use strict;
use warnings;

use Digest::MD5 qw( md5_hex );
use MLDBM;
use Fcntl;

tie my %o,  'MLDBM', 'tempdb', O_CREAT|O_RDWR, 0640 or die $!;

# First file we populate the hash.
process_file(  'infile1.txt',  \%o,  sub { $_[0]->{$_[1]} = [ $., $_[2] ]; }  );

# Second file we check for collisions.
process_file(  'infile2.txt',  \%o,  sub {
  my( $tied, $hash, $line ) = @_;
  print "\nCollision: infile1.txt line $tied->{$hash}->[0]:\n",
        "\t($tied->{$hash}->[1])\n",
        "-- collides with: infile2.txt line $.:\n",
        "\t($line)\n\n" if exists $tied->{$hash};
} );

END {    untie %o;    unlink glob 'tempdb.*';    }        # RAII.

sub process_file {
  my( $filename, $tied, $code ) = @_;
  open my $infh, '<', $filename or die $!;
  while( my $line = <$infh> ) {
    my ( $wanted ) = $line =~ m/((?:[^,]*,){10})/;
    next unless length $wanted;
    chomp $line;
    my $hash = md5_hex( $wanted );
    $code->($tied, $hash, $line);
  }
  close $infh;
}