#!/usr/bin/perl -w
use strict;

my $column_number =3;
my $prev = "";

my @input_lines = <DATA>;  #slurps DATA in all at once

@input_lines =    
        sort {my ($a_col) = (split(/\s+/,$a))[$column_number];
              my ($b_col) = (split(/\s+/,$b))[$column_number];
                  $a_col cmp $b_col
             }@input_lines;
                     
foreach (@input_lines)
{
   print unless $_ eq $prev;
   $prev = $_;
}   

__DATA__
FT9mWp d4fgMB gvZRJU XRRu0N X
4ewejk pFnjd4 ie0hZF pPipQJ A
4ewejk 4sqprx ie0hZF cqtexi 3
Fo1OKn qhZPvb qWZPrt ruBObs 2