sort with lexicographic order

Question

I see the results from the following code, but I don't understand exactly how the or knows what to do in the following sort example:

use Data::Dumper;

$animals{'man'}{'name'} = 'paul';
$animals{'man'}{'legs'} = 2;
$animals{'cheeta'}{'name'} = 'mike';
$animals{'cheeta'}{'legs'} = 3;
$animals{'zebra'}{'name'} = 'steve';
$animals{'zebra'}{'legs'} = 4;
$animals{'cat'}{'name'} = '';
$animals{'cat'}{'legs'} = 3;
$animals{'dog'}{'name'} = '';
$animals{'dog'}{'legs'} = 4;
$animals{'rat'}{'name'} = '';
$animals{'rat'}{'legs'} = 5;

@animals = sort {
      $animals{$a}{'name'} cmp $animals{$b}{'name'}
   or $animals{$a}{'legs'} <=> $animals{$b}{'legs'}
} keys %animals;

print Dumper(\@animals);

Answer 1

or is a short-circuit evaluator, so it will return the value of the left-hand side if it's true (which is any non-zero value), and otherwise will evaluate the right-hand side.

So in this case, if the animals' names compare as equal, (0 - false), the number of legs will be counted for sorting purposes.