How can I extract the list of redirect titles from MediaWiki::API in Perl?

I'm trying to use the MediaWiki API to get all redirects from a certain Wikipedia title and I think i'm almost there but I get lost in the complex data structure of hashes and arrays.

How can I extract the list of redirect titles?

In the example I query for 'Japan' and should get a list that looks like this:

'JPN',"Land der aufgehenden Sonne","Das Land der aufgehenden 
Sonne","Zipango","\x{65e5}\x{672c}","R\x{ec}b\x{11b}n"

(a side question: Why do I not get UTF-8 strings for all cases? )

The code below is adapted from MediaWiki::API documentation.

use MediaWiki::API;
use warnings;
binmode STDOUT, ':utf8';
use JSON;
use Data::Dumper;

my $LANG="de";

my $mw = MediaWiki::API->new( { api_url => 'https://en.wikipedia.org/w/api.php' }  );
my $mw_LANG = MediaWiki::API->new( { api_url => "https://$LANG.wikipedia.org/w/api.php" }  );

my $wikititle ="Japan";

my $alltitles = $mw_LANG->api( {
 action => 'query',
 titles => $wikititle,
 prop => 'redirects',
 format => 'json',
} )
|| die $mw_LANG->{error}->{code} . ': ' . $mw_LANG->{error}->{details};

#just print to know how the structure looks like
print Dumper($alltitles);

my ($pageid,$langlinks) = each ( %{ $alltitles->{query}->{pages} } );
print "pageid $pageid\n";#yes works:  this prints the page id

problem: how to get the actual titles in the redirect-array?

  my $relinks = $alltitles->{'query'}->{'pages'}->{$pageid}->{'redirects'}; #no does not work!

  foreach my $el ( @{ $relinks->{'title'} } ) {
    print " $el $el->{'*'}\n";
  }

Solution

The query returns a hashref. One of the entries in this structure is query which points to another hashref which contains pages. The pages hashref contains keys which are page ids. Each of these point to another hashref which contains a redirects entry which is a reference to an array containing all the pages to which this page redirects.

Putting all those together:

#!/usr/bin/env perl

use strict;
use warnings;

use open qw(:std :utf8);

use MediaWiki::API;
use JSON::MaybeXS;
use Data::Dumper;

my $LANG= "de";

my $mw = MediaWiki::API->new( { api_url => 'https://en.wikipedia.org/w/api.php' }  );
my $mw_LANG = MediaWiki::API->new( { api_url => "https://$LANG.wikipedia.org/w/api.php" }  );

my $wikititle ="Japan";

my $alltitles = $mw_LANG->api( {
        action => 'query',
        titles => $wikititle,
        prop => 'redirects',
        format => 'json',
    }
) or die sprintf '%d: %s', @{ $mw_LANG->{error} }{qw(code details)};

for my $pageid ( keys %{ $alltitles->{query}{pages} } ) {
    my $r = $alltitles->{query}{pages}{$pageid};
    printf "Redirects for page %d with title '%s'\n", @{$r}{qw(pageid title)};
    for my $redirect ( @{ $r->{redirects} }) {
        printf "\t%d: '%s'\n", @{$redirect}{qw(pageid title)};
    }
}

Postfix dereferencing makes things a bit cleaner:

for my $pageid ( keys $alltitles->{query}{pages}->%* ) {
    my $r = $alltitles->{query}{pages}{$pageid};
    printf "Redirects for page %d with title '%s'\n", $r->@{qw(pageid title)};
    for my $redirect ( $r->{redirects}->@* ) {
        printf "\t%d: '%s'\n", $redirect->@{qw(pageid title)};
    }
}

This requires perl 5.20 or later.