Albeit most of modern firewalls have its own embedded functions for blocking bots, but sometimes it isn't enough.
So here is my basic script for analyzing apache logs and block(or something else) suspicious addresses.
Feedback is appreciated. 
#!/usr/bin/perl -w

use strict;
use warnings;
use POSIX qw(strftime);

my $pattern = "\"GET \/ HTTP\/"; # request index page pattern
my $httpd_log = "/var/log/httpd-access.log"; # log file 
my $ok = "1000"; # allowed connections per ip for $check_period
my $check_period = 1; # check period in hours

my $date = strftime("%d/%b/%Y:%H", localtime(time-$check_period*3600))
+; # date minus $check_period hours
my (%ips, $ip, $start);

open (LOG, $httpd_log) or die $!;
while (<LOG>) {
        next unless m/$date/ || $start; # skipping old records
        $start=1;
        if (/^(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}).*$pattern/go) { # g
+etting ips
                $ips{$1}++;
        }
}
close LOG;

foreach $ip (keys %ips) {
        if ($ips{$ip} >= $ok) { #
                print "$ip = $ips{$ip}\n"; next; # comment out this li
+ne if you want to modify firewall rules and uncomment one of the foll
+owing
                #system("/sbin/pfctl -t bots -T add $ip"); # adding ad
+dress to table <bots> 
                #system("/sbin/ipfw table 5 add $ip"); # adding addres
+s to table 5
                #system("/sbin/iptables -A INPUT -s $ip -j REJECT"); #
+ adding denying rule
        }
}

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In reply to Getting bots ips from apache logs. by idle

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