#!/usr/bin/perl

use strict;
use warnings;

my @list = qw( one two three one one two_2 two_2 two two_2 two two_3 two one );

@list = make_unique( @list );
print "@list\n";

sub make_unique
  {
  my (%seen, $try);
  map 
    {
    my $n = $seen{$_};
    $n++ while $seen{$try = $n ? $_ . "_$n" : $_}++;
    $try
    } @_;
  }