Add a print when at least 1 of the words match if that's the output you want

while (my $line = <FIC>) {
  my @words = split /\s+/,lc $line;
  ++$uniq2{$_} for @words;
  $words2 += @words;
  ++$count2;
  my @match = grep $uniq1{$_}, @words;
  print $line if @match >= 1; # <-- add here
}
[download]

Thank you very much, this is really fast.

Can you please explain what are the major change that did you apply and the error that i must no do, to speed up my code like you?

Hope i can modify it later to have the output like i specified in the begening of the post: specially the number of the line that correspond to the intersecion

If i have problems il will let you now

You were very kind , thank you very mcuh

Regards

Looks like your code had 2 loops, each counting to +6 million

foreach my $che (@b){
  @aa=split(/\s/,$che);

  foreach my $kh (@a){
    @bb=split(/\s/,$kh);

    for ($l=0;$l<=$#bb;$l++){
      for ($m=0;$m<=$#aa;$m++){

      ## this code executes 6 million x 6 million times
      if(($bb[$l] eq $aa[$m]) ){
      ..

      }
    }
  }
}
[download]

But within the 6 million words, there are only few thousand different ones so your loops were checking the same word thousand of times more than required. By holding the unique words from file1 in a hash you don't have to loop through 6 million words every time to find a match with a word from file2

poj