Now Christmas was over, the Wise Old Elf was going to go sit on a beach (in the southern hemisphere, where it was summer) and kick back with some quality eggnog.

Of course, the Wise Old Elf doesn't get to be wise by sitting on his laurels, so he was going to take the oppuntinty to catch up with all the videos of the presentations from The Perl Conference 2017 DC on YouTube.

The only problem with his plan was that the beach he had in mind didn't have very good WiFi. So he decided to try and download all the videos to his laptop first. Maybe Perl couyld help him with that?

Scraping the playlist

Since he had learned about ojo it was easy for the Wise Old Elf to write something that would scrape the playlist webpage and print out, one line at a time, the URLs for the various videos in the playlist

    perl -Mojo -E \
      'g(shift)->dom(".pl-video-title-link")->map(sub{say $_->attr("href")})' \
      'https://www.youtube.com/playlist?list=PLA9_Hq3zhoFxdSVDA4v9Af3iutQxLI14m'

WWW::YouTube::Download

Now the Wise Old Elf had to write some code to parse the web page for each youtube video and then write some more code to download the video. Before he spent a lot of time doing that, he realized he could simply search the CPAN for such a utility. He not only found the wonderful WWW::YouTube::Download module, but also the youtube-download command line utility that shipped with it.

The way the command line utility works is simple; You pass youtube-download a URL and it downloads the video into the current directory. For example to download Dave Rolsky's lightning talk the Wise Old Elf would simply have to type:

    youtube-download /watch?v=DVKfBV2xngg

But how would the Wise Old Elf run youtube-download for each URL? With xargs!

   perl -Mojo -E \
     'g(shift)->dom(".pl-video-title-link")->map(sub{say $_->attr("href")})' \
     'https://www.youtube.com/playlist?list=PLA9_Hq3zhoFxdSVDA4v9Af3iutQxLI14m'\
     | xargs -n 1 youtube-download

The standard unix xargs command line tool takes arguments on STDIN - one command line argument per line - and runs the utility (in this case youtube-download) with those arguments. By specifying -n 1, xargs will run youtube-download with one argument (i.e. will run youtube-download with each URL passed to it on STDIN.)

All Done

    --> Working on oka4wcsrg0c
    Downloading `oka4wcsrg0c.mp4`
    126211392/126211392 (100.00%)
    Download successful!
    --> Working on DVKfBV2xngg
    Downloading `DVKfBV2xngg.mp4`
    42843944/42843944 (100.00%)
    Download successful!
    --> Working on vQ5qWey_SO4
    Downloading `vQ5qWey_SO4.mp4`
    36677196/36677196 (100.00%)
    Download successful!

A few minutes later - the North Pole has very good Internet - all the videos were downloaded to the Wise Old Elf's computer. Now all he had to do was go stock up on the sunblock!