use strict;
use warnings;
use Data::Dumper;

chomp(my @PatternArray = map { /^\s*$/ ? () : $_ } <DATA>);

my %occurance;
$occurance{$_}++ for @PatternArray;

print Dumper(\@PatternArray), Dumper(\%occurance);

# using occurance table
print "PPLLOO has appeared $occurance{PPLLOO} times.\n";

# using grep
print "TTRRDD has appeared ",
      scalar grep(m/TTRRDD/, @PatternArray),
      " times.\n";

__DATA__

PPLLOO
HHYYTT
TTRRDD
PPLLOO
TTRRDD
PPLLOO
PPLLOO