open (IN, "< ./someinputfile") || die $!;
open (OUT, "> ./someoutputfile") || die $!;

binmode IN;
binmode OUT;

my $read = 1;
my $result;

while($read > 0){
    $read = read IN,$result,1;

    #do some processing and checking here.
    #convert the bits to bytes

    print OUT $result;
		
}