use strict;
use warnings;

my $datafile = 'data.txt';
open( my $fh, $datafile )
    or die "Cannot open '$datafile' for reading: $!\n";

my %items;
while ( defined( my $line = <$fh> ) )
{
    chomp( $line );
    $line =~ s/[\r\n]*$//;

    my @values = split /--/, $line;
    @items{ @values } = undef;
}

close $fh;

# At this point, you have %items, which is a lookup table.