use strict;
use warnings;

use Data::Dumper;

open my $inFH, q{<}, \ <<EOD or die qq{open: < HEREDOC: $!\n};
COA213345
COA213345
COA213445
DOB213345
EOA213345
EOD

my %lookup = map { chomp; $_ => 1 } <$inFH>;

close $inFH or die qq{close: < HEREDOC: $!\n};

print Data::Dumper->Dumpxs( [ \ %lookup ], [ qw{ *lookup } ] );