Script to display all duplicate line in a file once

this script will display all the duplicate lines only once

Example:

$cat file
I like oranges
I like apples
I like pears
I like apples
I like guavas
I like oranges
I like apples

$./test.pl file

I like apples
I like oranges

#!/usr/bin/perl
#
open(FILE,"$ARGV[0]");
my @contents = ;
my %dup;
foreach $line (@contents)
{
  @keyz = keys %dup;
  if(!(grep(/$line/, @keyz)) || $dup{$line})
  {
      $dup{$line}++;
      if($dup{$line} > 1)
  {
          print $line;
          $dup{$line} = 0;
      }
  }
}