#!/usr/bin/perl -w
use strict;
use Data::Dumper::Simple;

my %strings;

while (<DATA>) {
    chomp;
    $strings{$_}++;
}

print Dumper(%strings);

__DATA__
string1
string2
string3
string1
string1
string7
string2

##</code><code>##

%strings = (
             'string3' => 1,
             'string7' => 1,
             'string1' => 3,
             'string2' => 2
           );