my %lookup = (); # initialize the hash
while (defined ($line = <DATA>)) {
  my @line = split /\s+/, $line;
  if (defined ($lookup{$line[1]})) { # array indexes start at 0 
       # if the hash key already has been defined (see below)...
    exit(0); # error out;
  } else {
    $lookup{$line[1]} = 1; # define the lookup value;
  }
}