2017 twenty four merry days of Perl Feed

Mojolicious on the Command Line

ojo - 2017-12-15

Mojolicious provides a utility class, ojo, that allows us to leverage the power of Mojolicious from the command line:

    perl -Mojo -E 'say g("http://goo.gl/EsGk3b")->text'

The -M flag tells perl to load the following module, so -Mojo, despite looking like a super secret Mojo flag to perl actually is a cheeky way of saying use ojo.

ojo provides a whole host of single letter functions that are shortcuts to Mojolicious utilities, allowing you to quickly do things like fetching urls, reading and writing files, encoding and decoding json, manipulating data structures and a whole host more.

A Worked Example

Since the things you can do with ojo are virtually limitless, I thought a good intro to ojo might be to show a worked example from the command line.

I like reading the Perl Weekly, the weekly Perl email newsletter that pops into my inbox every week. It's so good that I often find myself wanting to refer back to a linked article later in the week when the email has been buried deep in my ever increasing inbox. Rather than improving my email filing (I'll get around to that one day) I instead wrote a script to grab an archived copy of the email from the Perl Weekly website and print out all the links. How did I do that?

So, let's start by having ojo fetch the archive and print it out


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use ojo;

print g('http://perlweekly.com/archive/333.html')->text;

 

The g function creates a GET request, returning a Mojo::Message::Response object (which inherits a whole load of useful )

Printing the results of the text method output the entire HTML of the newsletter, of which the bit we're interested in looks like this:

    <div class="entry-title">
                <a href="http://perladvent.org/2017/index.html" style="
                   font-size: 18px;
                   font-weight: bold;
                   ">Perl Advent Calendar</a>
              </div>

So we can adapt our ojo script to use the dom method to pull out just these sections using a CSS selector:


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print g("http://perlweekly.com/archive/333.html")
      ->dom(".entry-title a")
      ->join("\n\n")

 

The dom method returns a Mojo::Collection - Mojolicious's super smart array wrapper - on which we can call methods. Here we're just joining them together (and stringifying the objects that dom returned) so we can check we got the right stuff. The output now looks like:

    <a href="http://perladvent.org/2017/index.html" style="
                        font-size: 18px;
                        font-weight: bold;
                        ">Perl Advent Calendar</a>

    <a href="https://perl6advent.wordpress.com/" style="
                        font-size: 18px;
                        font-weight: bold;
                        ">Perl 6 Advent Calendar</a>

    <a href="https://mojolicious.io/blog/" style="
                        font-size: 18px;
                        font-weight: bold;
                        ">Mojolicious Advent Calendar</a>
    (etc)

Okay, we now want to break apart the Mojo::DOM objects that dom returned to get the href and text of the link. To do this we use the map method on the collection that will call a subroutine on each element of the collection (similar to Perl's map keyword on arrays)


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print g("http://perlweekly.com/archive/333.html")
      ->dom(".entry-title a")->map( sub {
            $_->attr("href") . ": " . $_->text . "\n"
      })->join

 

Calling join with no arguments joins the elements with the empty string. The output is much much closer to what we want:

    https://perl6advent.wordpress.com/: Perl 6 Advent Calendar
    https://mojolicious.io/blog/: Mojolicious Advent Calendar
    http://www.lenjaffe.com/AdventPlanet/2017/: Advent Planet 2017
    http://blogs.perl.org/users/mohammad_s_anwar/2017/12/london-perl-workshop-2017---talks-review.html: London Perl Workshop 2017 - Talks Review
    http://blogs.perl.org/users/sawyer_x/2017/12/perl-5-porters-mailing-list-summary-november-21st---december-5th.html: Perl 5 Porters Mailing List Summary: November 21st - December 5th
    http://blogs.perl.org/users/ovid/2017/12/why-i-wrote-keyworddevelopment.html: Why I wrote Keyword::DEVELOPMENT
    http://blogs.perl.org/users/ovid/2017/12/why-i-wrote-keyworddevelopment.html: And here we go!
    https://p6weekly.wordpress.com/2017/12/04/2017-49-mischieventing/: 2017.49 Mischieventing
    http://blogs.perl.org/users/brian_d_foy/2017/12/nominate-perl-heroes-for-the-2017-white-camel-awards.html: Nominate Perl heroes for the 2017 White Camel Awards
    http://news.perlfoundation.org/2017/12/call-for-volunteers.html: Call for volunteers - TPC::NA 2018 (formerly knows as YAPC::NA)
    http://news.perlfoundation.org/2017/11/booking-sponsors-the-perl-5.html: Booking.com Sponsors the P5CMF
    http://niceperl.blogspot.com/: NICEPERL's lists
    https://perlmaven.com/open-to-read-and-write: Open file to read and write in Perl, oh and lock it too
    https://www.patreon.com/szabgab: Patreon for Gabor
    https://perl.careers/jobs/rapid-growth-in-perl---developers-wanted-for-an-expanding-central-london-company/?utm_source=perlweekly&utm_campaign=perlweekly&utm_medium=perlweekly: Rapid Growth in Perl - developers wanted for an expanding central London company
    https://perl.careers/jobs/be-a-trailblazer-in-a-time-of-growth---full-stack-architect-required-for-a-rapidly-expanding-london-company/?utm_source=perlweekly&utm_campaign=perlweekly&utm_medium=perlweekly: Be a trailblazer in a time of growth - Full Stack Architect required for a rapidly expanding London company
    https://perl.careers/jobs/londons-trendiest-office-space---lead-perl-developer/?utm_source=perlweekly&utm_campaign=perlweekly&utm_medium=perlweekly: London's Trendiest Office Space - Lead and Mid-Level Perl Developer roles

But oh dear, some of those links are really really long. Maybe we should use a URL shortener service to make these shorter?

Google's URL shortener works by posting a JSON data structure of the form:

    {
        "longURL": "https://developers.google.com/url-shortener/v1/getting_started"
    }

To the URL https://www.googleapis.com/urlshortener/v1/url?key=??? where the key is the API key obtained by clicking on the GET A KEY button in the Google URL Shortener documentation. It returns a JSON data structure of the form

    {
      "kind": "urlshortener#url",
      "id": "https://goo.gl/xwCNC",
      "longUrl": "https://developers.google.com/url-shortener/v1/getting_started"
    }

Doing this with ojo is straight forward. Instead of using g to make a GET request, we use p to make a POST request. Using json => ... we can pass in the datastructure to be serialized as JSON and posted to the URL.


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use ojo;

print p(
    "https://www.googleapis.com/urlshortener/v1/url?key=$ENV{API_KEY}",
    {},
    json => {
        longUrl => "https://developers.google.com/url-shortener/v1/getting_started"
    },
)->text

 

But of course we don't want the response from the server as a string, we want it as a Perl data structure so we can grab the id field. That's as simple as using json instead of text.


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use ojo;

print p(
    "https://www.googleapis.com/urlshortener/v1/url?key=$ENV{API_KEY}",
    {},
    json => {
        longUrl => "https://developers.google.com/url-shortener/v1/getting_started"
    },
)->json->{id};

 

Or, even better, we can pass a JSON pointer to json and have it extract the value we actually want for us


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use ojo;

print p(
    "https://www.googleapis.com/urlshortener/v1/url?key=$ENV{API_KEY}",
    {},
    json => {
        longUrl => "https://developers.google.com/url-shortener/v1/getting_started"
    },
)->json("/id")

 

Rolling that back into our original code like so:


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use ojo;

print g("http://perlweekly.com/archive/333.html")
    ->dom(".entry-title a")->map( sub {
            p(
                "https://www.googleapis.com/urlshortener/v1/url?key=$ENV{API_KEY}",
                {},
                json => {
                    longUrl => $_->attr('href')
                },
            )->json("/id") .
            ": " . $_->text . "\n"
    })->join

 

Produces the output we'd like:

    https://goo.gl/wS2jSu: Perl Advent Calendar
    https://goo.gl/B7HqqD: Perl 6 Advent Calendar
    https://goo.gl/xGpyAy: Mojolicious Advent Calendar
    https://goo.gl/f9LBKS: Advent Planet 2017
    https://goo.gl/8aigk1: London Perl Workshop 2017 - Talks Review
    https://goo.gl/j2FzgA: Perl 5 Porters Mailing List Summary: November 21st - December 5th
    https://goo.gl/ptZRF3: Why I wrote Keyword::DEVELOPMENT
    https://goo.gl/ptZRF3: And here we go!
    https://goo.gl/GxETF8: 2017.49 Mischieventing
    https://goo.gl/8q2g21: Nominate Perl heroes for the 2017 White Camel Awards
    https://goo.gl/VCCoHc: Call for volunteers - TPC::NA 2018 (formerly knows as YAPC::NA)
    https://goo.gl/9BRvSA: Booking.com Sponsors the P5CMF
    https://goo.gl/XmJ1wT: NICEPERL's lists
    https://goo.gl/zPKg2u: Open file to read and write in Perl, oh and lock it too
    https://goo.gl/RChQDF: Patreon for Gabor
    https://goo.gl/wn3c2Q: Rapid Growth in Perl - developers wanted for an expanding central London company
    https://goo.gl/mVZGDQ: Be a trailblazer in a time of growth - Full Stack Architect required for a rapidly expanding London company
    https://goo.gl/4UZctX: London's Trendiest Office Space - Lead and Mid-Level Perl Developer roles
Gravatar Image This article contributed by: Mark Fowler <mark@twoshortplanks.com>