[localhost:~/Perl] lynda% more arrays3.pl
#!/usr/bin/perl -w
#

@aa_names = ('alanine', 'arginine', 'aspartate', 'asparagine', 'cysteine',
'glutamate', 'glutamine', 'glycine', 'histidine', 'isoleucine',
'leucine', 'lysine', 'methionine', 'phenylalanine', 'proline',
'serine', 'threonine', 'tyrosine', 'tryptophan', 'valine');

@aa_1codes = ('A', 'R', 'D', 'N', 'C', 'E', 'Q', 'G', 'H', 'I', 'L', 'K',
'M','F', 'P', 'S', 'T', 'Y', 'W', 'V');

@aa_3codes = ("Ala", "Arg", "Asp", "Asn", "Cys", "Glu", "Gln", "Gly",
"His", "Ile", "Leu", "Lys", "Met", "Phe", "Pro", "Ser", "Thr", "Tyr",
"Trp", "Val");

print "\nEnter a single letter amino acid code: ";
chomp ($code = <STDIN>);

$i = 0;
while (defined ($aa_1codes[$i]) and $code ne $aa_1codes[$i]) {
 $i ++;
  }

if (defined ($aa_1codes[$i])) {
print $aa_names[$i], "  ", $aa_3codes[$i], "  ", $aa_1codes[$i], "\n\n";
                              }

exit;
[localhost:~/Perl] lynda% perl arrays3.pl

Enter a single letter amino acid code: A
alanine  Ala  A

[localhost:~/Perl] lynda% perl arrays3.pl

Enter a single letter amino acid code: B
[localhost:~/Perl] lynda% perl arrays3.pl

Enter a single letter amino acid code: a
[localhost:~/Perl] lynda%