#open data file
if (open(DNAInputFile, 'DNA_seq.txt')) {
	print "File DNA_seq.txt opened OK \n";
}
else {
	print "Cannot open file DNA_seq.txt\n";
	exit;
}

#read from file, store as array  @ for array variable
@DNA_array = <DNAInputFile>;
close DNAInputFile;  #close the input file
$RNA = join('',@DNA_array);   #convert array of chars to string

$RNA =~ s/T/U/g;   
open(RNAOutputFile, ">RNA_out.txt");

print RNAOutputFile "Here is the result of transcribing ";
print RNAOutputFile "the DNA to RNA (T to U): \n\n";
print RNAOutputFile "$RNA\n";
close RNAOutputFile;
exit;