my @data = qw(foo bar foo bar bar doz);

use DB_File;
use File::Temp qw(tempfile);

my ($fh, $fn) = tempfile(UNLINK => 1);
tie my %u, 'DB_File', $fn, O_RDWR, 0600;

$u{$_} = undef for @data;
@data = keys %u;

print "@data\n";