perl: matching an IPv4 address

SOLUTION 1: Jeffrey Friedl's "Mastering Regular Expressions"
source

my $ReIpNum = qr{([01]?\d\d?|2[0-4]\d|25[0-5])};
my $ReIpAddr = qr{^$ReIpNum\.$ReIpNum\.$ReIpNum\.$ReIpNum$};

my %ips = ('0.0.0.0' => 1,
           '1.2.3.4' => 1,
           '255.255.255.255' => 1,
           '000.34.2000.2' => 0,
           '' => 0,
           '24.23.23.' => 0);

for my $ip(keys %ips) {
    die "Failed: $ip"
    unless (($ip =~ m{$ReIpAddr}) == $ips{$ip});
    print "$ip passed\n";
}

SOLUTION 2: USE Regexp::Common
source

#!/bin/perl
use Regexp::Common;

while() {
    if(/$RE{net}{IPv4}{dec}{-keep}/) {
        print "IP Address: $1\n";
    }
}

__DATA__
24.113.50.245
0.42.523.2
255.242.52.4
2.5.3

Discussion:

IP addresses are difficult to match using a simple regular expression, because the regular expression must verify that the IP address against which it is matching is valid. A simple expression such as /\d{3}\.\d{3}\.\d{3}\.\d{3}/ will incorrectly match strings such as 789.23.2.900, which is outside the range of valid IP addresses (i.e., 0.0.0.0 to 255.255.255.255). Damian Conway's Regexp::Common module provides a very effective regular expression which matches only valid IP addresses.

perl: simple socket programming

Here's a telnet kinda program in perl (i.e. a generic TCP client):

#!/usr/bin/perl
use IO::Socket;

my $dest = shift;
my $port = shift;
my $message;
my $line;

my $sock = IO::Socket::INET -> new ( PeerAddr => $dest, PeerPort => $port, Proto => "tcp" ) or die "Could not establish TCP connection: $!";

$sock->autoflush(1);

while (1)
{
    $message = <stdin>;
    print $sock $message;

    while ($line = <$sock>)
    {
        print $line;
    }
}

close $sock;

smtp: sending an email from the telnet prompt

This mail relay must accept SMTP connection from your host and must accept relaying. To check if the mail relay is working try



telnet mailrelay.domain 25
.... answer from mail relay .....

helo 
mail from: root@
rcpt to: @

data

mail test from unix
.



mail server should answer something like mail sent. If this work you can try with a normal mail client like



mailx -s "subject" @
mail test from unix
.



To check if this has work look at /var/adm/syslog/mail.log

you should see a couple of lines stating the mail has been accepted locally and sent to the relay and accepted.