In order to use readdir, you first need to use opendir to create the directory handle.

Code

Please use the code tags, like I've done, when posint code blocks.

my @Files = <$dir/*.items>;

#!/usr/bin/perl 
use strict; 
use warnings; 
use Getopt::Std; 	 
use File::Copy; 
my $dir = "/home/test";  
my @Files = <$dir/*.items>; 
my %object = ();  
foreach my $f (@Files) {  
open (IN, $f) or die "can't open infile\n";  
my @items = <IN>;  
print @items; 
close (IN);  
my @unique = grep { ! $object{ $_ }++ } @items;  
open(OUT, ">tmp1"); 
print @unique;  
print(OUT @unique); 
close(OUT);  
print @unique; 
}  
exit

item 1 list
new data;
1 red_bat,
2 blue_bat,
3 red_car,
4 red_ball,
5 green_bat,
6 orange_ball,
7 blue_car,
8 orange_ball,
9 purple_bat,
10 red_car,
11 purple_ball,
12 purple_ball,
13 red_ball,
14 green_ball,
15 orange_ball,
16 purple_ball,
17 red_car,
18 purple_bat,
19 orange_
20 blue_bat,
21 red_ball,
22 orange_car,
23 blue_bat,
24 purple_ball,
25 green_car,
26 orange_car,
27 green_bat,
end list;
item 1 list
new data;
1 red_bat,
2 blue_bat,
3 red_car,
4 red_ball,
5 green_bat,
6 orange_ball,
7 blue_car,
8 orange_ball,
9 purple_bat,
10 red_car,
11 purple_ball,
12 purple_ball,
13 red_ball,
14 green_ball,
15 orange_ball,
16 purple_ball,
17 red_car,
18 purple_bat,
19 orange_
20 blue_bat,
21 red_ball,
22 orange_car,
23 blue_bat,
24 purple_ball,
25 green_car,
26 orange_car,
27 green_bat,
end list;
item 1 list
new data;
1 red_bat,
2 blue_bat,
3 red_car,
4 red_ball,
5 green_bat,
6 orange_ball,
7 blue_car,
8 orange_ball,
9 purple_bat,
10 red_car,
11 purple_ball,
12 purple_ball,
13 red_ball,
14 green_ball,
15 orange_ball,
16 purple_ball,
17 red_car,
18 purple_bat,
19 orange_
20 blue_bat,
21 red_ball,
22 orange_car,
23 blue_bat,
24 purple_ball,
25 green_car,
26 orange_car,
27 green_bat,
end list;