#!/usr/bin/perl -w

use strict;

my $infile  = shift;
my $outfile = shift;
my %seen;

open (IN, "<$infile")           or die "Can't open $infile RO: $!";
open (OUT, ">$outfile")         or die "Can't open $outfile RW: $!";
    foreach my $item (<IN>) {   # parse $infile into a hash and remove duplicate keys
        ++$seen{$item};
    }
    print OUT sort keys %seen;  # sort keys and save to $outfile
close IN                        or die "Cannot close $infile: $!";
close OUT                       or die "Cannot close $outfile: $!";