zsh 4.3.4% print 'N
H
H
K
L
K
K
H
K
N'|awk '{x[$1]++}END{for(i in x)printf "%s = %d\n",i,x[i]}' 
N = 2
H = 3
K = 4
L = 1

#!/usr/bin/env sh

# @(#) s1       Demonstrate counting with sort and uniq.

set -o nounset
echo

## Use local command version for the commands in this demonstration.

echo "(Versions of codes used in this script with local utility \"version\")"
version bash sort uniq

echo

FILE=${1-data1}

sort $FILE |
uniq -c

exit 0

% ./s1

(Versions of codes used in this script with local utility "version")
GNU bash, version 2.05b.0(1)-release (i386-pc-linux-gnu)
sort (coreutils) 5.2.1
uniq (coreutils) 5.2.1

      3 H
      4 K
      1 L
      2 N

#!/usr/bin/perl
# count_letters.pl
use strict;
my %letters;
while (<>) {
    chomp;
    $letters{$_}++;
}
foreach my $letter (keys (%letters)) {
    print "$letter = $letters{$letter} \n";
}

[ysawant@in-gcs-nas1 temp]$ perl  count_letters.pl  letters_file 
H = 3 
N = 2 
K = 4 
L = 1 
[ysawant@in-gcs-nas1 temp]$