pubDate>"(date)"</pubDate>" >> $itemfile;
              echo '<enclosure url="https://hub.xpub.nl/chopchop/river/public_html/podcasts/'$showid'/e/'$guid'/'$file'" length="'(soxi -D {$_flag_generate}/{$file})'" type="'(file -b --mime-type {$_flag_generate}/{$file})'"/>' >> $itemfile;
              sed -i 's/\\/\\/[^.]*\(\\/[^\\/]*.mp3\)/\1/' $itemfile;
              echo '<guid isPermaLink="false">'$guid'</guid>' >> $itemfile;
              set -l link "https://hub.xpub.nl/chopchop/river/public_html/podcasts/$showid/e/$guid/$file";
              echo '<link>'$link'</link>' >> $itemfile;
              echo '<description><![CDATA['$desc']]></description>' >> $itemfile;
              echo '</item>' >> $itemfile;
          end
          # concatenate items in reverse order and append to the channel file
          for item in (ls -t /tmp/skeleton/*/e/*/item-*);
              cat $item >> $channelfile;
          end
          # close the rss and channel tags
          echo '</channel>' >> $channelfile;
          echo '</rss>' >> $channelfile;
          # (re)move temporary files
          mkdir -p ~/public_html/podcasts/{$showid};
          mv /tmp/skeleton/{$showid}/* ~/public_html/podcasts/{$showid}/;
          touch ~/public_html/podcasts/index;
          cat /tmp/skeleton/index >> ~/public_html/podcasts/index;
          rm -r /tmp/skeleton/;
    end
    if set -ql _flag_add
        # echo $_flag_add
    end
end

Draft three of script

#!/usr/bin/fish
function skelegen -d "Generate an RSS channel for a podcast"
    set -l options (fish_opt -s h -l help);
    set options $options (fish_opt --short=g --long=generate --required-val); 
    set options $options (fish_opt --short=a --long=add --required-val --multiple-vals);
    set options $options (fish_opt --short=c --long=channel --required-val);
    argparse $options -- $argv;
    or return

    if set -ql _flag_help
        echo "skelegen [ -g DIR | -a FILE | -h ] -c XML_FILE
        -h --help                Display this text
        -g --genenerate DIR      Generate an RSS feed for DIR
        -a --add FILE            Add an item to a channel
        -c --channel XML_FILE    Specify an output channel

Skelegen is a command line application for generating and writing RSS feeds for podcasts. Skelegen is capable of generating an RSS feed for a directory of audio recordings. It is also possible to add audio recordings to a channel.

EXAMPLE USAGE
skelegen --generate ~/Music/podcast --channel ~/public_html/podcasts/mypodcast.xml
skelegen --add ~/Music/podcast/episode.mp3 --chamnel ~/public_html/podcasts/myotherpodcast.xml"

    end

    if set -ql _flag_generate and set -ql _flag_add;
        echo 'ERROR: skelegen cannot add and generate simultaneously';
        return 1;
    end

    if not set -ql _flag_channel;
        echo "ERROR: channel must be specified.";
        return 1;
    end

    if set -ql _flag_channel;
        set -l channelprefix (echo $_flag_channel | sed -E 's/\\/([^\\/]*.xml)/\\/\n\1/' | grep -Ev "[^/]*.xml");
        mkdir -p $channelprefix;
    end

    if set -ql _flag_generate
        set -l showid (uuidgen);
        set -l channelprefix (echo $_flag_channel | sed -E 's/\\/([^\\/]*.xml)/\\/\n\1/' | grep -Ev "[^/]*.xml");
        set -l publicprefix (echo $channelprefix | sed -E 's/\\/home\\/riviera\\/public_html\\/([^\\/]+\\/)/https:\\/\\/hub.xpub.nl\\/chopchop\\/~river\\/\1/');
        set -l channelfile (echo $_flag_channel | sed -E 's/\\/([^\\/]*.xml)/\\/\n\1/' | grep -Eo "[^/]*.xml");
        mkdir -p {$channelprefix}{$showid};
        set -l channel {$channelprefix}{$showid}/{$channelfile};
        # # write the channel data
        echo '<rss version="2.0" xmlns:atom="http://www.w3.org/2005/Atom">' > $channel;
        echo '<channel>' >> $channel;
        echo '<ttl>60</ttl>' >> $channel;
        echo '<generator>skeleton</generator>' >> $channel;

        read -l channelname -P "Channel Title: ";
        echo '<title>'$channelname'</title>' >> $channel;
        echo '<link>https://hub.xpub.nl/chopchop/worm/</link>' >> $channel;
        echo '<atom:link href="'$publicprefix$showid'" ref="self" type="application/rss+xml"/>' >> $channel;
        echo '<language>en</language>' >> $channel;

        read -l channeldesc -P "Channel Description: ";
        echo '<description><![CDATA['$channeldesc']]></description>' >> $channel;
        echo '<image><url>'{$publicprefix}{$showid}'/image.jpg</url>' >> $channel;
        echo '<link>https://hub.xpub.nl/chopchop/worm/</link>' >> $channel;
        echo '<title>'$channelname'</title>' >> $channel;
        echo '</image>' >> $channel;
        for file in (ls $_flag_generate);
            set -l guid (sha256sum {$_flag_generate}/{$file} | grep -Eo "[[:alnum:]]{64}");
            mkdir -p {$channelprefix}{$showid}/e/{$guid};
            ln -s {$_flag_generate}/{$file} {$channelprefix}{$showid}/e/{$guid}/{$file};
            set i (math $i + 1);
            set -l itemfile (printf '%s%s/e/%s/item-%i' $channelprefix $showid $guid $i);
            echo "<item>" > $itemfile;
            read -l title -P "Item $i Title: ";
            read -l desc -P "Item $i Description: ";
            echo "<title>"$title"</title>" >> $itemfile;
            echo "<pubDate>"(date)"</pubDate>" >> $itemfile;
            echo '<enclosure url="'$publicprefix$showid'/e/'$guid'/'$file'" length="'(soxi -D {$_flag_generate}/{$file})'" type="'(file -b --mime-type {$_flag_generate}/{$file})'"/>' >> $itemfile;
            sed -i 's/\\/\\/[^.]*\(\\/[^\\/]*.mp3\)/\1/' $itemfile;
            echo '<guid isPermaLink="false">'$guid'</guid>' >> $itemfile;
            set -l link "https://hub.xpub.nl/chopchop/~river/podcasts/$showid/e/$guid/$file";
            echo '<link>'$link'</link>' >> $itemfile;
            echo '<description><![CDATA['$desc']]></description>' >> $itemfile;
            echo '</item>' >> $itemfile;
        end
        # concatenate items in reverse order and append to the channel file
        for item in (ls -t {$channelprefix}*/e/*/item-*);
            cat $item >> $channel;
        end
        # close the rss and channel tags
        echo '</channel>' >> $channel;
        echo '</rss>' >> $channel;
        mkdir -p ~/.skeleton;
        touch ~/.skeleton/channellist;
        echo $channel >> ~/.skeleton/channellist;
    end

    if set -ql _flag_add
        ...
    end
end

The add flag

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