#!/usr/bin/perl

use strict;

my @old_arrays = qw( aa aa bb bb cc dd );
my @new_arrays;

push( @new_arrays, $old_arrays[0] );
for (my $i = 0; $i <= $#old_arrays; $i++) {
    push( @new_arrays, $old_arrays[$i] ) if ( ( $old_arrays[$i] ne $old_arrays[$i-1] ) && $i > 0 );
}

print "@new_arrays\n";