I don't understand if you want to count each occurrence of a single letter, that is: from:

@x = qw(a b c b c d c d e f)

you want a report, something like:

a: 1; b: 2; c: 3; and so on, or you want a sub count which counts the recurrences of a single item you pass to it. That is: print count('c',@x) ; # prints 3

Since you already had solutions in the first case, I'll try to answer for the second. The reply is: grep

That is: count should just be something like this:

sub count {
  my ($string,@array) = @_ ;

  # count recurrence of $string in @array
  return scalar grep $_ eq $string, @array ;
}
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For more information on grep you can just do a perldoc -f grep

Ciao!
--bronto