print "schreibe Dateinamen:  ";
my $dna =<STDIN>;
my $protein ='';
my $codon;   
my @datei;

unless (open (DNADATEI, $dna)) 
        {
                print "can not open file!\n"; 
                <>;
                exit;
        } 

@datei= <DNADATEI>;
close DNADATEI;

 $dna =join ('',@datei);
 $dna =~s/\s//g;


for (my $i=0; $i < (length($dna)-2);$i+=3)
        {
                 $codon =substr($dna,$i,3);
                 $protein .= codon2aa($codon); 
        }

        
print "Proteinstrang: ";
print "$protein"; 

<STDIN>;
exit;