gistfile1.txt

use warnings;
use strict;
use Data::Dumper;
use 5.10.1;

my @x = qw(mary had a little lamb);
my @y = qw(nothing common with the girl above);
my @z = qw(claire had a silent white lamb that will not bleat);

my %first;
@first{@x} = (1) x scalar @x;

my @matches = @first{@y};
print Dumper(\@matches);
say scalar(grep { defined $_ } @matches);

@matches = @first{@z};
print Dumper(\@matches);
say scalar(grep { defined $_ } @matches);