open my $file, '<', shift;
binmode($file);

my %seen = ();

$/ = \( 1024 * 1024 ); # Set default buffer size
while ( <$file> ) {
    for my $buf (split //, $_) {
      if ( !$seen{$buf} ) {
          $seen{$buf} = 1;
      }
      else {
          $seen{$buf}++;
      }
    }
}
print "$_ - $seen{$_}\n" for ( keys %seen );