# always use strictures (the following two lines)
use strict; 
use warnings;

my @array = qw(key1 key2 key3 key4);
my %hash = (key2 => undef, key4 => 'The goods', key5 => 'More goods');

for my $key (@array) {
    next if ! exists $hash{$key}; # Skip if the key is not used in the hash
    next if ! defined $hash{$key}; # Skip if the key exists, but is undefined
    print "The value for '$key' is '$hash{$key}'\n";
    last;
}

##</code><code>##

The value for 'key4' is 'The goods'