Hi,

The poor performance comes from the fact that you are opening and parsing the same (big) file many times.

You would be better off reversing your strategy and opening the file, parsing it and comparing each line with the contents of your array @tag.

You should also, if possible, consider loading your data into a hash instead of an array. If you do that, you will profit from exists. 
# your data is in %tag
open (IN, "<Input_file.dat") or die "Cannot read $!\n";
open (OUT,"+>Result_file.txt") or die "Cannot create file $!\n";
while (<IN>) {
    print OUT $_ if exists $tag{$_};
}

[download]

Lu.

In reply to Re: Better solution to the code by Lu.
in thread Better solution to the code by Anonymous Monk

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