I wrote a small script to parse my log files, retrieve ip addresses, add them to a blacklist and append rules to my firewall (iptables).

My first question is, in the first "while loop" I used some regex's to get the data that I wanted. Is there a better way to perhaps combine them on fewer lines?

My second question is, the second "while loop" opens the file that I just appended to, and filters out blank lines, IP addresses on my network and duplicate entries. Is there a way that I can do that possibly within the first "while loop"?

I guess what I'm trying to accomplish with my second question is cut down on the number of times I open and close the same file.

I am still learning and am open to any suggestions. Here is what I have now.

#!/usr/bin/perl -w
#
# This script grabs ip addresses from my firewall log file
# and adds them to a blacklist for my iptables ruleset.
#
## NOTE - This script must be run as root

use strict;

# Check to make sure root is running this
if ($< != 0) {
    print "You must run this program as root!\n";
    exit
    }
    
my $log = "/var/log/iptables.log";
my $blacklist = "/var/log/blacklist";
my @list;
my %seen;
my @sorted;

# Open log file, retrieve list of ip addresses and write them
# to the blacklist
open(IN, "<", $log) || die "Can not open $log $!";
open(BL, ">>", $blacklist) || die "Can not open $blacklist $!";
while (<IN>) {
    s/.*(SRC)/$1/;
    s/(DST).*/$1/;
    s/ DST//;
    s/SRC=//;
    print BL ;
    }
close IN;
close BL;

# Read blacklist into an array while eliminating blank lines,
# IP's from my network and duplicates
open(BL, "<", $blacklist) || die "can not open $blacklist $!";
while (<BL>) {
    next if /\A\s*\z/ ; # skip blank lines
    next if /192.168*/;
    $seen{$_}++;
    next if $seen{$_} > 1;
    push(@list, $_);
    }
close BL;

# Sort my list of IP addresses
@sorted = sort {
    pack('C4' => $a =~
      /(\d+)\.(\d+)\.(\d+)\.(\d+)/)
    cmp
    pack('C4' => $b =~
      /(\d+)\.(\d+)\.(\d+)\.(\d+)/)
  } @list;

# Create clean blacklist file and append iptables rules
open(BL, ">", $blacklist) || die "Cannot open $blacklist $!";
foreach my $ip(@sorted) {
    print BL "$ip";
    chomp($ip);
    system("/sbin/iptables -A BLACKLIST -p all -s $ip -d 0/0 -j LOG --
+log-prefix \"IPTABLES:Blacklist: \"");
    system("/sbin/iptables -A BLACKLIST -p all -s $ip -d 0/0 -j DROP")
+;
    }
close BL;
chmod 0600, "$blacklist";
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