Try "exists".

my @fruit = ('apple', 'pear', 'lemon', 'celery', 'pear');
my %seen  = ();
foreach (@fruit) {
    $seen{$_} = 1 if not exists $seen{$_};
}
my @unique = keys %seen;
[download]

.oO(exists $fruit{'celery'}?)

Cē