my @list2 = qw(one two three);
my %lookup_hash;
@lookup_hash{@list2} = 'foo';

use Data::Dumper;
print Dumper \%lookup_hash;

##</code><code>##

$VAR1 = {
          'three' => undef,
          'one' => 'foo',
          'two' => undef
        };

##</code><code>##

@lookup_hash{@list2} = ();

##</code><code>##

@lookup_hash{@list2} = ('foo') x @list2;