For the first point, like all things, there is more than one way to do it. Typically I'd use a hash, for example I'd do:

#!/usr/bin/perl -w
use strict;
my @dup_array = qw/this this array has has duplicates/;
my @unique_array;
my %uniques;

foreach my $elem (@dup_array)
{
      push @unique_array, $elem unless  $unique{$elem}++;
}

print "Unique elements are @unique_array";
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For the second problem, I think that you want to write something like

my @lines = <>;
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Using <> in a list context gives you every line of input as an element of your array. That is $line[0] is your first line of code.

Mind you, what a line of input is depends on whether you've messed around with $/;