I would use a hash to count the occurance of each digit in the numbers. Then, if the number has a count of two for any digit, keep it. Otherwise, discard it. For example: 

my @keep;     # numbers to keep
while(chomp( my $line = <NUMBERS> ) ) { 
    my @digits = split '', $line;
    my %count;
    ++$count{$_} for @digits;
    if( grep { $_ == 2 } values %count ) { 
        push @keep, $line;
    }
}

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In reply to Re: Find duplicate digits by friedo
in thread Find duplicate digits by Anonymous Monk

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