Everything you need is covered in perlintro (a 30 minute read), and perlfaq4#How can I get the unique keys from two hashes, plus a little imagination.

Here's a basic description:

1. Declare a hash... maybe call it %words.
2. Set up an input loop: while(my $line = <> ) { ...
3. Chomp your input.
4. Use the input as a hash key: $words{$line}++.
5. After the loop ends, print the keys of the hash.

c:\@Work\Perl\monks\rasy>perl -wMstrict -le
"use List::MoreUtils qw(uniq);
 ;;
 my @uniques = uniq map { chomp;  $_; } <>;
 print qq{(@uniques)};
"  < words.txt
(foo bar bax boff food wink wank fool zink zank)
[download]

words.txt:

foo
bar
foo
bax
boff
foo
foo
food
wink
wank
fool
zink
zank
foo
[download]

Sorry, but I don't quite understand your (pseudo)code. Could you further explain what you want to do?

In general, getting the unique lines of a file is a common task that you can find answers for easily if you Google it (just one example of many). Assuming you did that, what did you find, and did it work for you or not? If not, what problems did you have? See also How do I post a question effectively?

If you want to learn how to write it yourself, then the best place to start is perlintro. Combine the things you learned from there (especially the section "Files and I/O") with the FAQ How can I get the unique keys from two hashes? and you should have just about everything you need.

P.S. In the short time since you posted this node, you've edited it at least twice; it'd probably be better if you make use of the "preview" function.

Oops, the better link is How can I remove duplicate elements from a list or array?

(At least four edits by now...)

The code the OP provides is suggestive of an approach that works if the word list is sorted.

#!/usr/bin/perl

use strict;
use warnings;

my $num_duplicates = 0;
my $last           = '';
while (<DATA>) {
    chomp;
    if ( $_ eq $last ) {
        $num_duplicates++;
    }
    else {
        print "$_\n";
        $last = $_;
    }
}

print "There where $num_duplicates duplicates.\n";

__DATA__
apple
banana
banana
cherry
date
date
date
elderberry
[download]

Output:

apple
banana
cherry
date
elderberry
There where 3 duplicates.
[download]

Since the OP had the count variable, I kept it to track the total number of duplicates in the list.