print $line if defined $file2{$line};
I think that finds lines in file 1 that are also in file 2. To find lines in file 1 not in file 2, maybe change that to:

print $line unless defined $file2{$line};

In reply to Re^3: Faster grep in a huge file(10 million) by Cristoforo
in thread Faster grep in a huge file(10 million) by Thomas Kennll

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