my $char_string = "AAATAT"; my $bit_string = ""; my %lookup_table = ("A" => "00", "T" => "01", "C" => "10", "G" => "11"); my @char_array=(split //, $char_string); for (my $i=0; $i <= $#char_array ; $i++) { vec($bit_string,$i,2) = $lookup_table{$char_array[$i]}; }