use strict;
use warnings;
use feature qw(postderef);
no warnings qw(experimental::postderef);
use feature qw(say);

my $dna = 'TTA';
my @proteinString;
my $codon;

for(my $i=0; $i < (length($dna) - 2) ; $i += 3) {
    $codon = substr($dna,$i,3);
    push @proteinString, $codon .= codonToAminoAcid($codon);
}

my $proteinString = \@proteinString;

for my $element ( $proteinString->@* )
{
    say $element;
}

sub codonToAminoAcid {
     my($codon) = @_;

     if    ( $codon =~ /GC./i)        { return 'A' }    
     elsif ( $codon =~ /TG[TC]/i)     { return 'C' }    
     elsif ( $codon =~ /GA[TC]/i)     { return 'D' }    
     elsif ( $codon =~ /GA[AG]/i)     { return 'E' }    
     elsif ( $codon =~ /TT[TC]/i)     { return 'F' }    
     elsif ( $codon =~ /GG./i)        { return 'G' }    
     elsif ( $codon =~ /CA[TC]/i)     { return 'H' }    
     elsif ( $codon =~ /AT[TCA]/i)    { return 'I' }    
     elsif ( $codon =~ /AA[AG]/i)     { return 'K' }    
     elsif ( $codon =~ /TT[AG]|CT./i) { return 'L' }    
     elsif ( $codon =~ /ATG/i)        { return 'M' }    
     elsif ( $codon =~ /AA[TC]/i)     { return 'N' }    
     elsif ( $codon =~ /CC./i)        { return 'P' }    
     elsif ( $codon =~ /CA[AG]/i)     { return 'Q' }    
     elsif ( $codon =~ /CG.|AG[AG]/i) { return 'R' }    
     elsif ( $codon =~ /TC.|AG[TC]/i) { return 'S' }    
     elsif ( $codon =~ /AC./i)        { return 'T' }    
     elsif ( $codon =~ /GT./i)        { return 'V' }    
     elsif ( $codon =~ /TGG/i)        { return 'W' }    
     elsif ( $codon =~ /TA[TC]/i)     { return 'Y' }    
     elsif ( $codon =~ /TA[AG]|TGA/i) { return '_' }    
     else {
         print "Unrecognized codon: \"$codon\"!\n";
         exit;
     }
 }