perl loop avoid print duplicate in regex match - regex

Question

I Search, and research for a solution but without successful.
The file.txt:
Name Server: NS1.SERVER.COM
Name Server: NS2.SERVER.COM
..........................
..........................
Name Server: NS1.SERVER.COM
Name Server: NS2.SERVER.COM
Whois server: whois.directnic.com!
..........................
..........................
Name Server: NS1.SERVER.COM
Name Server: NS2.SERVER.COM
Whois server: whois.directnic.com!
..........................
..........................
When I run:
use strict;
use warnings;
my $filename = 'file.txt';
open(my $fh, '<:encoding(UTF-8)', $filename)
or die "Could not open file '$filename' $!";
while (my $row = <$fh>) {
if ($row =~ /^Name\sServer:\s+(.*+)?/) {
print "dns $1\n";
}
if ($row =~ /Whois.+server:.(.*)/) {
print "whois server: $1\n";
}
}
The output:
dns NS1.SERVER.COM
dns NS2.SERVER.COM
dns NS1.SERVER.COM
dns NS2.SERVER.COM
whois server: whois.directnic.com!
dns NS1.SERVER.COM
dns NS2.SERVER.COM
whois server: whois.directnic.com!
I want to get like this:
dns NS1.SERVER.COM
dns NS2.SERVER.COM
whois server: whois.directnic.com!
I know I can use Last
(If you’ve used the “break” operator in C or a similar language, it’s like that.)
If I set last; in the first condition I get this:
dns NS1.SERVER.COM
If I set last; in the second condition I get this:
dns NS1.SERVER.COM
dns NS2.SERVER.COM
dns NS1.SERVER.COM
dns NS2.SERVER.COM
whois server: whois.directnic.com!
I find a solution but using hash, while, increase count and grep, like this:
my %count_of;
my %count_of_two;
while (my $row = <$fh>) {
if ($row =~ /^Name\sServer:\s+(.*+)?$/) {
$count_of{$row}++;
}
if ($row =~ /Whois.+Server:.(.*)/) {
$count_of_two{$row}++;
}
}
print join "\n", grep { $count_of{$_} > 1 } keys %count_of;
print join "\n", grep { $count_of_two{$_} == 1 } keys %count_of_two;
¿How can I do this with while or foreach?
Note: I think I know why while loop print duplicate because that the functionality, but maybe exist another way.
I research about this but I can't find a solution.
Thanks for your patience.

Answer 1

The easiest approach is probably to use a hash (called %seen in my example below) which keeps track of the strings you have ever seen.
Making the smallest changes to your code, we get:
use strict;
use warnings;
my $filename = 'file.txt';
open(my $fh, '<:encoding(UTF-8)', $filename)
or die "Could not open file '$filename' $!";
my %seen;
while (my $row = <$fh>) {
if ($row =~ /^Name\sServer:\s+(.*+)?/) {
print "dns $1\n" unless $seen{$1}++;
}
if ($row =~ /Whois.+server:.(.*)/) {
print "whois server: $1\n" unless $seen{$1}++;
}
}