@unique{@lines} = (1) x @lines;

[download]

Also

@unique{@lines} = ();

[download]

since you don't use the values anyway. Whatever, if he wants them in the original order, then slurping the whole file in at once is, as is commonly the case, an overkill, and I would regard the usual print if !$seen{$_}++ technique as a superior solution. Of course if one needs or may need sorting then the slurping must take place in some form or another and yours is just as good as any other one. Probably you already knew, I'm just pinpointing some details for the benefit of the OP...

In reply to Re^2: Deleting duplicate lines from file by blazar
in thread Deleting duplicate lines from file by Win

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