Comparing two arrrays

Question

I have two arrays:

• first one is ip addresses from billing for blocking
• second is ip addresses from firewall - already blocked

My task is, compare it, and if ip address new in billing list - block it (run a command) if ip address not in billing list unblock it.

Current solutions is:

#billing->router
foreach $ip (@ipfw_ip) {
 if ( grep $_ eq $ip, @bill_ip ) {
 } else {
 `/sbin/ipfw table 11 add $ip`;
 print "$ip blocked\n";
 }
}
#router->billing
foreach $ip (@bill_ip) {
 if ( grep $_ eq $ip, @ipfw_ip ) {
 } else {
 `/sbin/ipfw table 11 delete $ip`;
 print "$ip unblocked\n";
 }
}

I hate 'grep' in the loops, and looking for better solution. Any advice?

UPD: difference function from Set::Functional helps me.

for(difference (\@ipfw_ip, \@bill_ip)) {
 ..._;
}
sub difference(@) {
 my $first = shift;
 return unless $first && @$first;
 my %set;
 undef @set{@$first};
 do { delete @set{@$_} if @$_ } for @_;
 return keys %set;
}

Answer 1

You can use Set::Functional to make the code very short:

use Set::Functional 'difference';
for(difference [@ipfw_ip], [@bill_ip]) {
 `/sbin/ipfw table 11 add $ip`;
 print "$ip blocked\n";
}

Another advantage of the approach above is that you don't have to worry about duplicate entries in the two arrays.

• Korjavin Ivan: Thank you alot! I dislike new dependencies but looks into Set::Functional and see the code. Its simple. I will update my question with solution.

Answer 2

The completely procedural way to write the same is:

foreach my $fw_ip (@ipfw_ip) {
 foreach my $bill_ip (@bill_ip) {
 if($fw_ip eq $bill_ip) {
 ...
 last;
 }
 }
}

The main advantage is that it is easy to understand for anybody, and not using too much perl-fu.

I find it odd that you write

 if ( grep $_ eq $ip, @bill_ip ) {
 } else {
 `/sbin/ipfw table 11 add $ip`;
 print "$ip blocked\n";
 }

In stead of

 if ( not grep $_ eq $ip, @bill_ip ) {
 `/sbin/ipfw table 11 add $ip`;
 print "$ip blocked\n";
 }

or even

 unless ( grep $_ eq $ip, @bill_ip ) {
 `/sbin/ipfw table 11 add $ip`;
 print "$ip blocked\n";
 }

P.s. always use strict; and use warnings;. It looks as if you aren't.

• Korjavin Ivan: 2xforeach the same then grep in foreach. I hope it possible do that task without loop in loop. And thank you about "if else" no idea how I writed that. Probably there was deleted code.
• Michael Zedeler: Sure - you can do the same completely without a loop. Will be back with that.