Hi,

If your logfile has it's data with fixed "width", then using unpack function can really come in handy! And you really wouldn't border on perl version you are using. see this:

use warnings;
use strict;

my $str =
'May  2 04:06:15 lon.mail.net exim[17905]: 2012-07-03 07:06:15 1SPPtO-
+0004en-PS <= me@ours.co.uk H=smtpout.mail.com [22.5.10.4] I=[6.5.14.4
+]:25 P=esmtp S=13333 id=6aeca3b79b8892d6105dab131c76f066@localhost.lo
+caldomain T="Half price offer"';

my ( $e_mail, $ip ) = unpack "x82A13x21A9", $str;
print "EMAIL: ", $e_mail, "\nIP: ", $ip, $/;

# OR

while (<DATA>) {
    my ( $e_mail, $ip ) = unpack "x82A13x21A9", $_;
    print "EMAIL: ", $e_mail, "\nIP: ", $ip, $/;
}

__DATA__
May  2 04:06:15 lon.mail.net exim[17905]: 2012-07-03 07:06:15 1SPPtO-0
+004en-PS <= me@ours.co.uk H=smtpout.mail.com [22.5.10.4] I=[6.5.14.4]
+:25 P=esmtp S=13333 id=6aeca3b79b8892d6105dab131c76f066@localhost.loc
+aldomain T="Half price offer"
[download]

OUTPUT
EMAIL: me@ours.co.uk
IP: 22.5.10.4

Check perldoc perlpacktut for more info.

UPDATE: Oops! my bad I missed that but was pointed out by Kenosis though, Please Note however, if the length of the field to be gotten varies, then unpack function will NOT also work.
However, I had mentioned perviously that the logfiles data MUST have a FIXED WIDTH.