As is oftne the case, the data structure you use makes a world of difference. In this case, I'd recommend a hash of the IP addresses found in file1. You could also store the actual line that triggered it for diagnostics, reporting, or debugging. This first example just records that file1 had the IP present. 

my %hash;
while ( my ( $ip, $other_stuff ) = parse_values_file_1() ) {
  $hash{ $ip } = 1;
}

while ( my ( $ip, $other_stuff ) = parse_values_file_2() ) {
  print "Not found: $ip ($other_stuff)\n" unless $hash{ $ip };
}

[download]

I'll leave the implementation of the parsing as an exercise for now. What you have here is a check for uniqueness. Whenever you think "uniqueness test" and "Perl", think "I can probably use a hash for that".

In reply to Re: Return rows from 2 csv files that don't match by mr_mischief
in thread Return rows from 2 csv files that don't match by meredib

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