The reason I ask the question is because the following subroutine does not work. 

sub Remove_duplicate_lines {

  my ($processed_file, $out_file) = @_;

  open (PROCESSED_FILE, "<$processed_file");
  open (OUTFILE, "+>$out_file");



  my @array;
  my @unique;

  while (<PROCESSED_FILE>) {
    chomp;
    push (@array, $_);
  }



  my %hash   = map { $_, 1 } @array;

  # or a hash slice: @hash{ @array } = ();
  # or a foreach: $hash{$_} = 1 foreach ( @array );
  
  my @unique = keys %hash;
  
  
  my @unique = ();
  my %seen   = ();
  
  foreach my $elem ( @array )
    {
      next if $seen{ $elem }++;
      push @unique, $elem;
    }
  


  foreach (@unique){
    print OUTFILE "$_";
  }

}

[download]

In reply to Re^2: What does 'next if $hash{$elem}++;' mean? by Win
in thread What does 'next if $hash{$elem}++;' mean? by Win

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.