my @strings = qw/ a a b c a b c d e a b c a b c d /;

my %count;
foreach ( @strings ) {
  $count{$_} ||= 0;
  $count{$_}++;
}

# Then, if you want to sort the results by value:

foreach ( sort { $count{$a} <=> $count{$b} } keys %count ) {
  print "$_ => $count{$_}\n";
}