use Modern::Perl;

while ( my $string = <DATA> ) {
    given ($string) {
        when (/<=/) {
            say '<= was found.';
        }
        when (/=>/) {
            say '=> was found.';
        }
        when (/==/) {
            say '== was found.';
        }
        when (/\*\*/) {
            say '** was found.';
        }
        default {
            say "The following was found: $_";
        }
    }
}

__DATA__
May  2 07:06:20 lon.mail.net exim[1234]: 2012-05-02 07:06:20 1PSPtU-0004en-1e <= it_ndt_bounces@new.itunes.com H=smtpmail.com [21.5.10.4] I=[8.4.14.4]:25 P=esmtp S=1966 id=1603882764.112965659.1335927964793.Mail.cboxp@ednabay.apple.com T="New on iTunes: One Thing And, Then Another, Cooking Apps,\n Great Deals on First Seasons, and M"
May  2 07:06:20 lon.mail.net exim[1234]: 2012-05-02 07:06:20 1PSPtU-0004en-1e <= it_ndt_bounces@new.itunes.com H=smtpmail.com [21.5.10.4] I=[8.4.14.4]:25 P=esmtp S=1966 id=1603882764.112965659.1335927964793.Mail.cboxp@ednabay.apple.com T="New on iTunes: One Thing And, Then Another, Cooking Apps,\n Great Deals on First Seasons, and M"
May  2 07:06:20 lon.mail.net exim[1235]: 2012-05-02 07:06:20 1PSPtU-0004en-1e => peterpiper <peterpiper@nosuchdomain.net> R=local_mail T=local_maildir_mail_drop
May  2 07:06:20 lon.mail.net exim[1235]: 2012-05-02 07:06:20 1PSPtU-0004en-1e == peterpiper <peterpiper@nosuchdomain.net> R=local_mail T=local_maildir_mail_drop
May  2 07:06:20 lon.mail.net exim[1234]: 2012-05-02 07:06:20 1PSPtU-0004en-1e ** it_ndt_bounces@new.itunes.com H=smtpmail.com [21.5.10.4] I=[8.4.14.4]:25 P=esmtp S=1966 id=1603882764.112965659.1335927964793.Mail.cboxp@ednabay.apple.com T="New on iTunes: One Thing And, Then Another, Cooking Apps,\n Great Deals on First Seasons, and M"
May  2 07:06:20 lon.mail.net exim[1235]: 2012-05-02 07:06:20 1PSPtU-0004en-1e -- peterpiper <peterpiper@nosuchdomain.net> R=local_mail T=local_maildir_mail_drop

##</code><code>##

<= was found.
<= was found.
=> was found.
== was found.
** was found.
The following was found: May  2 07:06:20 lon.mail.net exim[1235]: 2012-05-02 07:06:20 1PSPtU-0004en-1e -- peterpiper <peterpiper@nosuchdomain.net> R=local_mail T=local_maildir_mail_drop