Both methods change the string.

No, tr/a// will not delete characters unless you specify the d modifier. Characters that are not replaced are left alone.

And using a little trick to induce list context, you can use pattern matching to count the occurrences:

my @letters = qw(A B C D E F);

my $string = 'AFTYUBEWTWECRTUTYIYTDDDDRYJURTHJTREEEEEFGSDFF';

my @counts;

for (0..$#letters) {
  $counts[$_] = () = $string =~ /$letters[$_]/g;
}

print "@counts\n";
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