use Algorithm::Diff qw(sdiff);
use Data::Dumper;
my $a=sdiff(
  [split(/\W+/,"the quick brown fox")],
  [split(/\W+/,"before the quick brown fox")]
);
print Dumper($a);

$VAR1 = [
          [
            '+',
            '',
            'before'
          ],
          [
            'u',
            'the',
            'the'
          ],
          [
            'u',
            'quick',
            'quick'
          ],
          [
            'u',
            'brown',
            'brown'
          ],
          [
            'u',
            'fox',
            'fox'
          ]
        ];