print if /...(...).../ && $seen{$1}++;

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(The pattern you had made no sense.)

The above prints the duplicates. Don't forget to negate if you are trying to remove duplicates. 

print if /...(...).../ && !$seen{$1}++;

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In reply to Re: Perl using $seen with regex by ikegami
in thread Perl using $seen with regex by abdan

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